gms | German Medical Science

Objective: Mapping image space and physical space in neuronavigation is most commonly performed using fiducial based imaging approaches based on MR or CT imaging, whereas CT images show superior registration accuracy due to image distortion within the MR images. As CT imaging is associated with radiation exposure if used CT imaging should be kept to a minimum while allowing for accurate co-registration.

Methods: In September 2016, a 32 slice iCT scanner (AIRO, Brainlab, Munich) was implemented in our OR for pre-/intraoperative imaging, automated co-registration and microscope based navigation. Reflective markers on the CT scanner in combination with a detachable CT-compatible cranial reference array allowed for automated navigation registration instead of fiducial based registration. Navigation accuracy was visually measured by three independent skin fiducials not used for registration. To compare standard preoperative CT imaging for fiducial based registration with intraoperative CT imaging prior to surgery for automated co-registration with respect to radiation exposure, data of two groups of patients who were operated on intracranial lesions since January 2016 were compared, one receiving standard preoperative CT (n=64) imaging and one receiving intraoperative CT imaging prior to surgery (n=120). During the experience of iCT patient cases dosage reduce protocols (n=49/120) and reduced imaging volumes (n=25/120) were applied intraoperatively, while standard protocols remained the same due to a lack of information on intraoperative patient positions and surgical approach.

Results: Navigation accuracy assessed by three fiducials proved to be less than 2mm (target registration error) in all iCT cases. Standard preoperative CT-based imaging for fiducial based registration showed mean dose length products (DLP) of 996.11±87.48mGy.cm. While at the beginning of the implementation of the AIRO iCT scanner significantly (p=0.005) higher mean DLP of 1083.29±191.76mGy.cm was seen, dosage reduce protocols lead to a significantly (p<0.001) reduced mean DLP of 755.71±191.68mGy.cm and a change to low dose protocols resulted in an even significantly (p<0.001) lower mean DLP of 149.37±14.64mGy.cm, while keeping quality of navigation accuracy.

Conclusion: Intraoperative CT-based automatic registration allows for significantly reduced radiation exposure in contrast to standard preoperative CT imaging while maintaining high navigation accuracy in neurosurgical interventions.