Significance of Normalized Apparent Diffusion Coefficient in the Vesical Imaging‐Reporting and Data System for Diagnosing Muscle‐Invasive Bladder Cancer

BACKGROUND: Vesical Imaging-Reporting and Data System (VI-RADS) has been developed for assessing bladder cancer from multiparametric (mp) MRI but its performance in diagnosing muscle-invasive bladder cancer (MIBC) is suboptimal. PURPOSE: To investigate associations between normalized apparent diffusion coefficient (NADC) and clinicopathological characteristics and to determine whether the inclusion of NADC can improve the performance of VI-RADS in diagnosing MIBC. STUDY TYPE: Retrospective. POPULATION: Two hundred seventy-five patients with pathologically confirmed bladder cancer (101 MIBC and 174 non-MIBC [NMIBC]) underwent preoperative mpMRI (233 male, 42 female). FIELD STRENGTH/SEQUENCE: 3-T, T2-weighted imaging (turbo spin-echo), diffusion-weighted imaging (free-breathing spin-echo), and dynamic contrast-enhanced imaging (gradient-echo). ASSESSMENT: NADC was the mean ADC of tumor divided by that of the iliopsoas muscles in trans caput femoris plane. Associations between NADC and clinicopathological characteristics were evaluated. Models were established for differentiating MIBC and NMIBC: VI-RADS model; VN model (VI-RADS and NADC), Images model (significant variables from imaging associated with MIBC), LN model (Images model without NADC), and Full model (all significant variables associated with MIBC). STATISTICAL TESTS: Variables for model development were based on logistic regression. Models were evaluated by receiver operating characteristic (ROC) curve. Comparison of the area under the curves (AUCs) for the models used DeLong's test. A P value <0.05 was considered statistically significant. RESULTS: NADC was significantly lower in lesions with diameter ≥ 3 cm, MIBC, histological high grade, lymph node metastasis, and lymphovascular invasion. Compared with VI-RADS model, the AUCs for VN model (VI-RADS score and NADC), Images model (VI-RADS score, NADC and tumor size) and Full model (VI-RADS score, NADC, tumor size and histological grade) were significantly higher. No significant differences were observed between the AUCs for VN model and Images model (P = 0.051). DATA CONCLUSION: NADC reflects information about the aggressiveness of bladder cancer. Combining VI-RADS with NADC can improve performance in diagnosing MIBC. EVIDENCE LEVEL: 4 TECHNICAL EFFICACY: Stage 2.