Diffusion/perfusion MR imaging of acute cerebral ischemia

Abstract

In vivo echo-planar MR imaging was used to measure apparent diffusion coefficients (ADC) of cerebral tissues in a comprehensive noninvasive evaluation of early ischemic brain damage induced by occlusion of the middle cerebral artery (MCA) in a cat model of acute regional stroke. Within 10 min after arterial occlusion, ADC was significantly lower in tissues within the vascular territory of the occluded MCA than in normally perfused tissues in the contralateral hemisphere. Sequential echo-planar imaging was then used in conjunction with bolus injections of the magnetic susceptibility contrast agent, dysprosium DTPA-BMA, to characterize the underlying cerebrovascular perfusion deficits. Normally perfused regions of brain were identified by a dose-dependent 35-70% loss of signal intensity within 6-8 s of contrast administration, whereas ischemic regions appeared relatively hyperintense. These data indicate that sequential diffusion/perfusion imaging may be useful in differentiating permanently damaged from reversibly ischemic brain tissue.

Diffusion nuclear magnetic resonance imaging in experimental stroke. Correlation with cerebral metabolites.

“…TE was between 32 and 55 milliseconds to minimize a T 2 -dependent loss in signal to noise. At a TE of 32 milliseconds, the gradient power supply could produce b factors of up to 1500 s/mm 2 . The slight variation in TE has no significant effect on the contrast situation.…”

The role of imaging in acute ischemic stroke

“…3). Diffusion-weighted imaging (DWI) is approximately 4 to 5 times more sensitive in detecting acute stroke than NCHCT 25,33,57,65,92,116,219,221 ( Fig. 4).…”

The Role of Magnetic Resonance Imaging for Acute Ischemic Stroke

“…In ischemic tissue perfusion is decreasing and therefore the contrast agent has minimal or no concentration in this ischemic zone and signal is relatively increased 69 . Although the dynamics of signal changes provide some information about cerebral microcirculation, the relative signal loss does not correlate directly with any physiological parameter.…”

“…Although the dynamics of signal changes provide some information about cerebral microcirculation, the relative signal loss does not correlate directly with any physiological parameter. The derivation of a "signal -time" curve and "concentration of contrast agent -time" curve acquired during first passage of contrast agent are needed to calculate (semi-) quantitative parameters of cerebro vascular hemodynamics 69 . The results of these complicated derivations are several hemodynamic parameters: cerebral blood flow (CBF), cerebral blood volume (CBV).…”