Open Collections

Joseph, Tigris

University of British Columbia

Previous work has suggested that advanced magnetic resonance imaging (MRI) techniques for quantifying myelin may be dependent on the orientation of the myelin sheath relative to the external magnetic field. The extent these MRI metrics are dependent on orientation affects comparisons between regions in the brain oriented differently to the main magnetic field, longitudinal studies examining tissue that might be variably positioned within the MRI scanner, and comparisons between healthy and disease tissue as inflammation may disperse axons. In this study, 6 donated human spinal cord tissue samples were scanned using a 9.4T Bruker pre-clinical MRI. Data was collected using myelin water imaging (MWI), magnetization transfer (MT), and inhomogeneous magnetization transfer (ihMT, both cosine modulated and T1d filtered) experiments at 9-10 different angles relative to the main magnetic field. Four myelin metrics were extracted from the different scans (myelin water fraction (MWF), MT ratio (MTR), cosine modulated ihMT ratio (ihMTRcos), T1d filtered ihMT ratio (ihMTRT1d)) in all white matter (WM) and 5 WM regions of interest (ROIs). Reproducibility was assessed using coefficients of variation (COVs) for 5 angles that were rescanned after repositioning 3 of the spinal cord samples. Myelin metrics in all WM and specific WM ROIs were plotted against spinal cord angle, and plots were visually assessed. Overall MWF and ihMTRT1d had the largest COVs in all WM and individual WM ROIs, followed by ihMTRcos, and then MTR. The large COVs in ihMTRT1d may be due to a grainy artifact seen in some of the metric maps. MWF had the largest variation with angle, followed by ihMTRT1d, then ihMTRcos, and MTR with the least variation. MTR had similar patterns in the variation with angle between WM ROIs and within most participants suggesting that it is orientation dependent. The pattern of variation of the other 3 myelin metrics with angle appeared to vary between participants, suggesting that some of the orientation dependence may be due to issues with data collection and/or inter-individual differences. Future work should optimize scan protocols at oblique angles to study orientation dependence and create a correction model for orientation dependence of myelin MRI metrics.

Text

2023-08-31

Attribution-ShareAlike 4.0 International

http://hdl.handle.net/2429/85755

Medical Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-sa/4.0/