White matter lesion contrast in fast spin-echo fluid-attenuated inversion recovery imaging: effect of varying effective echo time and echo train length.

Abstract

Our aim was to determine whether the contrast between white matter lesions and normal-appearing white matter in fast spin-echo fluid-attenuated inversion recovery (FLAIR) images can be improved by lengthening the effective TE and the echo train length. Thirty patients with various white matter lesions were imaged using fast spin-echo FLAIR sequences (TR = 10,002 msec; inversion time = 2200) on a 1.5-T MR imaging system. For 14 patients, fast spin-echo FLAIR sequences with a TE of 165 msec and echo train length of 32 (fast spin-echo FLAIR 165/32) were compared with fast spin-echo FLAIR sequences with a TE of 125 msec and echo train length of 24 (fast spin-echo FLAIR 125/24). For 16 other patients, fast spin-echo FLAIR 165/32 sequences were compared with fast spin-echo FLAIR sequences with a TE of 145 msec and echo train length of 28 (fast spin-echo FLAIR 145/28). Signal difference-to-noise ratios were calculated between the lesions and normal-appearing white matter for a typical lesion in each patient. In both groups, a small but statistically significant increase in the signal difference-to-noise ratio was found on the fast spin-echo FLAIR sequences using the longer TE and echo train length. In the first group, signal difference-to-noise ratio increased from 18.7 +/- 4.7 (mean +/- SD) for fast spin-echo FLAIR 125/24 to 20.1 +/- 4.5 for fast spin-echo FLAIR 165/32 (p < .05). In the second group, the signal difference-to-noise ratio increased from 15.4 +/- 4.0 for fast spin-echo FLAIR 145/28 to 16.8 +/- 4.6 for fast spin-echo FLAIR 165/32 (p <.01). In addition, fast spin-echo FLAIR sequences with a longer TE and echo train length were obtained more rapidly (6 min for fast spin-echo FLAIR 125/24, 5 min 20 sec for fast spin-echo FLAIR 145/28, and 4 min 41 sec for fast spin-echo FLAIR 165/32). Lengthening the TE to 165 msec and echo train length to 32 in fast spin-echo FLAIR imaging allows both a mild improvement in the contrast between white matter lesions and normal-appearing white matter and shorter imaging times.