Improvement of target registration accuracy with deeply seated anatomical landmarks

In point-based registration between the patient and the image, skin-affixed markers are attached to the patient´s skin. Although registration accuracy is relatively high in the region around the markers, the accuracy decreases at deeply seated targets in the body, in proportion to the distance from the skin where the markers are attached. In this study, we propose a method that uses anatomical landmarks near the target as additional points for the registration to decrease target registration error (TRE). In the phantom experiment, it was confirmed that the target registration accuracy was improved when the additional points were used. If the error caused by the distortion of ultrasound imaging and insufficient calibration of the ultrasound probe are reduced, patient-image registration will become more accurate. Because of the distortion and insufficient calibration, the fiducal registration error (FRE) was increased. Nevertheless the reduced TRE shows the feasibility of the proposed idea.