Intraoperative Ultrasound Guidance for Transanal Endoscopic Microsurgery

Abstract

Local excision of rectal cancer with transanal endoscopic microsurgery has proved to be a viable alternative to conventional, more radical techniques, but the reduced sensory experience presents significant challenges for the surgeon. Accurate identification and complete removal of lesions and subsurface targets is currently a difficult task, often exacerbated by intraoperative tissue deformation. This work describes novel ultrasound calibration and effective visualisation methods designed to meet these requirements, relying solely on optical measurements and pattern tracking. Detailed quantitative phantom and porcine validation experiments confirm that the technique is both practical and an accurate means for assessing lesion thickness intraoperatively, leading directly to human clinical trials.

Robust ultrasound probe tracking: initial clinical experiences during robot-assisted partial nephrectomy

“…Visual identification of a geometric pattern rigidly attached to the probe is sufficient to estimate its pose, ultimately leading to direct registration [8,9] of the ultrasound image.…”

“…Preliminary work [8] described a general probe calibration method applicable to the UST-533 microsurgery probe. In total, seven degrees of freedom were determined, ultimately resulting in the transformation that takes pixels in the ultrasound image to the correct position in the probe pattern coordinate frame.…”

“…The X and Z components of the translation are determined by direct measurement of the transducer position relative to its outer casing. The remaining degree of freedom, the Y translation, is determined by alignment of the direct view of a single crosswire phantom feature [8] with its ultrasound image overlay.…”

“…To assess probe calibration accuracy, eight different standard-definition camera and transducer poses were used to compare ultrasound images of the validation phantom crossing point [8] against the corresponding direct line-of-sight views, afforded when the phantom is drained of water with its door removed. The mean, standard deviation and maximum of the overlay errors were found to be 537μm, 90μm and 653μm, respectively, and can be seen to be an improvement over the validation results (669μm, 255μm and 961μm, respectively) generated by the previous 7-DOF optimisation method.…”

“…Through comparison to the operational envelope results generated for the original chessboard pattern implementation [8], the extent of the incremental improvement can be calculated. An increase of 5.7% and 8.1% in the X and Y axis rotation ranges is observed, respectively.…”