Enhancing T1 signal of normal‐appearing white matter with divided subtracted inversion recovery: A pilot study in mild traumatic brain injury

Magnetic resonance imaging (MRI) and cognitive profiles in patients with mild traumatic brain injury (mTBI) are often discordant. Conventional MRI seldom captures the full extent of pathological changes in the normal‐appearing white matter (NAWM). The divided subtracted inversion recovery (dSIR) technique may enhance T1 differences in NAWM, making them easily visible. We aimed to implement dSIR on a clinical scanner and tested results in mTBI patients. To produce dSIR images, Inversion Recovery‐Turbo Spin Echo sequences were modified using six different inversion times (TI) on a 3‐T scanner in healthy participants and patients with mTBI. The multiple TIs determined normal white (TIshort) and gray matter (TIlong) nulling points in healthy subjects, which were used to create dSIR images. In one patient, the protocol was repeated at 3 months to identify changes after rehabilitation. Diffusion tensor imaging (DTI)‐derived mean diffusivity (MD) and fractional anisotropy (FA) maps were aligned to dSIR images to ensure that signal was not artefactual. Ten healthy participants (five females; age 24 ± 3 [95% CI: 21, 26] years) were included. TIshort and TIlong were set at 450 and 750 ms, respectively. In both patients (one male, age 17 years; one female, age 14 years), dSIR images revealed areas with increased T1 in the NAWM not visible on conventional MRI. dSIR‐based hyperintensities corresponded to elevated MD and reduced FA. Substantial changes were found at follow‐up with improvement in DTI‐based parameters. dSIR images enhance subtle changes in the NAWM of patients with mTBI by amplifying their intrinsic T1 signal. Divided subtracted inversion recovery (dSIR) is derived from IR sequences available on all scanners and represents pure T1 images. dSIR in mild traumatic brain injury identified hyperintense areas in the normal‐appearing white matter (NAWM), likely representing increased T1 due to injury. dSIR appears promising to enhance visualization of subtle T1‐based changes in NAWM and is readily obtained on any scanner.