PURPOSE: To prospectively evaluate the accuracy of 3D sonoelastography for detection of prostate cancer relative to gray scale sonography in vitro.METHODS: Using an Institutional Review Board-approved, HIPAA compliant protocol with informal consent, 19 prostatectomy specimens from patients 46 to 70 years of age with biopsy proven prostate cancer were scanned in 3D using conventional B-scan and sonoelastography using vibrations above 100Hz.Step-sectioned whole-mount histology was utilized to create a 3D volume of the prostate and tumors within it. B-scan ultrasound images and regions of low vibration in the sonoelastography images (hard regions) were formatted in 3D. The lesions in the nineteen cases were analyzed as two groups: G1) pathology-confirmed tumors of 1.0 cc or greater; and G2) pathology-confirmed tumor size less than 1.0 cc. G1 cases were evaluated for B-scan ultrasound and sonoelastography vs. histology as a reference standard and were scored as either a True Positive, a False Positive, a True Negative, or a False Negative. G2 cases were evaluated for sonoelastography only. True positives required 3D lesion correlation between pathology and imaging data. Conventional definitions of accuracy and sensitivity were employed to calculate these statistics. RESULTS: G1 (7 lesions with tumor volume 1.0 cc or greater): Sonoelastography: accuracy of 55%, sensitivity of 71%. B-scan: accuracy of 17%, sensitivity of 29%. Mean tumor size is 3.1cc +/-2.1cc. G2 (22 lesions with tumor volume less than 1.0 cc). Mean tumor size is 0.32 cc +/-0.21 cc. Sonoelastography: accuracy of 34%, sensitivity of 41%, false positives: 6.CONCLUSIONS: Sonoelastography performed considerably better than gray scale sonography in the detection of prostate cancer tumors over 1 cc.