Accuracy and anatomical coverage of perfusion CT assessment of the blood-brain barrier permeability: one bolus versus two boluses

Abstract

Purpose: To assess whether blood-brain barrier permeability (BBBP) values, extracted with the Patlak model from the second perfusion CT (PCT) contrast bolus, are significantly lower than the values extracted from the first bolus in the same patient.

Materials and methods: 125 consecutive patients (29 with acute hemispheric stroke and 96 without stroke) who underwent a PCT study using a prolonged acquisition time up to 3 min were retrospectively identified. The Patlak model was applied to calculate the rate of contrast leakage out of the vascular compartment. Patlak plots were created from the arterial and parenchymal time enhancement curves obtained in multiple regions of interest drawn in ischemic brain tissue and in nonischemic brain tissue. The slope of a regression line fit to the Patlak plot was used as an indicator of BBBP. Square roots of the mean squared errors and correlation coefficients were used to describe the quality of the linear regression model. This was performed separately for the first and the second PCT bolus. Results from the first and the second bolus were compared in terms of BBBP values and the quality of the linear model fitted to the Patlak plot, using generalized estimating equations with robust variance estimation.

Results: BBBP values from the second bolus were not lower than BBBP values from the first bolus in either nonischemic brain tissue [estimated mean with 95% confidence interval: 1.42 (1.10-1.82) ml x 100 g(-1) x min(-1) for the first bolus versus 1.64 (1.31-2.05) ml x 100 g(-1) x min(-1) for the second bolus, p = 1.00] or in ischemic tissue [1.04 (0.97-1.12) ml x 100 g(-1) x min(-1) for the first bolus versus 1.19 (1.11-1.28) ml x 100 g(-1)min(-1) for the second bolus, p = 0.79]. Compared to regression models from the first bolus, the Patlak regression models obtained from the second bolus were of similar or slightly better quality. This was true both in nonischemic and ischemic brain tissue.

Conclusion: The contrast material from the first bolus of contrast for PCT does not negatively influence measurements of BBBP values from the second bolus. The second bolus can thus be used to increase anatomical coverage of BBBP assessment using PCT.

Fig. 1

Example of graphical illustration of BBBP, calculated from the slope of a regression line fit to the Patlak plot. a PCT infarct core and tissue at risk threshold maps. b BBBP color maps; BBBP values from the second bolus (bolus 2) were not lower than the values from the first bolus (bolus 1). c Patlak plots that were constructed from arterial and parenchymal time enhancement curves, as explained in the appendix, in an infarcted tissue ROI and a nonischemic tissue ROI. These Patlak plots illustrate how small the differences in slope (BBBP) and linearity between bolus 1 and 2 are. Of note, the slope of the plot from the infarcted tissue ROI is steeper than that of the nonischemic tissue ROI.