• Barbara Carl, Miriam Bopp, Marko Gjorgjevski, and Christopher Nimsky.
• Department of Neurosurgery, University Marburg, Marburg and Marburg Center for Mind, Brain and Behavior (MCMBB), Marburg, Germany. Electronic address: carlb@med.uni-marburg.de.
• World Neurosurg. 2018 Oct 1; 118: e584-e592.

ObjectiveTo investigate how frameless navigational techniques can be implemented to support standard frame-based stereotactic procedures.MethodsIn 25 patients (18 deep brain stimulation procedures, 3 stereotactic biopsies, and 4 stereoencephalography procedures), 57 trajectories were planned. A navigation reference array was attached to the stereotactic frame for automatic registration applying intraoperative computed tomography.ResultsUser-independent automatic registration resulted in a low navigation registration error (0.76 ± 0.30 mm). Because the stereotactic scan is performed intraoperatively, it can also be used for automatic navigation registration without additional patient radiation exposure. Low-dose intraoperative computed tomography protocols allowed the effective radiation dose to be reduced to 0.39 mSv (i.e., by a factor of 7.7) compared with standard head protocols without impeding navigational accuracy with a registration error of 0.65 ± 0.05 mm. Additional use of navigation-facilitated surgery, in which entry points and alignments of trajectory paths could be easily checked, provided additional safety. Visualizing the depth of a biopsy needle or electrode during the procedure in relation to target and risk structures greatly enhanced the understanding of the procedure.ConclusionsIn a setting with intraoperative imaging, the combination of frameless and frame-based techniques offers new possibilities. Because of the high registration accuracy, the additional navigation provides improved safety and redundancy. Furthermore, the stereotactic procedure is supported by enhanced intuitive intraoperative visualization during the advancement of a biopsy needle or electrode. However, further technical refinements are necessary, such as possibilities to track microelectrodes during the advancement with a microdrive.Copyright © 2018 Elsevier Inc. All rights reserved.

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