Perfusion Magnetic Resonance Imaging Maps in Hyperacute Stroke

Abstract

Background and Purpose-In ischemic stroke, perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) provide important pathophysiological information. A PWIϾDWI mismatch pattern suggests the presence of salvageable tissue. However, improved methods for distinguishing PWIϾDWI mismatch tissue that is critically hypoperfused from benign oligemia are required. Methods-We investigated the usefulness of maps of relative cerebral blood flow (rCBF), volume (rCBV), and mean transit time (rMTT) to predict transition to infarction in hyperacute (Ͻ6 hours) stroke patients with PWIϾDWI mismatch patterns. Semiquantitative color-thresholded analysis was used to measure hypoperfusion volumes, including increasing color signal intensity thresholds of rMTT delay, which were compared with infarct expansion, outcome infarct size, and clinical status.

Heterogeneity in the penumbra

“…Problems with the MRI definition of the penumbra include the fact that there is no threshold within a region of oligemia (Kidwell et al, 2003;Kane et al, 2007;Toth and Albers, 2009), and that the PWI abnormality often overestimates the final infarction volume, and hence the amount of tissue at risk (Parsons et al, 2001). In addition, the initial diffusion lesion does not necessarily define the core of infarcted tissue because some diffusion lesions can be transiently or permanently reversed if blood flow is rapidly restored (Kidwell et al, 2000;Parsons et al, 2002;Chalela et al, 2004).…”

Hyperglycemia and the Fate of Apparent Diffusion Coefficient–Defined Ischemic Penumbra

“…Penumbra in acute stroke is usually investigated by using by the diffusion-perfusion mismatch, which requires a contrast agent injection. [12][13][14][15] We have developed a new neuroradiologic method for imaging the ischemic penumbra in acute stroke patients, based on DWI without the injection of intravenous contrast material. [16][17][18] The penumbra is defined on the initial ADC map by an algorithm based on the topobiology of natural infarct growth and the modeling of ADC abnormalities occurring in the penumbral tissue.…”

Hemodynamic segmentation of MR perfusion images in patients with unilateral carotid stenosis using independent component analysis

“…The differences in TTP, T max , and MTT for brain parenchyma on the normal and stenotic sides were widely used in diffusion-perfusion mismatch research (7)(8)(9)(10)(11)(12)(13)(17)(18)(19)(20). A delay of more than 4 or 6 s yields a fair estimate of hypoperfusion.…”

“…A delay of more than 4 or 6 s yields a fair estimate of hypoperfusion. Although prolongation of TTP, T max and MTT is proposed to be related to tissues at risk in diffusion-perfusion mismatch research, recent studies have shown that benign oligemia is included in hyperintense areas observed on TTP (8,(11)(12)(13), T max (13,19,20), and MTT (13,16,17) images. As an example, there is a large bright area on the TTP, T max , and MTT images for the second patient shown in Figure 2.…”

“…Ostergaard et al proposed using an arterial input function (AIF) and singular value decomposition (SVD) technique for the deconvolution calculation of relative cerebral blood flow (rCBF) and a residue curve (14,15). Using this technique, parametric images of rCBF (6,16,17), mean transit time (MTT) (6,13,16,17), and the time to maximum of the residue curve (T max ) (13,18 -20) are calculated to evaluate cerebral perfusion. Because it is difficult to manually identify normal and stenotic arteries at the same slice location, a proximal normal vessel (for example, carotid artery, vertebral artery, or middle cerebral artery) is generally selected to represent the AIF (2,6,15,19).…”