Correlation of apparent diffusion coefficient ratio on 3.0 T MRI with prostate cancer Gleason score

INTRODUCTION: The purpose was to investigate the usefulness of ADC(ratio) on Diffusion MRI to discriminate between benign and malignant lesions of Prostate. METHODS: Images of patients who underwent in-gantry MRI guided prostate lesion biopsy were retrospectively analyzed. Prostate Cancers with 20% or more Gleason score (GS) pattern 3 + 3 = 6 in each core or any volume of higher Gleason score pattern were included. ADC(ratio) was calculated by two reviewers for each lesion. The ADC(ratio) was calculated for each lesion by dividing the lowest ADC value in a lesion and highest ADC value in normal prostate in peripheral zone (PZ). ADC(ratio) values were compared with the biopsy result. Data was analysed using independent samples T-test, Spearman correlation, intra-class correlation coefficient (ICC) and Receiver operating characteristic (ROC) curve. RESULTS: 45 lesions in 33 patients were analyzed. 12 lesions were in transitional zone (TZ) and 33 in perpheral zone PZ. All lesions demonstrated an ADC(ratio) of 0.45 or lower. GS demonstrated a negative correlation with both the ADC value and ADC(ratio). However, ADC(ratio) (p < 0.001) demonstrated a stronger correlation compared to ADC value alone (p = 0.014). There was no significant statistical difference between GS 3 + 4 and GS 4 + 3 mean ADC(tumour) value (p = 0.167). However when using ADC(ratio), there was a significant difference (p = 0.032). ROC curve analysis demonstrated an area under the curve of 0.83 using ADC(ratio) and 0.76 when using ADC(tumour) value when discriminating Gleason 6 from Gleason ≥7 tumours. Inter-observer reliability in the calculation of ADC ratios was excellent, with ICC of 0.964. CONCLUSION: ADC(ratio) is a reliable and reproducible tool in quantification of diffusion restriction for clinically significant prostate cancer foci.