Dynamic contrast-enhanced MRI with two different-sized
contrast agents,
Gd-DTPA and
Gadomer-17, was used to study the effects of radiation on the pharmacokinetics of the paramagnetic enhancement of water relaxation in the rat R3230 AC
adenocarcinoma tumor model. The kinetics of enhancement was analyzed by a two-compartment pharmacokinetic model to derive parameters related to vascular volume (V(b)) and permeability (K(2)). Rats implanted with
tumors were divided into two groups; one received 5 Gy and the other received 20 Gy (137)Cs gamma rays. Sequential dynamic contrast-enhanced MRI studies were performed, one before irradiation, one at day 1 after irradiation, and another at day 3 after irradiation, to investigate the effect of the radiation dose and the changes that occurred over time. The analysis was performed on a pixel-by-pixel basis to study the heterogeneity within the
tumor. The pixel distribution profiles of V(b) and K(2) from each
tumor were obtained to assess the regional radiation-induced effects on vascular volume and permeability. No significant change in vascular volume was detected with either
Gd-DTPA or
Gadomer-17 after irradiation of the
tumor; however, a small dependence of K(2) on the radiation dose was observed. After low-dose (5 Gy) irradiation, the mean value of K(2) decreased by 46% at day 1 compared to the baseline, presumably due to cell swelling, and decreased further by 67% from the baseline on day 3. When the dose was increased to 20 Gy, the mean value of K(2) measured with
Gadomer-17 did not show any significant changes at either day 1 or day 3 after irradiation. The value of K(2) measured with
Gd-DTPA did not show any significant changes after either the low or the high radiation dose.