Transabdominal Micro-ultrasound Imaging of Bladder Cancer in a Mouse Model: A Validation Study

Objectives: To validate the use of transabdominal micro-ultrasound imaging (MUI) in an orthotopic murine bladder cancer model. The current in vivo imaging systems for murine bladder cancer include magnetic resonance imaging, bioluminescent and fluorescent imaging, and intravesical ultrasound. Methods: We implanted murine bladder tumor-2 tumor cells into C3H/He female mice. Mice underwent MUI before, and every 3 days after instillation of tumor cells. Three mice were killed at every MUI session. Bladder tumors were measured and tumor volumes were calculated during MUI and gross stereomicroscopy. Bladders were harvested and examined under gross stereomicroscopy to confirm the presence, location, and size of bladder tumors, and were prepared for histology review. Results: Overall, 15 of 33 (45%) mice were confirmed to have tumors, using MUI, gross stereomicroscopy, and histology. Measurements of tumor size by MUI and gross microscopy had a high correlation coefficient (r = 0.97). MUI identified all tumors that were present on final histology. The smallest confirmed tumor on MUI was detected at 0.52 mm³, and mean tumor volume was 0.95 mm³. No tumors that were not detected first using MUI were found on final histology. Conclusions: Transabdominal MUI is a valuable tool to use for translational studies involving orthotopic mouse bladder cancer models. MUI provides real-time, high resolution in vivo images of bladder tumors. Tumor presence can be confirmed with a high degree of accuracy pertaining to tumor volume before initiation of treatment. In addition, tumor growth or regression can be followed up in vivo longitudinally.