Effect of calibration on computerized analysis of prostate lesions using quantitative dynamic contrast-enhanced magnetic resonance imaging

In this study, we investigated the effect of different patient calibration methods on the performance of our CAD system when discriminating prostate cancer from non-malignant suspicious enhancing areas in the peripheral zone and the normal peripheral zone. Our database consisted of 34 consecutive patients with histologically proven adenocarcinoma of the prostate. Both carcinoma and normal tissue were annotated on MR images by a radiologist and a researcher using whole mount step-section histopathology as standard of reference. The annotated regions were used as regions of interest in the contrast enhanced MRI images. A feature set comprising pharmacokinetic parametes was extracted from the ROIs to train a support vector machine as classifier. The output of the classifier was used as a measure of likelihood of malignancy. General performance of the scheme was evaluated using the area under the ROC curve. The diagnostic accuracy obtained for differentiating normal peripheral zone and non-malignant suspicious enhancing areas from malignant lesions was 0.88 (0.81-0.95) when per patient calibration was performed, whereas fixed calibration resulted in a diagnostic accuracy of 0.77 (0.69-0.85). These preliminary results indicate that when per patient calibration is used, the performance is improved with statistical significance (p=0.026).