High-b diffusivity of MS lesions in cervical spinal cord using ultrahigh-b DWI (UHb-DWI)

The purpose of this study was to investigate UHb-rDWI signal in white matter tracts of the cervical spinal cord (CSC) and compare quantitative values between healthy control WM with both MS NAWM and MS WM lesions.

UHb-rDWI experiments were performed on (a) 7 MS patients with recently active or chronic lesions in CSC and on (b) 7 healthy control of similar age range and gender distribution to MS subjects. All MRI data were acquired using clinical 3T MRI system. Axial high-b diffusion images were acquired using 2D single-shot DW stimulated EPI with reduced FOV and a CSC-dedicated 8 channel array coil. High-b diffusion coefficient D_H was estimated by fitting the signal-b curve to a double or single-exponential function.

The high-b diffusivity D_H values were measured as (0.767 ± 0.297) × 10^-3 mm²/s in the posterior column lesions, averaged over 6 MS patients, and 0.587 × 10^-3 mm²/s in the corticospinal tract for another patient. The averaged D_H values of the 7 healthy volunteers from the posterior and lateral column were (0.0312 ± 0.0306) × 10^-3 and (0.0505 ± 0.0205) × 10^-3 mm²/s, respectively. UHb-rDWI signal-b curves of the MS patients revealed to noticeably behave differently to that of the healthy controls. The patient signal-b curves decayed with greater high-b decay constants to reach lower signal intensities relative to signal-b curves of the healthy controls.

UHb-DWI of the CSC reveals a marked difference in signal-b-curves and D_H values in MS lesions compared to NAWM and healthy control WM. Based on physical principles, we interpret these altered observations of quantitative diffusion values to be indicative of demyelination. Further studies in animal models will be required to fully interpret UHb-DWI quantitative diffusion values during demyelination and remyelination.