Conventional methods for positioning electroencephalography electrodes according to the international 10/20 system are based on the manual identification of the principal 10/20 landmarks via visual inspection and palpation, inducing intersession variations in their determined locations due to structural ambiguity or poor visibility. To address the variation issue, we propose an image guidance system for precision electrode placement. Following the electrode placement according to the 10/20 system, affixed electrodes are laser-scanned together with the facial surface. For subsequent procedures, the laser scan is conducted likewise after positioning the electrodes in an arbitrary manner, and following the measurement of fiducial electrode locations, frame matching is performed to determine a transformation from the coordinate frame of the position tracker to that of the laser-scanned image. Finally, by registering the intra-procedural scan of the facial surface to the reference scan, the current tracking data of the electrodes can be visualized relative to the reference goal positions without manually measuring the four principal landmarks for each trial. The experimental results confirmed that use of the electrode navigation system significantly improved the electrode placement precision compared to the conventional 10/20 system (p < 0.005). The proposed system showed the possibility of precise image-guided electrode placement as an alternative to the conventional manual 10/20 system.

We proposed and demonstrated the effectiveness of a hybrid method that uses both artificial and anatomical landmarks for patient-to-image registration. The experimental results confirmed that an improvement in TRE was evident by the proposed method, suggesting its feasibility in various spinal surgeries.

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In point-based registration between the patient and the image, skin-affixed markers are attached to the patient's skin. Although registration accuracy is relatively high in the region around the markers, the accuracy decreases at deeply seated targets in the body, in proportion to the distance from the skin where the markers are attached. In this study, we propose a method that uses anatomical landmarks near the target as additional points for the registration to decrease target registration error (TRE). In the phantom experiment, it was confirmed that the target registration accuracy was improved when the additional points were used. If the error caused by the distortion of ultrasound imaging and insufficient calibration of the ultrasound probe are reduced, patient-image registration will become more accurate. Because of the distortion and insufficient calibration, the fiducal registration error (FRE) was increased. Nevertheless the reduced TRE shows the feasibility of the proposed idea.