Keywords Image-guided surgery Á High accuracy Á Noninvasiveness Á Temporal bone
PurposeThe temporal bone that is drilled in otologic surgery conceals important organs inside small area, e.g. carotid artery, jugular vein, facial nerve, inner ear etc. Surgeons will reach some of these organs as surgical targets while not injuring others. Three dimensionally located complex anatomical structures in the bone imply a necessity for image-guidance with high accuracy. However, because most otologic surgery is basically less invasive, surgical navigation for otologic surgeries require demanding accuracy as well as less invasiveness. We recently introduced a new strategy (STAMP method) for less invasive, but accurate registration method for image-guided otologic surgery. In the original STAMP method we edited each patient's CT data to virtually place markers on the patient's bone. The template of the bone surface with small holes is then produced to transfer the virtual markers to the patient's bone during the surgery. In the operating room, the surgeon attaches the STAMP template on the patient's bone surface and transfer virtual markers to the patient's temporal bone. Then the surgeon finishes the paired-point registration using the transferred markers. In more than 20 cases of the imageguided cochlear implant surgery, we used this method and the registration errors were about 1 mm. This noninvasive and quick method was particularly useful in cases of children. However, this method is rather complex for surgeons who are unfamiliar with the image guided surgery. In phantom study, there is an apparent difference in the registration time and errors between surgeons.In this study, we modified this STAMP method to make the procedure as simple as possible in the operating room. We attached optical markers on the STAMP template and registered the relative points of virtual markers pre-operatively. The only procedure in the operating room is to attach the STAMP template on the patient's bone surface for \10 s. The engineers did the rest of the process either in the lab or in the operating room. We report the comparison of registration time and registration errors of original STAMP and preregistered STAMP methods.
MethodsThe registration methods were evaluated in phantom study. We used a synthetic model of a temporal bone (KEZLEX, Ono & Co., Japan). We edited the CT data of this model to virtually place 8 markers on the surface. The STAMP template that fits on the surface of the bone, and also shows the location of the 8 virtual markers, is then produced using laser-sintering process. The above process is the same with the original STAMP method except that the template now has a pole to fix the optical trackers for pre-registering purpose (Fig. 1a). The virtual markers were pre-registered to the attached optical trackers (Fig. 1b). The above process can be finished before the surgery by engineers. Then the surgeon performed the only required process in the operating room, which is to attach the pre-registered STAMP template on th...