Detectability of multiple sclerosis lesions with 3T MRI: a comparison of proton density-weighted and FLAIR sequences

Due to the high signal intensity of cerebrospinal fluid (CSF), proton density-weighted (PD-w) images with long repeat times (TR) may be less able to detect periventricular lesions in patients with multiple sclerosis (MS). However, we have found good detectability of MS lesions with PD-w using long TR at 3 Tesla (3 T). For this reason, the aim of this study was to prospectively investigate the detectability of MS lesions at 3 T in PD-w compared with fluid-attenuated inversion recovery (FLAIR) sequences.

A total of 11 MS patients were examined by a 3T magnetic resonance (MR) scanner, and their MS lesions were prospectively analyzed on PD-w and FLAIR images by two evaluators; detectability was rated by a three-point scoring system. The Wilcoxon signed-rank test was used for comparisons, and the level of significance was P<0.05.

Significantly more lesions were detectable on PD-w images (P<0.001 for both evaluators). In particular, PD-w was superior to FLAIR for the detection of periventricular (P=0.001 and P=0.013 for each evaluator respectively) and infratentorial (P<0.001 for both evaluators) lesions.

This was the first study to compare FLAIR and PD-w with long TR at 3 T; it revealed that PD-w is superior for detecting infratentorial and even periventricular MS lesions, despite the higher signal intensity of CSF. This might be due to the high spin density of MS lesions, thus distinguishing them from the surrounding brain tissue. For this reason, double-echo T2-weighted sequences at 3T are recommended to improve the detectability of MS lesions.