Time-of-flight camera technique for augmented reality in computer-assisted interventions

Augmented reality (AR) for enhancement of intra-operative images is gaining increasing interest in the field of navigated medical interventions. In this context, various imaging modalities such as ultrasound (US), C-Arm computed tomography (CT) and endoscopic images have been applied to acquire intra-operative information about the patient's anatomy. The aim of this paper was to evaluate the potential of the novel Time-of-Flight (ToF) camera technique as means for markerless intra-operative registration. For this purpose, ToF range data and corresponding CT images were acquired from a set of explanted non-transplantable human and porcine organs equipped with a set of marker that served as targets. Based on a rigid matching of the surfaces generated from the ToF images with the organ surfaces generated from the CT data, the targets extracted from the planning images were superimposed on the 2D ToF intensity images, and the target visualization error (TVE) was computed as quality measure. Color video data of the same organs were further used to assess the TVE of a previously proposed marker-based registration method. The ToF-based registration showed promising accuracy yielding a mean TVE of 2.5+/-1.1 mm compared to 0.7+/-0.4 mm with the marker-based approach. Furthermore, the target registration error (TRE) was assessed to determine the anisotropy in the localization error of ToF image data. The TRE was 8.9+/-4.7 mm on average indicating a high localization error in the viewing direction of the camera. Nevertheless, the young ToF technique may become a valuable means for intra-operative surface acquisition. Future work should focus on the calibration of systematic distance errors.