Is Weisskoff model valid for the correction of contrast agent extravasation with combined T₁ and T₂* effects in dynamic susceptibility contrast MRI?

Purpose: The Weisskoff model has been widely applied for correcting the T₁ effect of the contrast agent leakage in the measured dynamic susceptibility contrast (DSC)-MRI signals. This study aimed to modify the Weisskoff model for the inclusion of both T₁ and T₂ effects of the contrast agent extravasation. Methods: A two-compartment model was proposed and implemented into the original Weisskoff model to describe the combined T₁ and T₂ effects from the contrast agent leakage in the measured DSC-MRI signals. A computer simulation was performed to evaluate the dependence of T₁ versus T₂ dominance on imaging parameter, field strength, baseline T₁, and severity of the leakage. The modified Weisskoff model was employed to correct the relative cerebral blood volume (rCBV) maps in three patients with brain tumors to demonstrate its use. Results: The resultant equation had the same mathematical form as the original model, but with a different expression for the fitting constant K₂. This new parameter can be of either a positive or a negative value. Results of the computer simulation showed more probable T ₂ dominance with longer TE, higher field strength, shorter baseline T₁, and greater extraction of the contrast agent. Clinical data were well fitted by the model, with a positive K₂ indicating T₁ dominance and underestimated rCBV and a negative K₂ indicating T₂ dominance and overestimated rCBV. The K₂ values of normal-appearing brain tissues were distributed in a much smaller range than the K₂ values of enhancing tumors. The ratios of corrected over uncorrected normalized CBV (nCBV) for gray matter (GM) were in the range between 1.04 and 1.05, meaning that the nCBV remained rather stable before and after correction. The ratios for the tumors were 0.65, 0.42, and 2.81, either much smaller or greater than the ratios for GM. Conclusions: This study proposed a modified Weisskoff model that was able to explain both T₁ and T ₂ dominant effects of the contrast agent extravasation in DSC-MRI. Further development is needed to make the K₂ parameter a quantitative indicator of the vessel permeability.