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Final Infarct Size after Acute Stroke: Prediction with Flow Heterogeneity¹

¹ From the Departments of Neuroradiology (C.Z.S., L.R., P.V.P., C.G., L.Ø.) and Neurology (G.A.), Århus University Hospital, Nørrebrogade 44, DK-8000 Århus C, Denmark. Received July 23, 2001; revision requested August 31; final revision received March 29, 2002; accepted April 9. L.Ø. supported by the Danish Medical Research Council and the Danish National Research Foundation. Address correspondence to C.Z.S. (e-mail: claus@pet.auh.dk).

View larger version (31K): [in a new window]   Figure 1. Calculation of FH. The deconvolution of the tissue concentration-time curve with the arterial input function yields the R(t) (upper left). The negative slope of the residue function at a given time is the h(t) (lower left). Using the relation cerebral blood volume = cerebral blood flow · MTT turns this curve into a distribution of flow (right) (12). In the graph on the right, the x axis displays flow relative to the mean flow and the y axis displays the associated probability—that is, the distribution of relative flow rates, or w(f). The probability density functions of relative flow for normal and ischemic regions in one patient are shown. The functions for the ischemic area indicate a loss of the high-flow component relative to normal tissue. The distribution of flow becomes more narrow, and microscopic flow displays a more uniform velocity pattern—that is, a more homogeneous distribution of flow.

View larger version (35K): [in a new window]   Figure 2. Bar graph depicts MTT- and FH-predicted volumes and final infarct sizes at follow-up T2-weighted MR imaging, as normalized to the estimated acute-stage infarcted volumes at DW imaging, in the 23 patients.

View larger version (32K): [in a new window]   Figure 3. Graph depicts predictions of final infarct size based on MTT and FH measurements, as a function of final infarct volume at follow-up T2-weighted MR imaging. The dashed line is the fitted line for the MTT data (slope = 1.57, r2 = 0.87), and the solid line is the fitted line for the FH data (slope = 1.12, r2 = 0.83). Both lines are constrained by a forced zero intercept.

View larger version (174K): [in a new window]   Figure 4. DW (DWI), MTT map, FH map, and follow-up (F/U) T2-weighted MR images of three sections of the brain of patient 22. DW image shows areas that were estimated to be infarcted during the acute stage. The images in the two middle columns depict the predictions of final infarct volume based on MTT and FH measurements. The T2-weighted MR images in the far right column depict the final infarct size. Note that the MTT image findings suggest that the area between the arrowheads—that is, the entire right middle cerebral artery territory—is infarcted. However, the FH images, which correlate better with the follow-up MR images, show only the subcortical regions (arrows) to be infarcted. Note also that the DW, MTT, and FH images were acquired during the acute stroke stage, whereas the T2-weighted images were acquired 1 month after the stroke. On the FH images, only those pixels for which the P value was less than .01 are colored. The pixels for which the P value was normal are transparent and display the underlying cerebral blood flow map.