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

Abstract

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.

Keywords: Diffusion magnetic resonance imaging; Magnetic resonance imaging; Prostate; Prostatic cancer; Prostatic neoplasms.

Fig. 1

A. Peripheral Zone lesion with Gleason score 4 + 5 tumor. Axial ADC image with ADC ratio of 0.26. B. Corresponding Axial T2 image of a TZ/PZ lesion.

Fig. 2

ROC-curve analysis for determining tumor aggressiveness (GS) using ADC tumor value and ADCratio for all tumors to discriminate between (A) GS 6 and GS ≥ 7 and between (B) GS ≤ 7(3 + 4) and GS ≥ 7(4 + 3).

Fig. 3

Correlation of ADC_tumour and ADC_ratio values with Gleason score. A and B, Box-and-whisker plots show correlation of ADC_tumour values (A) and tumor ADC_ratio (B) with Gleason score. Top and bottom of boxes represent 25th and 75th percentiles of data, with line in box representing median value.