Zhaoqing Li^1,2, Yi-Cheng Hsu³, and Ruiliang Bai^1,2
1Interdisciplinary Institute of Neuroscience and Technology (ZIINT), School of Medicine, Zhejiang University, Hangzhou, China, HangZhou, China, ²College of Biomedical Engineering and Instrument Science, Zhejiang University, Hangzhou, China, HangZhou, China, ³MR Collaboration, Siemens Healthcare, Shanghai, China, ShangHai, China

Filter exchange imaging (FEXI) is a non-invasive method to measure water exchange among diffusion compartments by apparent exchange rate (AXR). However, in human white matter, it is still controversial whether the diffusion-encoding gradient direction will affect AXR measurement. In this study, we performed FEXI on human brain with 20 diffusion gradient directions to explore features of AXR in white matter. We found that AXR measured with diffusion direction perpendicular to fiber (~ 0.47 s^-1) is significantly larger than that parallel to fiber (~ 0.15 s^-1), suggesting FEXI at different directions might measure exchanges between different biological compartments in white matter.

Md Nasir Uddin¹, Abrar Faiyaz², and Giovanni Schifitto^1,3
1Department of Neurology, University of Rochester, Rochester, NY, United States, ²Electrical & Computer Engineering, University of Rochester, Rochester, NY, United States, ³Imaging Sciences, University of Rochester, Rochester, NY, United States

White matter microstructural abnormalities are well documented in HIV-infected individuals. DTI derived fractional anisotropy (FA) is frequently used to assess the abnormalities but it has some limitations. In this work, we compared FA and microscopic fractional anisotropy (μFA) in an HIV cohort, and our results indicate that μFA seems to provide better sensitivity than the conventional FA for detecting white matter microstructure changes associated with HIV infection, especially in the areas with crossing fibers.

Lisa Novello¹, Rafael Neto Henriques², Andrada Ianuş², Thorsten Feiweier³, Noam Shemesh², and Jorge Jovicich^1
1Center for Mind/Brain Sciences - CIMeC, University of Trento, Rovereto, Italy, ²Champalimaud Research, Champalimaud Centre for the Unknown, Lisbon, Portugal, ³Siemens Healthcare GmbH, Erlangen, Germany

Resolving the underlying sources of kurtosis in biological systems is emerging as a promising strategy for non-invasive quantitative characterization of tissue microstructure. Recently, a novel framework termed Correlation Tensor Imaging (CTI), based on double-diffusion-encoding MRI, was shown to disentangle anisotropic, isotropic, and microscopic kurtosis sources in mouse brains. Here, we implemented CTI on a clinical 3T MRI system and scanned normal humans for the first time. The ensuing CTI-driven non-Gaussian inter/intra-compartmental estimates are promising and agree with expectations: positive intra-compartmental kurtosis for gray and white matter, larger for gray than white matter, and around zero for cerebrospinal fluid.

Zhaoqing Li^1,2, Chaoliang Sun^1,2, Yi-Cheng Hsu³, Hui Liang⁴, Peter Basser⁵, and Ruiliang Bai^1,2
1Interdisciplinary Institute of Neuroscience and Technology (ZIINT), School of Medicine, Zhejiang University, Hangzhou, China, HangZhou, China, ²College of Biomedical Engineering and Instrument Science, Zhejiang University, Hangzhou, China, HangZhou, China, ³MR Collaboration, Siemens Healthcare, Shanghai, China, ShangHai, China, ⁴Department of Neurology, First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China, HangZhou, China, ⁵Section on Quantitative Imaging and Tissue Sciences, NICHD, National Institutes of Health, Bethesda, MD, USA, Bethesda, MD, United States

In this study, we aim to explore the feasibility of Filter-exchange imaging (FEXI) in measuring different water exchange processes in human brain by modulating the diffusion filter (b_f) and detection (b) blocks. We found the apparent exchange rate (AXR) estimated from a FEXI protocol with bf=250s/mm² are significantly larger than those with bf=900s/mm². Besides, the filter efficiency of FEXI with bf=250s/mm² shows a strong correlation with vascular density estimated as the fraction of water exhibiting intravoxel incoherent motion (IVIM). Collectively, our current results demonstrate that FEXI targeting the vascular water could help characterize the intra-to-extravascular water exchange process.

Tomasz Pieciak^1,2, Maryam Afzali³, Fabian Bogusz¹, Dominika Ciupek¹, Derek K. Jones³, and Marco Pizzolato^4,5
1AGH University of Science and Technology, Kraków, Poland, ²LPI, ETSI Telecomunicación, Universidad de Valladolid, Valladolid, Spain, Valladolid, Spain, ³Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff, United Kingdom, ⁴Department of Applied Mathematics and Computer Science, Technical University of Denmark, Kongens Lyngby, Denmark, ⁵Signal Processing Lab (LTS5), École polytechnique fédérale de Lausanne (EPFL), Lausanne, Switzerland

The nervous tissue microstructure can be characterized by sensitizing the MRI signal to diffusion. The advent of multi-parametric sequences enabled the collection of diffusion data at different echo and inversion times. While the link between diffusion and transverse relaxation has undergone several investigations, in this work we characterize the relationship between the diffusion and longitudinal relaxation, and quantify the reciprocal influence of b-values and inversion time on the quantification of T1 and of diffusion metrics, interpreting our findings on in vivo data in the light of numerical simulations, and showing evidence that longitudinal relaxation locally modifies the diffusion contrast.

Simona Schiavi¹, Sila Genc², Maxime Chamberland², Chantal M.W. Tax^2,3, Erika P. Raven⁴, Alessandro Daducci¹, and Derek K Jones^2,5
1Department of Computer Science, University of Verona, Verona, Italy, ²CUBRIC, School of Psychology, Cardiff University, Cardiff, United Kingdom, ³Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands, ⁴Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, ⁵Mary MacKillop Institute for Health Research, Australian Catholic University, Melbourne, Australia

We employed the Convex Optimization Modeling for Microstructure Informed Tractography (COMMIT) approach to construct microstructure-informed connectomes and study the distinct patterns of age-related development in structural whole-brain network and sub-networks using global graph metrics. Whole brain analyses showed that with the new edge-weighting, the shortest-path length between all pairs of nodes decreases with age and thus efficiency increases. This reduction in shortest-path length is probably driven by previously reported age-related increases in the intra-axonal signal fraction. Sub-networks analyses revealed unique visual network characteristics over development and confirmed previously observed maturational pattern of posterior regions across childhood and adolescence.

Xianjun Li¹, Congcong Liu¹, Mustafa Salimeen¹, Miaomiao Wang¹, Mengxuan Li¹, Chao Jin¹, Xiaocheng Wei¹, and Jian Yang^1
1Department of Radiology, The First Affiliated Hospital of Xi’an Jiaotong University, Xi'an, China

Cerebrospinal fluid (CSF) and interstitial fluid exchange via Virchow Robin space (VRS). It is reasonable to infer that VRS may be related to CSF dynamics. To investigate the association between CSF dynamics and VRS on infants, this work assessed CSF dynamics on infants by DTI with b values of 200 and 1000 s/mm² and segmented VRS on T2WI images. Results suggest that the ratio between diffusivities derived from low and high b-value DTI could provide complementary information for assessing infant cerebrospinal fluid dynamics. There may exist potential association between Virchow–Robin space volume and cerebrospinal fluid dynamics.

Maximilian Pietsch^1,2, Daan Christiaens^2,3, Jana Hutter^2,4, Lucilio Cordero-Grande², Anthony N. Price^2,4, Emer Hughes², A. David Edwards², Joseph V. Hajnal^2,4, Serena J. Counsell², Jonathan O'Muircheartaigh^1,2,5,6, and J-Donald Tournier^2,4
1Forensic & Neurodevelopmental Sciences, King's College London, London, United Kingdom, ²Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, Kings Health Partners, St. Thomas Hospital, London, SE1 7EH, UK, King's College London, London, United Kingdom, ³Department of Electrical Engineering (ESAT/PSI), KU Leuven, Leuven, Belgium, ⁴Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom, ⁵Department of Perinatal Imaging & Health, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom, ⁶MRC Centre for Neurodevelopmental Disorders, King's College London, London, United Kingdom

We decompose neonatal HARDI signal into four components that together capture the orientation dependency and temporal dependency of signal in neonatal white and grey matter and CSF. We show that the voxel-wise volume fractions of the associated components exhibit distinct sigmoid-shaped time dependencies between 33 to 44 weeks gestational age and clearly delineate anatomical structures in developing white and grey matter, allowing detailed characterisation of microstructural properties of developing white and grey matter.

Guido I. Guberman¹, Sonja Stojanovski^2,3, Alain Ptito¹, Danilo Bzdok⁴, Anne Wheeler^2,3, and Maxime Descoteaux^5
1Department of Neurology and Neurosurgery, McGill University, Montreal, QC, Canada, ²Neuroscience and Mental Health Program, Hospital for Sick Children, Toronto, ON, Canada, ³Department of Physiology, University of Toronto, Toronto, ON, Canada, ⁴Department of Biomedical Engineering, McGill University, Montreal, QC, Canada, ⁵Department of Computer Science, Université de Sherbrooke, Sherbrooke, QC, Canada

Concussion heterogeneity remains a major challenge for clinical and scientific research. Yet, most studies continue to employ group comparison approaches that assume consistent one-to-one relationships between brain structure and symptoms. To parse concussion heterogeneity, we employed a double-multivariate approach using diffusion MRI of children with histories of concussion. Multivariate white-matter structural features captured more information about symptoms than all individual features. Results also revealed how different white-matter abnormalities led to similar symptom profiles. Lastly, multivariate features significantly predicted adverse psychiatric outcomes. These results suggest that concussion heterogeneity arising from complex structure/symptom relationships can be well captured by our double-multivariate approach.

Alexandros Popov¹, Raïssa Yebga Hot¹, Justine Beaujoin¹, Ivy Uszynski¹, Fawzi Boumezbeur¹, Fabrice Poupon¹, Christophe Destrieux², and Cyril Poupon^1
1NeuroSpin (CEA), Paris, France, ²Université de Tours, Tours, France

In this study, we present the Chenonceau dataset : a novel 11.7T MRI dataset of the entire human brain, combining an ultra-high resolution anatomical scan at 100μm with diffusion scans at 200μm using strong diffusion sensitizations. To obtain this dataset, a unique acquisition protocol has been established : a fixed ex vivo brain has been cut into blocks compatible in size with a Bruker 11.7T MRI system. The blocks were scanned individually over an extended period of time. The collection of datasets was then registered back to a reference blockface acquired at 3T, thus resulting in a unique high resolution brain dataset.