An ex vivo imaging pipeline for producing high-quality and high-resolution diffusion-weighted imaging datasets

• Published in: Human brain mapping Vol. 32; no. 4; pp. 544 - 563
• Main Authors: Dyrby, Tim B., Baaré, William F.C., Alexander, Daniel C., Jelsing, Jacob, Garde, Ellen, Søgaard, Lise V.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.04.2011; Wiley-Liss; John Wiley & Sons, Inc
• Subjects: Algorithms; Animals; Biological and medical sciences; Brain Mapping - methods; cortical layers; crossing fibers; Diffusion; diffusion MRI; diffusion tensor imaging; Diffusion Tensor Imaging - methods; Electrocardiography. Vectocardiography; Electrodiagnosis. Electric activity recording; hippocampus; Image Processing, Computer-Assisted - methods; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Nervous system; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Reproducibility of Results; Species Specificity; Sus scrofa; tractography; validation; Validation; High resolution; Nervous system diseases; Radiodiagnosis; Tractography; Central nervous system; crossing fibers; Nuclear magnetic resonance imaging; Encephalon; Diffusion tensor imaging; cortical layers; Ex vivo; diffusion MRI; Diffusion; Hippocampus
• ISSN: 1065-9471; 1097-0193; 1097-0193
• DOI: 10.1002/hbm.21043

Diffusion tensor (DT) imaging and related multifiber reconstruction algorithms allow the study of in vivo microstructure and, by means of tractography, structural connectivity. Although reconstruction algorithms are promising imaging tools, high‐quality diffusion‐weighted imaging (DWI) datasets for verification and validation of postprocessing and analysis methods are lacking. Clinical in vivo DWI is limited by, for example, physiological noise and low signal‐to‐noise ratio. Here, we performed a series of DWI measurements on postmortem pig brains, which resemble the human brain in neuroanatomical complexity, to establish an ex vivo imaging pipeline for generating high‐quality DWI datasets. Perfusion fixation ensured that tissue characteristics were comparable to in vivo conditions. There were three main results: (i) heat conduction and unstable tissue mechanics accounted for time‐varying artefacts in the DWI dataset, which were present for up to 15 h after positioning brain tissue in the scanner; (ii) using fitted DT, q‐ball, and persistent angular structure magnetic resonance imaging algorithms, any b‐value between ∼2,000 and ∼8,000 s/mm2, with an optimal value around 4,000 s/mm2, allowed for consistent reconstruction of fiber directions; (iii) diffusivity measures in the postmortem brain tissue were stable over a 3‐year period. On the basis of these results, we established an optimized ex vivo pipeline for high‐quality and high‐resolution DWI. The pipeline produces DWI data sets with a high level of tissue structure detail showing for example two parallel horizontal rims in the cerebral cortex and multiple rims in the hippocampus. We conclude that high‐quality ex vivo DWI can be used to validate fiber reconstruction algorithms and to complement histological studies. Hum Brain Mapp, 2011. © 2010 Wiley‐Liss, Inc.