CONTRAST-ENHANCED MAGNETIC-RESONANCE-IMAGING ESTIMATION OF ALTERED CAPILLARY-PERMEABILITY IN EXPERIMENTAL MAMMARY CARCINOMAS AFTER X-IRRADIATION

RATIONALE AND OBJECTIVES. Dynamic magnetic resonance imaging (MRI) enh anced with a macromolecular contrast medium, albumin-(Gd-DTPA)(35), wa s used to detect changes in microvascular characteristics in R3230 mam mary adenocarcinomas induced by x-irradiation. METHODS. Tumors were im planted in either flank in nine rats, One of the tumors was exposed to single-dose x-irradiation (30 Gy) 3 days before MRI, The contralatera l control tumor was shielded from irradiation. RESULTS. Capillary perm eability to macromolecular contrast medium in irradiated tumors was el evated significantly (P < .05) compared to the control nonirradiated t umors, The mean estimated permeability surface area product for the ir radiated tumors increased more than three-fold; 0.511 +/- .046 mL hr(- 1) cm(-3) compared with 0.121 +/- .011 mt hr(-1) cm(-3) for the nonirr adiated tumors, This radiation-induced increase in permeability was co rroborated using a macromolecular Evans blue-protein complex measured in the same tumors using an invasive spectrophotometric technique. CON CLUSIONS. Dynamic MRI-enhanced with macromolecular contrast medium per mits noninvasive quantitative estimates of capillary permeability in t umors, with and without x-irradiation, Because the transendothelial pe rmeability for macromolecular solutes likely influences tumoral accumu lation of macromolecular chemotherapeutic agents, this noninvasive tec hnique may prove to be clinically useful in tailoring tumor treatment programs which combine radiation and chemotherapy.