IRM et cancer prostatique : mesure de la cinétique du gadolinium avec un système CAD

Abstract

To assess with a CAD in the peripheral (ZP) and transitional (ZT) zones the areas with modifications of the kinetic parameter Kep (ratio of exchanges between vascular compartment and extravascular extracellular spaces) in prostatic cancers with DCE MRI before radical prostatectomy. Forty-two consecutive patients (mean age 67 years, mean PSA: 8.9 ng/ml) with a prostatic cancer proved after a set of 12 biopsies underwent, before radical prostatectomy, a dynamic MRI (1.5T) with a surface coil after injection of gadolinium. We look with a CAD for foci of voxels with an abnormal Kep in ZP and/or in ZT. Foci of abnormal voxels computerized were compared with histological results of radical prostatectomies: prostates were shared in 12 sectors (six peripheral and six central) and a total of 504 sectors were studied. The links between prostatic capsule and foci of voxels with elevated Kep were systematically evaluated. The location and the local extension of the various cancerous foci were estimated. A comparison with the results of the T2W and T1 DCE MRI sequences without use of the CAD was made. Eighty-eight percent of investigated patients revealed at least a cancerous focus associated with a group of pathological voxels. Hundred and seventy-eight of the 504 investigated prostatic sectors revealed a cancerous lesion after radical prostatectomy (RP) and 116 a focus of voxels with a pathological Kep being linked to 71 isolated lesions, some of them filling several sectors (47 peripheral and 24 transitional). The automatic research with the software of foci of voxels with a parameter Kep more than 2,2 per minute to detect a cancerous lesion had a sensitivity by sector less than the reading without CAD (69% in ZP and 58% in ZT against respectively, 85 and 66% (p<0.01) but seemed more specific: 98% in PZ and 95% in ZT against respectively, 80 and 82% (p<0.01). After RP, 16 cancers were classified Pt2, 10 Pt2R+ and 16 Pt3. The CAD had a better accuracy (74%) than T2W MRI (60%) to look for an extracapsular extension (EPE) or a risk of positive margins: 86% of extraprostatic extension and 60% of positive margins were near a focus of pathological voxels. CAD allowed a computerized qualitative and quantitative study of DCE MRI. It identified and localized with a good specificity the significant foci. A focus of voxels with elevated Kep against the capsule increased significantly the risk of an extraprostatic extension or a positive margin after radical prostatectomy.