David Waddington^1,2,3, Thomas Boele^2,4, Richard Maschmeyer¹, Zdenka Kuncic^1,5, and Matthew Rosen^2,6,7
1Institute of Medical Physics, School of Physics, The University of Sydney, Sydney, Australia, ²A. A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, ³ACRF Image X Institute, Faculty of Medicine and Health, The University of Sydney, Sydney, Australia, ⁴ARC Centre of Excellence for Engineered Quantum Systems, School of Physics, The University of Sydney, Sydney, Australia, ⁵Sydney Nano Institute, The University of Sydney, Sydney, Australia, ⁶Department of Physics, Harvard University, Cambridge, MA, United States, ⁷Harvard Medical School, Boston, MA, United States

MRI scanners operating at ultra-low fields (ULF) promise to reduce the cost and expand the clinical accessibility of MRI. Here, we use a 6.5 mT MRI scanner and an efficient balanced steady-state free precession MRI protocol to image superparamagnetic iron oxide nanoparticles (SPIONS) in vivo by leveraging the extremely high magnetization of SPIONs at ULF. Further, we show how positive contrast imaging of SPIONs can be performed at ULF with susceptibility-based techniques. These advances overcome a key limitation of ULF MRI by enabling high-contrast in vivo imaging of clinically safe contrast agents with short acquisition times.

Shaowei Bo¹, KowsalyaDevi Pavuluri¹, Yunkou Wu², Farzad Sedaghat¹, Martin G. Pomper³, Max Kates⁴, and Michael T. McMahon^5
1The Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, The Johns Hopkins University School of Medicine, Baltimore, MD, United States, ²Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD, United States, ³Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Department of Psychiatry, The Johns Hopkins University School of Medicine, Baltimore, MD, United States, ⁴Department of Urology, The James Buchanan Brady Urological Institute, The Johns Hopkins University School of Medicine, Baltimore, MD, United States, ⁵The Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, The Johns Hopkins University School of Medicine, F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States

Urinary tract obstructions (UTOs) are blockages that inhibit the flow of urine through its normal path, which can lead to kidney injury and infection. Chemical exchange saturation transfer (CEST) MRI is a fast, noninvasive molecular MRI technique which has shown promise for clinical applications. In this study, we designed and tested a series of imidazoles as CEST MRI contrast agents and tested these for performing functional kidney imaging on a UTO mouse model. The results demonstrate that CEST MRI can facilitate early detection of loss in kidney function.

Kyeongseon Min¹, Tan Toi Phan^2,3, Sungkwon Chung⁴, Jongho Lee¹, Seung-Kyun Lee^2,3, and Jang-Yeon Park^2,3
1Laboratory for Imaging Science and Technology, Department of Electrical and Computer Engineering, Seoul National University, Seoul, Korea, Republic of, ²Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of, ³Center for Neuroscience Imaging Research, Institute for Basic Science, Suwon, Korea, Republic of, ⁴Department of Physiology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Korea, Republic of

In this study, the effects of membrane potential on T₁ and T₂ were examined using Jurkat T lymphocytes. We applied tetraethylammonium ion (TEA) to depolarize Jurkat cell membrane potential. Significant changes in T₁ and T₂, which were measured to be -10.39 ms/mM and 0.920 ms/mM, respectively, were observed. One potential explanation for the changes of T₁ and T₂ is the depolarization of membrane potential, while the underlying mechanism needs to be explored. Further studies are expected to utilize the membrane potential as a new contrast mechanism for MRI.

Patrick Schuenke¹, Patrick Werner^1,2, Matthias Taupitz³, and Leif Schröder^1
1Leibniz-Forschungsinstitut fuer Molekulare Pharmakologie (FMP), Berlin, Germany, ²BIOQIC, Charité Berlin, Berlin, Germany, ³Department of Radiology, Charité Berlin, Berlin, Germany

In this study, we quantified the dissociation of GBCAs at different ZnCl₂ concentrations and the subsequent chelation of Gd³⁺ to glycosaminoglycans (GAGs) like heparin. We showed that the relaxivity of the resulting Gd-GAG complexes is about seven times higher compared to that of GBCAs. Under physiological conditions, we further showed that ~20% of the Gd³⁺-ions transchelated from linear GBCAs to heparin and that these are accountable for more than 50% of the observed relaxation rate. Therefore, Gd-GAG complexes should be considered as the Gd-containing macromolecular substances with high relaxivity that are needed to explain the observed long-term enhancements in vivo.

Andreea Hertanu¹, Lucas Soustelle¹, Arnaud Le Troter¹, Julie Buron^1,2, Victor Carvalho^1,3, Myriam Cayre², Pascale Durbec², Gopal Varma⁴, David C. Alsop⁴, Olivier M. Girard¹, and Guillaume Duhamel^1
1Aix-Marseille Univ, CNRS, CRMBM, Marseille, France, ²Aix-Marseille Univ, CNRS, IBDM, Marseille, France, ³Aix-Marseille Univ, CNRS, ICR, Marseille, France, ⁴Division of MR Research, Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States

Inhomogeneous magnetization transfer (ihMT) is a myelin sensitive MRI technique that provides access to multiple contrast regimes by tuning the amount of dipolar relaxation time (T_1D) weighting of the sequence. This opens new perspectives to characterize the sensitivity and specificity of ihMT for myelin in a pathological context. In this study, multiple T_1D-weighting ihMT imaging was investigated in the cuprizone mouse model. IhMT signals compared to myelin imaging with fluorescence microscopy demonstrate that ihMT techniques that are weighted towards long T_1D values are more specifically related to myelin content during the demyelinating/remyelinating phases of the cuprizone model.

John J DeBevits¹, Devin Bageac¹, Leo Wolansky¹, Paul Dicamillo², Rong Wu¹, Chaoran Hu¹, and David Karimeddini^1
1UConn Health, Farmington, CT, United States, ²University of Iowa, Iowa City, IA, United States

In the BECOME trial, subjects experienced progressively increased T1W signal changes in deep grey matter nuclei.  This retrospective analysis concluded these signal changes also can be seen in the diploic space bone marrow.  While increasing trends in hypophosphatemia and leukopenia were also seen in the original study, this analysis has shown that these metabolic abnormalities are not associated with increased marrow signal and that low phosphate and low WBC were not associated with one another.  This rejects our hypothesis that gadolinium deposition might interact with a common osteoclast-WBC progenitor cell to result in the metabolic abnormalities.

Briana Meyer¹ and Matthew Budde^2
1Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States, ²Neurosurgery, Medical College of Wisconsin, Milwaukee, WI, United States

Dynamic susceptibility contrast (DSC) to monitor spinal cord perfusion and hemodynamics has the potential to inform the clinical care of spinal cord injury and other disorders. Acquisition of high spatial and temporal resolution images of the rodent spinal cord for DSC perfusion measurements was achieved using a golden-angle radial gradient-echo acquisition combined with iGRASP iterative undersampled reconstruction. 

Saurav Zaman Khan Sajib¹, Munish Chauhan¹, and Rosalind J Sadleir^1
1School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ, United States

Magnetic flux densities induced by tES currents can be measured from MR phase and used to reconstruct current density, electric field and conductivity tensor distributions, via diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT). Determination of tES electric field distributions from DT-MREIT conductivities is challenging, because DT-MREIT requires data from two independent current administrations, increasing acquisition time. We demonstrate a deep-learning model for DT-MREIT reconstruction, showing that conductivity tensors and electric fields can be measured in human subjects in-vivo using a single current administration. This strategy can be used to directly monitor tES electric fields and verify treatment precision.

Mehdi Sadighi¹, Mert Şişman¹, Berk Can Açıkgöz¹, and B. Murat Eyüboğlu^1
1Electrical and Electronics Engineering Dept., Middle East Technical University (METU), Ankara, Turkey

To obtain low-frequency anisotropic conductivity distribution of biological tissues recently Diffusion Tensor Magnetic Resonance Electrical Impedance Tomography (DT-MREIT), which is combination of the DTI and MREIT techniques, is proposed. There are two in vivo applications of DT-MREIT in the literature where two linearly independent current injection patterns are used. Decreasing the number of current injection patterns to one improves the feasibility of DT-MREIT in clinical applications. In this study, DT-MREIT using a single current injection pattern is experimentally realized. The obtained results approve the validity of the proposed single current DT-MREIT method.

Santhosh Iyyakkunnel^1,2, Jessica Schäper^1,2, and Oliver Bieri^1,2
1Department of Radiology, University Hospital Basel, Basel, Switzerland, ²Department of Biomedical Engineering, University of Basel, Basel, Switzerland

Only recently, phase imaging with balanced steady-state free precession (bSSFP) has been suggested for electrical properties tomography (EPT). Here we suggest exploring the SSFP configuration space retrieved from multiple phase-cycled bSSFP scans used for relaxometry also for electrical conductivity mapping. Consequently, the conductivity can be estimated in conjunction with standard quantitative tissue properties requiring no additional scan time.

Kyu-Jin Jung¹, Stefano Mandija^2,3, Jun-Hyeong Kim¹, Kanghyun Ryu¹, Soozy Jung¹, Mina Park⁴, Mohammed A. Al-masni¹, Cornelis A.T. van den Berg², and Dong-Hyun Kim^1
1Department of Electrical and Electronic Engineering, Yonsei University, Seoul, Korea, Republic of, ²Department of Radiotherapy, Division of Imaging & Oncology, University Medical Center Utrecht, Utrecht, Netherlands, ³Computational Imaging Group for MR diagnostics and therapy, Center for Image Sciences, University Medical Center Utrecht, Utrecht, Netherlands, ⁴Department of Radiology, Gangnam Severance Hospital, Seoul, Korea, Republic of

 Electrical Properties Tomography reconstruction technique is highly sensitive to noise, as it requires Laplacian calculations of phase data. To alleviate the noise amplification, large derivative kernels combined with image filters are used. However, this leads to severe errors at tissue boundaries. In this study, we employ a deep learning-based denoising network allowing for noise robust conductivity reconstructions obtained using smaller derivative kernels sizes. This comes with the intrinsic advantage of reduced boundary errors. The feasibility study was performed using cylindrical numerical simulations. Then, the proposed technique was tested using spin echo in-vivo data, and clinical patient data.

Wyger Brink¹, Loes Huijnen¹, Reijer Leijsen¹, Remco Overdevest¹, Andrew Webb¹, and Lucia Bossoni^1
1C.J. Gorter Center for High Field MRI, dept. Radiology, Leiden University Medical Center, Leiden, Netherlands

This work demonstrates a clinically feasible protocol and reconstruction pipeline which is relatively straightforward to implement, and achieves reliable conductivity reconstructions of the human breast. We aim to establish a reliable MR protocol with a scan time of 6 minutes to further develop the clinical potential of this technique.

Mehrgan Shahryari¹, Helge Herthum¹, Gergely bertalan¹, Tom Meyer¹, Heiko Tzschätzsch¹, Carsten Warmuth¹, Jürgen Braun², and Ingolf Sack^1
1Department of Radiology, Charité - Universtitätsmedizin Berlin, Berlin, Germany, ²Institute of Medical Informatics, Charité - Universtitätsmedizin Berlin, Berlin, Germany

MR elastography can provide high-resolution stiffness maps of abdominal organs. However, MRE – in particular when applied with multiple drive frequencies – requires measure times which significantly exceed single breath holds. Therefore, reduction strategies for motion artifacts are required including breath-holds, navigators and image registration, which all were consistently applied and analyzed in this in-vivo study. Our results show that displacement of organs is smallest during breath-hold MRE while, remarkably, mean stiffness values are not significantly affected by breathing. Overall image quality is comparable between breath-hold and free-breathing MRE when the latter is corrected by 2D-image registration during post processing.

Gergely Bertalan¹, Bettina Müller², Leif Schröder³, Heiko Tzschätzsch¹, Mehrgan Shahryari¹, Helge Herthum¹, Jing Guo¹, Jürgen Braun⁴, and Ingolf Sack^1
1Department of Radiology, Charite Universitätsmedizin Berlin, Berlin, Germany, ²Tierhaltung CCM, Charite Universitätsmedizin Berlin, Berlin, Germany, ³Molecular Imaging, Leibniz Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany, ⁴Department of medical Informatics, Charite Universitätsmedizin Berlin, Berlin, Germany

The purpose of this study was the development of multifrequency MR elastography (MRE) of tissue samples with 40 micrometer pixel edge size for analyzing the mechanical properties of murine neural tissue. The new technique revealed in specimens of cerebellum and cortical brain areas that white matter is significantly stiffer than gray matter. Microscopic multifrequency MRE provides insight into micro mechanical structures of ex-vivo soft tissues and might be used in the future to investigate fresh biopsy samples.

Yi Sui¹, MyungHo In¹, Ziying Yin¹, Matthew A. Bernstein¹, Richard L. Ehman¹, and John III Huston^1
1Radiology, Mayo Clinic, Rochester, MN, United States