In-vivo diffusion MRI protocol optimization for the chimpanzee brain and examination of aging effects on the primate optic nerve at 3T |
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| Affiliation: | 1. Department of Neurosurgery, The Chinese PLA General Hospital, Beijing 100853, China;2. State Key Laboratory of Brain and Cognitive Science, Beijing MR Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China;3. University of Chinese Academy of Sciences, Beijing 100049, China;4. Department of Neurological Surgery, University of Pittsburgh, Pittsburgh, PA 15213, USA;1. The Roslin Institute, University of Edinburgh, Easter Bush Campus, Midlothian, Edinburgh EH25 9RG, UK;2. Euan MacDonald Centre, Chancellor’s Building, University of Edinburgh, 49 Little France Crescent, Edinburgh EH16 4SB, UK;3. Donald Danforth Plant Science Center, 975 N Warson Rd., St. Louis, MO 63132, USA;4. Proteomics and Metabolomics Facility, Center for Biotechnology, Beadle Center, University of Nebraska, Lincoln, 1901 Vine St., Lincoln, NE 68588, USA;5. Oregon National Primate Research Center, 505 NW 185th Ave., Beaverton, OR 97006, USA;6. Edinburgh Medical School, Biomedical Sciences, Hugh Robson Building, George Square, Edinburgh EH8 9XD, UK;7. FingerPrints Proteomic Facility, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK;8. Centre for Dementia Prevention, University of Edinburgh, 9A Bioquarter, 9 Little France Road, Edinburgh EH16 4UX, UK;9. Centre for Discovery Brain Sciences, University of Edinburgh, Hugh Robson Building, Edinburgh EH8 9XD, UK |
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| Abstract: | BackgroundDiffusion MRI (dMRI) data acquisition protocols are well-established on modern high-field clinical scanners for human studies. However, these protocols are not suitable for the chimpanzee (or other large-brained mammals) because of its substantial difference in head geometry and brain volume compared with humans. Therefore, an optimal dMRI data acquisition protocol dedicated to chimpanzee neuroimaging is needed.MethodsA multi-shot (4 segments) double spin-echo echo-planar imaging (MS-EPI) sequence and a single-shot double spin-echo EPI (SS-EPI) sequence were optimized separately for in vivo dMRI data acquisition of chimpanzees using a clinical 3T scanner. Correction for severe susceptibility-induced image distortion and signal drop-off of the chimpanzee brain was performed and evaluated using FSL software. DTI indices in different brain regions and probabilistic tractography were compared. A separate DTI data set from n=34 chimpanzees (13 to 56 years old) was collected using the optimal protocol. Age-related changes in diffusivity indices of optic nerve fibers were evaluated.ResultsThe SS-EPI sequence acquired dMRI data of the chimpanzee brain with approximately doubled the SNR as the MS-EPI sequence given the same scan time. The quality of white matter fiber tracking from the SS-EPI data was much higher than that from MS-EPI data. However, quantitative analysis of DTI indices showed no difference in most ROIs between the SS-EPI and MS-EPI sequences. The progressive evolution of diffusivity indices of optic nerves indicated mild changes in fiber bundles of chimpanzees aged 40 years and above.ConclusionThe single-shot EPI-based acquisition protocol provided better image quality of dMRI for chimpanzee brains and is recommended for in vivo dMRI study or clinical diagnosis of chimpanzees (or other large animals) using a clinical scanner. Also, the tendency of FA decrease or diffusivity increase in the optic nerve of aged chimpanzees was seen but did not show significant age-related changes, suggesting aging may have less impact on optic nerve fiber integrity of chimpanzees, in contrast to previous results for both macaque monkeys and humans. |
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