PURPOSE: Neurosurgical registration using optical tracking in prone position is problematic due to a lack of anatomical landmarks on the posterior skull. The current method of registration involves insertion of screws into the skull. Surface registration using ultrasound has been proposed as a less invasive method of registration. Obtaining full access to the posterior skull would require patient hair removal, which is not favored by patients as it can cause an increased risk of surgical site infection and a less aesthetic outcome. We performed ultrasound scans on participants with no hair removal to evaluate the visibility of the mastoid processes and occipital base of the posterior skull in ultrasound imaging.
METHODS: Participants were scanned using a linear and a curvilinear ultrasound probe. Scans were taken at the maximum and minimum frequency of each probe. Ultrasound scans captured the region around each mastoid process, the external occipital protuberance, and the occipital base of the skull. Scans were recorded using the Sequences extension in 3D Slicer and replayed for visual analysis.
RESULTS: At its minimum frequency, the linear probe was found to have identifiable bone surfaces with some level of uncertainty. At its maximum frequency, clear identification of the mastoid processes and occipital base was possible. The curvilinear probe did not allow identification of bone surfaces in the ultrasound image.
CONCLUSION: A linear probe at a high frequency provides clearly identifiable bone surfaces, allowing for the selection of points used in an iterative closest point algorithm for surface registration. (Read More)