Perspective pinhole model with planar source for augmented reality surgical navigation based on C-arm imaging.

PURPOSE: For augmented reality surgical navigation based on C-arm imaging, accuracy of the overlaid augmented reality onto the X-ray image is imperative. However, overlay displacement is generated when a conventional pinhole model describing a geometric relationship of a normal camera is adopted for C-arm calibration. Thus, a modified model for C-arm calibration is proposed to reduce this displacement, which is essential for accurate surgical navigation. METHOD: Based on the analysis of displacement pattern generated for three-dimensional objects, we assumed that displacement originated by moving the X-ray source position according to the depth. In the proposed method, X-ray source movement was modeled as variable intrinsic parameters and represented in the pinhole model by replacing the point source with a planar source. RESULTS: The improvement which represents a reduced displacement was verified by comparing overlay accuracy for augmented reality surgical navigation between the conventional and proposed methods. The proposed method achieved more accurate overlay on the X-ray image in spatial position as well as depth of the object volume. CONCLUSION: We validated that intrinsic parameters that describe the source position were dependent on depth for a three-dimensional object and showed that displacement can be reduced and become independent of depth by using the proposed planar source model.

Augmented reality-based electrode guidance system for reliable electroencephalography.

BACKGROUND: In longitudinal electroencephalography (EEG) studies, repeatable electrode positioning is essential for reliable EEG assessment. Conventional methods use anatomical landmarks as fiducial locations for the electrode placement. Since the landmarks are manually identified, the EEG assessment is inevitably unreliable because of individual variations among the subjects and the examiners. To overcome this unreliability, an augmented reality (AR) visualization-based electrode guidance system was proposed. METHODS: The proposed electrode guidance system is based on AR visualization to replace the manual electrode positioning. After scanning and registration of the facial surface of a subject by an RGB-D camera, the AR of the initial electrode positions as reference positions is overlapped with the current electrode positions in real time. Thus, it can guide the position of the subsequently placed electrodes with high repeatability. RESULTS: The experimental results with the phantom show that the repeatability of the electrode positioning was improved compared to that of the conventional 10-20 positioning system. CONCLUSION: The proposed AR guidance system improves the electrode positioning performance with a cost-effective system, which uses only RGB-D camera. This system can be used as an alternative to the international 10-20 system.

A Preliminary Study on Precision Image Guidance for Electrode Placement in an EEG Study.

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.

A preliminary study on surgical navigation for epiduroscopic laser neural decompression.

Epiduroscopic laser neural decompression is an emerging therapeutic modality to treat lumbar spine pathologies including chronic low back pain, spinal stenosis, and disk herniation via catheter insertion followed by laser ablation of the lesion. Despite the efficacy of epiduroscopic laser neural decompression, excessive radiation doses due to fluoroscopy during epiduroscopic laser neural decompression have limited its widespread application. To address the issue, we propose a surgical navigation system to assist in epiduroscopic laser neural decompression procedures using radiation-free image guidance. An electromagnetic tracking system was used as the basic modality to track the internal location of the surgical instrument with respect to the patient body. Patient-to-image registration was carried out using the point-based registration method to determine the transformation between the coordinate system of the patient and that of the medical images. We applied the proposed system in epiduroscopic laser neural decompression procedures to assess its effectiveness, and the outcomes confirmed its clinical feasibility. To the best of our knowledge, this is a report on the first surgical navigation applied for epiduroscopic laser neural decompression procedure.

A hybrid method to improve target registration accuracy in surgical navigation.

BACKGROUND: The accuracy of surgical navigation depends greatly on that of registration between the patient and the medical image. Point-based registration has been the most common and reliable method, which typically uses skin markers. Unfortunately, high registration accuracy around the markers is not sustained at targets deeply seated within the body. To address such increase in target registration error (TRE), we proposed a hybrid point-based registration method that incorporates anatomical landmarks near the target. MATERIAL AND METHODS: Ultrasound calibration is performed with an optical tracker for coordinate frame conversion of image coordinates into the real world. With the calibrated ultrasound probe, we could non-invasively obtain landmark positions near the target, being used together with skin markers for registration. RESULTS: In the experiment, we examined registration accuracies achieved with and without use of an anatomical landmark. We confirmed that using an additional anatomical landmark in registration resulted in an increase in fiducial regsitration error (FRE), but a significant decrease in TRE (p < 0.001). CONCLUSION: 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.