3-Dimensional elastic registration system of prostate biopsy location by real-time 3-dimensional transrectal ultrasound guidance with magnetic resonance/transrectal ultrasound image fusion.

PURPOSE: We determined the accuracy of the novel Urostation 3-dimensional transrectal ultrasound system (Koelis, La Tranche, France) for image based mapping biopsies in a prostate phantom. The system is capable of 1) registering the 3-dimensional location of each biopsy track in the 3-dimensional prostate volume data and 2) performing elastic image fusion of transrectal ultrasound with magnetic resonance imaging.

MATERIALS AND METHODS: We used 3 CIRS-053 prostate phantoms containing 3 hypoechoic lesions to perform ultrasound guided biopsy and 3 CIRS-066 phantoms (Computerized Imaging Reference Systems, Norfolk, Virginia) containing 3 isoechoic but magnetic resonance imaging visible lesions to perform magnetic resonance fusion guided biopsy. Three targeted biopsies were done per lesion. Each biopsy tract was injected with gadolinium based magnetic resonance contrast mixed with india ink. Phantoms were then subjected to 1 mm slice magnetic resonance imaging and serial step sectioning to assess the accuracy of targeted biopsy.

RESULTS: A total of 27 ultrasound guided biopsies were targeted into 9 hypoechoic lesions. All 27 biopsies (100%) successfully hit the target lesion. For hypoechoic lesions mean ± SD procedural targeting error was 1.52 ± 0.78 mm and system registration error was 0.83 mm, resulting in an overall error of 2.35 mm. Of the 27 magnetic resonance fusion biopsies 24 (84%) hit the lesion. For isoechoic lesions mean procedural targeting error was 2.09 ± 1.28 mm, resulting in an overall error of 2.92 mm.

CONCLUSIONS: The novel, computer assisted, 3-dimensional transrectal ultrasound biopsy localization system achieved encouraging accuracy with less than 3 mm error for targeting hypoechoic and isoechoic lesions. The ability to register actual biopsy trajectory and perform elastic magnetic resonance/ultrasound image fusion is a significant advantage for future focal therapy application.