Dynamic Contrast-Enhanced Magnetic Resonance Imaging Evaluation of VX2 Carcinoma in a Rabbit Model

Abstract

To compare the enhancement characteristics and diagnostic performance of 1.0-M gadobutrol with those of 0.5-M gadopentetate dimeglumine in rabbit VX2 tumor models. Our study was approved by the Animal Care Committee of our hospital. VX2 carcinomas were implanted in both thighs of 14 rabbits 4 days before magnetic resonance (MR) imaging. The animals underwent 2 identical MR examinations with 2 different contrast media separated by 8 hours with the use of a 3.0 T magnet. T2-, T1- weighted fast spin echo images were obtained. Sequential MR imaging with the 3-dimensional-SPGR sequence were performed before and at 1, 2, 3, 4, 5, 10, 15, 20, and 30 minutes after injection of 0.05 mmol/kg of 1.0-M gadobutrol or 0.5-M gadopentetate dimeglumine. Four rabbits without tumor implantation underwent the same MR examinations. Percentage enhancement of the tumor was assessed by 2 radiologists in consensus. Three different readers without knowledge of the histopathologic results interpreted both MR images in terms of presence of tumor. Receiver operating characteristic analysis was conducted to compare the diagnostic value of both contrast agents. Sensitivities and specificities were also calculated. In addition, lesion-to-muscle contrast, degree of lesion delineation, and global preferences of the readers were determined using a scoring system. A total of 56 VX2 tumors were identified by histopathologic review. For the VX2 tumors, the percentage enhancement at each time point was consistently higher with injection of 1.0-M gadobutrol than with injection of 0.5-M gadopentetate dimeglumine (P < 0.01). The area under the receiver operating characteristic curve (Az) values for the use of 1.0-M gadobutrol-enhanced MR imaging were 0.937, 0.886, and 0.938 for readers 1, 2, and 3, respectively. The Az values for the use of 0.5-M gadopentetate dimeglumine-enhanced MR imaging were 0.908, 0.903, and 0.947. Sensitivities were 89.3%, 85.7%, and 89.3% for 1.0-M gadobutrol-enhanced MR imaging and 87.5%, 85.7%, and 89.3% for 0.5-M gadopentetate dimeglumine-enhanced MR imaging. Specificities were 87.5%, 75.0%, and 87.5% for 1.0-M gadobutrol-enhanced MR imaging and 100%, 81.3%, and 100% for 0.5-M gadopentetate dimeglumine-enhanced MR imaging. No significant differences were noted for the Az values, sensitivities, and specificities with the use of the 2 contrast agents. Lesion-to-muscle contrast, degree of lesion delineation, and global preferences of the readers were ranked significantly higher for 1.0-M gadobutrol-enhanced MR imaging in all readers (P < 0.001). Using a 3.0-T magnet, equivalent doses of 1.0-M gadobutrol-enhanced MR imaging showed a superior degree of enhancement for a VX2 tumor than 0.5-M gadopentetate dimeglumine-enhanced MR imaging, and a significant preference for readers was noted for 1.0-M gadobutrol-enhanced MR imaging.