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MRI in the Detection of Prostate Cancer: Combined Apparent Diffusion Coefficient, Metabolite Ratio, and Vascular Parameters

¹ CR-UK and EPSRC Cancer Imaging Center, Royal Marsden NHS Foundation Trust and Institute of Cancer Research, Sutton, Surrey SM2 5PT, United Kingdom.
² Department of Urology, Royal Marsden NHS Foundation Trust, London, United Kingdom.
³ Department of Histopathology, Royal Marsden NHS Foundation Trust, London, United Kingdom.

OBJECTIVE. The purpose of this study was to compare apparent diffusion coefficients, metabolic ratios, and vascularity values within histologically defined prostate tumors with those in nontumor tissue to determine which functional parameter or combination of parameters is best for differentiating tumor from nontumor tissue.

SUBJECTS AND METHODS. Twenty patients due for prostatectomy underwent endorectal MRI at 1.5 T. Transverse T2-weighted, diffusion-weighted, 2D chemical shift, and dynamic contrast-enhanced images were acquired. After prostatectomy, the gland was sectioned transversely. Fresh slices and stained whole-mount sections with histologically defined tumor outlines were photographed. The tumor outlines were mapped onto images, and the apparent diffusion coefficient (ADC), choline-to-citrate (Cho/cit) ratio, and vascularity of the histologically defined tumor, normal peripheral zone, and central gland were quantitatively measured. Area under the receiver operating characteristics (ROC) curve (A_z) was used to determine the sensitivity and specificity of parameter combinations in cancer detection.

RESULTS. In tumor regions larger than 1 cm², the Cho/cit ratio was higher in tumor than in nontumor tissue (p < 0.001), in the peripheral zone alone (p = 0.007), and in the central gland alone (p = 0.005). ADC was lower and tumor vascularity greater in tumor than in nontumor tissue (ADC, p = 0.003; initial area under the gadolinium plasma concentration–time curve [initial gadolinium AUC], p = 0.012; forward rate constant [K^trans], p = 0.011; return rate constant [k_ep], p = 0.036). No single parameter had a significantly greater A_z (ADC, 0.71; Cho/cit ratio, 0.79; initial gadolinium AUC, 0.60; K^trans, 0.62; k_ep, 0.65). Pairs of parameters, however, did increase A_z: ADC and initial gadolinium AUC (A_z = 0.94) versus ADC (p = 0.001) and initial gadolinium AUC (p < 0.001); ADC and Cho/cit ratio (A_z = 0.94) versus ADC (p = 0.001) and Cho/cit ratio (not significant); and Cho/cit ratio and initial gadolinium AUC (A_z = 0.88) versus Cho/cit ratio (not significant) and initial gadolinium AUC (p < 0.001). All three functional techniques together had an A_z of 0.95, showing no further improvement.

CONCLUSION. The combination of two functional parameters is associated with significant improvement in prostate cancer detection over use of any parameter alone. Use of a third parameter does not increase the rate of detection.

Keywords: diffusion • dynamic contrast-enhanced MRI • perfusion • prostate • spectroscopy

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