Assessment of registration accuracy in three-dimensional transrectal ultrasound images of prostates

In order to obtain a definitive diagnosis of prostate cancer, over one million men undergo prostate biopsies every year. Currently, biopsies are performed under two-dimensional (2D) transrectal ultrasound (TRUS) guidance with manual stabilization of a hand-held end-or side-firing transducer probe. With this method, it is challenging to precisely guide a needle to its target due to a potentially unstable ultrasound probe and limited anatomic information, and it is impossible to obtain a 3D record of biopsy locations. We have developed a mechanically-stabilized, 3-dimensional (3D) TRUS-guided prostate biopsy system, which provides additional anatomic information and permits a 3D record of biopsies. A critical step in this system's performance is the registration of 3D-TRUS images obtained during the procedure, which compensates for intra-session motion and deformation of the prostate. We evaluated the accuracy and variability of surface-based 3D-TRUS to 3D-TRUS rigid and non-rigid registration by measuring the target registration (TRE) error as the post-registration misalignment of manually marked, corresponding, intrinsic fiducials. We also measured the fiducial localization error (FLE), to measure its contribution to the TRE. Our results yielded mean TRE values of 2.13 mm and 2.09 mm for rigid and non-rigid techniques, respectively. Our FLE of 0.21 mm did not dominate the overall TRE. These results compare favorably with a clinical need for a TRE of less than 2.5 mm.