Moritz Schneider¹, Thomas Gaaß^1,2, Julien Dinkel^1,2, Michael Ingrisch¹, Maximilian F Reiser¹, and Olaf Dietrich^1
1Institute for Clinical Radiology, Ludwig-Maximilians-University Hospital Munich, Munich, Germany, ²Comprehensive Pneumology Center, German Center for Lung Research, Munich, Germany

In this study we present intravoxel incoherent motion (IVIM) measurements in a flow phantom consisting of a 3-dimensional capillary network made from melt-spun, sacrificial sugar structures embedded in a synthetic resin. IVIM parameters were determined at varying water flow rates. The pseudodiffusion D* (associated with flow velocity) as well as the product D*×f (which constitutes a measure of flow) show proportionality to the applied flow rates. These results demonstrate that the presented flow phantom is ideal to assess the applicability of IVIM measurements and influence factors such as flow rates, capillary diameter or acquisition parameters.

Xiaoke Wang¹, Scott B Reeder^1,2,3,4,5, and Diego Hernando^2
1Biomedical Engineering, University of Wisconsin-Madison, Madison, WI, United States, ²Radiology, University of Wisconsin-Madison, Madison, WI, United States, ³Medical Physics, University of Wisconsin-Madison, Madison, WI, United States, ⁴Medicine, University of Wisconsin-Madison, Madison, WI, United States, ⁵Emergency Medicine, University of Wisconsin-Madison, Madison, WI, United States

Practical diffusion phantoms are urgently needed for technique development, protocol harmonization and quality assurance of quantitative diffusion MRI. Ideally, a diffusion phantom should have a single-peak NMR spectrum, Gaussian diffusion, with a wide range of tunable apparent diffusion coefficients (ADC). In this work, we developed and validated a novel diffusion phantom based on acetone-water mixtures doped with MnCl₂. This phantom exhibits the desired signal behavior, where water modulates the ADC of acetone, and MnCl₂ both eliminates water signal (through T2 shortening) and shortens the T1 of acetone. 

Irvin Teh¹, Darryl McClymont¹, Marie-Christine Zdora^2,3, Valentina Davidoiu⁴, Hannah J Whittington¹, Christoph Rau², Irene Zanette², and Jürgen E Schneider^1
1Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom, ²Diamond Light Source, Didcot, United Kingdom, ³Department of Physics and Astronomy, University College London, London, United Kingdom, ⁴Department of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom

Diffusion tensor imaging (DTI) is widely used to assess tissue microstructure, but is limited in resolution and cannot resolve multiple fibre populations within a voxel. Existing methods for validating DTI are limited in either resolution or coverage. 2D histological methods are additionally destructive and prone to tissue distortion. In contrast, synchrotron imaging strikes an excellent balance between resolution and coverage. Here, we demonstrate for the first time, the prospect of validating DTI with structure tensor analysis of synchrotron imaging data. Tensors reconstructed with DTI and structure tensor synchrotron imaging were consistent across the left ventricular wall of the heart.

Julie Constanzo¹, Matthieu Dumont², Luc Tremblay¹, Philippe Sarret³, Jean-Michel Longpré³, Karyn Kirby³, Sameh Geha⁴, Laurence Masson-Côté¹, Benoit Paquette¹, and Maxime Descoteaux^2
1Nuclear Medicine and Radiobiology, Sherbrooke University, Sherbrooke, QC, Canada, ²Computing Science, Sherbrooke University, Sherbrooke, QC, Canada, ³Pharmacology and biophysics, Sherbrooke University, Sherbrooke, QC, Canada, ⁴Pathology, Sherbrooke University, Sherbrooke, QC, Canada

Despite its high efficiency for treating brain tumors and metastases, stereotactic radiosurgery (SRS) may lead to brain swelling, necrosis, and neuronal dysfunction, thus inducing delayed adverse effects such as cognitive decline and stroke-like symptoms. Altogether, our results revealed that SRS treatment induces region-specific plasticity (i.e. structural and function changes), as demonstrated by neuronal matrix remodeling using diffusion MRI and appropriate HARDI reconstruction, corresponding to histopathological modifications and changes in behavioral responses.

Kurt Schilling¹, Vaibhav Janve¹, Yurui Gao¹, Iwona Stepniewska¹, Bennett Landman¹, and Adam Anderson^1
1Vanderbilt University, Nashville, TN, United States

It has been reported that diffusion tractography has a tendency for streamlines to terminate preferentially on gyral crowns rather than on sulcal walls or fundi. Rather than anatomical reality, it has been suggested that this is a bias associated with tractography. To better understand this issue, we compare histology to diffusion MRI of the same specimen. We measure the trajectories and density of axons crossing the gray matter/white matter boundary and compare to diffusion tensor measures and deterministic tractography. The results of this study lead to a better understanding of gyral anatomy and potential limitations of fiber tractography.

Justine Beaujoin^1,2,3, Fawzi Boumezbeur^1,2,3, Jérémy Bernard^1,2,3, Markus Axer⁴, Jean-François Mangin^2,3,5,6, and Cyril Poupon^1,2,3,6
1CEA NeuroSpin / UNIRS, Gif-sur-Yvette, France, ²Université Paris-Saclay, Orsay, France, ³FLI / Noeud Paris-Sud, Orsay, France, ⁴Forschungszentrum Jülich, INM1, Jülich, Germany, ⁵CEA NeuroSpin / UNATI, Gif-sur-Yvette, France, ⁶http://cati-neuroimaging.com/, Gif-sur-Yvette, France

In this work, we demonstrate that post-mortem ultra-high field (11.7T) / ultra-high gradients (760mT/m) diffusion-weighted MRI allows to finely map the inner connectivity of the human hippocampus and we show that the polysynaptic intra-hippocampal pathway can be accurately reconstructed using fiber tractography techniques at very high spatial/angular resolutions.

Wieke Haakma^1,2,3, Lidy Kuster², Martijn Froeling¹, Lars Uhrenholt², Michael Pedersen^3,4, Jeroen Hendrikse¹, Alexander Leemans⁵, and Lene Warner Thorup Boel^2
1Radiology, University Medical Center Utrecht, Utrecht, Netherlands, ²Forensic Medicine, Aarhus University, Aarhus, Denmark, ³Comparative Medicine Lab, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark, ⁴MR Research Center, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark, ⁵Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands

In this work we examined the architecture and diffusion measures of the cervical spine and nerves in non-fixated post-mortem subjects. We were able to display the architectural configuration of the cervical nerves at the level of C4-C8 and we computed reference values for the diffusion measures in these nerves. We showed with great detail the ventral and dorsal nerve roots with fiber tractography. Microscopic examination revealed normal anatomy. We expect that post-mortem diffusion MRI will be valuable for understanding of pathological mechanisms underlying degenerative neurological diseases, as it is possible to compare any findings directly to histological examinations. 

Colleen Bailey¹, Bernard Siow², Eleftheria Panagiotaki¹, John H Hipwell¹, Sarah E Pinder³, Daniel C Alexander¹, and David J Hawkes^1
1Centre for Medical Image Computing, University College London, London, United Kingdom, ²Centre for Advanced Biomedical Imaging, University College London, London, United Kingdom, ³Breast Research Pathology, King's College London and Guy's Hospital, London, United Kingdom

A variety of one- and two-compartment models were fitted to rich diffusion data sets from ex vivo breast tissue samples containing tumour. Two compartment models with restriction explained the data better than conventional ADC and bi-exponential models, as determined by the Akaike Information Criterion. In four of seven samples, anisotropy was also observed, although parametric maps of the primary eigenvector direction show that regions of coherence are small (~1 mm diameter).

Tanguy Duval¹, Blanche Perraud¹, Manh-Tung Vuong¹, Nibardo Lopez Rios^1,2, Nikola Stikov^1,3, and Julien Cohen-Adad^1,4
1Polytechnique Montréal, Montréal, QC, Canada, ²Medical Biophysics Center, Oriente University, Santiago de Cuba, Cuba, ³Montreal Heart Institute, Montréal, QC, Canada, ⁴Functional Neuroimaging Unit, CRIUGM, Université de Montréal, Montréal, QC, Canada

In this work we propose to validate and compare AxCaliber/ActiveAx/Noddi/MTV in the spinal cord using full slice histology with axon/myelin segmentation. High resolution data (150µm/px) were acquired on an ex vivo spinal cord and compared voxel by voxel with histology. We found that q-space metrics were precise enough to distinguish between various fiber distributions. A correlation coefficient of r=0.62 was found between AxCaliber and histology for axon diameter metric. Also, good agreement were found between the different q-space models and with MTV.

Sean Foxley¹, Jeroen Mollink¹, Saad Jbabdi¹, Stuart Clare¹, Moises Hernandez Fernandez¹, Connor Scott², Olaf Ansorge², and Karla Miller^1
1FMRIB Centre, University of Oxford, Oxford, United Kingdom, ²Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom

In this work we present voxel-wise orientation estimates from diffusion-weighted steady state free precession MRI data of post-mortem human brain, acquired with three resolutions at 7T. Data were acquired with 0.5mm, 1mm, and 2mm isotropic resolution over 90 directions. These resolutions were chosen because 1mm and 2mm are typical of in vivo DTI. Deterministic tractography was produced in various regions using the highest resolution dataset. Orientation maps demonstrate small structures that are less apparent in lower resolution data. Orientation estimates and tractography results were validated with polarized light microscopy imaging.