Magnetic resonance imaging of prostate cancer: diffusion-weighted imaging in comparison with sextant biopsy.

ABSTRACT

PURPOSE: To retrospectively evaluate the impact of diffusion-weighted imaging (DWI) on the detection of prostate cancer in comparison with sextant biopsy. MATERIALS AND METHODS: Fifty patients with clinical suspicion of prostate cancer underwent a combined endorectal-body-phased array magnetic resonance imaging examination at a 1.5 T magnetic resonance imaging (Siemens, Erlangen, Germany). The DWI was performed using b values of 50, 400, 800 s/mm. The prostate was divided into sextants, including the apex, the middle aspect, and the base for the left and right sides, separately. Regions of interest were placed in the peripheral zone of each sextant to evaluate the apparent diffusion coefficient (ADC) values. The results of the DWI were compared side by side with the findings of the histological examination of endorectal sonographically guided sextant biopsy. The sensitivity and specificity of ADC for the identification of the tumor tissue were computed for variable discrimination thresholds to evaluate its receiver operating characteristic. An association between ADC and Gleason score was tested for both the whole study group and on an individual basis using the nonparametric Spearman ρ test and the Pearson correlation, respectively. RESULTS: Histopathology identified tumor tissue in 21 (42%) of the 50 patients. The ADC value was 1.65 ± 0.32 mm/s 10 in normal tissue and 0.96 ± 0.24 mm/s 10 in tumor tissue (mean ± 1 SD). The area under the receiver operating characteristic curve was 0.966. Using the discrimination threshold 1.21 mm/s 10, for example, the ADC value provided a sensitivity of 0.92 and a specificity of 0.93. There was a highly significant negative correlation between the ADC value and the Gleason score in the tumor-positive tissue probes (n = 62, ρ = -0.405, P = 0.001) in the whole study group. On the individual patient basis, the Pearson correlation revealed a mean coefficient of r = -0.89 (SD ± 0.12) with a P < 0.001. CONCLUSIONS: Diffusion-weighted imaging of the prostate can be used to differentiate benign from malignant tissue in the peripheral zone. In the present study, ADC values were significantly lower in prostate cancer than in benign tissue.