High-b-value diffusion-weighted MR imaging of suspected brain infarction

BACKGROUND AND PURPOSE: Recent technological advances in MR instrumentation allow acquisition of whole-brain diffusion-weighted MR scans to be obtaine d with b values greater than 1000. Our purpose was to determine whether hig h-b-value diffusion-weighted MR imaging improved contrast and detection of signal changes in acute and chronic brain infarction. METHODS: We prospectively evaluated the MR scans of 30 subjects with a hist ory of possible brain infarction on a 1.5-T MR imager with 40 mT/meter grad ients (slew rate 150 T/m/s) by use of the following single-shot echo-planar diffusion-weighted MR sequences: 1) 7999/ 71.4/1 (TR/TE/excitations, b = 1 000; 2) 999/ 88.1/3, b = 2500; and 3) 7999/ 92.1/4, b = 3000. Diffusion-wei ghted MR imaging was performed in three orthogonal directions during all se quences. All subjects were scanned with fast fluid-attenuated inversion rec overy (FLAIR) (10,006/145/2200/1 [TR/TE/TI/excitations]) and fast spin-echo T2-weighted (3650/95/3 [TR/TE/ excitations], echo train length, 8). The di agnosis of brain infarction was established by clinical criteria. RESULTS: Twenty women and 10 men with a mean age of 67.7 years mere enrolle d in the study. One subject was excluded owing to poor image quality. Twelv e of 29 subjects had a clinical diagnosis of acute infarction. All 12 had l esions that were hyperintense on diffusion-weighted images at all three b v alues; five were cortical and seven subcortical. There was increased contra st of all lesions on high-b-value scans (b = 2500 and 3000). Lesions that w ere hypointense on diffusion-weighted images were identified and evaluated at the three different b values. At b = 1000, there were 19 hypointense les ions, whereas at b = 2500 and 3000 there were 48 and 55 lesions, respective ly. On FLAIR and T2-weighted images, these low-signal lesions were predomin antly chronic, subcortical, ischemic lesions and lacunar infarcts, but four chronic cortical infarcts, one porencephalic cyst, and one primary brain t umor were also found. Low-signal lesions were also noted to have increased contrast on high-b-value diffusion-weighted scans. CONCLUSION: High-b-value diffusion-weighted MR imaging (b = 2500 or b = 300 0) had no impact on diagnosis of acute infarction. High-b-value diffusion-w eighted MR imaging (b = 2500) combined with diffusion-weighted MR imaging a t b = 1000 improves tissue characterization by increasing the spectrum of o bserved imaging abnormalities in patients with suspected brain infarction.