Diagnostic value of ADC in patients with prostate cancer: influence of the choice of b values

To evaluate the influence of the choice of b values on the diagnostic value of the apparent diffusion coefficient (ADC) for detection and grading of prostate cancer (PCa). Forty-one patients with biopsy-proven PCa underwent endorectal 3-T MRI before prostatectomy. Different combinations of b values (0-800 s/mm(2)) were used to calculate four representative ADC maps. Mean ADCs of tumours and non-malignant tissue were determined. Tumour appearance on different ADC maps was rated by three radiologists as good, fair or poor by assigning a visual score (VS) of 2, 1 or 0, respectively. Differences in the ADC values with the choice of b values were analysed using one-way ANOVA. Choice of b values had a highly (P < 0.001) significant influence on the absolute ADC in each tissue. Maps using b = [50, 800] and [0, 800] were rated best (VS = 1.6 +/- 0.3) and second best (1.1 +/- 0.3, P < 0.001), respectively. For low-grade carcinomas (Gleason score a parts per thousand currency signaEuro parts per thousand 6, 13/41 patients), only the former choice received scores better than fair (VS = 1.4 +/- 0.3). Mean tumour ADCs showed significant negative correlation (Spearman's rho -0.38 to -0.46, P < 0.05) with Gleason score. Absolute ADC values strongly depend on the choice of b values and therefore should be used with caution for diagnostic purposes. A minimum b value greater than zero is recommended for ADC calculation to improve the visual assessment of PCa in ADC maps. aEuro cent Absolute ADC values are highly dependent on the choice of b values. aEuro cent Absolute ADC thresholds should be used carefully to predict tumour aggressiveness. aEuro cent Subjective ratings of ADC maps involving b = 0 s/mm (2) are poor to fair. aEuro cent Minimum b value greater than 0 s/mm (2) is recommended for ADC calculation.