Registration of physical space to laparoscopic image space for use in minimally invasive hepatic surgery

While laparoscopes are used for numerous minimally invasive (MI) procedures , MI liver resection and ablative surgery is infrequently performed. The pa ucity of cases is due to the restriction of the field of view by the laparo scope and the difficulty in determining tumor location and margins under vi deo guidance, By merging MI surgery with interactive, image-guided surgery (IIGS), we hope to overcome localization difficulties present in laparoscop ic liver procedures. One key component of any IIGS system is the developmen t of accurate registration techniques to map image space to physical or pat ient space. This manuscript focuses on the accuracy and analysis of the dir ect linear transformation (DLT) method to register physical space with lapa roscopic image space on both distorted and distortion-corrected video image s. Experiments were conducted on a liver-sized plastic phantom affixed with 20 markers at various depths. After localizing the points in both physical and laparoscopic image space, registration accuracy was assessed for diffe rent combinations and numbers of control points (n) to determine the quanti ty necessary to develop a robust registration matrix. For n = 11, average t arget registration error (TRE) was 0.70 +/- 0.20 mm. We also studied the ef fects of distortion correction on registration accuracy. For the particular distortion correction method and laparoscope used in our experiments, ther e was no statistical significance between physical to image registration er ror for distorted and corrected images. In cases where a minimum number of control points (n = 6) are acquired, the DLT is often not stable and the ma thematical process can lead to high TRE values. Mathematical filters develo ped through the analysis of the DLT were used to prospectively eliminate ou tlier cases where the TRE was high. For n = 6, prefilter average TRE was 17 .4 +/- 153 mm far all trials; when the filters were applied, average TRE de creased to 1.64 +/- 1.10 mm for the remaining trials.