Contrast-Enhanced MR Imaging in Acute Ischemic Stroke: T2* Measures of Blood-Brain Barrier Permeability and Their Relationship to T1 Estimates and Hemorrhagic Transformation

A schematic representing a typical ΔR₂* versus time curve (ΔR₂*_measured), as well as its γ-variate fit (ΔR₂*_theoretical), where ΔR₂*_max is the maximum of ΔR₂*_theoretical, A is the dynamic phase corresponding to the onset of the recirculation phase measured at half height of the descending aspect of the ΔR₂*_theoretical curve, and N is the final dynamic phase. The difference in area encompassed by the ΔR₂*_measured and ΔR₂*_theoretical curves is indicated by C. Four DSC parameters were calculated for each region of interest: rR = [C/ΔR₂*_max], Peak Height, %Recovery = [100% × (Peak Height − mean postbolus ΔR₂*_measured)/Peak Height], and Slope = slope of ΔR₂*_measured (t) between 50 and 60 seconds postinjection. Note that for %Recovery, the mean postbolus ΔR₂*_measured, was the average ΔR₂*_measured from phases A through N, inclusive.

Mean values for the 4 candidate T2*-based surrogate measures (rR, Peak Height, %Recovery, and Slope) are displayed for both infarct and contralateral regions of interest. Wilcoxon signed rank tests revealed that Slope was the only T2*-based metric unable to delineate infarct from contralateral regions of interest (P = .84). The mean infarct rR was significantly elevated (P < .0001), while both Peak Height and %Recovery were significantly reduced, relative to contralateral regions of interest (P = .028 and P < .0001, respectively).

Mean values for the 4 candidate T2*-based surrogate measures (rR, Peak Height, %Recovery, and Slope) are displayed for infarct regions of interest corresponding to patients who subsequently hemorrhaged (HT) and those who did not (non-HT). Mann-Whitney U testing indicated that rR was capable of discriminating between HT and non-HT infarcts. While the mean rR for patients with HT was significantly elevated (P = .006 versus non-HT infarcts), there was a trend toward decreased %Recovery (P = .092 versus non-HT infarcts).

Scatterplots depict the relationship between KPS and each T2*-based measure: rR (A), Peak Height (B), %Recovery (C), and Slope (D). Of the 4 T2*-based measures investigated, only rR was significantly correlated with KPS (r = 0.64, P = .004). No significant correlations were identified between KPS and any of the other 3 T2*-based measures (%Recovery: r = −0.44, P = .07; Peak Height: r = 0.11, P = .65; Slope: r = −0.31, P = .22).

Scatterplots depict the relationship between rR and each of the other 3 candidate T2*-based measures: Peak Height (A), %Recovery (B), and Slope (C). Linear regression revealed a significant negative correlation between %Recovery and rR (r = −0.88, P < .001). No significant correlations were determined for either Peak Height or Slope with rR (r = −0.19, P = .46 and r = −0.18, P = .48, respectively).