Line scan diffusion imaging: characterization in healthy subjects and stroke patients.

OBJECTIVE: Our objective was to evaluate a new scanning method, MR line scan diffusion imaging, and assess the apparent diffusion coefficient in the brains of healthy subjects and stroke patients. SUBJECTS AND METHODS: Line scan diffusion imaging without cardiac gating or head restraints was implemented on low- (0.5 T) and medium- (1.5 T) field-strength scanners with conventional hardware. Diffusion-weighted images were obtained in six healthy subjects and eight stroke patients. Unidirectional diffusion encoding was used for fast localization of stroke lesions. For further characterization, orthogonal diffusion encoding was applied, and the trace of the apparent diffusion coefficient was calculated. Single-shot diffusion-weighted echoplanar imaging served as the reference standard. For healthy subjects, imaging was repeated four times on each scanner. Mean and relative precision of the apparent diffusion coefficient trace values were calculated for each pixel. In stroke lesions and adjacent normal tissue, apparent diffusion coefficient trace values were determined.
RESULTS: In the 108 scans obtained, line scan diffusion imaging proved to be robust, virtually free of artifact (independent of slice location and orientation), reproducible, and rapid for localization of a stroke. Scan time for 14 slices at 7-mm thickness was 8 min at 0.5 T and 7 min at 1.5 T. Image qualities with line scan diffusion imaging and single-shot diffusion-weighted echoplanar imaging were comparable. At 1.5 T, precision was essentially the same for line scan diffusion imaging (4.3%) and echoplanar imaging (4.7%). With line scan diffusion imaging at 0.5 T and 1.5 T, normal paraventricular apparent diffusion coefficient trace values averaged 0.71 microm2/msec, and with echoplanar imaging these values averaged 0.69 microm2/msec. In acute lesions apparent diffusion coefficient trace values were low, and in chronic lesions these values were high.
CONCLUSION: Line scan diffusion imaging on low- and medium-field-strength MR scanners equipped with conventional hardware was reliable and practical for measuring brain apparent diffusion values, which can be applied to the early diagnosis, and hence timely management, of stroke.