[Automatic registration of patients with A-mode ultrasound for computer-assisted surgery. Laboratory proof of...

The main source of error in 3D navigation is the patient-to-image registration process. Anatomical landmarks or adhesive markers perform sub-optimally. Bone-anchored invasive markers significantly change the clinical workflow of navigated ENT surgery, are invasive and cause patient discomfort. In order to minimize registration errors and to further streamline the clinical use of intraoperative 3D navigation we demonstrate that A-mode ultrasound allows an accurate 3D surface profile of the os occipitale to be created which can be reliably registered on preoperative patient CT data.

The transducer is mechanically positioned with sub-millimeter accuracy on the patient's occiput. From the sound echos a 3D surface is generated and registered to the preoperative CT images with the iterative closest point (ICP) algorithm. The evaluation of our setup was performed on three anatomic specimens and one bony skull.

The ultrasound echoes from the occiput allowed the creation of an adequate 3D surface which could be registered to a segmentation of the CT image with an accuracy greater than 1.5 mm. The experiments were evaluated by an intuitive representation of the spatial deviation between CT and ultrasound data as a color-coded map.

The approach to scan the posterior skull with A-mode ultrasound enables automatic intraoperative registration and can be integrated into the intraoperative setup.