SENSITIVITY OF MAGNETIC-RESONANCE DIFFUSION-WEIGHTED IMAGING AND REGIONAL RELATIONSHIP BETWEEN THE APPARENT DIFFUSION-COEFFICIENT AND CEREBRAL BLOOD-FLOW IN RAT FOCAL CEREBRAL-ISCHEMIA

Background and Purpose Magnetic resonance (MR) diffusion-weighted imag ing (DWI), a noninvasive procedure, may play an important role in dete cting and accurately localizing the extent of evolving infarction with in the period immediately following stroke. We evaluated the sensitivi ty and specificity of DWI in detecting ischemia and compared a quantit ative measure derived from the DWI, the apparent diffusion coefficient (ADC), with autoradiographic cerebral blood flow (CBF) in an experime ntal model of focal cerebral ischemia in rats. Methods MR imaging data were obtained with a General Electric 4.7-T horizontal bore magnet CS I II system with self-shielded gradients. DWI was acquired within 41+/ -6 minutes (mean+/-SD) after onset of ischemia and repeated at 169+/-1 4 minutes, followed by CBF determination at 237+/-21 minutes. DWI, ADC , and CBF images from each animal were then compared. Results The sens itivities for detecting an abnormality at 1 and 3 hours for DWI were s ignificantly different, and the sensitivity of 3-hour DWI did not diff er from the CBF sensitivity of 99%. A mean+/-SD ADC threshold of 460+/ -95 mu m(2)/s was defined as 45% higher than the low ADC in the ischem ic core compared with the contralateral ADC. Subthreshold ADC area and ischemic area were significantly correlated (r(2)=.69, P<.05). In 19 of 48 regions of interest classified as ischemic (<35 mL . 100 g(-1). min(-1)) from both the 3-hour ADC and CBF images, 3-hour ADC correlate d significantly with CBF (r(2)=.27, n=19, P<.05), whereas in the nonis chemic regions ADC was inversely correlated with CBF. Several ischemic regions showed a sharp drop in ADC to 37% (P<.001, n=5) compared with all other regions (n=43) from 1 to 3 hours. Conclusions Because of th e change in the sensitivity of detecting ischemia with DWI, the differ ence in correlation of CBF with ADC between ischemic and nonischemic c ortex, and the presence of several regions in which ADC dropped to 37% from 1 to 3 hours, our data suggest that ADC values potentially can b e used to monitor evolving infarction.