Application of R2* and Apparent Diffusion Coefficient in Estimating Tumor Grade and T Category of Bladder Cancer

Abstract

<b>OBJECTIVE.</b> The objective of our study was to compare the feasibility of R2* and apparent diffusion coefficient (ADC) for differentiating tumor grade and T category of bladder cancer. <b>SUBJECTS AND METHODS.</b> In this prospective study, 58 patients with pathologically confirmed bladder cancers underwent pretreatment T2*-weighted imaging and DWI on a 3-T MRI unit. The apparent transverse relaxation rate R2*, which is derived from T2*-weighted imaging, and ADC, which is derived from DWI, were calculated and compared between low- and high-grade bladder cancers as well as between non-muscle-invasive bladder cancers (NMIBCs) and muscle-invasive bladder cancers (MIBCs) using the Mann-Whitney <i>U</i> test. The diagnostic performances of R2*, ADC, and the combination of R2* and ADC were evaluated through an ROC analysis. <b>RESULTS.</b> Significant differences were found in R2* (mean ± SD, 16.55 ± 5.54 vs 20.96 ± 7.75 s^-1; <i>p</i> = 0.001) and ADC (1.62 ± 0.31 vs 1.33 ± 0.21 × 10^-3 mm²/s; <i>p</i> < 0.001) between lowand high-grade bladder cancers. R2* was significantly higher (22.56 ± 8.41 vs 18.06 ± 6.46 s^-1; <i>p =</i> 0.008) and ADC was considerably lower (1.21 ± 0.18 vs 1.53 ± 0.27 × 10^-3 mm²/s; <i>p</i> < 0.001) in MIBCs than in NMIBCs. The AUCs for differentiating low-from high-grade groups were 0.714 using R2* and 0.779 using ADC. AUCs for distinguishing between NMIBC and MIBC groups using R2* and ADC were 0.682 and 0.850, respectively. <b>CONCLUSION.</b> In addition to ADC, R2* can be used as a quantitative imaging biomarker to provide additional information for tumor characterization of bladder cancer.