Marco Castellaro, Erica Silvestri, Ilaria Boscolo Galazzo, Matteo Tonietto, Alessandro Palombit, Francesca Pizzini, Stefania Montemezzi, Enrico Grisan, Matthias Van Osch, Alessandra Bertoldo

Time-Encoded Arterial Spin Labelling (TE-ASL) has been proposed as a tool to efficiently sample the kinetics of the ASL signal. We propose a model comparison based on Bayesian Model Selection (BMS), to provide insights on which is the optimal model for the quantification of TE-ASL. Our results show how important it is to consider both T₁ decay and dispersion in the quantification process. When mainly interested in GM, it is advisable to incorporate the dispersion of the bolus in the model with a Gamma kernel dispersion model and to use a single T₁ value of 1.3s.  

Dimo Ivanov, Josef Pfeuffer, Anna Gardumi, Kâmil Uludag, Benedikt Poser

Arterial spin labelling (ASL) is the primary non-invasive MRI approach to measure cerebral blood flow in healthy subjects and patients. Recently, a consensus paper has recommended segmented versions of 3D spin-echo readouts like GRASE, but these are susceptible to motion and have poor temporal resolution. To alleviate these drawbacks, we propose to accelerate the 3D GRASE readout and utilize 2D CAIPIRINHA for the reconstruction. We demonstrate that our approach is superior or at least equivalent to the 2D GRAPPA technique, depending on the acceleration factor used. The proposed approach will particularly benefit functional and clinical ASL applications.  

Michael Chappell, Bridget Fryer, Anton Firth, Robert Wight, Thomas Kirk, Thomas Okell

Vessel encoded arterial spin labelling allows the visualisation of perfusion territories in the brain. However, the accuracy of perfusion measurements from VE-ASL and the associated analysis methods is difficult to establish without ground truth. Perfusion phantom devices have been prosed for conventional ASL, but don't currently attempt to model the full cerebral vasculature anatomy of the brain, limiting their value in evaluation of VE-ASL methods. Thus in this work we set out to create a multi-compartment, multi 'artery' perfusion phantom based on normal vascular anatomy.

Li Zhao, David Alsop

Conventional 3D arterial spin labeling images suffer from pronounced T2 blurring. In this work, new variable flip angle schemes, which can provide a Hann or Fermi window response across the slice direction, or which can be easily corrected to the designed window response and provide optimal SNR, were evaluated. Volunteers’ results show reduced blurring, improved SNR and contrast with the proposed methods.

Marta Vidorreta, Li Zhao, Sheila Shankar, Daniel Wolf, David Alsop, John Detre

Despite recent consensus in the ASL community on pseudo-continuous ASL as preferred labeling method, several challenges still exist towards optimizing pCASL labeling efficiency in-vivo, including its sensitivity to vessel tortuosity and off-resonance effects. In this work, we assess the impact of labeling plane location and labeling scheme on the ASL perfusion signal.

Kenneth Wengler, Xiang He

Pseudo-continuous arterial spin labeling (pCASL) with segmented 3D-GRASE acquisition is widely accepted as the optimal ASL technique. However, the method suffers from blurring along the partition direction caused by point spread function (PSF) broadening. In this study, a PSF deconvolution method for pCASL images with 3D-GRASE acquisition is developed and evaluated in simulations and in-vivo experiments. The deconvolution method greatly reduces the effects of the PSF and recover the perfusion signal for segmentation factors of at least 2_PAR x 2_PE. The proposed deconvolution method improves the accuracy of cerebral blood flow quantification and facilitates the use of lower segmentation factors.

Anna Gardumi, Dimo Ivanov, Roy Haast, Josef Pfeuffer, Benedikt Poser, Kamil Uludag

Arterial spin labeling (ASL) measures cerebral blood flow (CBF) non-invasively. Compared to the BOLD signal, CBF is quantitative and more directly linked to neural activation, albeit with lower SNR. Due to increased SNR and T1 relaxation time, ultra-high field MRI promises benefits for ASL. However, technical challenges remain to exploit its full potential. Here, we compared 3T and 7T ASL implementations and studied the influence of labeling schemes, resolution, parallel imaging, and field strength on the CBF and BOLD functional contrast. We found 3T pCASL being advantageous for low-resolution and 7T FAIR for high-resolution and acquisitions utilizing parallel imaging.

Yuriko Suzuki, Matthias van Osch, Thomas Okell

Hadamard-encoded vessel-encoded pCASL is a vessel-selective ASL technique that enables SNR-efficient vascular territory mapping for perfusion MRI. For vessel-selective ASL-MRA, however, minimising the number of encodings is necessary to achieve clinically feasible scan times. The spatial modulation of inversion in ve-pCASL is gradual, which could potentially reduce SNR-efficiency and cause mislabeling of arteries when reducing the number of encodings. In this study, the modulation of ve-pCASL was optimized to achieve sharper inversion to avoid signal contamination of non-targeted arteries and achieve 4D-MRA with a minimal number of Hadamard-encodings.

Neville Gai, John Butman

Pseudo-continuous arterial spin labeling (pCASL) with 3D non-segmented acquisition scheme allows assessment of full brain CBF with sufficiently high SNR and resolution in an efficient manner. Post-labeling delay is a critical parameter which needs to be determined preferably on a per subject basis since PLD can change based on the physiological condition of a subject. Multiple post-labeling delay (PLD) pCASL could address this issue. However, multiple PLD pCASL is not feasible for the 3D non-segmented acquisition scheme. In this work, we related the velocity in carotid artery (CA) measured using two schemes to PLD in ten volunteers. A relationship between the CA velocity and optimal PLD was derived which allows for optimal PLD to be determined on the fly for each subject. 

Jonas Schollenberger, C. Alberto Figueroa, Luis Hernandez-Garcia

We investigate how to improve the SNR of vessel-selective ASL images by off-resonance compensation and label rotation scheme optimization.

Michael Helle, Kim van de Ven, Fabian Wenzel

Super-Selective Pseudo-continuous Arterial Spin Labeling (pCASL) requires the labeling focus to be optimized to each artery of interest individually. This might be time-consuming especially for inexperienced users, and suboptimal results are possible as the labeling efficiency depends on the location of the labeling spot, as well as its angulation, which should be perpendicular to the artery. This study demonstrates an automatic planning approach for Super-Selective pCASL measurements in the major brain feeding vessels and subsequently compares the results to images acquired using a manual positioning of the labeling spot.  

Joshua Greer, Xinzeng Wang, Marco Pinho, Ivan Pedrosa, Ananth Madhuranthakam

Arterial spin labeling can non-invasively measure perfusion, but offers low SNR compared to contrast-enhanced perfusion techniques. A novel 3D TSE with a Cartesian Acquisition with SPiral Reordering (CASPR) was implemented and combined with pCASL in the brain and kidneys. This sampling technique samples the center of k-space early in each echo train, and was shown to provide significantly improved 3D perfusion images compared to 3D linear acquisitions, and more extensive coverage than 2D acquisitions in a similar scan time. 

Xingfeng Shao, Danny JJ Wang

We present a single-shot 3D GRASE pCASL technique, which reduces the data loss due to motion, using 2D CAIPI sampling strategy, and reconstruct the under-sampled data using ESPIRiT. Proposed sequence employs 4-fold acceleration and achieves whole brain volume with isotropic 3×3×3 mm³ resolution. This technique was successfully applied for high resolution multi-delay ASL imaging, and CBF, ATT and T1 map could be simultaneously calculated in 4 min 14 sec.

Kalen Petersen, Daniel Claassen, Manus Donahue

The overall goal of this work is to optimize arterial spin labeling (ASL) MRI techniques to enable the use of baseline cerebral blood flow (CBF) fluctuations to identify major intrinsically-connected resting state networks (RSNs). We provide data in support of 3D GRASE pCASL being able to provide similar functional resting state networks as BOLD. Additionally, extremely low-frequency fluctuations, less than 0.01 Hz, were present in the CBF-weighted pCASL data, suggesting that application of pCASL may provide additional functional information relative to BOLD, which generally requires low-frequency filtering. 

Alvaro Galiano, Reyes García de Eulate, Marta Vidorreta, Miriam Recio, María Fernández-Seara

Cognitive decline is associated with aging even in the absence of disease. In this study ASL perfusion fMRI was used to investigate changes in perfusion and resting state networks connectivity due to aging, by comparing two groups of healthy subjects (young and elderly). Results showed perfusion deficits in the elderly group, in association areas, related with advanced cognitive abilities. Disruptions in varios core RSNs were also detected. Assessment of perfusion and resting functional connectivity jointly could be a good predictor of cognitive decline and a good biomarker for treatments aiming to extend cognitive abilities.

Alexander Cohen, Andrew Nencka, Yang Wang

When too short a post-labeling delay (PLD) is used for ASL, intravascular artifacts can be present. This issue is amplified in multiband (MB) ASL where superior slices are acquired early in the acquisition. Here, MB pseudocontinuous ASL (pCASL) and a dual regression approach were used to analyze functional connectivity with PLD=1000ms and 1525ms. Increased whole-brain tSNR was observed for the PLD=1000ms data, but intravascular signal was present. Group connectivity was similar between PLDs, and no significant differences in mean or max z-score were seen between PLD. Thus, shorter PLDs may be appropriate for MB-ASL rsfMRI despite the presence of intravascular artifacts.

Mareike Buck, Matthias Günther, Federico von Samson-Himmelstjerna

In this abstract the reproducibility of absolute CBF as well as the M0- and an optional calibration-image is assessed during individual scanning-sessions and also over the entire day. Comparably high reproducibility was found for all three types of images, which agrees with similar earlier findings. However, also the uncertainty of the corresponding fits was found to be high.

Cagdas Ulas, Stephan Kaczmarz, Christine Preibisch, Jonathan Sperl, Marion Menzel, Axel Haase, Bjoern Menze

We present a new spatio-temporal denoising method for arterial spin labelling MR image repetitions, and mainly aim to improve the quality of perfusion-weighted images and cerebral blood flow (CBF) maps obtained from a subset of all dynamics available. Our technique is based on a two-step 3D total variation regularization, which is applied to subsets of control/label pairs in the first step and to resulting perfusion-weighted (difference) images in the second step. We demonstrate that our method leads to improved quality of perfusion-weighted images and CBF maps compared to existing spatial filtering techniques in short computation time.

Stefan Spann, Kamil Kazimierski-Hentschel, Christoph Aigner, Rudolf Stollberger

Arterial spin labeling perfusion imaging permits a noninvasive approach to measure cerebral blood flow. The poor SNR of this technique makes denoising essential. ASL images are often corrupted with motion, physiological or scanning artifacts or acquired using parallel imaging leading to spatial dependent noise. To account for those artifacts and spatial varying noise we propose a denoising approach based on total generalized variation (TGV) using a spatial dependent regularization parameter. The performance of the proposed technique is evaluated on synthetic and in-vivo data and compared with the non-local means combined dual-tree complex wavelet transform (DT-CWT) denoising method.

Zhengjun Li, Marta Vidorreta, Daniel Wolf, John Detre

We used latent state-trait theory to examine trait specificity of regional cerebral blood flow (CBF) acquired using arterial spin labeled (ASL) perfusion MRI in four different resting-state conditions (eyes-open, eyes-closed, fixation, and a low-level attention task (psychomotor vigilance task, PVT)). Most brain regions accepted the latent state-trait model. Fixation exhibited the lowest latent trait specificity, while PVT, eyes-open, and eyes-closed showed progressively higher trait specificity.  We confirmed that ASL CBF shows trait-like properties, which are optimally fit using eyes-open or eyes-closed conditions.

Xiufeng Li, Xingfeng Shao, Dingxin Wang, Sudhir Ramanna, Steen Moeller, Kamil Ugurbil, Essa Yacoub, Danny Wang

Recently 2D multi-band (MB) imaging has emerged as a promising alternative to 3D acquisitions for arterial spin labeling imaging. As part of the Human Connectome Project, we evaluated a segmented 3D GRASE and 2D MB-EPI for multi-delay PCASL imaging in terms of test-retest repeatability and CBF/ATT quantification. The results indicated that compared to 3D GRASE, 2D MB-EPI is less sensitive to subject motion, provided comparable but more reproducible ATT and CBF estimates, and suffered less from data loss. 2D MB-EPI appears promising for multi-delay PCASL imaging, especially with limited imaging time and where higher spatial resolution is of interest.  

Qin Qin

Velocity-selective arterial spin labeling (VSASL) has only been realized with 2D multi-slice acquisition. ASL with 3D readout is preferred for clinical applications and background suppression technique is essential for successful implementation of segmented 3D ASL. In this study, various strategies for background suppression are evaluated for 3D VSASL which are labeled with conventional T2prep VS pulse train, and new Fourier transform based velocity-selective saturation and inversion pulse trains, respectively. The optimal 3D whole-brain VSASL protocol is compared with PCASL for mapping cerebral blood flow on normal volunteers at 3T.

André Ahlgren, Ronnie Wirestam, Freddy Ståhlberg, Linda Knutsson, Esben Petersen

The calibration factor (equilibrium magnetization of arterial blood) in arterial spin labeling is usually calculated by dividing a PD image with a constant brain-blood partition coefficient, $$$\lambda$$$. A more accurate approach would be to divide a map corresponding to the PD of the perfused parenchymal tissue with a $$$\lambda$$$ map (i.e, taking into account different values of $$$\lambda$$$ in different tissue types). In this work, we demonstrate how this can be achieved using partial volume (PV) estimates. In vivo results are demonstrated and compared with the conventional method.

Yuriko Suzuki, Thomas Okell, Wouter Teeuwisse, Sophie Schmid, Merlijn van der Plas, Michael Chappell, Matthias van Osch

Recently, incorporation of multi-band (MB-) EPI into ASL has been reported, enabling increased spatial coverage without compromising SNR of distal slices due to longer post-labeling delay time. However, the combination of MB-EPI and ASL with the background suppression (BGS) could potentially induce problems when motion correction (MoCo) is required. In this study, we demonstrate that subtraction artefacts can be introduced when performing MoCo of MB-BGS-pCASL and that these artefacts can degrade image quality considerably. We propose a new framework that corrects for image degradation caused by MoCo of MB-BGS-pCASL data, thereby greatly improving robustness and thus usefulness of MB-BGS-pCASL.

Stefano Mandija, Paul de Bruin, Andrew Webb, Peter Luijten, Cornelis van den Berg

The focus of the presented work is to understand the relation between electrical conductivity and tissue composition in terms of ²³Na concentration and water fraction. This would be relevant to evaluate the potential value of electrical conductivity imaging as a new endogenous biomarker and the validity of accessing conductivity from water content. For this purpose, MR-EPT and waterEPT conductivity reconstructions are performed and compared to network analyzer measurements. To evaluate whether conductivity is directly related to the total sodium concentration in free water, ²³Na images are acquired at 7T and conductivity reconstruction are then performed using the Stogryn’s model.

Yicun Wang, Pierre-Francois Van de Moortele, Bin He

Magnetic Resonance based Electrical Properties Tomography holds promise to provide valuable information on tissue functional changes, such as Tumorigenesis. We propose a novel technique based on multi-channel transmission to reconstruct quantitative electrical properties maps by exploiting the intermediate contrast information with jointly promoted sparsity. The resultant optimization problem was solved by Alternating Direction Method of Multipliers within seconds. Numerical simulations, phantom and human subject experiments were performed at 7T using a multi-channel transceiver coils array, demonstrating improved accuracy and visual outcome. CONCEPT does not rely on anatomical assumptions, and therefore represents a general approach suitable for broader applications.

Ulrich Katscher, Max Herrmann, Christian Findeklee, Mariya Doneva, Thomas Amthor

Electric Properties Tomography (EPT) derives tissue conductivity and permittivity according to the Helmholtz equation via the second derivative of the measured complex B1 map, or by iteratively solving the corresponding forward problem. This abstract presents a different type of EPT reconstruction: the measured B1 map is compared locally with entries of a dictionary, which are small B1 maps of a priori known electric properties. This "dictionary-based EPT" (db-EPT) could be able to solve the transceive phase problem as well as the boundary problem of EPT. This study applies db-EPT to numerical and experimental data comparing different types of dictionaries.

Yusuf Ider, Gokhan Ariturk, Gulsah Yildiz

Clarification of the contrast resolution (CR) and spatial resolution (SR) limits of phase based MREPT for conductivity imaging is essential for assessing its success  success in clinical applications. Noise analysis of conventional phase based MREPT is performed to find the SNR needed for the MR sequence used for measuring B1-phase. It is found that with 1000-2000 SNR values about 0.01 S/m CR can be achieved. For SR evaluation, generalized phase based MREPT, which does not suffer from internal boundary artefacts, is considered. It is found by phantom experiments that 3.5mm spatial resolution is easily obtained with the state-of-art MR methods. 

Jun-Hyeong Kim, Jaewook Shin, Ho-Joon Lee, Kang-Hyun Ryu, Donghyun Kim

Weighted polynomial fitting method was proposed to resolve boundary artifact and noise amplification of Electrical Property Tomography. Weighted polynomial fitting method employs T1/T2 tissue contrast as prior information under assumption that pixels with similar magnitude intensity have similar conductivity. However, for non-simply connected structures make the fitting inaccurate. Therefore, in this study, we propose a modified weighted polynomial fitting technique including spatial constraint.    

Lin Chen, Congbo Cai, Tianhe Yang, Jianzhong Lin, Shuhui Cai, Jiaxing Zhang, Zhong Chen

Environmental factors may influence brain iron concentration. We investigated the changes of magnetic susceptibility and R₂^* values of cerebral regions especially in six deep gray matter nuclei of twenty-nine participants after high altitude exposure for four weeks. The results show that the susceptibility values of gray matter, especially in caudate nucleus, putamen, globus pallidus, substantia nigra, red nucleus, increased significantly. Traditional R₂^* maps verify the results of QSM evaluation except in red nucleus. Therefore, high altitude hypoxia can lead to significant increase of cerebral iron concentration. 

Bup Kyung Choi, Nitish Katoch, Saurav Sajib, Jin Woong Kim, Hyung Joong Kim, Oh In Kwon, Eung Je Woo

Liver tissues mainly consist of single cell, the variations of ion concentration and mobility inside the liver have similar pattern. This indicates that liver tissues can exhibit uniform distribution of electromagnetic tissue properties such as electrical conductivity. MREIT is typical method which can provide electrical conductivity information of suspicious tissue using a current-injection MRI method. Mapping of liver tissue damage using MREIT conductivity imaging may provide direct, immediate, and high sensitive information based on the changes of ion concentration and mobility at cellular levels. This study experimentally imaged in vivo liver tissue damage based on the changes of tissue conductivity.

Aditya Kumar Kasinadhuni, Aprinda Indahlastari, Kevin Castellano, Christopher Saar, Casey Weigel, Bakir Mousa, Michael Schär, Munish Chauhan, Thomas Mareci, Rosalind Sadleir

Characterizing current density distributions in the brain of healthy volunteers can provide important information to guide electrical stimulation therapies. Current-induced magnetic fields, produced as a result of electrical stimulation, can be mapped from phase changes in the MR imaging then current density can be computed using Maxwell’s equations. In this study, we present the first current density distribution induced magnetic field maps in healthy volunteers resulting from electrical stimulation using low frequency (10 Hz) transcranial alternating current simulation (tACS).

Kathleen Ropella, Douglas Noll

We propose a method for combining phase data from multiple receiver channels for phase-based conductivity mapping that does not require a reference scan or reference coil. The proposed method combines a background phase removal step, to reduce bias from individual coil phases, and local coil compression, which maximizes SNR in the combined phase data. 

Jose Serralles, Ioannis Georgakis, Athanasios Polimeridis, Luca Daniel, Jacob White, Daniel Sodickson, Riccardo Lattanzi

Magnetic resonance-based inverse scattering has been proposed to extract tissue electrical properties (EP). We present an improved implementation of the Global Maxwell Tomography (GMT) EP mapping technique, with two new cost functions and an extension that uses piecewise linear basis functions to represent fields for higher accuracy. GMT does not make symmetry assumptions, is fully 3D, and is robust to noise. We validated the new GMT version with various numerical experiments, using a heterogeneous head model with realistic EP and a phantom with tissue-mimicking EP. We showed, for the first time, that artifact-free accurate reconstruction of EP is possible.

Yuyao Zhang, Hongjiang Wei, Naying He, Christian Langkammer , Stefan Ropele , Fuhua Yan, Chunlei Liu

QSM is able to provide high contrast for iron-rich deep-brain nucleus. This is attributed to the sensitivity of magnetic susceptibility to the spatial variations of cellular components that exhibit different magnetic susceptibility properties, especially for brain iron and myelin. Although there have been atlases proposed for certain age groups, a longitudinal statistical atlas construction from general healthy population based on QSM is still lacking. We constructed longitudinal QSM atlases over the whole lifespan (from 1 to 83 years-old). One common QSM atlas is built for every 10-years interval to demonstrate the unique age-specific morphology and appearance of human brains. 

Yuyao Zhang, Hongjiang Wei, Naying He, Fuhua Yan, Chunlei Liu

The crucial role of iron for normal neurological function in human brain has been well recognized. The iron concentration evolution trajectories in human brain deep nucleus have been shown monotonously increased with aging. However, previous studies concern only on iron concentration. At the same time, atrophy occurs in healthy ageing brains. These two competing effects raise an interesting possibility that the total iron content in deep brain nuclei may decrease. Surprisingly, the iron content, investigated by QSM, in globus pallidus, substantia nigra and red nuclei appear to decrease after the iron content reaching a peak.

Jeam Barbosa, Rafael Emidio, Ana Tereza Alho, Maria Otaduy, Edson Amaro, Fernando Barbosa Junior, Oswaldo Baffa Filho, Carlos Salmon

QSM, R2* and R2 values for post-mortem intra and extra cranial human brain samples were statistically correlated with only total iron and Fe3+ present in ferritin.

TaeHyun Hwang, JinGu Lee, JunYeol Choi, SangJoon Kim, GeonHo Jahng, Jongho Lee

In this study, we developed a computer simulation to demonstrate the importance of reference in QSM. The results show that QSM values are substantially affected by spatial coverage for reconstruction. Only when the data are referenced using a neighboring region, the QSM results provide correct susceptibility values. Additionally, we suggest a new “differential ROI” reference method. This approach reports the susceptibility value as a difference between two (neighboring) ROIs. We demonstrate this new approach for a Parkinson’s disease patient study. 

Ryota Sato, Toru Shirai, Yo Taniguchi, Takenori Murase, Atsushi Kuratani, Taisei Ueda, Takashi Tsuneki, Yoshitaka Bito, Hisaaki Ochi, Yoshihisa Soutome

To reduce the calculation error and artifacts of susceptibility in the boundary region between water and fat, a new reconstruction method is presented and applied to a prostate QSM. In the proposed method, susceptibility maps of the water region and the fat region are calculated separately and differently and then combined. Numerical simulation and human prostate imaging using a 3T-MRI are performed to evaluate accuracy and artifacts of the proposed method. The results suggest that the proposed method reduces calculation error and the shading artifacts in the boundary region between water and fat near the prostate.

Reyhaneh Nosrati, Abraam Soliman, Alexey V. Dimov, Hirohito Kan, Gerard Morton, Ana Pejovic-Milic, William Song

Post-implant dosimetry is an important quality assurance for prostate low-dose-rate (LDR) permanent seed brachytherapy. Despite the superior soft tissue contrast in MRI that is required for tumor delineation, there are some unresolved issues with seed depiction on MR images as they appear as signal void. In addition, calcified regions have similar characteristics on MR images making them indiscernible. This work investigates the feasibility of an MR-only workflow based on quantitative susceptibility mapping (QSM) and 3D k-means clustering for post-implant localization of the seeds.

Xiang Feng, Alexander Loktyushin, Andreas Deistung, Jürgen Reichenbach

The aim of this study was to quantitatively assess the improvement of image quality on motion corrupted quantitative susceptibility mapping (QSM) and the effective transverse relaxation rate (R₂*) maps, after applying retrospective motion correction. Image quality was assessed using the following metrics: SNR in different brain tissues, histogram analysis, and linear correlation between susceptibility and R₂* values in subcortical structures. 

Barbara Dymerska, Klaus Bohndorf, Paul Schennach, Alexander Rauscher, Siegfried Trattnig, Simon Robinson

Growing epiphyseal cartilage of children contains vessels and more complex layer structure than adult hyaline cartilage. Phase imaging is sensitive to deoxyhemoglobin in venous blood and to orientation of magnetic tissues, but it is challenging since many established methods for combining and unwrapping data fail in the thin cartilage of the knee. In this study different phase reconstruction methods were tested at 7T and high resolution SWI was applied to visualize veins and collagen fiber architecture in healthy young subjects.

Yicheng Chen, Clare Poynton, Suchandrima Banerjee, Janine Lupo

There is a growing interest in using QSM to detect and quantitatively evaluate cerebral microbleeds (CMBs). We compared several algorithms proposed in recent years for QSM on patients with CMBs after radiation therapy at 3T and 7T by quantitatively analyzing the noise and contrast of the susceptibility maps. Although RESHARP+ iLSQR had the least noise among methods, CMB and vessel contrast were more affected by incomplete background field removal, especially at 7T.

Lukas Buschle, Christian Ziener, Michael Breckwoldt, Artur Hahn, Julia Bode, Björn Tews, Martin Bendszus, Heinz-Peter Schlemmer, Felix Kurz

In this work, the effect of inhomogeneous microstructure on quantitative susceptibility mapping (QSM) is simulated for typical microstructural geometries. The results suggest that the susceptibility of blood-filled capillaries can not be measured using quantitative susceptibility mapping due to the symmetry of the local Larmor frequency around a capillary. However, numerical simulations show that the concentration of spherically-shaped magnetic particles (contrast agents) is determinable with QSM. These results are therefore essential for a detailed analysis of quantitative susceptibility images.

Emma Dixon, David Thomas, Anna Barnes, Karin Shmueli

Automatic Region of Interest (ROI) generation is useful for large clinical studies using Quantitative Susceptibility Mapping (QSM) as this allows mean susceptibility values for anatomical regions to be reported without manual intervention.

Several methods to generate ROIs are compared in this work. We found that methods based on T1 contrast showed little variation whether a typical magnitude image from a susceptibility protocol or a structural MPRAGE image was used. An additional method based on a QSM atlas showed greater variability in ROIs.

Mean susceptibility values for ROIs were shown to vary greatly depending on the method used to generate ROIs.

Caiyun Shi, Xiaoyong Zhang, Shi Su, Hairong Zheng, Xin Liu, Guoxi Xie, Jim Ji

Previous studies have demonstrated that a susceptibility-based positive contrast MR method exhibits excellent efficacy for visualizing MR compatible metal devices by taking advantage of their high magnetic susceptibility. However, the method was not evaluated in the visualization of stents. Therefore, the purpose of this study is to assess whether the susceptibility-based positive method can be used to visualize the nitinol stents, with the comparison of two typical MR positive contrast techniques, i.e., SUMO and GRASP. Experiment results showed that the susceptibility-based method provides much better visualization and localization of the stent than SUMO and GRASP.

Benjamin Tendler, Richard Bowtell

The magnetic properties of skeletal muscle tissue were examined in a phantom consisting of a piece of muscle tissue embedded in agar. Frequency perturbation maps were generated from phase maps measured at 7T, with the phantom oriented at 29 angles to the external magnetic field. Using a novel minimisation technique, susceptibility and chemical exchange properties of the muscle tissue were obtained simultaneously. From this it was determined that skeletal muscle is significantly more diamagnetic than agar; there is a small anisotropic susceptibility component and a large, orientation independent positive offset within the tissue, hypothesised to be due to chemical exchange. 

Hansol Lee, Se Young Chun, Jae-Hyeok Lee, Sun-Yong Baek, HyungJoon Cho

 Spatial characterizations of neuromelanin and iron contents in human substantia nigra provide critical information in diagnosing and treating Parkinson's disease. In this work, MR investigations of susceptibility weighted imaging (SWI), R2* mapping, and quantitative susceptibility mapping (QSM) were performed with three post-mortem human substantia nigra samples at 7T and correlated with corresponding histological slides. Magnetization transfer (MT) based T1-weighted MRI technique was also conducted to validate its reputed neuromelanin sensitivity as well.

Zhe Liu, Yihao Yao, Yi Wang

One challenge in Quantitative Susceptibility Mapping (QSM) identified in a recent QSM workshop is zero reference. Cerebrospinal fluid (CSF) with little cellular content has been a popular choice. However, current QSM often shows inhomogeneous CSF, which may be regarded as artifacts caused by surrounding anisotropic white matter fibers in the scalar dipole inversion. We propose  a regularization of minimal CSF variation for projecting out CSF inhomogeneity artifacts. Our proposed new QSM incorporates automated segmentation and regularization specific to CSF and outputs susceptibility values with automatic and uniform CSF zero reference. Accordingly, we term this novel QSM method as QSM0

Sagar Buch, Yongsheng Chen, E. Mark Haacke

In QSM, every effort is made to reduce background field induced by the air-tissue interfaces. In this abstract, we propose a method to: correct the phase of boundary regions by using background field extrapolation methods such as Taylor expansion; preserve the internal phase for the superior sagittal sinus (SSS) and transverse sinuses using an arterial-venous (MRAV) image; and predict the phase outside the brain and SSS using forward modeling. Further, we combine these steps to obtain an estimate of the venous oxygen saturation levels inside dural sinuses.

Balint Sule, Robert Zivadinov, Jannis Hanspach, Michael Dwyer, Jesper Hagemeier, Nicola Bertolino, Dhaval Shah, Niels Bergsland, Ferdinand Schweser

Magnetic susceptibility in the deep gray matter varies substantially between subjects of similar age or disease state. This work employs a blind source separation technique to 239 healthy controls to determine, without prior assumptions, the spatial patterns that drive inter-subject variation of magnetic susceptibility in the human brain.

Xin Miao, Yi Guo, Krishna Nayak, John Wood

High-resolution B₀ mapping suffers from long scan time, and issues with phase-wraps. We present an acquisition and reconstruction technique that resolves both problems.  We utilize “X” sampling in k-TE space, in which multiple phase-encoding lines are acquired exactly twice per TR. The echo spacing is shortest for central k-space and largest for outer k-space. A multi-scale reconstruction enables pixel-wise phase unwrapping. This technique may be particularly useful for quantitative susceptibility mapping (QSM), as it could a) shorten scan time while maintaining the sensitivity to high-order field variation and b) simplify phase-unwrapping, which are the key features of interest in QSM.

Hongfu Sun, Yuhan Ma, M. Ethan MacDonald, G. Bruce Pike

An advanced dipole field inversion method for whole brain quantitative susceptibility mapping (QSM) without a traditional background field removal step, is proposed. To aid this ill-posed inversion process and obtain successful QSM, a Tikhonov regularization of the local susceptibility distribution is included. It is shown that the proposed method (Tikhonov-QSM) can substantially suppress reconstruction artefacts. More importantly, Tikhonov-QSM does not require edge erosion like in other QSM methods involving background field removal steps, preserving the cerebral cortex of the final images.

Carlos Milovic, Berkin Bilgic, Bo Zhao, Julio Acosta-Cabronero, Cristian Tejos

This abstract presents a fast nonlinear solver for the QSM reconstruction using the total generalized variation regularization. The proposed method utilizes the alternating direction method of multipliers to obtain close-form solution to each sub-problem. To handle the non-linear data fidelity, a two-step algorithm is described, including a global optimum search and a local Newton-Raphson iteration. Compared to conventional linear solvers, nonlinear solutions reduce streaking artifacts and better handle noise in poor SNR regions. Reconstruction results are at least comparable to nonlinear MEDI in quality, but with an order of magnitude improvement in the computational efficiency.

Debra Horng, Samir Sharma, Scott Reeder, Diego Hernando

The Poisson Estimation for Ascertaining Local fields (PEAL) kernel is a recently-introduced method for background field removal in quantitative susceptibility mapping (QSM). The PEAL kernel is determined by two parameters: radius and spatial shift. The choice of these two parameters may have a substantial effect on the accuracy of background field removal. In this work, we assessed the effect of PEAL kernel size and shift on the accuracy of background field removal and susceptibility estimation.

Zhe Liu, Yan Wen, Pascal Spincemaille, Yi Wang

Preconditioned Total Field Inversion (TFI) allows QSM for the entire head and chest. The preconditioner determines the TFI convergence. Can we choose a preconditioner that maximizes QSM quality within limited computational time? To answer this question, we conducted two numerical simulations specific to these applications to search for an optimal preconditioner. We found that preconditioner too small or too big for a targeted susceptibility distribution would have less computational acceleration and consequently greater errors for a given computational time. Our results here suggest that the optimal preconditioner should be identified to match the image content.

Shrinath Kadamangudi, Viktor Vegh, Surabhi Sood, David Reutens

Ultra-high field GRE-MRI phase images present great promise for structural brain studies. Multi-echo GRE-MRI data has been shown to contain signal compartments, which may eventually be used to characterise brain microstructure. Existing studies considered three signal compartments, however it remains unclear how compartments co-localise throughout the brain. We compartmentalised the signal via frequency shift signatures in a mixture of grey-white matter brain regions and implemented quality of fit measures to select the most parsimonious model for each region. We utilised k-means cluster analyses to investigate signal compartment commonalities across different brain regions and found four dominant frequency shift signatures. 

Liangdong Zhou, Jae Kyu Choi, Youngwook Kee, Yi Wang, Jin Keun Seo

We provide a mathematical understanding for artifacts in QSM, particularly streaking artifacts. 1) The local field data can be decomposed into a dipole-compatible part and a dipole-incompatible part. 2) In spatially continuous space, the streaking-free susceptibility solution is obtained from the dipole-compatible field data only, and the dipole-incompatible data leads to artifacts defined by a wave propagator with z as time, specifically, streaking artifacts from granular noise and shadow artifacts from white matter noise error. Although it is not known how to filter out such dipole-incompatible data, its artifacts can be suppressed in regularization-based Bayesian methods such as MEDI, which can efficiently penalize streaking artifacts. k-space-truncation-based methods that generate additional dipole-incompatible data near the zero cone amplify streaking artifacts.

Saifeng Liu, Jean-Christophe Brisset, Sagar Buch, Jing Jiang, E. Mark Haacke, Yulin Ge

Susceptibility weighted imaging (SWI) has been widely used to image cerebral venous structures and in vivo iron content. However, it has not been used to image arteries, because of the lack of susceptibility contrast between arteries and the surrounding tissue. In this study, the susceptibility of the arterial blood was purposely modified to make it visible with SWI, by using the USPIO (ultra-small superparamagnetic iron oxide) agent Ferumoxytol. The purpose of this study is to determine the relationship between Ferumoxytol concentration and susceptibility using phantom and simulation studies, and compare these findings with those obtained from in vivo data.

Youngwook Kee, Pascal Spincemaille, Junghun Cho, Yi Wang

The current regularization in morphology-enabled dipole inversion (MEDI) does not take into account orientation information in morphology between QSM and its corresponding magnitude image. In this abstract, we consider such orientation information to enhance structural coherence between the two images. In doing so, we achieve better image quality as well as higher RMSE (root mean square error) and HFEN (high frequency error norm) with respect to COSMOS and $$$\chi_{33}$$$. 

Yihao Guo, Li Guo, Yingjie Mei, Jijing Guan, Yanqiu Feng

Morphology enabled dipole inversion (MEDI) has been proposed to reconstruct QSM without obvious streaking artifacts at the smooth regions of susceptibility map. However, reconstruction errors or streaking artifacts near edges are not addressed by MEDI. In this work, we aim to improve MEDI by constraining the edges of susceptibility map with prior information.

Albert Rechberger, Barbara Dymerska, Karin Poljanc, Georg Langs, Simon Robinson

A method for automatic venous vessel segmentation is presented that uses a Random Forest classifier supplied with a number of appearance and shape features computed separately from magnitude images, phase images and QSMs of a multi-echo T2*-weighted GE scan. The importance of each feature, and thus each echo, is investigated.  The approach was tested on whole-brain 7T scans of four subjects, two of which were manually annotated, and was effective in segmenting both internal and surface veins.

Anita Karsa, Shonit Punwani, Karin Shmueli

Magnetic Susceptibility Mapping is moving closer to clinical application. To reduce scan time, clinical images are often acquired with reduced resolution and coverage in the through-slice dimension. The effect of these factors has been studied using only balloon phantoms and downsampled brain images. Here, we used MR images acquired at low resolution or low coverage and compared these with images simulated in volunteers and a realistic numerical phantom. Simulated susceptibility maps were very similar to maps from acquired images. Our results show that low resolution and very low coverage both lead to loss of contrast and errors in susceptibility maps. 

Véronique Fortier, Ives R. Levesque

Phase unwrapping and background removal algorithms directly impact quantitative susceptibility maps. Phase processing techniques have been thoroughly studied for brain applications, but accuracy in the presence of large susceptibility and negligible signal, such as bone and air regions, is unknown. The performance of phase processing algorithms was evaluated quantitatively in simulations with a numerical head phantom and qualitatively in vivo in three head datasets. In these experiments, Laplacian-based unwrapping performed poorly. Accurate background removal remains an open question. Results suggest that Quality-Guided unwrapping should be preferred with background removal using Projection onto Dipole Fields. 

Emma Dixon, David Thomas, Anna Barnes, Karin Shmueli

Due to the difference in magnetic susceptibility of air, teeth and bone, magnetic susceptibility mapping has the potential to enable segmentation of these regions despite the absence of direct MRI signal. Several methods have been described which attempt to calculate the magnetic susceptibility within air and bone. Two datasets are used to test the ability of these methods to distinguish between air and bone. The performance of all methods varied between datasets and depended strongly on the parameters selected. None of the methods performed consistently better across groups, but all showed potential to improve air/bone segmentation using susceptibility mapping.

Simon Robinson, Korbinian Eckstein, José Marques, Berkin Bilgic, Siegfried Trattnig, Ferdinand Schweser

Methods for combining phase data from array RF coils are quantitatively compared at 7 T. Of the reference-free approaches (which all leave arbitrary contributions to the total phase), the Virtual Reference Coil method yielded the best phase matching. The reference-free method COMPOSER removed non-B0-related phase but requires an artifact-free short echo-time reference measurement. Of the multi-echo methods, SVD, HIP and ASPIRE all had uniform phase matching. ASPIRE has higher CNR for a narrow range of echo times, but requires TE2=2 x TE1. The data and assessment scripts used in this study will be made publicly available.

Yongquan Ye, Li Yang, Mengsu Zeng, Shengxiang Rao, Ying Ding, Jinguang Zong, Xixi Wen

Computer simulation was performed to evaluate the relationship between a voxel's bulk susceptibility and its R₂* or phase behavior. A virtual voxel with multi-dipole model was created, and the effects of dipole properties on the accuracy and consistency of R₂* and phase on reflecting the voxel’s bulk susceptibility was investigated. Linearity is only observed at low bulk susceptibility regime, and phase is much more robust against various susceptibility dipole properties than R₂*. 

Gaiying Li, Guoqiang Zhai, Xinxin Zhao, Hedi An, Tian Liu, Yi Wang, Dongya Huang, Jianqi Li

QSM provides excellent contrast of iron-rich deep nuclei to quantify iron in the brains. Clinicians are interested in using QSM to diagnose patients with Parkinson’s disease (PD). Texture analyses of QSM images in substantia nigra (SN) was performed to differentiate PD from healthy controls (HC). Most of the texture parameters were significantly different between PD and HC. The second-order textures were more efficient in differentiating PD from HC than did the first-order ,which suggests that the second-order texture parameters are more suitable and sensitive for the diagnosis of PD.

Xing Lu, Alexey Dimov, Qun He, Yajun Ma, Yi Wang, Eric Chang, Jiang Du

Iron overload can affect not only the central nervous system, but the liver, pancreas, myocardium, endocrine glands, and musculoskeletal structures. A reliable quantitative method to detect and measure high concentration iron in vivo would be of great clinical utility. Ultrashort echo time (UTE) sequences have echo times (TE) 100-1000 times shorter than clinical sequences, and may detect signal from high iron concentration. In this study, we aimed to evaluate the capability of UTE-QSM sequence in quantifying high iron concentration with an Iron phantom study and the results show that UTE-QSM techniques can quantify high iron concentration up to 22 mM or higher. 

Hanneke Geut, Louise van der Weerd, Itamar Ronen

This study compares the currently publically available algorithms for quantitative susceptibility mapping, including different phase unwrapping, background field removal and dipole inversion methods. Numerical and human in vivo brain MRI data are used for a qualitative and quantitative assessment of the various methods. In 3T in vivo MRI data, phase unwrapping with combined spatial and temporal fitting and background field removal using V-SHARP results in the least artifacts. MEDI and iLSQR are currently the most accurate dipole inversion algorithms, with a significantly shorter processing time for the iLSQR method.

Joana Loureiro, Gisela Hagberg, Elisa Tuzzi, Rolf Pohmann, Zora Schickardt, Marc Himmelbach, Thomas Ethofer, Matthias Valverde, Wolgang Grodd, Klaus Scheffler

In this study we use relaxometry and susceptibility mapping to obtain enhanced contrast in the midbrain, in particular in the superior colliculus (SC). High resolution GRE images were obtained in 11 subjects at 9.4T.  We calculated CNR values for each contrast for three midbrain regions (superior colliculus,red nucleus and aqueductal gray).  were  were obtained across 11 subjects in individual and MNI space. These measurement were validated with ex-vivo measurements in the 9.4T, 14.1T and PLI imaging.

Andreas Deistung, Verena Endmayr, Simon Hametner, Max Prihoda, Xiang Feng, Hans Lassmann, Jürgen Reichenbach, Simon Robinson, Evelin Haimburger, Christian Menard, Thomas Haider, Hannes Traxler, Siegfried Trattnig, Günther Grabner

We investigated the effect of brain tissue fixation on iron concentration and on quantitative maps of the magnetic susceptibility and effective transverse relaxation rate (R2*). Both R2* and susceptibility distributions of unfixed and fixed tissue were found to be similar, indicating similar underlying proportions of iron across tissues. Quantitatively, however, severe decreases of iron concentration of 25% in putamen and about 15% in white matter were measured after tissue fixation. The iron concentration change due to tissue fixation was captured by R2* and susceptibility which needs to be considered when directly comparing experiments performed with unfixed and fixed brain tissue.

Tom Hilbert, Jose Marques, Jean-Philippe Thiran, Reto Meuli, Gunnar Krueger, Tobias Kober

We propose an algorithm that can reconstruct 0.9mm³ isotropic T2 maps based on multiple 2D multi-echo spin-echo acquisitions that were highly undersampled. The data is reconstructed by combining a classical super-resolution approach with an iterative model-based reconstruction. Thereby, the reconstruction problem is split into multiple sub-problems to improve the convergence of the algorithm. Resulting T2 values within structures of the midbrain and the hippocampus from four healthy volunteers showed good reproducibility. This kind of high-resolution relaxometry may enable additional insight in pathologies of small brain structures and increased sensitivity to disease-induced changes.

Kenneth Johnson, N Addy, Reeve Ingle, Michelle Nystrom, William Overall, Galen Reed, Juan Santos

Typical magnetization prepared phantoms require paramagnetic salts such as copper, nickel and manganese chloride, which are toxic. Accordingly, governing bodies label these as hazardous materials requiring special storage, labeling and disposal. In search of a simpler and cheaper solution we have revisited this topic to make a kitchen-safe phantom recipe that is both cheap and easy to make. We used glycerine (a sweetener or for skin care) and Agar agar powder (a food additive for thickening or gel) to make phantoms with a physiological range of T1 and T2, and characterize these non-hazardous materials for 1.5 T MRI scanners.

Shu-Juan Fan, Yajun Ma, Eric Chang, Jiang Du

Myelin protons have ultrashort-lived MR signals and are not accessible by clinical MRI. Such signals were probed herein using ultrashort echo time imaging (UTE) and inversion-recovery UTE (IR-UTE) with bi-component analysis in native and deuterated ovine brain specimens. UTE detected a fraction of ultrashort T2 components (STC) of < 4% in native specimens, and up to ~54% in deuterated specimens. Choice of inversion time in IR-UTE significantly affected such bi-component signal decay behavior in native samples in heavily deuterated samples. These results support the application of UTE and IR-UTE in quantitative myelin imaging.

Shengwen Deng, Eric Muir, Wei Zhou, Timothy Duong

T1 mapping is showing great potential for mapping oxygen in human organs such as eyes and lungs. And yet, accuracy of oxygen using fast T1 imaging methods is of great concern especially in tissue with radical temperature changes. In the current study we improve fast T1 mapping with temperature correction and explore its potential in mapping oxygen in eyes. With combination of inversion-recovery Look-Locker bSSFP and diffusion weighted thermometry, we calibrate the temperature dependence of ADC and T1, and use it to adjust the R1 for measuring partial pressure of oxygen(pO2). Fast T1 mapping could be a reliable way to pO2 that well agrees with invasive oxygen-sensitive optic fibers.  

Hedok Lee, Simon Sanggaard, Kristian Mortensen, Palle Koch, Maiken Nedergaard, Helene Benveniste

3D whole brain T1 mapping technique at 9.4T is studied because of a lack of methodological consideration in spite of its utility in pre-clinical paramagnetic and manganese contrast enhanced imaging studies. We report a simple and accurate 3D T1 mapping technique using variable flip angles spoiled gradient echo sequence with B1+ correction. Accuracy of the technique was validated using phantoms and a population averaged 3D rat T1 map was constructed.

Emilie Mussard, Tom Hilbert, Christoph Forman, Reto Meuli, Jean-Philippe Thiran, Tobias Kober

Brain T2 relaxometry can provide sensitive biomarkers for pathological tissue alterations, especially inflammation. But their acquisition is often 2D-based and typically comes with long acquisition times. To improve through-slice resolution while keeping a clinically feasible scan time, we propose a centric T2-prepared variable-density Cartesian spiral phyllotaxis FLASH sequence combined with a compressed sensing reconstruction. Phantom experiments and a preliminary in-vivo scan show that T2 values can be reliably measured in 3D with high resolution. Parameter dependencies are evaluated and an initial protocol optimisation yields an acquisition time of 8.48min for a 1x1x1.2mm3 whole-brain acquisition.

Dongyeob Han, Taehwa Hong, Dong-Hyun Kim

 Magnetic resonance fingerprinting (MRF) is a novel technique which provides rapid proton density, T1 and T2 mapping. However, susceptibility related parameters such as T2* were not acquired simultaneously. In this study, FISP and multi-echo SPGR acquisition were combined within MRF scheme to allow proton density, T1, T2, T2* and field mapping.

Zhitao Li, Ali Bilgin, Diego Martin, Maria Altbach

A golden angle radial IR-FLASH technique and a principle component based iterative algorithm are developed for high-resolution T1 mapping using highly undersampled 3D radial data. The novel method yields T1 maps of a 3D volume with high spatial and temporal resolution and can cover 144 slices within 5 minutes.

Nuno Santos, Rui Teixeira, Joseph Hajnal, Rita Nunes

Interpretation of T2-weighted images still remains highly reliant on subjective clinical evaluation. Quantitative mapping using the gold standard approach (single spin-echo), although appealing, remains unfeasible in clinical practice. Multi-SE sequences have emerged as viable solutions allowing much shorter scan times at the expense of signal contamination by indirect echoes.  A method based on the MR Fingerprinting concept has recently been proposed, estimating T2 and B1+ maps from pre-computed Echo Modulation Curves. This study evaluated the performance of this method performing Monte Carlo simulations followed by an in vivo acquisition. The method provided accurate T2 maps, despite highly biased B1+ estimates.

N. Jon Shah, Seong Dae Yun

Quantitative measurement of the T₁ relaxation time is of great importance for the clinical diagnosis or optimisation of image contrast. Numerous Look-Locker method have been proposed for T₁ mapping. One of them demonstrated by the community is TAPIR which has been shown to be fast and robust. However, TAPIR still demands substantial acquisition time for whole-brain coverage. This work aims to develop a fast Look-Locker method with whole-brain coverage on a basis of EPIK. It was shown that the proposed method acquired whole-brain T₁ data (2.1 mm²resolution × 50 slices × 30 time-points) within 3.5 minutes.

Christoph Rettenmeier, V. Andrew Stenger

A 3D radial UTE sequence optimized for the selective detection of fast relaxing tissue in the range of 500-60 μs using a composite hard pulse is presented. Its imaging properties on a T2-phantom are analyzed and used for the discussion of human brain images. 

Kelly McPhee, Ashmita De, Alan Wilman

We examine RF field variation on a modern 3T and illustrate T2 quantification using only PD and T2w fast spin echo images and a rapid flip angle map in the abdomen, spine, head, neck, and leg. Across the whole body at 3T or higher fields, RF field variation yields a wide variation in flip angles, requiring direct sequence modelling to achieve accurate T2.

Kelly McPhee, Alan Wilman

Through exact sequence response modeling using the Bloch equations, we propose direct extraction of quantitative T1 and T2 relaxation maps from standard clinical MRI sequences. This approach eliminates the need for excess specialized and complex sequences by measuring relaxation directly from clinical sequences.  We demonstrate this method to determine T2 and T1 using a standard brain protocol of fast spin echo images weighted by proton-density, T2 and FLAIR at 3 T. Our approach opens the door to wider use of quantitative MRI.

Brendan Garrett, Simon Duckett, David Smith, Victor Chechik

We present here the preparation and properties of new Gd³⁺-containing nanogel-based contrast agents. These gel nanoparticles are prepared by simple ionotropic gelation from sodium alginate and Gd³⁺.  The nanogels are 100-200 nm in diameter and have a high R₁ relaxivity of ≈ 30 mM^-1 s^-1 at 1 T, however,  they have poor stability in high ionic strength media. Adding further covalent crosslinks with a suitable agent such as epichlorohydrin dramatically increased the relaxivity of the nanogels to ≈ 60 mM^-1 s^-1 at 1 T and provides a viable strategy to increases their stability against transmetallation.

Paul Kinchesh, Philip Allen, John Beech, Stuart Gilchrist, Ana Gomes, Veerle Kersemans, Robert Newman, Borivoj Vojnovic, Michael Brady, Ruth Muschel, Sean Smart

Prospective gating and automatic reacquisition of data corrupted by respiration motion were implemented in variable flip angle (VFA) and actual flip angle imaging (AFI) scans to enable cardio-respiratory synchronised T₁ mapping of the whole mouse. T₁ calculation for each mouse took approximately 6 s using a robust and efficient nonlinear least squares process. 16 cardio-respiratory gated VFA scans and a respiration gated AFI scan were acquired in less than 14 minutes. T₁ was calculated in the whole mouse with a voxel size of 0.075 mm³ and with a standard deviation less than 6.2% within ROIs from multiple organs.

Gregory Lemberskiy, Els Fieremans, Dmitry Novikov, Martijn Cloos

Proton density (PD) measurements derived from single Spin Echo and PnP-MRF,  which is a fingerprinting protocol that enables simultaneous estimation of the excitation field (B1+), were validated using the ISMRM/NIST MRI system phantom that contains known D2O/H2O solutions at 14 different concentrations. We also expanded the PnP-MRF protocol by exploiting the symmetry between B1+ and the receive field, B1-, produced by a quadrature body coil at 3 Tesla in order to remove all B1 contribution from our PD. Ultimately, all methods showed remarkable correlation with the known water fraction from NIST samples (Pearson’s rho>0.99). 

Andreas Petrovic, Christoph Aigner, Rudolf Stollberger

T₂ quantification with multi-echo spin-echo sequences is often hampered by flip angle inhomogeneities and non-rectangular slice profiles. Here, we present a novel time domain signal equation for multi-echo spin-echo sequences with arbitrary excitation and refocusing flip angles and phases. To evaluate the equation simulations and phantom measurements were compared. Excellent agreement was found for the simulated and measured evolution of the transverse magnetization across the slice profile in a CP and a CPMG sequence. T₂ mapping using the proposed signal equation and the incorporation of scanner specific RF pulse shapes will greatly improve T₂ quantification accuracy. 

Emil Ljungberg, Alykhan Thobani, Thorarin Bjarnason, Piotr Kozlowski, Alexander Rauscher, Jing Zhang, Anthony Traboulsee, Cornelia Laule, Alex MacKay, Shannon Kolind

T₂ relaxation using combined gradient and spin echo (GRASE) is a fast and robust approach for myelin water imaging in vivo. For long echo trains, when the noise floor is reached, the magnitude signal will converge towards a non-zero mean due to the Rician noise characteristics of the magnitude data. This can give rise to artificial long-T₂ components in analysis. In this study we employed temporal phase correction to multi-echo GRASE data and showed that for echo trains longer than 300ms, phase correction will effectively reduce artificial long-T₂components, thus improving the ability to interpret the T₂ distribution.

Feng Qi, Samuel Hurley, Menuka Pallebage-Gamarallage, Olaf Ansorge, Martin Turner, Ricarda Menke, Sean Foxley, Karla Miller

MRI of fixed post-mortem tissue can be used to relate MR signals to histopathology. However, MR relaxation parameters are altered by the process of fixation. We propose a “kinetic tensor” model that simulates the influx of fixative into the brain using diffusion tensor data, and demonstrate a correction by fitting a fixative concentration map to quantitative T2 measurements. Compared to correction methods based on distance-to-surface or isotropic diffusion, our approach captures an individual brain’s morphology and microstructure, both of which influence fixation. T2 maps corrected with the kinetic tensor model are more homogeneous than those with alternate corrections.

Karthik Gopalan, Jonathan Tamir, Ana Arias, Michael Lustig

We aim to design and build reproducible phantoms with anatomy-mimicking resolution and image contrast. We mix solutions of paramagnetic ions in agar gel to target specific relaxation parameters. Chambers for different tissue types are 3D printed and filled with the agar gels. Microfiber cloths are added to create additional high-resolution structure. We validate the ability to reproduce target relaxation values through spin-echo imaging and quantitative mapping, and present two 3D printed phantom designs.

Eric Muir, Shengwen Deng

Fast measurement of T1 and T2 can be made using inversion-recovery Look-Locker (LL) bSSFP methods. However, the LL-bSSFP signal is dependent on the off-resonance frequency which can affect calculated T1 and T2. In this study we develop and test methods to correct for effects of off-resonance on T1 and T2 calculation using multiple phase-cycled LL-bSSFP. The phase-cycled LL-bSSFP data could be combined with a maximum-T1* projection method to improve T1 and T2 accuracy in the case of off-resonance.

Steven Kecskemeti, Andrew Alexander

A method to retrospectively correct both in- and through-plane motions that occur during the acquisition of inversion recovery images is developed and used for motion-corrected T1-mapping of the pediatric human brain.   Both intra- and inter-scan motions are corrected.

Ana Rodríguez-Soto, Michael Langham, Osheiza Abdulmalik, Felix Wehrli

The transverse relaxation rate (1/T₂) of blood water protons is governed by deoxyhemoglobin concentration, therefore providing a means to determine oxygen saturation (HbO₂) in vivo. However, besides CPMG inter-pulse interval of the T₂ preparation and field strength, whole-blood T₂ depends on sequence-specific parameters. Balanced SSFP allows for rapid image acquisition and higher in-plane resolution and thus provides an ideal readout for T₂-based oximetry. Here, we quantified T₂ of human blood at 1.5T for the entire range of HbO₂ saturation levels using T₂-prepared bSSFP sequence. The data show the expected linearity of 1/T₂ with (1-HbO₂)² with the y-intercept depending on hematocrit.

Jean-David Jutras, Keith Wachowicz, Guillaume Gilbert, Nicola De Zanche

Quantitative parametric mapping is becoming increasingly promising for improving the diagnostic quality and reproducibility of structural brain MR images. The variable flip angle technique with FLASH (VFA-FLASH) is a popular technique for mapping the proton-density, T₁ and T₂^*. Recently, the MP2RAGE pulse sequence was developed to map T₁ with robustness to RF inhomogeneity. If a multi-echo (bipolar) MP2RAGE is employed, proton-density and T₂^* can also be mapped simultaneously. In this study we compare the SNR efficiency and accuracy of VFA-FLASH and MP2RAGE for multi-parameter mapping at 3T. Both methods yield comparable T₁-to-noise ratios, but VFA-FLASH is superior for PD and T₂^* mapping.

Thomas Roberts, May Zaw-Thin, Angela D'Esposito, Yanan Zhu, John Connell, Mark Lythgoe, Simon Walker-Samuel

Imaging of drug delivery is useful for improving our understanding of the physical factors that contribute to the efficacy of anticancer therapies. Gemcitabine, a standard chemotherapeutic agent, has two hydroxyl groups and one amine group, making it potentially amenable to CEST imaging via proton exchange with tissue water. Recently, Li et al. (2016) showed that many anticancer drugs can induce CEST contrast and demonstrated that liposome-encapsulated gemcitabine can be imaged 5-hours post-administration in a pre-clinical model of cancer¹. Here, we extend this exciting work and investigate the use of CEST to image acute gemcitabine uptake within 30 minutes of administration. 

Mohammed Salman Shazeeb, Rubina Corazzini, Dinesh Bangari, Robert Fogle, Jennifer Johnson, Paul Konowicz, Xiaoyou Ying, Pradeep Dhal

Hyaluronic acid (HA) hydrogels have a wide range of applications in biomedicine from regenerative medicine to drug delivery applications. In vivo quantitative assessment of these hydrogels using magnetic resonance imaging (MRI) provides a powerful technique to assess the biodegradability of HA hydrogels. This study investigated the potential of chemical exchange saturation transfer (CEST) MRI in tracking HA hydrogels with varying degradation profiles in vivo in a mouse subcutaneous injection model over 77 days. Since CEST-MRI provides a unique chemical signature to visualize HA hydrogels, this technique can be used as a guide in hydrogel optimization process for drug delivery applications.

Kai Jiang, Christopher Ferguson, John Woollard, Roger Grimm, James Krier, Xiangyang Zhu, Lilach Lerman

In this study, we tested the capability of magnetization transfer (MT) imaging for measuring renal fibrosis in a swine model of atherosclerotic renal artery stenosis (ARAS) at 3.0 T. A collagen phantom study was performed to select appropriate offset frequencies of MT pulses for collagen detection. In an in vivo study, the MT ratio (MTR) and percent change in MTR between two offset frequencies were quantified, and both showed a good correlation with renal fibrosis measured ex vivo by Picro-Sirius red staining, supporting the use of MT to assess renal fibrosis in swine ARAS. 

Kevin Ray, James Coates, Rathi Puliyadi, Thomas Ashton, Paul Kinchesh, Sean Smart, Michael Chappell, Geoff Higgins, Nicola Sibson

Tumours often have areas of hypoxia, which renders cancer cells resistant to many therapies. Recently the anti-malarial drug Atovaquone has been shown to modify the oxygen consumption rate of cancer cells, reducing tumour hypoxia. Non-invasive mapping of tumour hypoxia would be particularly useful for translation of these preclinical findings into a clinical environment. Here, we tested the hypothesis that CEST MRI could be used to visualise changes in tumour hypoxia.

Rong-Wen Tain, Alessandro Scotti, Weiguo Li, Xiaohong Joe Zhou, Riya Thomas, Leon Tai, Kejia Cai

Reactive oxygen species (ROS) contribute to pathogenesis of many human diseases including Parkinson’s and Alzheimer's diseases, cancer, and diabetes. There is a crucial need for using fully noninvasive imaging to further evaluate the role of ROS in pathogenesis and the potential treatment strategies. Our previous phantom studies demonstrated that ROS containing unpaired electrons can be detected with endogenous CEST and T₁ weighted contrasts. However, in vivo detection of ROS using MRI has not yet been demonstrated. This study therefore aimed to demonstrate the feasibility of in vivo ROS detection using endogenous MRI. 

Jérémy Pépin, Pierrick Jego, Julien Valette, Gilles Bonvento, Julien Flament

GluCEST imaging has been proposed to image brain glutamate distribution with a better resolution than spectroscopic methods and has many potential applications for the study of neurodegenerative diseases. In this study, we pushed further the limits of gluCEST imaging by combining high magnetic field and high performance cryoprobe to acquire gluCEST images with the best resolution so far. Thanks to the organization of hippocampal cell layers and the high resolution, we acquired gluCEST data in regions mostly reflecting the neuronal compartment.

Corin Miller, Jin Cao, Chunlian Zhang, Eduard Chekmenev, Bruce Damon, Alan Cherrington, John Gore

Despite being integral to whole body glucose homeostasis, liver glycogen remains difficult to measure non-invasively.  Recent works have demonstrated the feasibility of detecting liver glycogen using CEST MRI.  In this presentation we present data that builds upon this observation and investigate whether CEST can be used to monitor glycogen synthesis and breakdown in mice in real time both ex vivo in a perfused liver system, and in vivo.  Treatment with hyperglycemia or glucagon resulted in increases or decreases, respectively, in the CEST MTRasym AUC over time.  This demonstrates that CEST-based approaches can be used to non-invasively monitor glycogen metabolism.

Maria Yanez Lopez, Nicoleta Baxan, Miriam Ries, David Sharp, Magdalena Sastre

The aim of the study is to examine the feasibility of using GlucoCEST to evaluate subtle BBB dysfunction in the mouse brain, by comparing it with conventional gadolinium DCE. DCE and GlucoCEST showed no significant differences between WT and 5XFAD mice (3 months). However, the degree of the response after injection was similar for DCE and GlucoCEST for all animals except one, indicating shared contributions to the signal and supporting the potential for biodegradable d-glucose as a cheap, low-risk alternative/complement to DCE MRI. More work is required to assess GlucoCEST sensitivity to low-level BBB dysfunction, such as in Alzheimer’s disease.

Ping-Huei Tsai, Fei-Ting Hsu, Hua-Shan Liu, Hsiao-Wen Chung, Yu-Chieh Kao, Chia-Feng Lu, Huai-Lu Chen, Paul Blakeley, Gilbert Aaron Lee, Cheng-Yu Chen

Our proposed method provides an alternative to extract glucose profile and could be more robust to the field drift, which may be helpful in the implementation of in vivo brain glucoCEST imaging for further application.

Shanrong Zhang, Matanel Yheskel, Vishal Patel, Masaya Takahashi, A. Dean Sherry

The objective is to develop a new 3D-CEST imaging method (3-dimensional chemical exchange saturation transfer) to investigate a mouse model of polycystic kidney disease (PKD). It is based on 3D magnetization prepared rapid acquisition gradient echo sequence (3D MPRAGE) by applying a pre-saturation pulse consisting of three continuous Gauss shaped pulses.

Kevin Ray, James Larkin, Brad Sutherland, George Harston, Andrew Baldwin, Alastair Buchan, Peter Jezzard, James Kennedy, Michael Chappell, Nicola Sibson

Studies employing CEST MRI to study ischemic stroke focus on the sensitivity of amide proton transfer (APT) MRI signals to tissue pH, assuming identical intracellular protein concentration as healthy tissue. This study shows that whilst cytoplasmic protein concentration remains stable in penumbral stroke regions, it decreases in the infarct core. By analysing APT MRI data with APTR*, which is specifically sensitive to amide proton exchange effects, we demonstrate that the APT signal change in infarct core is dominated by decreased protein concentration, whilst penumbral APT changes can be attributed to decreased tissue pH.

Shu Zhang, Jochen Keupp, Ivan Dimitrov, Robert Lenkinski, Elena Vinogradov

CEST-MRI is increasingly evolving from brain to body applications. One of the known problems in body imaging is the presence of strong lipid signals. Their influence on the CEST signal is acknowledged but underexplored. The goal is to investigate the effects of lipids on the Z-spectrum taking TE into account. We performed simulations and verified the results in phantoms and in vivo. We demonstrate the mutual influence of fat fraction and TE on the Z-spectrum for gradient echo based sequences. This study provides a systematic understanding of lipid artifacts in CEST imaging and lays the foundations for their efficient removal.

Erwin Krikken, Vitaliy Khlebnikov, Moritz Zaiss, Wybe J.M. van der Kemp, Tijl A. van der Velden, Hanneke W.M. van Laarhoven, Dennis W.J. Klomp, Jannie P. Wijnen

Treatment monitoring is of importance for breast cancer patients receiving systemic therapy. Metabolic imaging methods such as CEST and ³¹P-MRS may have potential to predict treatment efficacy in an early stage of the treatment. In this study we assessed the amide proton transfer (APT) signal and the pH change in breast cancer patients before and after the first cycle of neoadjuvant chemotherapy to explore the relation between APT and pH. We observed changes in both the APT signal and the pH between the two measurements. These changes may serve as biomarkers for predicting treatment response to NAC in an early stage. 

Nicolas Geades, Olivier Mougin, Simon Shah, Penny Gowland

The origin of the Nuclear Overhauser Enhancement (NOE) signal observed in the CEST spectrum of the brain is still under debate. The effect is detected upfield from water, in the frequency range of non-exchangeable aliphatic/olefinic protons, indicating that the transfer of magnetization is not occurring via proton or chemical exchange; furthermore the lineshape is relatively narrow, suggesting the signal is coming from mobile protons with T2 of the order of 300μs. This study investigates the correlation between NOE and MT in the human brain at 7T, and shows the two effects are strongly coupled, across a wide age range.

Moritz Zaiss, Philipp Ehses, Klaus Scheffler

Selective quantitative CEST MRI was shown to be feasible at 7T and for single-slice readout. In this study we extend qCEST MRI to a field strength of 9.4 T making use of the increase spectral resolution, and by employing a single-shot 3D CEST approach, more coverage of the human brain was realized.

Jan-Eric Meissner, Andreas Korzowski, Sebastian Adeberg, Steffen Goerke, Nicolas Behl, Heinz-Peter Schlemmer, Jürgen Debus, Mark Ladd, Peter Bachert, Daniel Paech

Chemical Exchange Saturation Transfer (CEST) offers unique contrasts sensitive to micro environmental information such as protein concentration and pH. Thus CEST could be a promising biomarker to investigate radiotherapy-induced changes in tissue. In this study we examine brain tumor patients in the course of definitive radiotherapy on a 7 T whole-body scanner using the relaxation compensated contrast AREX. We compare the results of CEST imaging to Single Voxel Spectroscopy and high-resolution T₂-weighted imaging.

Koji Sagiyama, Yuji Watanabe, Ryotaro Kamei, Sungtak Hong, Jochen Keupp, Hiroshi Honda

Amide proton transfer (APT) imaging has been reported to be useful for assessing malignancy or evaluating treatment efficacy. In this study, we evaluated the validity of APT signals in brain tumors by direct voxel-wise comparison with standardized uptake values (SUVs) from fluorodeoxyglucose positron emission tomography (FDG-PET) on a PET-magnetic resonance (PET/MR) system. APT imaging showed discrepancies with FDG-PET due to structural inhomogeneity, and the correlation between APT signals and SUVs was poor. The correlation was significantly improved after correcting for the apparent diffusion coefficient (ADC). APT/ADC could be a reliable metabolic marker with better correlation with SUVs.

Yunus Msayib, George Harston, Yee Tee, Fintan Sheerin, Nicholas Blockley, Thomas Okell, Peter Jezzard, Stephen Payne, James Kennedy, Michael Chappell

The aim of this study was to identify the analysis technique with the optimum repeatability for quantifying APT CEST imaging for use in the clinical setting. The repeatability of eight quantification techniques was assessed across imaging time points in healthy subjects, and between the contralateral hemispheres of stroke patients. Model-based techniques exhibited better repeatability compared to simpler model-free methods, and are thus better-suited for use in clinical imaging at 3T.

Eugene Lin, Hua Li, Zhongliang Zu, Elizabeth Louie, Xiaoyu Jiang, Daniel Gochberg

It has been shown that the changes in chemical exchange saturation transfer (CEST), and specifically amide proton transfer (APT) and nuclear Overhauser effect (NOE), reflect abnormal tissues in tumor, stroke and other diseases. However, quantitative and specific imaging of these effects is challenging due to the influences from asymmetric magnetization transfer and direct water saturation. These obstacles can be avoided with chemical exchange rotation transfer (CERT), which is a pulsed version of CEST with the constraint of constant average power and varying rotation angle. In this study, we present initial CERT results in human brain at 3 T, with the goal of quantifying APT and NOE.

Simon Shah, Olivier Mougin, Andrew Carradus, Nicolas Geades, William Morley, Penny Gowland

CEST maps at 7T display higher APT and amine signal from the sagittal-sinus compared to elsewhere in the brain. We investigate CEST and NOE signals detected in ex-vivo blood under with varying oxygenation, haematocrit levels, pH and cell structure. Showing that human blood produces significant amounts of CEST and NOE, dominated by the cellular components of blood and independent of blood oxygenation. Clotting and lysing red-blood-cells has no impact on the observed CEST and NOE. We also observed increased APT and NOE with increasing pH. These result are important when interpreting exchange in conditions associated with blood volume change. 

Hye-Young Heo, Yi Zhang, Shanshan Jiang, Jinyuan Zhou

Current APT imaging studies have used a moderate repetition time or relaxation delay to reduce the scan time. However, when a relatively short relaxation delay compared with T₁ is applied, the steady-state water longitudinal magnetization is reduced, resulting in a decrease in APT effect. Therefore, experimental parameters must be optimized on a combination of the RF saturation power, saturation length, and relaxation delay. Here, we quantitatively investigated the dependence of APT and NOE signals on the experimental parameters using Bloch simulations and rat brain tumor models at 4.7 T.

Kristin O'Grady, Samantha By, Bailey Box, Seth Smith

Cognitive impairment (CI) is a significant symptom of multiple sclerosis (MS), is the strongest predictor of unemployment in MS patients, and is critical to the decline of quality of life. There is an unmet need for imaging techniques that probe the pathological substrate of CI at a clinically relevant field strength. To address this need, we have investigated the translation of glutamate-sensitive chemical exchange saturation transfer (GluCEST) MRI to 3T, as glutamate abnormalities have been linked to CI in MS. Our results demonstrate the clinical feasibility of GluCEST imaging for application to studying cortical gray matter glutamate signals in vivo.

Ferdinand Zimmermann, Steffen Görke, Johannes Breitling, Kerstin Klopries, Johannes Windschuh, Heinz-Peter Schlemmer, Mark Ladd, Daniel Paech, Peter Bachert

Chemical Exchange Saturation Transfer (CEST) MRI in the mammary gland is affected by the high fat content in the human breast. Chemical shift induced artifacts are visible in the Z-Spectrum. We showed a method to test and verify water-fat separation techniques in vitro. Transfer of the gained insights to realize water-only CEST-MRI in the human breast is currently under investigation.

Esau Poblador Rodriguez, Philipp Moser, Barbara Dymerska, Siegfried Trattnig, Wolfgang Bogner

Once the time resolution and specificity of Cr-CEST become comparable with 31P-MRS, it may replace it for the diagnosis of muscular disorders and treatment assessment due to its superior spatial resolution and sensitivity. The need of a complete Z-spectrum acquisition for B0 inhomogeneity correction limits the achievable time resolution and is unable to track temporal ?B0 due to subject movement or B0 field drifts that occur during a CEST experiment. Temporal B0 field tracking allows independent B0 inhomogeneity correction for each z-spectral point, which may substantially improve the reliability of spectral CEST asymmetry analysis.

Gopal Varma, Olivier Girard, Valentin Prevost, Samira Mchinda, Guillaume Duhamel, David Alsop

The inhomogeneous (ihMT) technique represents a relatively simple addition to MT, but provides a different contrast that is sensitive to the dipolar relaxation time T_1D. A review is provided of: method(s) for its application; considerations for optimizing the ihMT signal; the use of models to obtain quantitative parameters and guide acquisition; and its application in vivo.

Manh-Tung Vuong, Tanguy Duval, Julien Cohen-Adad, Nikola Stikov

There is an ongoing debate in the myelin imaging community about which MR-based biomarker has the greatest precision, sensitivity and specificity to myelin.  In this work, we compared several MR-based myelin imaging techniques (quantitative magnetization transfer, myelin water fractions, and macromolecular tissue volume) by evaluating their repeatability and their relation to large-scale histology in dog spinal cord. Qualitatively the contrasts were similar, and all techniques had comparable scan-rescan and correlations with histology.  Surprisingly, the correlations between the various myelin measures were almost as high as the scan-rescan correlations. The correlations decreased when only white matter was considered, which could be due to the small dynamic range of the measurement, or due to artifacts related to the preparation and panoramic scanning of the tissue.

Scott Swanson, Mario Fabiilli, Dasha Malyarenko, Ashok Srinivasan, Zhongliang Zu, Daniel Gochberg

We report here a study of MT and enhanced MT (eMT), using dual-sided RF saturation, in model membrane system to measure lipid dynamics and structure in systems of known lipid order. The eMT signal generated by dual-sided RF saturation of phospholipid vesicles is well described by Gaussian line shape and T_2b is easily determined. T_2b of the lipids is related to the lipid order with T_2b(liquid disorder) > T_2b(liquid order) > T_2b(solid order). These tools provide a method to estimate lipid order in vivo.

Peter van Gelderen, Jeff Duyn

Combining multi-gradient-echo (MGRE) acquisitions with inversion/saturation preparation pulses allows for separation of white matter signal in several water compartments and estimation of both their T₁ and exchange properties. A model of multiple myelin, myelin water and axonal/interstitial water compartments was implemented, including exchange from and across individual lipid bi-layers. Fitting this model to the inversion prepared MGRE-data resulted in T₁'s and exchange rates for all compartments. The results from a corpus-callosum region of interest indicate that the single layer myelin water residence time is a few hundred microseconds, while the average residence time of all myelin water combined is around 15ms.

Samira Mchinda, Gopal Varma, Valentin Prevost, Arnaud Le Troter, Maxime Guye, Jean Pelletier, Jean-Philippe Ranjeva, David Alsop, Guillaume Duhamel, Olivier Girard

Inhomogeneous magnetization transfer (ihMT) is a new MRI technique that shows promise for myelin imaging. A significant boost of the ihMT signal intensity is achievable when using a concentrated energy deposition scheme. Here we characterized the power dependency of ihMT for various energy deposition schemes (distributed vs. concentrated RF) and we identified distinct regimes with linear, sub-linear and saturated B1 dependency.  This has a strong impact on the ihMT response to variable sequence configurations and on the most suitable conditions for different field strengths, e.g. to enhance sensitivity or provide immunity to B1⁺ inhomogeneities.

Siawoosh Mohammadi, Jan Sedlacik, Martina Callaghan, Jens Fiehler, Gunther Helms, Christian Sprenger

Ex vivo histology remains the gold standard against which MRI biophysical models, e.g. the MR g-ratio which characterises the fraction of a fibre’s diameter that is myelinated, are evaluated. The MR g-ratio model requires a measure of myelin density, for which magnetization transfer saturation (MT) has been used as a biomarker. However, changes occurring post mortem, e.g. autolysis, temperature changes and fixation, significantly alter the MRI signal. Here we investigate how these changes impact MT. We found that MT decreased post mortem but greatly increased upon fixation. These effects are similar to reported changes of other established MRI myelin-markers. 

Valentin Prevost, Olivier Girard, Samira Mchinda, Gopal Varma, David Alsop, Guillaume Duhamel

A new implementation of inhomogeneous magnetization transfer (ihMT) has recently been introduced, consisting of concentrating the RF energy deposition within the saturation period and demonstrating a significant boost of the ihMT sensitivity. The boost effect has been characterized in this study among different ihMT sequences, species and field strengths and reveals common features. The optimal sequence settings vary with the number of consecutive MT pulses and are presumably related to the timescale of the underlying T_1D components and magnetization exchange rates.

Huajun She, Bian Li, Joshua Greer, Jochen Keupp, Ivan Dimitrov, Ananth Madhuranthakam, Robert Lenkinski, Elena Vinogradov

Chemical exchange saturation transfer (CEST) is a new contrast mechanism in MRI. However, a successful application of CEST is hampered by its slow acquisition and fast acquisition is desired. Compressed sensing (CS) is powerful for perfect reconstruction of highly undersampled data. Existing works mostly focus on the retrospectively downsampled studies, but few implementation and analysis of truly undersampled scheme with CEST has been reported. This work experimentally implements the random Cartesian undersampled scheme and the golden angle radial sampling sequence for CEST. The results demonstrate influence of experimental conditions that are not accounted for in the retrospectively undersampled studies.

Tobias Wech, Herbert Köstler

A robust motion correction technique for in vivo CEST-acquisitions is proposed. The algorithm exploits a low-rank plus sparse decomposition of the Z-spectrum to separate signal variations due to different off-resonance preparations from accompanying motion. The method was validated in a phantom study and subsequently used to register a CrCest acquisition of the human thigh during exercise.

Moritz Zaiss, Philipp Ehses, Klaus Scheffler

In this study, we present a single-shot 3D MRI readout that allows acquisition of a CEST prepared volume within 2 s. This makes it possible to correct for motion, which otherwise can cause severe artifacts in CEST imaging.

Xiufeng Li, Jialu Zhang, Wendy Elvendahl, Dingxin Wang, Kamil Ugurbil, Gregory Metzger

To overcome the limitations of traditional magnetization contrast (MTC) preparation methods, the Multi-Banded (MB) RF-pulse Enhanced Magnetization Transfer Contrast (MBE-MTC) preparation was proposed by using the multi-banded RF pulses for the MTC preparation. Such an approach has been evaluated via studies in the skeleton muscle, kidneys and the brain with demonstrated benefits. The proposed MBE-MTC preparation provides an alternative way for MTI either for increased MTC or simultaneous and symmetric capture of the MTC or its changes in tissue.  

Tobias Lenich, André Pampel, Toralf Mildner, Riccardo Metere, Harald Möller

In CEST/NOE experiments, induced saturation intended for certain metabolites also saturates other moieties, leading to mingled backgrounds in Z-spectra. Precise quantification of endogenous metabolites is impeded by slow acquisition times and confounding background contributions. We present an optimization framework targeting a flattened baseline in Z-spectra, with direct water saturation and non-specific macromolecular contributions fully compensated. Saturation pulse amplitudes as a function of frequency offset were derived using optimal-control-based calculation. Feasibility of this approach is demonstrated in vitro for NOE/CEST in the presence of tissue-like background and accelerated acquisition by distinct offset selection. Experimental results show good agreement with concentration levels.

Lin Chen, Xiang Xu, Haifeng Zeng, Kannie Chan, Nirbhay Yadav, Shuhui Cai, Kathryn Schunke, Nauder Faraday, Peter van Zijl, Jiadi Xu

We demonstrate that off-resonance VDMP can be used as an exchange rate filter to distinguish and quantify the slow- and fast-exchanging components in Z-spectra by applying an appropriate number of pulses and varying the mixing times. The method can be used to extract predominantly fast-exchanging protons by separating out the slow-MTC pool, and provides information about the chemical exchanging species in tissue that conventional MT/CEST technique cannot access.

Zhongliang Zu, Elizabeth Louie, Eugene Lin, Xiaoyu Jiang, Mark Does, John Gore, Daniel Gochberg

The CEST signal around 2 ppm may have applications in cancer and muscle imaging and is likely related to an important energy molecule, creatine. In this work, we provide a specific metric to better quantify this signal based on modification of our previously developed CERT approach and an inverse analysis. Results show that the CEST signal at 2 ppm is hypointense in tumors which may be due to decreased creatine content.

Ken-Pin Hwang, Chunxiao Guo, Joshua Yung, Christopher MacLellan, Erik Cressmann, R. Stafford

Chemical exchange saturation transfer (CEST) is observed by applying off-resonance saturation pulses at multiple frequencies and measuring the change in water signal. However, if lipid molecules are present, signals from both species contribute to overall voxel signal, confounding spectral measurement. A multiple gradient echo sequence was developed to simultaneously perform chemical shift imaging with CEST to decouple these signals and measure the independent effect of off-resonance saturation transfer to water. 2D spectra were reconstructed, from which individual water-only z-spectra were obtained. In data from a mixed species phantom, amide proton peaks were clearly visible despite the presence of lipid signal.

Julius Chung, Wonmin Choi, Tao Jin, Jung Hee Lee, Seong-Gi Kim

With chemical-exchange sensitive imaging, increasing field narrows the linewidth of magnetization transfer effects and shifts relative exchange rates (exchange rate vs. chemical shift) toward a slower exchange regime.  This study is intended to explore the interplay of contrast mechanisms and sensitivity benefits by comparing phantom and in-vivo data acquired at the fields of 9.4T and 15.2T.  The linewidth narrowing effect between the fields is demonstrated in agar phantoms with nicotinamide as well as spectra from the rat cortex.  Spectra taken at higher power shows increase of sensitivity by shifting toward a slower exchange regime. 

Robert Brand, Nicholas Blockley, Michael Chappell, Peter Jezzard

We propose a novel 3D method called Dual-CEST, which simultaneously captures the CEST contrast stored in the longitudinal and transverse magnetisation of the bulk water. By including ADC events and a hexagonal spoiling scheme during the CEST preparation phase we collected the usually neglected transverse signal, generated by direct water saturation (a method we call NoXi-CEST). The unaffected longitudinal magnetisation is then acquired using a 3D-GRASE readout resulting in one (Dual-CEST) sequence (3:15 min) that provides XY-spectra, in addition to conventional Z-spectra, and producing additional CEST-contrast and B₀-maps without loss of contrast or additional scan time (compared with conventional imaging). 

Jane Ellis, Mabel Li, Michael Chappell, Mathew Robson, Christopher Rodgers

The development of a novel CEST technique optimised to measure creatine in the human heart. After unsuccessful measurement of in vivo creatine concentrations using MTR_asym, more robust model-based analysis methods based on spectral line shapes were tested and implemented on phantom data, with these model-based methods showing significant improvement to MTR_asymanalysis. Going forward, the developed pulse sequence combined with the model-based analysis methods are a promising step towards human cardiac creatine CEST.

Yin Wu, Iris Zhou, Jing Zhao, Phillip Sun

Routinely used magnetization transfer (MT) asymmetry in measurement of pH-sensitive amide proton transfer (APT) effect is susceptible to concomitant contributions, including semisolid MT and nuclear overhauser effect (NOE). In this study, multi-pool contribution from NOE, MT, CEST at 2 ppm and APT during the acute stroke was resolved with a sum of five Lorentzian functions. Results confirmed the changes in MT and NOE offset each other, and reduction of APT was approximately two-fold of the CEST effect decrease at 2 ppm, dominating the commonly observed pH-sensitive MTR_asym change during acute stroke.

Alex Smith, Richard Dortch, Seth Smith

Basic models to characterize the CEST effect in vivo suffer from competing magnetization transfer (MT) effects. Here, we use qMT to model the CEST effect and derive CEST indices that are independent of MT. Additionally, simultaneously assessing the MT and CEST effects provides more robust estimates of other elements of the MT effect. Simulations and initial in vivo findings suggest that combining MT and CEST fitting provides a more accurate fit of CEST z-spectra than a traditional single pool Lorentzian fit, and thus provides estimates of the CEST effect that are not dependent on the MT effect.

Frederico Severo, Noam Shemesh

Chemical Exchange Saturation Transfer (CEST) affords metabolic imaging at high spatial resolution, especially at ultrahigh fields. However, when spectral overlap exists downfield, metabolite maps may be contaminated by other unwanted signals. Here, we present a methodology termed overlap-resolved-CEST (orCEST), which, through subtraction in CESTasym spectra, provides enhanced specificity. We demonstrate how this technique can be used to resolve the signals of Glutamate and GABA – the Central Nervous System’s primary neurotransmitters in vivo. 

Paula Croal, Kevin Ray, Yunus Msayib, James Larkin, Brad Sutherland, George Harston, Andy Baldwin, Alastair Buchan, Peter Jezzard, James Kennedy, Nicola Sibson, Michael Chappell

Model-based analysis of APT MRI has been shown to quantitatively outperform conventional approaches such as asymmetry analysis. However clinical application is hindered by slow acquisition of whole z-spectra, and processing times. Here, we demonstrate that by using only  a subset of frequency offsets, acquisition and processing time can be reduced by ~70% and ~90%, respectively. Using an MCAO model of ischemic stroke, we demonstrate that our Reduced Frequency Offset approach is able to detect significant differences in APTR* between healthy and ischemic tissue.

Tobias Lenich, André Pampel, Toralf Mildner, Riccardo Metere, Harald Möller

Here, we aim to demonstrate the effects of complex multi-pool background systems with magnetization transfer (MT) on asymmetry and ratio-based analyses for CEST/NOE experiments. By using creatine in cross-linked BSA as a model, we show effects of background variations on such analyses for creatine CEST (CrCEST) based on experimentally obtained spin system parameters. For changes of up to 50% in background pool fractions, the CrCEST peak was found to change by up to 35% in asymmetry analysis. The necessity of model-based fitting with inclusion of complex background systems in contrast to conventional lineshape-based analysis is outlined.

Yee Kai Tee, Badrul Abidin, Alexandr Khrapitchev, Brad Sutherland, James Larkin, Kevin Ray, George Harston, Alastair Buchan, James Kennedy, Nicola Sibson, Michael Chappell

CEST and NOE effects in ischemic stroke at 9.4T were studied using a Lorentzian multi-pool approach. It was found that both the CEST and NOE signals had significant changes in region of acute ADC reduction when compared with contralateral tissue. The contrast or relative values to the contralateral tissues of MTRasym(3.5 ppm) was found to correlate moderately strongly with the relative amide signal at 3.5 ppm but not the relative reference signal at –3.5 ppm, suggesting that it is should be used in the group analysis in a population-wide basis to assess the change of APT in the ischemic stroke.

Rachelle Crescenzi, Paula Donahue, Allison Scott, Vaughn Braxton, Helen Mahany, Sarah Lants, Manus Donahue

We demonstrate for the first time abilities to perform lymphangiography non-invasively using turbo-spin-echo 3.0T MRI pulse sequences. Contrast consistent with lateralizing disease was observed in patients with known secondary lymphedema from breast cancer treatment-related lymphedema, which also adjusted in an expected manner following manipulation of lymphatic stasis through manual lymphatic drainage therapy. These findings suggest that MRI may be well-suited to evaluate lymphatic functioning and lymphedema treatment response, and may have relevance for informing personalized lymphedema risk before surgery or following breast cancer therapies. 

Lukas Buschle, Christian Ziener, Martin Rückl, Ke Zhang, Volker Sturm, Gergely Solecki, Frank Winkler, Martin Bendszus, Sabine Heiland, Heinz-Peter Schlemmer, Felix Kurz

The gradient echo and spin echo signal in brain tissue depend both on diffusion and susceptibility effects around and from capillaries, i.e. on structural and functional information that arise from the microvascular networks. In this work, the dependence of the relaxation rates R2 and R2* on capillary radius are considered for a random arrangement of capillaries in the strong collision approximation, and a closed-form solution is derived. Radius maps are then constructed for glioblastoma mice (N=8) to reveal an increased vessel radius in tumorous tissue as compared to non-affected brain tissue.

Olivier Girard, Victor Carvalho, Pierre Thureau, Valentin Prevost, Samira Mchinda, Gopal Varma, David Alsop, Guillaume Duhamel

Inhomogeneous magnetization transfer (ihMT) is a promising technique for central nervous system imaging. Although ihMT signal is mostly observed in myelinated tissues, weaker ihMT signal may be revealed in other biological tissue. The fundamental relationship between the underlying NMR lineshape and the ihMT signal is still an open question. Here we investigate high resolution magic-angle spinning (HR-MAS) NMR to provide insight into the mechanisms underpinning line broadening of ihMT responsive samples. The resulting spectra evidence different dipolar Hamiltonian components contributing to line broadening and support ihMT as being dominated by inhomogeneous interaction in myelinated tissues.

Weiqiang Dou, Simone Mastrogiacomo, Olga Koshkina, Andor Veltien, Mangala Srinivas, X. Frank Walboomers, Arend Heerschap

To enhance MR image contrast of calcium phosphate cement (CPC) to bone, CPC was tagged with ¹⁹F loaded nanoparticles.  This ¹⁹F labeled CPC material, after implantation into bone defects in rat legs, was monitored in vivo at 11.7T by longitudinal ¹⁹F zero echo time (ZTE) MR imaging. We demonstrate that the overlay of ¹⁹F ZTE images on ¹H images allows for an excellent qualitative view of CPC with no background. By a quantitative evaluation of the ¹⁹F signal the in vivo degradation of CPC over weeks can be followed by MRI. 

Nicholas Payne, Lionel Broche, David Lurie

Fast Field-Cycling MRI (FFC-MRI) has the ability to access contrast invisible to conventional scanners – that resulting from the dependence of T₁ on magnetic field strength. Simulating FFC-MRI sequences by iteratively applying the Bloch equations as the magnetic field strength changes with time was found to give highly accurate predictions of signal intensity at the end of each cycle. This information was used to optimise parameters of the FFC-MRI scans.

Nicolas Chanet, Geneviève Guillot, Ludovic de Rochefort

Fast Field Cycling (FFC) MRI enables rapid and precise relaxometry measurements as a function of magnetic field B₀. Up to now, it was possible to measure longitudinal R₁-NMRD profiles and to generate innovative R₁-dispersive contrasts. However, the ability to measure transverse R₂-NMRD profiles has still to be investigated. Here, a spin-echo based FFC sequence is developed to measure R₂-dispersion, and is applied to ferritin and Gd-DOTA in the range 1.15 to 1.85 T. It is shown that measurements of R2 dispersion could be obtained accurately with the FFC-MRI technology.

Martin Lizak, Natella Maglakelidze, Brittany Oliver, Don Farthing, Hellmut Merkle, Ronald Gress, Nataliya Buxbaum

In vivo deuterium labeling via ingestion of deuterated water was combined with magnetic resonance imaging to demonstrate a method for studying diseases with groups of rapidly dividing cells.  This method was applied to a mouse model of chronic graft versus host disease to demonstrate feasibility.

Pascal Spincemaille, Qihao Zhang, Thanh Nguyen, Yi Wang

A vector field perfusion (VFP) approach is proposed to quantify three dimensional blood flow in tissue. The traditional lumped-element Kety equation for characterizing perfusion is fundamentally flawed with the indetermination of arterial input function. The standard continuity equation based on velocity vector field is proposed for fitting tomographic data. Preliminary analysis of dynamic contrast enhanced MRI and arterial spin labelled MRI of the brain demonstrate the feasibility of this VFP approach.

Andrea Horváth, Csanad Varallyay, Daniel Schwartz, Joao Prola Netto, Peter Varallyay, Laszlo Szidonya, Gerda Toth, Rongwei Fu, Prakash Ambady, Peter Bogner, Edward Neuwelt

Ferumoxytol is a nano-sized iron oxide particle approved for iron replacement therapy and may be used off label as an MRI contrast agent. While gadolinium-based contrast agents leak into the brain parenchyma where the blood brain barrier is not intact several minutes after administration, ferumoxytol remains intravascular for hours due to its high molecular weight, enabling excellent vascular visualization, with visible parenchymal enhancement peaking 24 hours after administration. In this study, we compared ferumoxytol T1 enhancement to standard of care gadoteridol enhancement with a quantitative method, which is an important step to develop ferumoxytol as an alternative MR imaging agent. 

Lionel Broche, Yang Huang, Sandra Pierre, Francois Berger, David Lurie, Pascal Fries, Hana Lahrech

FFC-NMR is a unique tool for the measurements of molecular dynamics in the range of nano- to microseconds. With the development of FFC-MRI scanner, it is now possible to investigate new contrasts using field-dependant variations of T₁ to obtain quantitative markers in diseases. In this work we investigate what information FFC-NMR can provide in the context of glioma, using frozen human brain resection from glioma and epileptic surgery. We found that the quadrupolar peaks and T₁ dispersions values may be useful biomarkers.

Elena Kleban, Richard Bowtell, Penny Gowland, Molly Bright

We propose that a two-compartment model of the evolution of signal phase, processed using Frequency Difference Mapping, could be applied to study venous oxygenation and architecture at the microscopic scale. This study demonstrates proof-of-concept, quantifying Yv in large vessels, and tests the sensitivity of these values to hyperoxia. We discuss how this new method can be adapted to probe venous microstructure within grey matter, providing more sensitive measures of brain tissue function.

Tameshwar Ganesh, Marvin Estrada, James Duffin, Hai-Ling Cheng

The ability of blood vessels to modulate vascular tone (i.e. blood volume) is an important normal physiological function, which is compromised in multiple diseases, including diabetes and heart diseases.  To date, there is no non-invasive imaging technique to assess dynamic microvascular blood volume response. Herein we present a novel MRI technique to assess vasoactive response in “near” real-time in extra-cranial tissues.  We employ a blood-pool agent Gadofosveset (Vasovist) together with a variety of vasoactive gas stimuli. In-vivo results in kidney and liver demonstrate we can visualize dynamic changes in gas-induced blood volume changes, as confirmed on laser Doppler perfusion. 

Jinil Park, Soon Ho Yoon, Chanhee Lee, Jin Mo Goo, Jang-Yeon Park

Some contrast mechanisms like in- and out-of-phase contrasts of fat and water come into play at sub-millisecond echo times(TE) at high field strengths above 3T, and under-recognition of them can lead to misunderstanding of signal intensities and inappropriate interpretation of normal and disease pathology. Here the TEs including the sub-millisecond ones were estimated at various field strengths and it was demonstrated by phantom and human lung imaging that contrast mechanisms are apparently seen at the sub-millisecond TE and thus should not be overlooked at high field strengths when using UTE imaging techniques that can cover the range of sub-millisecond TE.

Ciara McErlean, Yann Jamin, Jessica Boult, James D'Arcy, Martin Leach, David Collins, Simon Robinson, Simon Doran

Functional MRI measurements of vasculature must be robustly validated pre-clinically. Optical computed tomography (CT) offers high-resolution ex vivo 3D imaging of perfused vasculature using India ink staining. We compared optical CT measurements of murine kidney blood volume with previously published MRI relative blood volume measurements. Fractional blood volumes of different kidney regions in optical CT images were calculated using Frangi vessel filtering, for three concentrations of India ink-staining. Significant positive correlations were found between optical CT and MRI measurements for 10% and 15% India ink staining. This is a potentially promising method for easily and cheaply validating MRI vasculature measurements. 

Sebastien Bär, Matthias Weigel, Dominik von Elverfeldt, Jürgen Hennig, Jochen Leupold

For applications like dynamic imaging, the relatively fast decaying hyperpolarized signal must be acquired over a higher number of sequence cycles and the optimal refocusing flip angle needs to be determined. Optimizing the RARE refocussing flip angles allow to optimize the signal exploitation. Furthermore, optimizing the flip angles of a RARE-based varying flip-angle TRAPS sequence enables an even longer prolongation of the signal lifetime.

Yan Luo, Hao Yu, Yaqi Shen

Threonine manganese chelate is a widely used nutritional food addictive. In this pilot study, we investigated the feasibility of threonine manganese chelate as a gastrointestinal contrast agent for MRI in rat models. Our study found that threonine manganese chelate aqueous solution created dark lumen on T1w, T2w and DWI images on rat models without obvious side effect. Threonine manganese chelate might be a promising enteral contrast agent for MRI on animal models.

Hyunyeol Lee, Michael Langham, Cheng Li, Ana Rodriguez-Soto, Felix Wehrli

The OxFlow method provides a global CMRO2 estimation in a single pulse sequenc by combining phase-contrast-based flow mapping with estimation of venous oxygen saturation via susceptometry-based oximetry. However, four-interleave in convenional OxFlow makes it difficult to measure rapid changes of brain metabolic states such as response to apneic stimuli. Thus, in this work a highly efficient, multiplexed imaging based OxFlow method was developed and its feasibility was demonstrated in estimation of dynamic CMRO2 in response to an apneic challenge.

Stefano Mandija, Petar Petrov, Jord Vink, Sanne Schuite-Koops, Peter Luijten, Cornelis van den Berg, Sebastian Neggers

In the field of neurostimulation, Transcranial Magnetic Stimulation is gaining more and more momentum since it allows direct control on brain activation in a non-invasive and non-painful manner. However, accuracy of TMS administrations and precise knowledge on its biological effects are still limited. To better understand TMS induced effects, we propose a novel combined TMS-MRI framework which allows us to map the TMS induced magnetic field and to map subject-specific brain activation by means of concurrent TMS-MRI measurements. These subject-specific measurements, will allow us to validate neuronal models which are currently used to predict TMS induced brain activations.

Chengyan Wang, Fei Gao, Hanjing Kong, Li Jiang, Wenjian Huang, Rui Wang, Kai Zhao, Yan Jia, Hui Xu, He Wang, Xiaodong Zhang, Li Yang, Jue Zhang, Xiaoying Wang, Jing Fang

Since the use of angiographic and endovascular procedures increased rapidly during the past decades, the frequency of atheroembolic renal disease raised recently. This study demonstrates the feasibility of applying an MRI based oxygenation imaging to evaluate renal ischemia in an atheroembolic renal disease model. The average renal oxygen extraction fraction (OEFs) as well as the ratios between embolized kidney and contralateral kidney show significant differences between groups. Renal OEF measurement appears to be able to delineate different severities of renal ischemia by revealing information about the balance between tubular workload and delivery of oxygen. 

Harshan Ravi, Wen-Tung Wang, Dzung Pham, John Butman

Susceptibility-weighted imaging (SWI) is a MRI sequence which exploits the susceptibility contrast between various tissues by incorporating MRI phase data. In some clinical applications it may be useful to increase such contrast (e.g. identification of plaque associated veins) and in other cases it may be useful to suppress or decrease such contrast (e.g. visualization of microhemorrhage). Here we explore the use of gas inhalation (oxygen and carbogen) to modulate the conspicuity of brain vasculature.

Joshua Greer, Xinzeng Wang, Keith Hulsey, Robert Lenkinski, Ananth Madhuranthakam

Arterial spin labeling (ASL) is a rapidly growing area of interest, primarily because of its ability to provide non-contrast quantitative perfusion maps. For the technique to be adopted for clinical use, these quantitative measurements need to be accurate and robust, which will require a quality controlled perfusion phantom to ensure consistency for different magnet strengths and manufacturers. In this study, we demonstrate a 3D printed perfusion flow phantom that can be easily replicated, and used to test the precision and repeatability of ASL perfusion measurements.

Erin Englund, Zachary Rodgers, Hyunyeol Lee, Felix Wehrli

Hyperoxia gas mixture breathing causes additional oxygen to be dissolved in blood plasma thereby shortening the T₁ of arterial blood (T_1a). Here, we propose a method estimate T1a during hyperoxia gas breathing by solving a perfusion quantification model for T_1a given CBF measured during hyperoxia via phase contrast (PC) of the feeding arteries in the neck. The ratio between PC-based total CBF and ASL-based regional CBF was first determined at baseline, and then applied to normalize the expected ASL-based CBF during hyperoxia. T_1a was estimated as 1.46±0.09 s during hyperoxia gas mixture breathing, in reasonable agreement with previous reports. 

Huici Zhu, Jianyu Liu, Lizhi Xie

To determine which method is better for the observation of vaginal vault and rectocele, this research compared the routine dynamic MRI with the dynamic MRI with vaginal and rectum contrast. There was statistically significant difference between the dynamic MR imaging and dynamic MR imaging with vaginal and rectum contrast. For the observation of vaginal vault prolapse and rectocele, the dynamic MR imaging with vaginal and rectum contrast was better than the routine method. 

Frederick Damen, Rong-Wen Tain, Weigo Li, Xiaohong Zhou, Leon Tai, Kejia Cai

Arterial spin labeling (ASL) MRI, based on endogenous contrast from blood water, is used for research and diagnosis of cerebral vascular conditions. However, artifacts due to imperfect imaging conditions such as B₀ inhomogeneity could lead to variations in the quantification of cerebral blood flow (CBF).  In this study, we investigated the CBF variation artifacts due to B₀-inhomogeneity using Signal Targeting with Alternating Radio frequency (STAR) based ASL. We developed a novel technique, TADDZ, similarly to the corrections for chemical exchange saturation transfer (CEST) experiments, to remove the B₀ inhomogeneity induced CBF artifacts.