Tissue at risk is overestimated in perfusion-weighted imaging: MR imaging in acute stroke patients without vessel recanalization.

BACKGROUND AND PURPOSE: The volume of decreased cerebral blood flow (CBF) in acute stroke perfusion-weighted imaging frequently overestimates final infarct volume. We hypothesized that surviving tissue exists even in patients without recanalization and tried to determine perfusion thresholds from initial MR imaging. METHODS: Stroke MR imaging including MR angiography was carried out at days 0, 1, and 7 after stroke onset in 19 patients without recanalization at least until day 1. The following lesions were defined: L0 = diffusion restriction at day 0; LG1 = lesion growth until day 1; LG7 = lesion growth until day 7; ST7 = initially hypoperfused, but surviving tissue. These lesions were transferred on initial MR imaging within 4.7 hours and perfusion values at day 0 were determined. RESULTS: Median lesion volume L0 at day 0 was 18.2 mL and increased to 39.4 and 43.8 mL at days 1 and 7. Volume of decreased rCBF not progressing to infarction was 148.5 mL (ST7). Mean ST7 perfusion values were different from L0 and LG1, but only mean relative cerebral blood volume (rCBV) was different from LG7, discriminating survival against death of tissue. A threshold value of 0.82 CBV for death versus survival was determined with a sensitivity of 0.56 and specificity of 0.95. Carotid T occlusions showed the greatest potential of lesion growth. CONCLUSION: Even when vessel occlusion persists, hypoperfused tissue on MR imaging does not necessarily progress toward infarction. The most conclusive inferences can be drawn from CBV images. The site of arterial occlusion also determines progression to infarction.

Cerebral perfusion impairment correlates with the decrease of CT density in acute ischaemic stroke.

Within the first 6 h of ischaemic stroke, changes on computed tomography (CT) scans are known as early ischaemic signs. We tested the hypothesis that the severity of perfusion impairment correlates with the degree of CT density decrease. Water uptake in ischaemic brain tissue results in a subtle decrease of CT density, and was quantified by delineation of the corresponding decrease of the apparent diffusion coefficient (ADC). Regions of decreased ADC and CT density in 29 acute-stroke patients were superimposed on the corresponding magnetic resonance perfusion images. Mean values of ADC and CT density decrease were correlated with the corresponding relative changes of cerebral blood flow (rCBF) and volume (rCBV), mean transit time (rMTT) and time-to-peak (rTTP). The decrease of CT density was 1.2 +/- 0.6 Hounsfield units and showed a linear correlation with rCBF (0.42, p < 0.01) as well as rCBV (0.62, p < 0.01), but not with the prolongation of rMTT (1.43, p = 0.78) or rTTP (1.34, p = 0.26). Therefore, the reduction of rCBF determines the severity of the early ischaemic oedema (EIOE) on CT, as well as reduction of the ADC. These findings provide a coherent view on the pathophysiology of the EIOE.