Flow versus permeability weighting in estimating the forward volumetric transfer constant (Ktrans) obtained by DCE-MRI with contrast agents of differing molecular sizes (original) (raw)

2017, Magnetic Resonance Imaging

To quantify the differential plasma flow-(F p-) and permeability surface area product per unit mass of tissue-(PS-) weighting in forward volumetric transfer constant (K trans) estimates by using a low molecular (Gd-DTPA) versus high molecular (Gadomer) weight contrast agent in dynamic contrast enhanced (DCE) MRI. Materials and methods: DCE MRI was performed using a 7T animal scanner in 14 C57BL/6J mice syngeneic for TRAMP tumors, by administering Gd-DTPA (0.9 kD) in eight mice and Gadomer (35 kD) in the remainder. The acquisition time was 10 min with a sampling rate of one image every 2 s. Pharmacokinetic modeling was performed to obtain K trans by using Extended Tofts model (ETM). In addition, the adiabatic approximation to the tissue homogeneity (AATH) model was employed to obtain the relative contributions of F p and PS. Results: The K trans values derived from DCE-MRI with Gd-DTPA showed significant correlations with both PS (r 2 = 0.64, p = 0.009) and F p (r 2 = 0.57, p = 0.016), whereas those with Gadomer were found only significantly correlated with PS (r 2 = 0.96, p = 0.0003) but not with F p (r 2 = 0.34, p = 0.111). A voxel-based analysis showed that K trans approximated PS (b30% difference) in 78.3% of perfused tumor volume for Gadomer, but only 37.3% for Gd-DTPA. Conclusions: The differential contributions of F p and PS in estimating K trans values vary with the molecular weight of the contrast agent used. The macromolecular contrast agent resulted in K trans values that were much less dependent on flow. These findings support the use of macromolecular contrast agents for estimating tumor vessel permeability with DCE-MRI.