Introduction:

Preclinical bladder cancer drug development depends on the accurate assessment of tumor burden in mice, with a preference for longitudinal in vivo imaging. We aimed to compare transabdominal micro-ultrasound imaging (MUI) and computer tomography (CT) Urogram for the detection and measurement of bladder cancer in a mouse model.

Methods:

Male C57/B6 mice at least 6 weeks old received BBN at a dose of 0.05% in drinking water ad libitum for 6 weeks. Bladder tumor presence was evaluated by CT urogram via retro-orbital injection of 1/10 dilution of iodinated contrast and Vega ^® ultrasound imaging (SonoVol).starting at week 19 with confirmation of bladder tumors.After imaging,mice were euthanized by CO₂ with secondary cervical dislocation. Bladders were removed and divided in the sagittal plane, and fixed in 10% formalin. Three-dimensional (3-D) UL and CT data sets were collected. ROIs were drawn around the tumor borders for every slice to assess tumor size in a 3-D dimensional plane and the image analysis software. 4 μm sections of bladder tissue were cut and stained with hematoxylin-eosin (HE) for histopathological analysis. All slides were anonymized and digitized at 40x, and 100x magnification using a high-resolution scanner. Statistical analysis performed in R.

Results:

Average tumor volume detected by US at 19 weeks was (10.48mm³) vs CT (17.09mm³) with one tumor undetectable by CT at 19 weeks. Tumor size increased at 22-23 weeks by US to (47.33mm³) and CT (47.51mm³), albeit 4/7 tumors on CT Urogram were unable to be measured due to uncertainty. When assessing US vs CT imaging sensitivity (Sn), specificity (Sp)and accuracy (Ac) for prediction were: Sn 100% vs 54.55%, Sp 89% vs 95%, Ac 75% vs 61.54%, respectively.  CT imaging alone was unable to determine status of tumor presence in 7 mice, with histopathologic confirmation of tumors in three of those mice (1 CIS, 2 T3+) indicating difficulty in identification of advanced disease and flat tumors. US allowed for visualization of both samples of CIS due to bladder wall thickening allowing for early tumor detection, and tumor growth kinetics.

Conclusion:

In the present study, we have utilized a multimodal approach of US and CT Urogram imaging of murine BBN model of bladder cancer with histopathologic confirmation. Due to increased accuracy of US imaging, this approach would be better suited for future testing of therapeutic agents. Ultrasound imaging provides enhanced visualization tumor growth kinetics, including anatomical and functional aspects of tumor development and treatment response.

Funding: N/A