Correlation between Gd-enhanced MR imaging and histopathology in treated and untreated 9L rat brain tumors.

Gadolinium-based MR imaging contrast agents cause signal enhancement of intracerebral tumors on T1-weighted MR images because they cross the compromised blood-brain barrier, increasing the T1 relaxation rate of extracellular water. Tumor extent measured by Gd-enhanced MR imaging often does not agree with T2-weighted MRI or biopsy measurements, due to possible peritumoral barrier defects or infiltration of tumor cells beyond the region of enhancement. In this study, the 9L rat brain tumor model was used to measure the correlation between tumor size measured by Gd-enhanced and unenhanced MRI and histological measurements. There was excellent agreement between Gd-enhanced MRI measurements and histology. Morphological features of untreated 9L intracranial tumors and those treated with radiation and/or cisplatin were compared with histological features. No significant change in intracranial tumor size was detected in the treated animals up to 7 days following treatment, despite substantial tumor necrosis evident on histological analysis.