Comparison of Voxel-Wise Tumor Perfusion Changes Measured With Dynamic Contrast-Enhanced (DCE) MRI and Volumetric DCE CT in Patients With Metastatic Brain Cancer Treated with Radiosurgery

Dynamic contrast-enhanced (DCE)-MRI metrics are evaluated against volumetric DCE-CT quantitative parameters as a standard for tracer-kinetic validation using a common 4-dimensional temporal dynamic analysis platform in tumor perfusion measurements following stereotactic radiosurgery (SRS) for brain metastases. Patients treated with SRS as part of Research Ethics Board-approved clinical trials underwent volumetric DCE-CT and DCE-MRI at baseline, then at 7 and 21 days after SRS. Temporal dynamic analysis was used to create 3-dimensional pharmacokinetic parameter maps for both modalities. Individual vascular input functions were selected for DCE-CT and a population function was used for DCE-MRI. Semiquantitative and pharmacokinetic DCE parameters were assessed using a modified Tofts model within each tumor at every time point for both modalities for characterization of perfusion and capillary permeability, as well as their dependency on precontrast relaxation times (TRs), T(10), and input function. Direct voxel-to-voxel Pearson analysis showed statistically significant correlations between CT and magnetic resonance which peaked at day 7 for K(trans) (R = 0.74, P ≤ .0001). The strongest correlation to DCE-CT measurements was found with DCE-MRI analysis using voxel-wise T(10) maps (R = 0.575, P < .001) instead of assigning a fixed T(10) value. Comparison of histogram features showed statistically significant correlations between modalities over all tumors for median K(trans) (R = 0.42, P = .01), median area under the enhancement curve (iAUC(90)) (R = 0.55, P < .01), and median iAUC(90) skewness (R = 0.34, P = .03). Statistically significant, strong correlations were found for voxel-wise K(trans), iAUC(90), and v(e) values between DCE-CT and DCE-MRI. For DCE-MRI, the implementation of voxel-wise T(10) maps plays a key role in ensuring the accuracy of heterogeneous pharmacokinetic maps.