On the Use of DSC-MRI for Measuring Vascular Permeability

BACKGROUND AND PURPOSE: Contrast agent extravasation has been shown to confound brain tumor perfusion measurements with DSC–MR imaging, necessitating the use of correction techniques (eg, Weisskoff, Bjornerud). Leakage parameters (K₂ and K_a) postulated to reflect vessel permeability can be extracted from these correction methods; however, the biophysical interpretation of these parameters and their relationship to commonly used MR imaging measures of vascular permeability (eg, contrast agent volume transfer constant, [K^trans]) remain unclear. Given that vascular density, as assessed by blood volume, and vascular permeability, as reflected by K^trans (and potentially K₂ or K_a), report on unique and clinically informative vascular characteristics, there is a compelling interest to simultaneously assess these features.

MATERIALS AND METHODS: We acquired multiecho DSC–MR imaging data, allowing the simultaneous computation and voxelwise comparison of single- and dual-echo derived measures of K₂, K_a and K^trans in patients with glioma. This acquisition enabled the investigation of competing T1 and T2* leakage effects and TE dependency on these parameters.

RESULTS: K₂ and K_a displayed nonsignificant (P = .150 and P = .060, respectively) voxelwise linear correlations with K^trans, while a significant (P < .001) inverse relationship was observed between K₂ and K_a (coefficient of determination [r²] = 0.466–0.984). Significantly different (P < .005) mean estimates were found between voxels exhibiting predominately T1 and T2* effects for K₂ and K_a. K^trans, however, was observed to be similar between these voxels (0.109 versus 0.092 minutes⁻¹). Significant differences (P < .001) in extracellular-extravascular volume fraction (v_e) (0.285 versus 0.167) were also observed between cohorts. Additionally, K₂ and K_a were found to have a significant quadratic relationship (P = .031 and P = .005, respectively) with v_e.

CONCLUSIONS: Estimates of vascular permeability in brain tumors may be simultaneously acquired from multiple-echo DSC–MR imaging via K^trans; however, caution should be used in assuming a similar relationship for K₂ and K_a.