Sajjad Feizollah^1,2 and Christine L. Tardif^1,2,3
1Department of Neurology and Neurosurgery, McGill University, Montreal, QC, Canada, ²McConnell Brain Imaging Center, Montreal Neurological Institute, McGill University, Montreal, QC, Canada, ³Department of Biomedical Engineering, McGill University, Montreal, QC, Canada

Several strategies have been used to increase the SNR of diffusion-weighted imaging including the use of partial Fourier EPI and spiral trajectories. Although these methods increase the SNR and sequence efficiency significantly, they affect the image quality and resulting diffusion measures causing loss of microstructural information of fine structures. Blurring caused by the T2* decay is one of the important effects resulting in low effective resolutions. Shorter T2* at ultra-high magnetic fields reduces the effective resolution in spite of providing higher SNR. This study shows about 60% lower effective resolution than the nominal resolution using PF-EPI and spiral at 7T.

Jae-Kyun Ryu¹, Chuluunbaatar Otgonbaatar², Seok-Jin Yeo³, Jeonghak Song⁴, Eunseok Jang⁴, Jaebin Lee⁴, and Hackjoon Shim^1,4
1Medical Imaging AI Research Center, Canon Medical Systems Korea, Seoul, Korea, Republic of, ²Department of Radiology, Seoul National University, Seoul, Korea, Republic of, ³Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of, ⁴Magnetic Resonance Business Unit, Canon Medical Systems Korea, Seoul, Korea, Republic of

Diffusion-weighted MRI is a highly sensitive to alteration in the movement of water molecules and allows the assessment of various pathologies. Interpretation of the changes can be obscured by signal-dropout due to tissue-air susceptibility difference at the boundaries of nasal cavities, especially in the prefrontal region. The head tilting (chin-up) method during the brain scan could be considered as an accessible way without additional hardware- or sequence to prevent those susceptibility-induced signal-dropout. We demonstrated DWI with head-tilting (up to 20°) resulted in had less severe signal dropout and improved image quality than normal scan in the prefrontal cortex.

Wenbo Sun¹, Dan Xu¹, Yunfei Zhang², Yongming Dai², and Haibo Xu^1
1Department of Radiology, Zhongnan Hospital of Wuhan University, Wuhan, China, ²Central Research Institute, United Imaging Healthcare, Shanghai, China

This study aimed to investigate whether the FROC diffusion model could help predict molecular biomarkers in gliomas. It was found that FROC has the potential in comprehensively characterizing heterogeneity of gliomas, not only in glioma grading, but also in predicting tumor cell proliferation rate and isocitrate dehydrogenase-1 (IDH-1) gene mutation status.

Ariel J Hannum^1,2,3, Tyler E Cork^1,2,3, Merlin J Fair^1,2, Kawin Setsompop^1,4, and Daniel B Ennis^1,2
1Department of Radiology, Stanford University, Stanford, CA, United States, ²Division of Radiology, Veterans Administration Health Care System, Palo Alto, CA, United States, ³Department of Bioengineering, Stanford University, Stanford, CA, United States, ⁴Department of Electrical Engineering, Stanford University, Stanford, CA, United States

Conventional brain DWI acquisitions are sensitive to physiological motion, which causes shot-to-shot phase variations between images. This makes accelerated, multi-shot imaging harder to achieve. We propose that motion compensated gradient waveforms will improve shot-to-shot phase stability. We found that both velocity and acceleration gradient moment nulling, particularly when diffusion encoding along the z-axis, improves shot-to-shot phase consistency at different cardiac trigger-delay times and reduces phase variation between repetitions for a fixed trigger-delay. We conclude that motion-compensated diffusion encoding gradients improve the phase stability between image shots.
 

Julian Rauch^1,2, Frederik B. Laun³, Dominik Ludwig¹, Maxim Zaitsev^4,5, Mark E. Ladd^1,2,6, Peter Bachert^1,2, and Tristan A. Kuder^1
1Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Faculty of Physics and Astronomy, Heidelberg University, Heidelberg, Germany, ³Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany, ⁴Medical Physics, Department of Radiology, Faculty of Medicine, Medical Center University of Freiburg, Freiburg, Germany, ⁵High Field Magnetic Resonance Center, Center for Medical Physics and Biomedical Engineering Medical University of Vienna, Vienna, Austria, ⁶Faculty of Medicine, Heidelberg University, Heidelberg, Germany

Intravoxel dephasing caused by Maxwell or concomitant fields can lead to image artifacts as signal voids or falsify the quantitation. In this study, a framework for compensation of concomitant field effects for double diffusion encoding sequences with single pairs of bipolar gradients on each axis is presented. Using pulse-width modulated oscillating gradients with an optimized timing of the oscillating lobes allows for simultaneous diffusion weighting and compensation of the self-squared terms of the concomitant fields as well as for the cross terms. Simulations with realistic parameters reveal the possibility of a signal gain with the proposed method without significant drawbacks.

Jens Johansson¹, Kerstin Lagerstrand^2,3, Pär-Arne Svensson⁴, Jr-yuan George Chiou⁵, Bruno Madore⁵, Hanna Hebelka^1,4, and Stephan Maier^1,5
1Department of Radiology, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden, ²Medical radiation sciences, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden, ³Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden, ⁴Department of Radiology, Sahlgrenska University Hospital, Gothenburg, Sweden, ⁵Department of Radiology, Brigham and Women's Hospital, Boston, MA, United States

The inherent low bandwidth along the phase encoding direction in diffusion-weighted imaging with echo-planar signal readout can cause severe image distortions. These artifacts arise near tissue boundaries and are caused by static magnetic field inhomogeneities. Correction of such artifacts can considerably improve clinical value. We combine a previously presented segmented accelerated multi-shot diffusion imaging method with reverse polarity gradient (RPG) for markedly improved reduction of geometric distortions.

Matthew J. Middione¹, Alimohammad S. Moalem¹, Cheng William Hong¹, Arnaud Guidon², Daniel B. Ennis¹, and Ryan L. Brunsing^1
1Department of Radiology, Stanford University, Stanford, CA, United States, ²GE Healthcare, Boston, MA, United States

DWI of the pancreas is challenging due to artifacts from physiologic motion, image distortion, and blurring, but has promising applications in pancreatic cancer detection. We conducted a pilot study of pancreatic DWI comparing single-shot and multi-shot EPI protocols as well as multi-shot EPI protocols with and without a new commercially available deep learning (DL) based denoising reconstruction method. Image quality was subjectively scored with key metrics. Multi-shot EPI reduced perceived distortion within the pancreatic bed, while the combination of multi-shot EPI and DL reconstruction subjectively reduced noise.

Dariya Malyarenko¹, Yuxi Pang¹, Ajit Devaraj², Johannes Peeters³, Harry Friel², Kristen M Pettit⁴, Moshe Talpaz⁴, Brian D Ross¹, Gary D Luker¹, and Thomas L Chenevert^1
1Radiology, University of Michigan, Ann Arbor, MI, United States, ²Philips Healthcare, Highland Heights, OH, United States, ³Philips MR Sclinical Science, Best, Netherlands, ⁴Internal Medicine, University of Michigan, Ann Arbor, MI, United States

Apparent diffusion coefficient (ADC) metric is evaluated as a potential alternative to biopsy for disease grading and therapy response assessment in bone marrow of myelofibrosis (MF) patients.  Spatially dependent bias in diffusion weighting due to systematic gradient nonlinearity (GNL) results in false heterogeneity of ADC maps over the imaged bone space. Here we illustrate deployment of prospective GNL bias correction based on technology developed in an academic industrial partnership to reduce technical variability of ADC in a MF clinical imaging trial.

Alfredo Ordinola¹, Walker Jackson², and Evren Özarslan^1
1Department of Biomedical Engineering, Linköping University, Linköping, Sweden, ²Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden

We demonstrate the experimental determination of the diffusion propagator, indicating a conditional probability density function with two spatial arguments. To this end, a recently introduced method was implemented on a benchtop MR scanner and incorporated into imaging sequences. The data involving two independent wavenumbers were transformed from the measurement domain to the spatial domain, yielding an apparent diffusion propagator. Experiments on freely diffusing water provides accurate determination of the diffusion propagator while apparent propagators measured in mouse spinal cord reveal significant differences between white and gray matter regions.

Athanasia Kaika¹, Geoffrey J. Topping¹, Simone Ballke², Thomas Theodor Metzler², Irina Heid³, Mathias Schillmaier¹, Rickmer Braren³, and Franz Schilling^1
1Department of Nuclear Medicine, TUM School of Medicine, Klinikum Rechts der Isar, Technical University of Munich, Munich, Germany, ²Institute of Pathology, TUM School of Medicine, Technical University of Munich, Munich, Germany, ³Institute of Radiology, TUM School of Medicine, Klinikum Rechts der Isar, Technical University of Munich, Munich, Germany

Filter-exchange spectroscopy (FEXSY) and imaging (FEXI) are sensitive to transmembrane water exchange, which is commonly altered during cell death¹. Yeast cells in different permeabilization stages were studied with FEXI, DWI and CFDA-AM/ propidium iodide (PI) staining using flow cytometry. Cell populations with 3.8% PI positive staining had 44% increased AXR, but unchanged ADC. At 33% nonvital cells, detection of AXR became unreliable and ADC increased. In vivo FEXI and DWI in EL4 lymphoma, with H&E-confirmed necrotic tumor cells and edema, showed AXR and ADC variations across the tumor, possibly due to differing vitality cell stages.