Patient registration

In computer assisted surgery, the first step is to gather a 3D dataset that reproduces with great accuracy the geometry of the normal and pathological tissues in the region that has to be operated on.

It was based on cartesian principles and allowed them to accurately and reproductibly guide needle-like electrodes for neurophysiological experiments.

Patient registration for the head area has developed for nearly two decades on the same principle of combining CT scans with mechanical reference devices such as headframes or halo rings.

But the clinical experience showed that headgear is very uncomfortable to wear and even impossible to apply on little children, because their lack of cooperation; furthermore, the headframes can create artifacts in preoperative data gathering, or during surgery.

Based on this concept, a further technique was used: to implant temporary markers into bone structures that are superficial to the skin, under local anestesia.

[6] The technique has the disadvantage of a further minimal surgical procedure of placing the bone implants, with some risk of infection for the patient.

[8] The method was based on identifying certain antropometrical points and other anatomical landmarks on the skull, in correlation with the CT registration.

But the landmarks cannot be exactly pointed out and reproduced during patient dataset registration and surgery, therefore the method is not precise enough.

A research group at Ryerson University (now Toronto Metropolitan University) developed a method to use optical topographical imaging (OTI) to create a 3D model of the surface of open surgical sites and perform surface registration to CT and MRI data sets for neurosurgical navigation.