Jianxun Qu¹, Tianye Lin^1,2, Karthik Prabhakaran³, M. Dylan Tisdall¹, and John A. Detre^1,3
1Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States, ²Chinese Academy of Medical Sciences, Peking Union Medical College, PUMCH, Beijing, China, ³Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States

Fast spin echo is widely used for ASL acquisition. However, if the flip angle reduced to minimize SAR and/or stabilize signal evolution over the echo train, the fluctuation of CSF increases markedly. This work explored the influence of minimum flip angle, and crusher strength in ASL acquisition. A CSF-prioritized background suppression (BS) planning was also performed. We found that increasing minimum flip angle together with reducing crusher in superior-inferior direction benefits the stability of ASL acquisitions. Prioritizing CSF suppression in BS was also helpful.

Jianxun Qu¹, Tianye Lin^1,2, Priti Balchandani³, M. Dylan Tisdall¹, and John A. Detre^1,4
1Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States, ²Chinese Academy of Medical Sciences, Peking Union Medical College, PUMCH, Beijing, China, ³Icahn School of Medicine at Mount Sinai, New York, NY, United States, ⁴Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States

Inflow blood during the post labeling delay is a significant source of physiological noise in arterial spin labeling. This study utilized a novel inflow saturation method to address this issue. Compared to traditional inflow saturation approach where a 90^o thick saturation slab is used to null blood within the interval of background suppression inversion pulses, the proposed method employs serial of thin slab sub-bolus saturations, with the saturation strength planned adaptively to return the blood to nulling point at the excitation point. The proposed method reduces the inflow artifacts markedly and mitigates global signal fluctuations.

Manuel Taso¹ and David C. Alsop^1
1Division of MRI research, Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States

While widely used for perfusion imaging, the flow-driven inversion labeling commonly used with pseudo-continuous ASL (PCASL) presents a significant off-resonance sensitivity as well as high power deposition potentially limiting high-field applications. We therefore investigated an alternate labeling scheme that takes advantage of the multiple aliased labeling planes that arise within the labeling RF envelope when reducing the peak-to-average gradient ratio. First numerical simulations and experiments show the potential for low-SAR, B0 and flow-velocity robust saturation labeling.

Joshua S. Greer^1,2, Yiming Wang², Limin Zhou², Tarique Hussain^1,2, and Ananth J. Madhuranthakam^2,3
1Pediatrics, UT Southwestern Medical Center, Dallas, TX, United States, ²Radiology, UT Southwestern Medical Center, Dallas, TX, United States, ³Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States

Pulmonary perfusion imaging using ASL has been demonstrated using the pCASL technique with varying degrees of reproducibility. In this study, a pCASL labeling strategy is proposed to improve the stability of perfusion signal in the lungs using cardiac triggering to reduce flow-induced signal variations, and background suppression to improve SNR. With the proposed technique, high SNR perfusion images are created with a limited number of signal averages. This optimized approach may allow full coverage of the lungs in clinically reasonable scan times.

Wenjing Xu^1,2, Jiadi Xu^3,4, and Xiaoyong Zhang^1,2
1Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China, ²Key Laboratory of Computational Neuroscience and Brain-Inspired Intelligence (Fudan University), Ministry of Education, Shanghai, China, ³Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ⁴F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States

We developed a drift-corrected steady pulsed imaging and labeling (dSPIL) to measure CBF with high-resolution and whole brain coverage. We applied a metric of low band pass to remove MRI signal drift using interleaved label-control images. We also optimized several key imaging parameters in an effort to minimize scan time while covering the whole brain. With the optimized dSPIL scheme, quantification of high-resolution CBF in 22 mouse brain regions can be obtained. As a demonstration and validation of the method, the volume of ischemic lesion regions in mice was quantified by calculating CBF reductions.
 

Chenwei Tang¹, Mu-Lan Jen¹, Laura Eisenmenger², and Kevin M Johnson^1,2
1Department of Medical Physics, University of Wisconsin-Madison, Madison, WI, United States, ²Department of Radiology, University of Wisconsin-Madison, Madison, WI, United States

While
pseudo-continuous ASL (pCASL) is still the recommended technique for clinical
and research applications, it suffers from subject vascular
anatomy dependent variations in tagging efficiency which may lead to inaccurate
quantification of perfusion, or gross misrepresentations of perfusion
heterogeneity. In this work, we explore a strategy in which a span of tagging
plane offsets and rotations is performed and cerebral blood flow (CBF) is robustly
estimated retrospectively from the series of images with differential tagging
efficiency. Our results demonstrate significant fluctuation of measured CBF for
different relative labeling plane locations and robust recovered CBF against
these fluctuations.

Yiming Wang¹, Limin Zhou¹, Sheng Qing Lin¹, Joshua S. Greer^1,2, and Ananth J. Madhuranthakam^1,3
1Radiology, UT Southwestern Medical Center, Dallas, TX, United States, ²Pediatrics, UT Southwestern Medical Center, Dallas, TX, United States, ³Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States

3D arterial spin labeled (ASL) MRI using turbo spin echo (TSE) based acquisitions suffer from image blurring, due to T₂ decay along the echo train. To date, several methods have been proposed to reduce T₂ blurring, including k-space filtering and variable flip angle schemes. In this study, the performances of k-space filtering was compared with variable flip angle scheme to compensate or reduce T₂ blurring of 3D ASL images acquired with Cartesian TSE. Results showed k-space filtered images provided similar sharpness improvement compared with variable flip angle method.

Yiming Wang¹, Limin Zhou¹, Joshua S. Greer^1,2, Marco C. Pinho^1,3, Joseph A. Maldjian^1,3, and Ananth J. Madhuranthakam^1,3
1Radiology, UT Southwestern Medical Center, Dallas, TX, United States, ²Pediatrics, UT Southwestern Medical Center, Dallas, TX, United States, ³Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States

3D Cartesian turbo spin echo (TSE) acquisition has shown robustness for arterial spin labeled (ASL) MRI. However, 3D Cartesian TSE are acquired with single average due to relatively long TR and longer scan times, which may lead to suboptimal signal to noise ratio (SNR). In this study, we implemented variable density sampling of 3D Cartesian TSE that acquires the center of the k-space with higher signal averages, and improves the robustness and SNR without significantly prolonging the scan time. We further combined this with M₀ images using partial k-space to compensate for increased scan time, but without compromising perfusion quantification.  

Nora-Josefin Breutigam¹, Daniel Christopher Hoinkiss¹, Mareike Alicja Buck¹, Amnah Mahroo¹, Federico von Samson-Himmelstjerna¹, and Matthias Günther^1,2
1MR Physics, Fraunhofer MEVIS, Bremen, Germany, ²MR-Imaging and Spectroscopy, Faculty 01 (Physics/Electrical Engineering, University of Bremen, Bremen, Germany

The presented automated inner-scan timing adjustment for subject-specific pCASL measurements can reduce uncertainties in perfusion quantification. The high variability of arterial transit times often leads to undesired arterial transit delay (ATD) artifacts. The method evaluated here allows the optimal FL-bolus duration to be individually adjusted by analyzing intermediate decoded perfusion-weighted images and directly adjusting the sub-bolus durations without increasing the measurement time. The aim is to reduce the FL-bolus duration as much as necessary, but to keep it as long as possible in order to obtain a maximum signal. 

Jörn Huber¹, Daniel Christopher Hoinkiss¹, and Matthias Günther^1,2
1Fraunhofer MEVIS, Bremen, Germany, ²University of Bremen, Bremen, Germany

This study introduces a subject-specific automated approach for optimization of background suppression (BS) in 3D pseudo-continuous arterial spin labeling perfusion imaging. Optimised timing of BS related FOCI pulses is calculated from the T1 spectrum, obtained from a M0 scan of the organ of interest. Results show strong suppression of brain tissue, when magnetization is nulled at the time of excitation as well as high quality perfusion images, when a slight delay between nullpoint and excitation is introduced for different numbers of FOCI pulses.

Tianye Lin^1,2, Jianxun Qu², and John A. Detre^2
1Chinese Academy of Medical Sciences, Peking Union Medical College, PUMCH, Beijing, China, ²University of Pennsylvania, Perelman School of Medicine, Philadelphia, PA, United States

The purpose of our study was to demonstrate that the inflow of arterial blood in post-labeling delay can cause intravascular high signal in multi-PLD ASL that resembles arterial transit artifact and potentially interfere with clinical interpretation. An optimized inflow-saturation method was used to suppress this artifact and improve the image quality of Hadamard-encoded and sequential multi-PLD ASL.

Shota Ishida¹, Hirohiko Kimura², Naoyuki Takei³, Yasuhiro Fujiwara⁴, Tsuyoshi Matsuda⁵, Yuki Matta¹, Masayuki Kanamoto¹, Nobuyuki Kosaka², and Eiji Kidoya^1
1Radiological center, University of Fukui Hospital, Eiheiji, Japan, ²Department of Radiology, Faculty of Medical Sciences, University of Fukui, Eiheiji, Japan, ³Global MR Applications and Workflow, GE Healthcare Japan, Hino, Japan, ⁴Department of Medical Image Sciences, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan, ⁵Division of Ultra-high Field MRI, Institute for Biomedical Science, Iwate Medical University, Shiwa-gun, Japan

Delays alternating with nutation for tailored excitation (DANTE) pulse is capable of uniform and flow velocity related signal suppression. DANTE-ASL was compared to T₂-mesurement in ASL (T₂-ASL) to validate what spin-compartment is suppressed by DANTE. T₂-ASL showed labeled signal remained in vascular compartment even at a PLD of 2.0 s. However, ASL signals using DANTE were approximately similar value in all the PLDs (0.5, 1.0, 2.0, and 3.0 s), because ASL signals in vascular compartment were suppressed selectively and sufficiently with concurrently preserving signals in tissue compartment. We could eliminate vascular compartment from total ASL signal using DANTE.

Moss Y Zhao¹, Audrey P Fan¹, David Yen-Ting Chen^1,2, David D Shin³, Mohammad Mehdi Khalighi¹, Dawn Holley¹, Kim Halbert¹, Andrea Otte¹, Brittney Williams¹, Jun-Hyung Park¹, Bin Shen¹, and Greg Zaharchuk^1
1Department of Radiology, Stanford University, Stanford, CA, United States, ²Department of Radiology, Shuang-Ho Hospital, Taipei Medical University, Taipei, Taiwan, ³GE Healthcare, Menlo Park, CA, United States

This work investigates the repeatability of CVR (induced by acetazolamide) using ASL on a healthy cohort. Single and multi-PLD PCASL data were collected before and after the administration of acetazolamide in two identical sessions. Results showed that the mean CVR of both ASL techniques were between 20% and 60% and not significantly different. Measurement using single-PLD PCASL demonstrated higher repeatability based on a lower coefficient of variation and a higher intraclass correlations.

Xin Logan Zhang¹, Joseph G. Woods^1,2, Flora Kennedy McConnell¹, Thomas W. Okell¹, and Michael A. Chappell^1
1Institute of Biomedical Engineering & Wellcome Centre for Integrative Neuroimaging, University of Oxford, Oxford, United Kingdom, ²Department of Radiology, University of California San Diego, La Jolla, CA, United States

A general framework has been proposed for optimising PLD sampling protocols in pCASL under an ideal kinetic model. In this study, the performance of CBF and ATT estimation of two optimised protocols CBF-ATT_opt and CBF_opt, along with a reference multi-PLD and single-PLD protocol, was investigated using simulations and in vivo when accounting for dispersion and macrovascular contamination (MVC) over a prolonged ATT range. CBF_opt showed the least sensitivity among all protocols for CBF estimation when ATT was prolonged and when MVC was present. Future work can optimise for both macrovascular component and tissue component with a prolonged ATT range.

Mu-Lan Jen¹, James H Holmes², Laura Eisenmenger², and Kevin M Johnson^1,2
1Medical Physics, University of Wisconsin-Madison, Madison, WI, United States, ²Radiology, University of Wisconsin-Madison, Madison, WI, United States

In this work, we investigate a strategy to acquire single-shot, multi b-value, multi-delay ASL scans using the combination of an undersampled spiral in-out 3D fast spin echo readout with reconstructions enforcing a low rank constraint with an expanded encoding model. Images are demonstrated in healthy volunteers, acquiring single 3D ASL images in as short as 11s.

Xinqiang Yan^1,2, Manus J. Donahue^1,2, and William A. Grissom^1,2,3
1Department of Radiology, Vanderbilt University Medical Center, Nashville, TN, United States, ²Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, ³Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States

Arterial spin labeling (ASL) is a primary approach for non-invasive perfusion measurements with MRI. Theoretically, performing ASL at ultrahigh magnetic field strength can be beneficial because of the increased SNR as well as the lengthened T1-relaxation time. However, ASL is still not widely used at 7T due to the obstacles of B₁⁺ inhomogeneity and high SAR associated with labeling. To overcome this problem, we apply array compressed parallel transmission (acpTx) in ASL and find that the optimized coil achieved 2x better B₁⁺ homogeneity, and 4x lower SAR than a conventional 8-channel coil, which could enable 7T ASL with neck labeling.

Oliver Maier¹, Stefan M Spann¹, Daniela Pinter², Thomas Gattringer², Lukas Pirpamer², Christian Enzinger², Josef Pfeuffer³, and Rudolf Stollberger^1,4
1Institute of Medical Engineering, Graz University of Technology, Graz, Austria, ²Deptartment of General Neurology, Medical University of Graz, Graz, Austria, ³Application Development, Siemens Healthcare, Erlangen, Germany, ⁴Biotechmed, Graz, Austria

Multi-Delay single-shot ASL imaging provides accurate CBF and, in addition, ATT maps but the inherent low SNR can be challenging. State-of-the-art fitting techniques can improve the SNR in the estimated maps but typically suffer from spatial blurring. To this end, we propose a new reconstruction method with a joint TGV regularization on CBF and ATT to reconstruct sharp maps with improved noise suppression. Validation of the proposed method on a healthy subject and five stroke patients showed preservation of even small features in CBF and ATT while increasing SNR and sharpness over recent approaches.

Nam Gyun Lee¹, Ahsan Javed², Terrence R. Jao¹, and Krishna S. Nayak^2
1Biomedical Engineering, University of Southern California, Los Angeles, CA, United States, ²Electrical and Computer Engineering, University of Southern California, Los Angeles, CA, United States

We propose a numerical approximation to Buxton's general kinetic model (GKM) for ASL quantification that will enable greater flexibility in ASL acquisition methods. The proposed method combines the Bloch-McConnell equations with the flow effects and hence model the effects of flow simultaneously with magnetization transfer, T2 effects, off-resonance, and irregular timing of labeling. These can be solved using Jaynes’ matrix formalism. The proposed approximation is compared with GKM using simulations for PASL, PCASL, steady-pulse ASL, and MR fingerprinting ASL. Accuracy of the approximation is studied as a function of a key “time interval” parameter using Monte-Carlo simulations.

Thomas Kirk^1,2, Flora Kennedy McConnell^1,2, Dimo Ivanov³, Sriranga Kashyap³, Martin Craig^1,2, and Michael Chappell^1,2
1Institute of Biomedical Engineering, University of Oxford, Oxford, United Kingdom, ²Wellcome Centre for Integrative Neuroimaging, University of Oxford, Oxford, United Kingdom, ³Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands

We have recently developed a new approach to partial volume estimation that uses surface segmentations (for example, those produced by FreeSurfer). We compare this approach to conventional volumetric PV estimation for the application of PV correction to two ASL datasets and find evidence in support of using surface-derived PV estimates.

Piet Bladt¹, Quinten Beirinckx¹, Merlijn C.E. van der Plas², Sophie Schmid², Wouter M Teeuwisse², Ben Jeurissen¹, Arnold J den Dekker¹, Jan Sijbers¹, and Matthias J.P. van Osch^2,3
1imec - Vision Lab, Department of Physics, University of Antwerp, Antwerp, Belgium, ²C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands, ³Leiden Institute of Brain and Cognition, Leiden University, Leiden, Netherlands

Super-resolution reconstruction (SRR) allows for high-resolution image reconstruction from a set of low-resolution multi-slice images with different orientations. Arterial spin labeling (ASL) is an interesting albeit complicated candidate for SRR, as it relies on subtraction. SRR-ASL can be performed on low-SNR subtracted or on low-contrast unsubtracted ASL data. Different ASL-SRR implementations were applied to single-PLD PCASL data and validated against traditional ASL-scans. Combining motion correction, super-resolution post-processing and pairwise subtraction of label-control pairs in a single framework yielded comparable CBF maps as with traditional HR-ASL. Furthermore, in certain slices, SRR-ASL appears to reconstruct the underlying anatomical structure with higher fidelity.

Iris Asllani^1,2, Alicia Plaindoux³, Jan Petr⁴, Joseph G. Woods^5,6, Matthias J. P. van Osch⁷, and Mara Cercignani^1
1Neuroscience, University of Sussex, Brighton, United Kingdom, ²Biomedical Engineering, Rochester Institute of Technology, Rochester, NY, United States, ³Grenoble Institute of Technology, Grenoble, France, ⁴Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany, ⁵University of California San Diego, San Diego, CA, United States, ⁶University of Oxford, Oxford, United Kingdom, ⁷Leiden University Medical Center, Leiden, Netherlands

Intra- and extra-neurite perfusion in gray and white matter were estimated by applying a spatial linear regression algorithm on ASL images using the micro-structural anatomical information derived from the NODDI analysis of the DWI data. Baseline ASL images were acquired with 4 post-labeling delay (PLD) values in order to test the hypothesis of redistribution of ASL signal across the micro-compartments with increasing PLD. Motor activation was used to investigate the sensitivity of the method for detecting changes in perfusion at the micro-structural level.  

Qihao Zhang¹, Liangdong Zhou², John Morgan³, Thanh D Nguyen⁴, Pascal Spincemaille³, and Yi Wang^2
1Cornell University, Ithaca, NY, NY, United States, ²Weill Cornell Medicine, New York, NY, United States, ³Radiology, Weill Cornell Medicine, New York, NY, United States, ⁴Weill Cornell Medicine College, New York, NY, United States

Tissue flow vector field is generated by solving the inverse problem of a voxelized transport equation using multi-delay ASL data and an optimization method. The accuracy of the flow estimation is validated on a vasculature model. For calculating flow vector field in vivo, time resolved 3D (4D) tracer concentration data is acquired using a multi-delay pseudo continuous ASL sequence. The background suppression pulse is interleaved into labeling pulse to generate short post label delay. The output flow magnitude map shows a more anterior-poster-uniform CBF than the traditional Kety’s method.

Paul Kyu Han¹, Yanis Djebra^1,2, Thibault Marin¹, Georges El Fakhri¹, Jinsong Ouyang¹, and Chao Ma^1
1Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, United States, ²LTCI, Télécom Paris, Institut Polytechnique de Paris, Palaiseau, France

Multi-delay arterial spin labeling (ASL) is a powerful MRI technique that allows to non-invasively measure both cerebral blood flow and arterial transit time quantitatively, which has great potential for clinical applications. However, usage of multi-delay ASL is limited by the prolonged scan time with the number of post-labeling delay times used for acquisition. Up to date, low-rank property has been observed in signals of various MR applications where low-rank approach has demonstrated promising results. This work shows that the dynamics of ASL signal display low-rank property and the scan time of multi-delay ASL can be accelerated using low-rank image reconstruction.

Flora A. Kennedy McConnell^1,2, Jack Toner¹, Thomas Kirk^1,2, Martin Craig^1,2, Andrew R. Segerdahl², Michael P. Harms³, and Michael A. Chappell^1,2
1Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, United Kingdom, ²Wellcome Centre for Integrative Neuroimaging, University of Oxford, Oxford, United Kingdom, ³Department of Psychiatry, School of Medicine, Washington University, St Louis, MO, United States

Surface-based analysis is a popular approach to fMRI analysis as, compared with volumetric analysis, it allows easier registration of functional regions between individuals. This work sought to move towards surface-based perfusion analysis of arterial spin labelling data. It presents a comparison of the results of a surface-based analysis pipeline with results from a conventional volumetric perfusion analysis pipeline projected onto the cortical surface. Bayesian inference of cortical surface perfusion is demonstrated here and is shown to produce substantially lower perfusion estimates than conventional voxelwise analysis. Future work will investigate to origins of these perfusion differences.

Flora Kennedy McConnell^1,2, Sana Suri^2,3, Eniko Zsoldos^2,3, Klaus Ebmeier³, Clare MacKay^2,3, and Michael Chappell^1,2
1Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, United Kingdom, ²Wellcome Centre for Integrative Neuroimaging, University of Oxford, Oxford, United Kingdom, ³Department of Psychiatry, University of Oxford, Oxford, United Kingdom

Within and between subject variability in ASL perfusion data can obscure subtle perfusion changes indicative of neurodegenerative disease. It prohibits the production of a 'healthy' population-average perfusion atlas to which individuals can be compared. This work used a GLM to produce subject-specific perfusion references based on tissue partial volumes. Results show that such a linear model can successfully decompose perfusion, at the population level, into components related to tissue partial volumes. However, the model struggles to capture variability at the individual subject level and thus, the problem will in future be addressed with non-linear modelling techniques.

Danfeng Xie¹, Yiran Li¹, Hanlu Yang¹, Li Bai¹, and Ze Wang^2
1Temple University, Philadelphia, PA, United States, ²University of Maryland School of Medicine, Philadelphia, MD, United States

In this study, we showed that without a noise-free reference, Deep Learning based ASL denoising network  can produce cerebral blood flow images with higher signal-to-noise-ratio (SNR) than the reference. In this learning-from-noise training scheme, cerebral blood flow images with very high noise level can be used as reference during network training. This will remove any deliberate pre-processing step for getting the quasi-noise-free reference when training deep learning neural networks. Experimental results this learning-from-noise training scheme preserved the genuine cerebral blood flow information of individual subjects while suppressed noise.

Dan Zhu^1,2, Dapeng Liu^2,3, Wenbo Li^2,3, Michael Schär², and Qin Qin^2,3
1Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ²Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ³. F.M. Kirby Research Center for Functional Brain Imaging, Johns Hopkins University School of Medicine, Baltimore, MD, United States

Renal perfusion has clinical significance in diagnosis of renal diseases. Velocity-selective arterial spin labeling (VSASL) has minimal sensitivity to arterial transit time delay and velocity-selective inversion (VSI) labeling could improve SNR of perfusion signal. Here renal VSASL images were acquired using different post-labeling delay time and under different B1 shimming conditions. The feasibility of VSI based ASL for renal perfusion mapping at 3T under free breathing is demonstrated on healthy volunteers.

Dapeng Liu^1,2, Wenbo Li^1,2, Feng Xu^1,2, Dan Zhu³, Taehoon Shin^4,5, and Qin Qin^1,2
1Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ²F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States, ³Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ⁴Division of Mechanical and Biomedical Engineering, Ewha Womans University, Seoul, Korea, Republic of, ⁵Department of Medicine, Case Western Reserve University, Cleveland, OH, United States

In Fourier-transform based velocity-selective inversion (FT-VSI) arterial spin labeling (ASL), either velocity-insensitive or velocity-compensated waveforms could be applied for control modules. Under poor B0/B1 conditions with inefficient refocusing, the scheme with velocity-insensitive control is susceptible to strong false signal but maintained high labeling efficiency, while the scheme with velocity-compensated control has poor velocity-selective labeling profiles. This study overcome these problems by proposing a dynamic phase-cycling scheme based on velocity-insensitive waveform and improve the robustness to B0/B1 field inhomogeneities for VSI ASL. Simulation, phantom and brain ASL scans were conducted for demonstration.  

Sophie Schmid^1,2, Leonie Petitclerc^1,2, André Paschoal³, Suzanne Franklin^1,4, Merlijn Van der Plas^1,2, and Matthias Van Osch^1,2
1Radiology, Leiden University Medical Center, Leiden, Netherlands, ²Leiden Institute of Brain and Cognition (LIBC), Leiden, Netherlands, ³Physics, InBrain Lab, University of Sao Paulo, Ribeirao Preto, Brazil, ⁴University Medical Center Utrecht, Center for Image Sciences, Utrecht, Netherlands

In this study the variation in the measured apparent T₂ was assessed over different slices for venous velocity selective inversion (vVSI) with 2D EPI readout in the sagittal sinus and we compared vVSI with 2D EPI and 3D multi-echo spin echo EPI (mTE-SE-EPI) readout to the gold standard TRUST. With the 2D EPI readout the T₂ increases significantly over the slices. 

Shaurov Das¹, Luis Hernandez-Garcia², Ryan Daniel Hernandez³, and Jia Guo^1
1Bioengineering, University of California, Riverside, Riverside, CA, United States, ²Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States, ³Physics, University of California, Riverside, Riverside, CA, United States

Velocity selective ASL (VSASL) is the latest addition to the family of ASL techniques, with good promise on resolving transit delay sensitivity in ASL. Though an improvement in SNR efficiency has been reported by using two-module VS saturation and VS inversion pulse, the comparison between them is yet to be done. This study aims to compare their theoretical performance with Bloch simulation and a few realistic scenarios and look for knowledge about existing limitations which can, in turn, lead to further improvement of these techniques. Additionally, a few variants of VSI pulses including most recent improvement were explored and compared. 

Juliet Polkey¹, Lydiane Hirschler², Suzanne Franklin², Matthias van Osch², and Sophie Schmid^2
1University College London Hospital, London, United Kingdom, ²Leiden University Medical Center, Leiden, Netherlands

To the best of our knowledge this work is the first implementation of VSASL at 7T.  The VSASL technique was compared with FAIR in 3 healthy volunteers. The temporal bolus width was sampled in each case and compared between the two ASL methods. 

Luis Hernandez-Garcia¹ and Jia Guo^2
1FMRI Laboratory, University of Michigan, Ann Arbor, MI, United States, ²University of California at Riverside, Riverside, CA, United States

This work presents an experimental comparison of different velocity selective (VS) labeling strategies for non-contrast perfusion MRI, including new variants of VS saturation and VS inversion, in relation to pseudo-continuous labeling pulses (PCASL).

Kelly Tung Smith¹, Alvin Silva¹, Jonathan Flug¹, Justin Yu¹, and Anshuman Panda^1
1Radiology, Mayo Clinic Arizona, PHOENIX, AZ, United States

In this age of specialized imaging sequences such as liver MR elastography, inexperience with the technical image acquisition and unawareness of artifacts and pitfalls confound diagnostic accuracy due to poor image quality.  We feel there is a knowledge gap in those at the front line involved with image acquisition, and that by defining and filling in this knowledge gap with an educational tutorial module, MR elastography image quality can be optimized and callback rates can be decreased. In turn, decreased callbacks will translate into reduced cost for unnecessary repeated scans; reduced patient time and frustration; and increased MR scheduling access.

Christian Guenthner¹ and Sebastian Kozerke^1
1University and ETH Zurich, Zurich, Switzerland

RF-spoiling is employed in order to reduce transverse coherences. While spoiling angles are typically optimized for contrast, efficacy for bias-free phase-contrast measurements is yet to be proven. Here, we investigate the influence of the RF-spoiling angle on displacement estimates in fast GRE-MR Elastography sequences using Extended Phase Graph simulations. Theoretical findings are validated using a novel RF-spoiling test sequence as well as conventional MRE phantom experiments. An optimal spoiling angle of 158° degrees is identified allowing for bias-free MRE acquisitions at repetition times as low as 5ms.

Daiki Ito^1,2,3, Tomokazu Numano^1,3, Tetsushi Habe^1,2, Toshiki Maeno¹, Kazuyuki Mizuhara^3,4, Surendra Maharjan¹, Kouichi Takamoto⁵, and Hisao Nishijo^6
1Department of Radiological Sciences, Graduate School of Human Health Sciences, Tokyo Metropolitan University, Tokyo, Japan, ²Office of Radiation Technology, Keio University Hospital, Tokyo, Japan, ³Health Research Institute, National Institute of Advanced Industrial Science and Technology, Ibaraki, Japan, ⁴Department of Mechanical Engineering, Tokyo Denki University, Tokyo, Japan, ⁵Department of sport and Health Sciences, Faculty of Human Sciences, University of East Asia, Yamaguchi, Japan, ⁶System Emotional Science, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan

MR elastography (MRE) requires acquisitions of multiple phase offset images. Patient movement between acquisitions of phase offset images is not only difficult to be detected, but also leads to calculate shear modulus incorrectly. To resolve this problem, we present a novel MRE technique that can acquire multiple phase offset images simultaneously (SAMURAI-MRE) using a motion-encoding gradient (MEG)-less multi-echo sequence. MRE images obtained at spin-echo (SE)- and gradient-echo (GRE)-based SAMURAI-MRE were compared with those at conventional SE- and GRE-based MEG-less multi-echo MRE. The results demonstrate that it is possible to perform SAMURAI-MRE, and SE-based SAMURAI-MRE was superior to GRE-based SAMURAI-MRE.

Yi Sui¹, MyungHo In¹, Armando Manduca², Matthew A. Bernstein¹, Richard L. Ehman¹, John III Huston¹, and Ziying Yin^1
1Radiology, Mayo Clinic, Rochester, MN, United States, ²Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, United States

Simultaneous fat-water EPI-MR elastography imaging was developed for acquisition of the brain (water) and skull (bone marrow fat) MRE motion. Compared to our previous dual-saturation and dual-sensitivity motion encoding (DSDM) technique,  the proposed method minimize the EPI distortion and misalignment between skull and brain. This technique could offer a unique opportunity to quantify the skull-brain mechanical decoupling performance modulated by the pia-arachnoid complex, and its potential alterations in response to repetitive head impacts (RHI) in our future studies.

Shahed Khan Mohammed¹, Mohammad Honarvar¹, Davood Karimi¹, Piotr Kozlowski^2,3, and Septimiu Salcudean^1
1Electrical and Computer Engineering, University of British Columbia, Vancouver, BC, Canada, ²UBC MRI Research Center, Vancouver, BC, Canada, ³Department of Radiology, University of British Columbia, Vancouver, BC, Canada

Iterative reconstruction methods in magnetic resonance elastography (MRE) inversion can allow incorporating sparsity prior and can provide displacement filtering. However the problem is difficult to converge as MRE inversion is a non-convex and ill-conditioned problem.  Here, we presented 3D ERBA with total variation prior on the elasticity, which showed good convergence by utilizing a bi-convex optimization of 3D finite element modeling of elastic wave. Extensive experiments on numerical phantom, agar phantom, and in-vivo liver study showed promising indications in detecting inclusion and abnormality, and improving the diagnostic efficacy of MRE. 

Tomokazu Numano^1,2, Daiki Ito^2,3,4, Kazuyuki Mizuhara⁵, Toshikatsu Washio², Tetsushi Habe^3,4, Toshiki Maeno³, Masaki Misawa², and Naotaka Nitta^2
1Radiological Sciences, Tokyo Metropolitan University, Tokyo, Japan, ²National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan, ³Tokyo Metropolitan University, Tokyo, Japan, ⁴Keio University Hospital, Tokyo, Japan, ⁵Tokyo Denki University, Tokyo, Japan

We developed a new technique for dynamic MR elastography (MRE) using a MR magnitude image. A general MRE uses a MR phase image as a wave image. Proposed technique was used a MR magnitude image instead of MR phase image as a wave image by using a special vibration. Proposed technique (special vibration MRE) performance was comparable to that of a continuous vibration MRE. Since special vibration MRE need an only few second vibration, it could dramatically eliminated the patients' vibration-related discomfort.

Cemre Ariyurek^1,2, Yusuf Ziya Ider¹, and Ergin Atalar^1,2
1Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, ²National Magnetic Resonance Research Center (UMRAM), Ankara, Turkey

In Helmholtz inversion an equation is obtained for each MR elastography displacement data collected for each motion direction and each excitation frequency. Under high SNR, SNR of the estimated elasticity map by the Helmholtz inversion can be derived. Prior to the inversion, each equation can be weighted by the SNR of the elasticity estimate to improve SNR of the elastogram and low SNR ones can be thresholded to reduce bias in the elasticity estimation. Simulation and experiment results demonstrate that the original inversion underestimates the elasticity when there is noise and this bias can be corrected by the proposed reconstruction. 

Paul Kennedy^1,2, Daniel Stocker^1,2, Octavia Bane^1,2, Stefanie Hectors^1,2,3, Bradley D Bolster Jr. ⁴, and Bachir Taouli^1,2
1BioMedical Engineering and Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States, ²Department of Diagnostic, Molecular and Interventional Radiology, Icahn School of Medicine at Mount Sinai, New York, NY, United States, ³Department of Radiology, Weill Cornell Medicine, New York, NY, United States, ⁴Siemens Medical Solutions USA, Inc., Salt Lake City, UT, United States

In this study we assess the variation in 2D and 3D MR elastography (MRE) measures in patients, volunteers and a phantom across two MR system vendors. Interobserver variability was also examined. 2D and 3D MRE liver measurements were not significantly different across systems and showed excellent intraclass correlation coefficient (ICC) between readers. Spleen measurement showed excellent ICC between readers but significant variation in 3D MRE spleen stiffness was found between systems. Liver 3D MRE is stable across platforms however further study is required to assess the bias in 3D MRE spleen measurements from multiple vendors.

Shudan Min¹, Jilei Zhang², and Shenghong Ju^1
1Jiangsu Key Laboratory of Molecular Imaging and Functional Imaging,, Southeast University, Nanjing, Jiangsu, China, ²Clinical Science, Philips Healthcare, Shanghai, China

Renal fibrosis is the final common consequence of chronic kidney disease (CKD) and is the mechanism of CKD progressing to end-stage renal failure. Here we employed ASL and IVIM to assess longitudinal changes of kidney perfusion to reflect renal fibrosis in an animal model of ADR nephropathy. A significant decline in renal microcirculation was detected in the ADR group compared with the sham group. Administration of VCP979 could prevent the renal perfusion, and the treatment response was also detected by the two imaging technology.

Mohammed Salman Shazeeb^1,2,3, Robert King^1,2, Karl Helmer³, Josephine Kolstad¹, Christopher Raskett¹, Natacha Le Moan⁴, Jonathan A. Winger⁴, Lauren Kelly⁴, Ana Krtolica⁴, Nils Henninger¹, and Matthew Gounis^1
1University of Massachusetts Medical School, Worcester, MA, United States, ²Worcester Polytechnic Institute, Worcester, MA, United States, ³Massachusetts General Hospital & Harvard Medical School, Boston, MA, United States, ⁴Omniox Inc., San Carlos, CA, United States

In acute ischemic stroke due to large vessel occlusion (LVO), variability of infarct evolution observed in humans is closely captured by the canine LVO model, which can predict dogs to be slow or fast evolvers. The extent of collateral blood supply has shown good correlations with infarct growth rate. This study investigated the use of intravoxel incoherent motion (IVIM) MRI to quantify microvascular perfusion. Longitudinal IVIM parameters clearly differentiated between slow and fast evolvers depicting collateral blood flow changes, which can determine the severity of ischemic injury and also track longitudinal changes in response to therapeutic treatments/interventions in preclinical studies.

Eric R. Muir¹ and Timothy Q. Duong^1
1Radiology, Stony Brook University, Stony Brook, NY, United States

Different retinal diseases likely affect the retinal, choroidal, and optic nerve head (ONH) circulations differently. Methods to quantitatively measure ONH blood flow with depth resolution are lacking. In this study, a blood flow MRI method was optimized to image blood flow of the ONH, retina, and choroid in the mouse eye at 42x42x275µm. This method could be useful to study models of retinal disease, such as glaucoma.

Eric R. Muir¹, Saurav B. Chandra², Divya Narayanan³, Nikolay P. Akimov⁴, René C. Rentería^4,5, and Timothy Q. Duong^1
1Radiology, Stony Brook University, Stony Brook, NY, United States, ²Icon Clinical Research Inc, North Wales, PA, United States, ³Ora Clinical, Andover, MA, United States, ⁴Ophthalmology, University of Texas Health Science Center, San Antonio, TX, United States, ⁵School of Osteopathic Medicine, University of the Incarnate Word, San Antonio, TX, United States

Diabetic retinopathy is a microvascular disease of the retina, in which basal blood flow and the vascular responses to metabolic conditions in diabetic eyes are perturbed. To determine if diabetic mice have impaired retinal/choroidal blood flow and vascular reactivity, we measured ocular blood flow using MRI during hypercapnia. In diabetic mice, basal choroidal blood flow was significantly decreased.  In both control and diabetic mice, hypercapnia caused a significant increase in retinal and choroidal blood flow, but the choroidal response was significantly reduced in diabetic mice, indicating impaired vascular reactivity.

Xiaobing Fan¹, Xueyan Zhou², Devkumar Mustafi¹, Federico Pineda¹, Erica Markiewicz¹, Marta Zamora¹, Deepa Sheth¹, Olufunmilayo I. Olopade³, and Gregory S. Karczmar^1
1Radiology, The University of Chicago, Chicago, IL, United States, ²School of Technology, Harbin University, Harbin, China, ³Medicine, The University of Chicago, Chicago, IL, United States

We compared dynamic contrast enhanced (DCE) MRI with low (0.04mmol/kg) and high doses (0.2mmol/kg) of contrast agent on C3H mice at 9.4T with 1.5s temporal resolution before and after a bolus injection. The standard Tofts model was used to extract physiological parameters (K^trans and v_e) with arterial input function derived from muscle reference tissue. On average, rate constants were larger for low dose than high dose data. There were strong correlations for K^trans and v_e between low and high dose data. Therefore, low dose may be as effective as a high dose of contrast agent for cancer diagnosis.

Zhuo Shi¹, Lizhi Xie², Peng Wang¹, Xinming Zhao¹, and Han Ouyang^1
1National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences, Beijing, China, ²GE Healthcare, MR Research China, Beijing, Beijing, China

Dynamic contrast-enhanced (DCE) MRI provides additional information on blood-brain barrier integrity. The Ktrans is a measure of capillary permeability obtained using DCE MRI that is directly proportional to the level of permeability of the blood-brain barrier. The purpose of this study was to evaluate the effect of SRS on cerebral metastases using Ktrans derived from DCE MRI and to explore the ability of Ktrans measurements on predicting midterm tumor outcomes after Stereotactic radiosurgery (SRS).

Xiaoqian Jia¹, Jianxin Guo², Xiaocheng Wei³, and Jian Yang^2
1Ridiology, The First Affiliated Hospital of Xi'an Jiao Tong University, xi'an, China, ²The First Affiliated Hospital of Xi'an Jiao Tong University, xi'an, China, ³MR Research China, GE Healthcare, xi'an, China

In this study, we try to provide a wider cohort of subjects with continuous low flow oxygen inhalation during dynamic contrast-enhancedMR liver imaging to reduce “Transient Severe Motion” (TSM) after administration of gadoxetate disodium.In addition, separate comparison of arterial phase motion scores was conducted among: category of combined Pleural Effusion, category of combined Ascites, and category of None.The results show that continuous oxygen can significantly reduce the occurrence of TSM; and  1) pleural effusion may reduce image quality, and can be alleviated by oxygen inhalation, and 2) oxygen inhalation is less effective under the condition of ascites.

Yanis Djebra^1,2, Thibault Marin¹, Jinsong Ouyang¹, Georges El Fakhri¹, Chao Ma¹, and Paul Kyu Han^1
1Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States, ²LTCI, Télécom Paris, Institut Polytechnique de Paris, Palaiseau, France

Arterial spin labeling (ASL) is a powerful magnetic resonance imaging (MRI) technique that allows to measure tissue perfusion, potentially an important biomarker for assessing cerebral tissue viability, without the use of contrast agent. However, the main drawback of ASL is in the intrinsically low signal-to-noise ratio (SNR). In this work, we investigate the low-rank property of ASL signal and explore the feasibility of improving the SNR of ASL signal using low-rank denoising approach. Results show that the ASL signal indeed display low-rank property and that the SNR in multi-delay ASL imaging can be improved using compartmental low-rank denoising method.

Lucy V Hiscox¹, Matthew DJ McGarry², and Curtis L Johnson^1
1University of Delaware, Newark, DE, United States, ²Dartmouth College, Hanover, NH, United States

Magnetic resonance elastography of the brain has shown promise as a sensitive neuroimaging biomarker for neurodegenerative disorders; however, the feasibility and reliability of performing MRE of the cerebral cortex warrants investigation due to the unique challenges of studying thinner and more complex geometries. In this work, we found good agreement between realistic simulated MRE data versus recovered displacement data of an older adult participant at various levels of applied Gaussian noise. Future work should consider additional and more advanced imaging and inversion approaches to improve the reliability and sensitivity of cortical MRE measures.

Siri Flogstad Svensson¹, Jorunn Fraser-Green², Omar Darwish³, José Rodriguez de Arcos³, Tryggve Holck Storås¹, Sverre Holm⁴, Ralph Sinkus^3,5, and Kyrre Eeg Emblem^1
1Department for Diagnostic Physics, Oslo University hospital, Oslo, Norway, ²The Intervention Center, Oslo University hospital, Oslo, Norway, ³Division of Imaging Sciences & Biomedical Engineering, King's College, London, United Kingdom, ⁴Department of Informatics, University of Oslo, Oslo, Norway, ⁵INSERM U1148, LVTS, University Paris Diderot, Paris, France

We assessed the test-retest reliability of MR Elastography, and compared the estimates of the shear storage modulus G’ (tissue elasticity) from two different reconstruction methods; a localized divergence-free finite-element approach and a local curl approach. The median coefficient of variation for two scans of the brain was 2.8 %, whereas the intraclass correlation coefficient between scan 1 and scan 2 was 0.80. G’ values estimated using the local curl method were 19% lower than with the divergence-free method. MRE of the human brain appears robust, while absolute values are dependent on the reconstruction method and should be used with care.

Helge Herthum¹, Heiko Tzschätzsch¹, Felix Schrank¹, Mehrgan Shahryari¹, Gergely Bertalan¹, Carsten Warmuth¹, Jürgen Braun², and Ingolf Sack^1
1Department of Radiology, Charité Universitätsmedizin Berlin, Berlin, Germany, ²Institute of Medical Informatics, Charité Universitätsmedizin Berlin, Berlin, Germany

In this work, we applied single-shot steady-state MR elastography with spiral readout for quantifying shear wave speed (SWS) from endogenous pulsation to 40 Hz external vibrations with high sampling rate for first-time measurement of SWS dispersion of in vivo human brain in the ultra-low frequency regime. Ground truth SWS was determined by profile fitting approaches and reproduced by SWS mapping based on frequency-adaptive multi-component wave-number inversion. The obtained SWS dispersion was fitted by two-parameter viscoelastic models showing that brain tissue is dominated by fluid properties in this ultra-low frequency regime. Our method is potentially sensitive to vessel-related neurological disorders.

Shujun Lin¹, Brad Sutton², Richard Magin¹, and Dieter Klatt^1
1Richard and Loan Hill Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, United States, ²Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana-Champaign, IL, United States

Simultaneous acquisition of diffusion tensor imaging (DTI) and magnetic resonance elastography (MRE) has been proven feasible in previous pre-clinical studies. DTI-MRE requires the identification of experimental parameter ranges that depend on the specific target. Here we identify valid experimental parameter sets in simulations for in vivo human brain applications and the DTI-MRE technique is implemented by modifying a single-shot spin-echo EPI sequence. A good agreement was found between DTI-MRE and conventional acquisitions. DTI-MRE may increase the clinical acceptance of MRE and DTI by providing co-registered diffusion and tissue mechanical property maps within the scan time of a conventional DTI acquisition.

Ling Fang¹, Matthew C. Murphy², Sujuan Liu¹, Qiuxia Luo¹, Jingbiao Chen¹, Bingjun He¹, Wei Qiu³, Jun Chen², Meng Yin², Kevin J. Glaser², Richard L. Ehman², and Jin Wang^1
1Department of Radiology, the Third Affiliated Hospital, Sun Yat-sen University, Guangzhou, China, ²Department of Radiology, Mayo Clinic, Rochester, MN, United States, ³Department of Neurology, the Third Affiliated Hospital, Sun Yat-sen University, Guangzhou, China

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system. MR Elastography (MRE) can quantitatively measure biomechanical tissue properties in vivo noninvasively. In this study, we investigated the potential value of MRE for the evaluation of centrum ovale viscoelasticity (including shear stiffness, storage modulus, shear loss modulus, and damping ratio) in Southern Chinese MS patients and to try to analyze its relevance to clinical manifestations. Our results showed that only the damping ratio of the centrum ovale was significantly decreased in MS patients and may provide a potential quantitative biomarker to evaluate MS.

Faisal S Fakhouri^1,2, Vincent Esguerra³, and Arunark Kolipaka^1,2
1Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States, ²Department of Radiology, The Ohio State University Wexner Medical Center, Columbus, OH, United States, ³Division of Pulmonary, Critical Care, and Sleep Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, United States

Interstitial lung diseases alter the mechanical properties of the lung parenchyma. Lung stiffness is a potential diagnostic marker. Standard breath hold techniques are difficult for patient with pulmonary disease. By using a free breathing Spin-Echo Dual-Density Spiral (SE-DDS) MRE sequence, a feasibility study was performed on 6 idiopathic pulmonary fibrosis (IPF) patients. It was found that the shear stiffness of IPF diseased lung is 2±0.48kPa for the right lung and 1.99±0.42kPa for the left lung which is significantly higher (P=0.0108 and P=0.0072) than healthy lungs, which has shear stiffness of 1.29±0.35kPa and 1.43±0.16kPa for right and left lungs, respectively.

Huiming Dong^1,2, Rizwan Ahmad², and Arunark Kolipaka^1,2
1Department of Radiology, The Ohio State University Wexner Medical Center, Columbus, OH, United States, ²Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States

Lung stiffness is a potential biomarker for multiple lung diseases. MR elastography (MRE) allows non-invasive measurement of lung stiffness. However, it is challenging to estimate stiffness using direct Helmholtz inversion due to low signal-to-noise ratio (SNR) from lung MRE. In this work, a compressed-sensing-based Helmholtz inversion is proposed where noise is reduced via Laplacian of Gaussian (LoG) and Morozov’s discrepancy principle, while the sparsity of stiffness map is explored in a wavelet domain. Results demonstrated that the proposed inversion yielded robust stiffness estimation and successfully detected higher stiffness at total lung capacity (TLC) compared to residual volume (RV).

Huiming Dong^1,2, Richard D White^1,3, and Arunark Kolipaka^1,2,3
1Department of Radiology, The Ohio State University Wexner Medical Center, Columbus, OH, United States, ²Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States, ³Internal Medicine-Division of Cardiology, The Ohio State University Wexner Medical Center, Columbus, OH, United States

In vivo MR elastography (MRE) allows non-invasive estimation of aortic stiffness. Recently, the feasibility of multi-slice free-breathing (FB) spin-echo echo-planar imaging (SE-EPI) aortic MRE was investigated. In this study, a single breath-hold (SBH) SE-EPI aortic MRE protocol was proposed and compared to FB SE-EPI aortic MRE. Moreover, in vivo FB and SBH SE-EPI aortic MRE were studied using both1.5T and 3T scanners. The main aim was to assess inter-scanner reproducibilities of FB and SBH SE-EPI aortic MRE.

Faisal S Fakhouri^1,2, Youjin Cho^1,3, Joshua Englert⁴, Samir Ghadiali^1,4, and Arunark Kolipaka^1,2
1Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States, ²Department of Radiology, The Ohio State University Wexner Medical Center, Columbus, OH, United States, ³College of Medicine, The Ohio State University, Columbus, OH, United States, ⁴Division of Pulmonary, Critical Care, and Sleep Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, United States

Many pulmonary diseases alter lung mechanical properties making lung stiffness an important biomarker. By using a Spin-Echo Echo Planar Imaging (SE-EPI) MRE sequence, a feasibility study was performed on 6 indeterminate pulmonary nodules (IPN) patients to determine the shear stiffness within the nodule and compare it with stiffness in the contralateral lung. It was found that in all the patients the median shear stiffness within the IPN was significantly higher than in the contralateral lung (1.77kPa vs 0.86kPa, p=0.008) Computational models based on MRE stiffness measurements also indicate decreased strain and increased strain gradients within the IPN.

Ayse Sila Dokumaci¹, Torben Schneider², Daniel Fovargue¹, Anthony Price¹, Omar Darwish¹, George Jolly¹, Stefan-Heinz Hoelzl¹, Jelizaveta Sudakova¹, Ralph Sinkus^1,3, and David Nordsletten^1,4
1Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom, ²Philips Healthcare, Guildford, United Kingdom, ³Inserm U1148, University Paris, Paris, France, ⁴Departments of Biomedical Engineering and Cardiac Surgery, University of Michigan, Ann Arbor, Ann Arbor, United Kingdom

MR Elastography is a technique to evaluate the biomechanical properties of soft tissues noninvasively. Its application in the heart is very challenging due to several factors including actuator hardware, robust MR sequences, and suitable reconstruction strategies. One of the biggest limitations for data acquisition of cardiac MRE scans is the breath hold duration which is up to 21 heart beats, repeated several times for a full dataset. The main goal of this study was the implementation of an MR sequence with simultaneous multi slice acquisition capability to reduce the breath hold duration and increase comfort and compliance for the subjects.  

Elijah Van Houten¹, Guillaume Gilbert², and An Tang^3
1Génie mécanique, Université de Sherbrooke, Sherbrooke, QC, Canada, ²MR Clinical Science, Philips Healthcare, Markham, ON, Canada, ³Département de radiologie, Université de Montréal, Montréal, QC, Canada

A new intrinsic activation MR Elastography method is presented through a proof of concept for imaging the viscoelasticity of a liver tumor. Results are presented for a healthy volunteer and a focal nodular hyperplasia subject. Relative stiffness, damping and compressibility maps clearly indicate the location of the tumor and are in agreement with mechanical property values previously reported in the literature. The method shows promise for the diagnosis of focal liver lesions and provides insight into new physiologically related biomarkers for these lesions.

Mehrgan Shahryari¹, Gergely Bertalan¹, Helge Herthum¹, Heiko Tzschätzsch¹, Jürgen Braun², Marcus R. Makowski¹, Sarah Keller¹, and Ingolf Sack^1
1Department of Radiology, Berlin, Germany, ²Institute of Medical Informatics, Berlin, Germany

MR elastography is a clinical imaging technique for the mapping of viscoelastic tissue properties on the millimeter scale. However, basic studies in tissue samples require a compact MRE setup which provides sub-millimeter resolution. We here introduce compact 0.5-Tesla tabletop multifrequency MRE for high-resolution mapping of viscoelasticity and water diffusion in VX2-liver tumors and surrounding liver tissue. Ex-vivo tumors were stiffer, more viscous and showed higher water diffusivity than adjacent tissue. In tumors, viscosity was inversely correlated with water diffusion while in liver tissue, stiffness was inversely correlated with diffusion.

Deirdre McGrath^1,2, Christopher Bradley^1,2, and Susan Francis^1,2
1NIHR Nottingham Biomedical Research Centre, Radiological Sciences, Division of Clinical Neuroscience, Queens Medical Centre, Nottingham, United Kingdom, ²Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham, United Kingdom

In this novel study, magnetic resonance elastography (MRE) of the liver is simulated in a detailed 3D anthropomorphic finite element model of the human torso, to explore the influence of imaging spatial resolution and motion-based signal to noise ratio (SNR) on the accuracy of elastograms calculated by direct inversion. It was found that MRE accuracy was highly dependent on imaging voxel dimensions, motion-SNR and the ground truth material properties. These findings will guide the optimisation and development of future liver MRE methodology. 

Rolf Reiter^1,2, Heiko Tzschätzsch¹, Matthias Haas¹, Christian Bayerl¹, Dieter Klatt², Meltem Uyanik², Shreyan Majumdar², Marion Muche³, Bernd Hamm¹, Jürgen Braun⁴, Ingolf Sack¹, and Patrick Asbach^1
1Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany, ²Bioengineering, University of Illinois at Chicago, Chicago, IL, United States, ³Hepatology, Charité - Universitätsmedizin Berlin, Berlin, Germany, ⁴Medical Informatics, Charité - Universitätsmedizin Berlin, Berlin, Germany

Primary sclerosing cholangitis (PSC) is a rare chronic liver disease that leads to stricturing of bile ducts and a heterogeneous distribution of hepatic fibrosis. Despite the success of MR cholangiopancreaticogram and liver biopsy for the detection of PSC, they do not correlate with the severity of disease. Currently, there is no accurate diagnostic reference standard for monitoring the disease activity in PSC which limits patient management. Tomoelastography has the potential to quantify heterogeneity in PSC-related hepatic fibrosis using a normalized standard deviation index as a new biomarker besides overall stiffness.

Rolf Reiter¹, Florian Nino Loch², Carsten Kamphues², Stephan Rodrigo Marticorena Garcia¹, Bernd Hamm¹, Jürgen Braun³, Ingolf Sack¹, and Patrick Asbach^1
1Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany, ²Surgery, Charité – Universitätsmedizin Berlin, Berlin, Germany, ³Medical Informatics, Charité - Universitätsmedizin Berlin, Berlin, Germany

Despite its success in the detection of inflammatory bowel disease (IBD), standard clinical MRI and other imaging modalities do not correlate with disease severity and cannot differentiate fibrotic and inflammatory bowel strictures. Anatomical details such as the descending colon and other parts of the intestine were demarcated on tomoelastography stiffness and fluidity maps, even without superimposed morphological images. Preliminary results demonstrate the feasibility of investigating IBD using tomoelastography. This study motivates larger trials and the assessment of fibrosis and inflammation in active IBD.

Tetsushi Habe^1,2, Tomokazu Numano^1,3, Daiki Ito^1,2,3, Toshiki Maeno¹, Kazuyuki Mizuhara⁴, Kouichi Takamoto⁵, and Hisao Nishijo^6
1Department of Radiological Sciences, Tokyo Metropolitan University, Tokyo, Japan, ²Office of Radiation Technology, Keio University Hospital, Tokyo, Japan, ³Human Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki, Japan, ⁴Department of Mechanical Engineering, Tokyo Denki University, Tokyo, Japan, ⁵Department of Sport and Health Sciences, University of Ease Asia, Yamaguchi, Japan, ⁶Department of System Emotional Science, Toyama University, Toyama, Japan

We developed psoas major muscle (PM) MR elastography (MRE) technique and reported shear modulus of the PM for the first time in the world. However, measurement precision (repeatability and reproducibility) of this technique was not assessed. In this study, repeatability with three repetitions and reproducibility with different three operators were evaluated. Repeatability of this technique was about the same as required for clinical liver MRE and reproducibility was almost perfect. The original vibration pad was focused on generating shear wave in the PM efficiently. The development of the vibration pad specialized for PM MRE resulted in acceptable repeatability and reproducibility.