MAGNETIC-RESONANCE DIFFUSION-WEIGHTED IMAGING - SENSITIVITY AND APPARENT DIFFUSION CONSTANT IN STROKE

Magnetic resonance diffusion-weighted imaging (MR-DWI) is sensitive to the diffusibility of water and may offer characterization and anatomi cal localization of stroke leading to early tailored therapeutic inter vention. We compared DWI, the apparent diffusion constant (ADC), and a utoradiographic cerebral blood flow (CBF) in a model of focal cerebral ischemia in the rat. Sprague-Dawley rats were embolized with a single silicone cylinder injected into the internal carotid artery. Both com mon carotids were permanently ligated. The animals were anesthetized ( isoflurane in O2), and paralyzed (gallamine). MR-DWI were obtained wit h a GE 4.7 T magnet (TE = 3 s, TR = 80 msec, b = 2393 . 10(-3) mm2/s, slice thickness 3 mm). DWI and CBF autoradiograms were compared visual ly. ADC was assessed in various regions, including ischemic cortex and a region homologous to ischemic cortex. Imaging times from stroke ons et were 50 +/- 6 min (mean +/- SEM) for DWI, 185 +/- 17 min for a seco nd DWI. CBF was determined at 258 +/- 15 min. The specificity was 100% at both 50 min and 185 min, indicating that there were no false posit ives; in 3 animals ischemia was not present, However, the sensitivity analysis indicated that early DWI yields some false negatives: at 50 m in the sensitivity was 60%. We attribute our result of low early sensi tivity to small infarcts in relation to the slice thickness. Later, at 185 min, sensitivity was 100%. The first ADCs were higher than the se cond ADC values in ischemic cortex. For infarcts larger than the slice thickness, early MR-DWI is highly sensitive for imaging evolving isch emia. Unlike other imaging methodologies (e.g. T2 or CT Scan), MR-DWI will contribute to the diagnosis and treatment of early stages of cere bral ischemia.