External Validation of Prostate MRI QCAD/Lyon

Multiparametric magnetic resonance imaging (mpMRI) of the prostate combines T2-weighted imaging, diffusion-weighted imaging and dynamic contrast-enhanced imaging. Correlation with radical prostatectomy specimens has demonstrated that mpMRI has excellent sensitivity in detecting prostate cancers (PCa) with a Gleason score ≥7 and cancers with a Gleason 6 and a volume ≥0.5 cc. Nevertheless, its specificity is poor and there is large overlapping between the appearances of benign and malignant prostate lesions. As a result, the use of a 5-point subjective score has been widely encouraged to describe the level of suspicion of prostate lesions. This so-called 'Likert score' is a highly significant predictor of the malignant nature of prostate focal lesions. However, because there are no descriptions of specific criteria to be used in the scoring process, the Likert score relies heavily on the reader's experience. In an attempt to standardize mpMRI interpretation, the European Society of Urogenital Radiology and the American College of Radiology recently endorsed the so-called Prostate Imaging-Reporting and Data System (PIRADS) score. The second version of this scoring system (PI-RADS v2 score) gave good results in characterizing prostate focal lesions. However, Inter-reader agreement remains moderate at best, even after training, and there is still a high-rate of false positives. These results have led some authors to suggest that there might be structural limits to the ability of any score based on MR imaging to allow detection of prostate cancer with high specificity. Using quantitative magnetic resonance (MR) image features to characterize prostate lesions seen on mpMRI could improve interpretation standardization, and recently, several computer-aided diagnosis (CAD) systems combining various image features have shown promising results in characterizing prostate tissues. However, most CAD systems have been trained and evaluated on images from the same MR scanner. Unfo