Effect of b Value on Imaging Quality for Diffusion Tensor Imaging of the Spinal Cord at Ultrahigh Field Strength

Abstract

Objective. To explore the optimal $b$ value setting for diffusion tensor imaging of rats’ spinal cord at ultrahigh field strength (7 T). Methods. Spinal cord diffusion tensor imaging data were collected from 14 rats (5 healthy, 9 spinal cord injured) with a series of $b$ values (200, 300, 400, 500, 600, 700, 800, 900, and 1000 s/mm2) under the condition that other scanning parameters were consistent. The image quality (including image signal-to-noise ratio and image distortion degree) and data quality (i.e., the stability and consistency of the DTI-derived parameters, referred to as data stability and data consistency) were quantitatively evaluated. The min-max normalization method was used to process the calculation results of the four indicators. Finally, the image and data quality under each $b$ value were synthesized to determine the optimal $b$ value. Results. $b=200\text{s}/\text{m}{\text{m}}^2$ and $b=900\text{s}/\text{m}{\text{m}}^2$ ranked in the top two of the comprehensive evaluation, with the best image quality at $b=200\text{s}/\text{m}{\text{m}}^2$ and the best data quality at $b=900\text{s}/\text{m}{\text{m}}^2$ . Conclusion. Considering the shortcomings of the ability of low $b$ values to reflect the microstructure, $b=900\text{s}/\text{m}{\text{m}}^2$ can be used as the optimal $b$ value for 7 T spinal cord diffusion tensor scanning.