# Biparametric Versus Multiparametric MRI for VI-RADS Assessment: Reproducibility Relative to Routine mpMRI Reporting and Impact of Radiologist Experience in a Single-Center Study

## TL;DR

This study compares contrast-free and contrast-enhanced MRI for bladder cancer staging, finding that contrast-free MRI works best in specific cases when used by experienced radiologists.

## Contribution

The study evaluates the reproducibility of VI-RADS scoring using contrast-free MRI and highlights the impact of radiologist experience on diagnostic accuracy.

## Key findings

- Expert radiologists had higher agreement with contrast-enhanced MRI results compared to non-experts.
- Contrast-free MRI showed acceptable performance in low-risk pre-surgery cases but was less reliable in equivocal or post-surgery settings.
- Sensitivity for detecting muscle-invasive tumors was high, but specificity varied between readers.

## Abstract

Bladder cancer treatment depends heavily on whether the tumor is still limited to its muscle invasiveness playing a pivotal role in its management. Doctors often use magnetic resonance imaging to estimate the chance of muscle invasion, but the full examination usually includes an injected contrast agent, which adds time and cost and cannot be given to some patients. This study tested whether a simpler, contrast-free magnetic resonance imaging approach can provide the same practical risk grading as the standard contrast-enhanced examination in routine care. The authors compared scores from two readers with different levels of experience and examined where and why disagreements occur, including after prior tumor removal surgery. The results suggest that contrast-free imaging may be acceptable only in carefully selected pre-TURBT cases with clearly low-risk, non-equivocal imaging features when interpreted by experienced radiologists, whereas standard contrast-enhanced imaging remains important for equivocal, higher-risk, and post-surgery settings.

Background: We tested whether a contrast-free protocol can reproduce contrast-enhanced VI-RADS scoring and whether reader expertise influences results. Methods: In this retrospective single-center study (January–December 2024), 65 patients (69 lesions) underwent bladder multiparametric MRI. Two blinded radiologists assigned VI-RADS scores using only T2-weighted and diffusion-weighted imaging (biparametric, non-contrast MRI): an expert (>15 years in urogenital radiology) in genitourinary MRI and a non-expert (5 years of experience in genitorurinary radiology). Two complementary reference standards were used. For reproducibility analysis, the reference standard was the VI-RADS score from the original clinical report based on the full multiparametric examination including contrast-enhanced imaging. For diagnostic accuracy analysis, histopathology was used as the reference standard for muscle-invasive versus non-muscle-invasive disease. Agreement was evaluated with confusion matrices, overall agreement, and weighted Cohen’s kappa. Discrimination for high likelihood of muscle invasion (VI-RADS ≥ 4) was assessed with receiver operating characteristic analysis. Results: Reference scores were VI-RADS 2 (34.8%), 3 (14.5%), 4 (20.3%), and 5 (30.4%). Agreement was higher for the expert than the non-expert (73.9% vs. 56.5%; weighted kappa 0.74 [95% confidence interval 0.56–0.89] vs. 0.58 [0.37–0.75]). The area under the curve for VI-RADS ≥ 4 was 0.87 (0.78–0.95) for the expert and 0.81 (0.69–0.91) for the non-expert. Sensitivity at a biparametric threshold of VI-RADS ≥ 4 was 88.6% for both readers; specificity was 85.3% vs. 73.5%. Post-resection cases showed more discrepancies, mainly overstaging. Conclusions: Contrast-free biparametric MRI may approximate multiparametric VI-RADS scoring only in treatment-naïve pre-TURBT cases with clearly low-risk, non-equivocal imaging features, but performance is reader-dependent and less reliable in equivocal, higher-risk, and post-resection examinations. Contrast-enhanced multiparametric MRI remains preferred for staging.