The Histogram Analysis of Apparent Diffusion Coefficient Maps with Standard- or Ultrahigh-b Value Diffusion-Weighted MR Imaging for Differentiating the Gleason Grade of Prostate Cancer

Objective: To evaluate the role of histogram analysis of apparent diffusion coefficient (ADC) derived from entire tumor volume in differentiating low and high Gleason score in prostate cancer and to evaluate the diagnostic performance of ADC maps at standard and ultrahigh-b value. Method: Restrospective analysis was performed on 89 patients with prostate cancer which underwent DWI with 1000 and 2000 sec/mm² b values. Tumor ADC measurement was performed using histogram analysis by outlining the entire-tumor regions from histological–radiological correlation. The correlation of the histogram parameters with tumor GS was assessed using Spearman rank-order correlation, independent-sample t test, and Mann-Whitney U test. The receiver operating characteristic curve determined the optimum threshold for each histogram parameter, and sensitivity and specificity were assessed. Result: The high GS tumor had lower ADC result except at the 90th percentile ADC for both ADC₁₀₀₀ and ADC₂₀₀₀. The histogram of the mean, minimum and 25th percentile ADC for ADC₁₀₀₀ showed significant difference as well as the histogram of the mean, minimum, 10th and 25th percentiles ADC for ADC₂₀₀₀. There were significant histogram differences for the 10th and 25th percentiles ADC in the comparison between AUC of ADC₁₀₀₀ and ADC₂₀₀₀. The 10th percentile histogram of ADC for ADC₂₀₀₀ was best correlated with the prostate cancer GS. Conclusion: The histogram measurement of the ADC could be used as an objective diagnostic tool for grading prostate cancer. The 10th percentile histogram of ADC that was obtained at ultrahigh-b value DWI was best correlated with the prostate cancer GS.