In targeted 3D transrectal ultrasound (TRUS)-guided biopsy, patient and prostate movement during the procedure can cause target misalignments that hinder accurate sampling of preplanned suspicious tissue locations. Multiple solutions have been proposed for displacement compensation via registration of intraprocedural TRUS images to a baseline 3D TRUS image acquired at the beginning of the biopsy procedure. While 2D TRUS images are widely used for intraprocedural guidance, some solutions utilize richer intraprocedural images such as bi- or multiplanar TRUS or 3D TRUS, acquired by specialized probes. In this work, the impact of such richer intraprocedural imaging on displacement compensation accuracy was measured to evaluate the tradeoff between cost and complexity of intraprocedural imaging versus improved displacement compensation.
Baseline and intraprocedural 3D TRUS images were acquired from 29 patients at standard sextant-template biopsy locations. Planes extracted from 3D TRUS images acquired at sextant positions were used to simulate 2D and 3D intraprocedural information available in different potential clinically relevant scenarios for co-registration with the baseline 3D TRUS image. In practice, intraprocedural 3D information can be acquired either via the use of specialized ultrasound probes (e.g., multiplanar or 3D probes) or via axial rotation of a tracked 2D TRUS probe. Registration accuracy was evaluated by calculating the target registration error (TRE) using manually identified homologous intrinsic fiducial markers (microcalcifications). The TRE was analyzed separately at the base, mid-gland and apex regions of the prostate.
The results indicate that TRE improved gradually as the number of intraprocedural imaging planes used in registration was increased, implying that 3D TRUS information assisted the registration algorithm to robustly converge to more accurate solutions. The acquisition of a partial volume up to the angle of rotation supported more accurate displacement compensation than acquiring biplane configurations. Additional intraprocedural 3D TRUS image information was more beneficial to registration accuracy in the base and apex regions as compared with the mid-gland region.
While the majority of the registrations using 2D TRUS images provided a clinically desired level of accuracy, intraprocedural 3D imaging helped improve the overall registration accuracy and robustness, especially in the base and apex regions of the prostate. These results are helpful for devising image-based registration methods for displacement compensation when designing 3D TRUS-guided biopsy systems.
The authors are grateful for the funding granted from the Canadian Institutes of Health Research (CIHR), the Ontario Institute of Cancer Research (OICR), and Cancer Care Ontario (CCO) for this work. A. Fenster holds a Canada Research Chair in Biomedical Engineering, and acknowledges the support of the Canada Research Chair Program. A. D. Ward holds a Cancer Care Ontario Research Chair in Cancer Imaging.
II. MATERIALS AND METHODS
II.B. Image registration
II.C. Registration error measurement
III. EXPERIMENTAL METHODS
III.A. TRE for different fixed image configurations
III.B. TRE for base, mid-gland, and apex regions
IV.A. TRE for different fixed image configurations
IV.B. TRE for base, mid-gland, and apex regions
V.A. TRE for different fixed image configurations
V.B. TRE for base, mid-gland, and apex regions
- Three dimensional image processing
- Image registration
- Digital image processing
- Image detection systems
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