Acute ischemic stroke caused by large vessel occlusion is treated with endovascular thrombectomy, but treatment failure may occur when clot composition and thrombectomy technique mismatch. In this proof-of-concept study, diffuse reflectance spectroscopy (DRS) is evaluated for identification of clot composition ex vivo. DRS spectra and histology were acquired from 45 clot units retrieved from 29 stroke patients. DRS spectra correlated to clot RBC content, R= 81, p < .001, and could discriminate between RBC-rich and fibrin-rich clots, p < 0.001. Sensitivity and specificity for detection of RBC-rich clots were 0.722 and 0.846 respectively. Applied in an intravascular device, DRS could potentially provide intraprocedural information on clot composition that could increase endovascular thrombectomy efficiency.

Background: Neurosurgical procedures are complex and require years of training and experience. Traditional training on human cadavers is expensive, requires facilities and planning, and raises ethical concerns. Therefore, the use of anthropomorphic phantoms could be an excellent substitute. The aim of the study was to design and develop a patient-specific 3D-skull and brain model with realistic CT-attenuation suitable for conventional and augmented reality (AR)-navigated neurosurgical simulations. Methods: The radiodensity of materials considered for the skull and brain phantoms were investigated using cone beam CT (CBCT) and compared to the radiodensities of the human skull and brain. The mechanical properties of the materials considered were tested in the laboratory and subsequently evaluated by clinically active neurosurgeons. Optimization of the phantom for the intended purposes was performed in a feedback cycle of tests and improvements. Results: The skull, including a complete representation of the nasal cavity and skull base, was 3D printed using polylactic acid with calcium carbonate. The brain was cast using a mixture of water and coolant, with 4 wt% polyvinyl alcohol and 0.1 wt% barium sulfate, in a mold obtained from segmentation of CBCT and T1 weighted MR images from a cadaver. The experiments revealed that the radiodensities of the skull and brain phantoms were 547 and 38 Hounsfield units (HU), as compared to real skull bone and brain tissues with values of around 1300 and 30 HU, respectively. As for the mechanical properties testing, the brain phantom exhibited a similar elasticity to real brain tissue. The phantom was subsequently evaluated by neurosurgeons in simulations of endonasal skull-base surgery, brain biopsies, and external ventricular drain (EVD) placement and found to fulfill the requirements of a surgical phantom. Conclusions: A realistic and CT-compatible anthropomorphic head phantom was designed and successfully used for simulated augmented reality-led neurosurgical procedures. The anatomic details of the skull base and brain were realistically reproduced. This phantom can easily be manufactured and used for surgical training at a low cost.

[This corrects the article DOI: 10.1371/journal.pone.0227312.].

In neurosurgery, technical solutions for visualizing the border between healthy brain and tumor tissue is of great value, since they enable the surgeon to achieve gross total resection while minimizing the risk of damage to eloquent areas. By using real-time non-ionizing imaging techniques, such as hyperspectral imaging (HSI), the spectral signature of the tissue is analyzed allowing tissue classification, thereby improving tumor boundary discrimination during surgery. More particularly, since infrared penetrates deeper in the tissue than visible light, the use of an imaging sensor sensitive to the near-infrared wavelength range would also allow the visualization of structures slightly beneath the tissue surface. This enables the visualization of tumors and vessel boundaries prior to surgery, thereby preventing the damaging of tissue structures. In this study, we investigate the use of Diffuse Reflectance Spectroscopy (DRS) and HSI for brain tissue classification, by extracting spectral features from the near infra-red range. The applied method for classification is the linear Support Vector Machine (SVM). The study is conducted on ex-vivo porcine brain tissue, which is analyzed and classified as either white or gray matter. The DRS combined with the proposed classification reaches a sensitivity and specificity of 96%, while HSI reaches a sensitivity of 95% and specificity of 93%. This feasibility study shows the potential of DRS and HSI for automated tissue classification, and serves as a first step towards clinical use for tumor detection deeper inside the tissue.

Background The safe and accurate placement of pedicle screws remains a critical step in open and minimally invasive spine surgery, emphasizing the need for intraoperative guidance techniques. Diffuse reflectance spectroscopy (DRS) is an optical sensing technology that may provide intraoperative guidance in pedicle screw placement. Purpose The study presents the first in vivo minimally invasive procedure using DRS sensing at the tip of a Jamshidi needle with an integrated optical K-wire. We investigate the effect of tissue perfusion and probe-handling conditions on the reliability of fat fraction measurements for breach detection in vivo. Methods A Jamshidi needle with an integrated fiber-optic K-wire was gradually inserted into the vertebrae under intraoperative image guidance. The fiber-optic K-wire consisted of two optical fibers with a fiber-to-fiber distance of 1.024 mm. DRS spectra in the wavelength range of 450 to 1600 nm were acquired at several positions along the path inside the vertebrae. Probe-handling conditions were varied by changing the amount of pressure exerted on the probe within the vertebrae. Continuous spectra were recorded as the probe was placed in the center of the vertebral body while the porcine specimen was sacrificed via a lethal injection. Results A typical insertion of the fiber-optic K-wire showed a drop in fat fraction during an anterior breach as the probe transitioned from cancellous to cortical bone. Fat fraction measurements were found to be similar irrespective of the amount of pressure exerted on the probe ( p = 0.65). The 95% confidence interval of fat fraction determination was found in the narrow range of 1.5–3.6% under various probe-handling conditions. The fat fraction measurements remained stable during 70 min of decreased blood flow after the animal was sacrificed. Discussions These findings indicate that changes in tissue perfusion and probe-handling conditions have a relatively low measureable effect on the DRS signal quality and thereby on the determination of fat fraction as a breach detection signal. Conclusions Fat fraction quantification for intraoperative pedicle screw breach detection is reliable, irrespective of changes in tissue perfusion and probe-handling conditions.

Safe and accurate placement of spinal screws remains a critical step during open and minimally invasive spinal fusion surgery. We investigated the application of diffuse reflectance spectroscopy (DRS) for real-time instrument guidance during a spinal screw placement procedure. A custom-built screw probe with integrated optical fibers was inserted into a vertebra under image guidance in an ex vivo human setting. We found that fat content derived from the spectra gradually changed as the probe approached the cortical bone boundary. The results indicate that DRS integrated into surgical instruments has the potential to improve the safety and accuracy of spinal screw placement procedures.

Objective Surgical navigation is a well-established tool in endoscopic skull base surgery. However, navigational and endoscopic views are usually displayed on separate monitors, forcing the surgeon to focus on one or the other. Aiming to provide real-time integration of endoscopic and diagnostic imaging information, we present a new navigation technique based on augmented reality with fusion of intraoperative cone beam computed tomography (CBCT) on the endoscopic view. The aim of this study was to evaluate the accuracy of the method. Material and methods An augmented reality surgical navigation system (ARSN) with 3D CBCT capability was used. The navigation system incorporates an optical tracking system (OTS) with four video cameras embedded in the flat detector of the motorized C-arm. Intra-operative CBCT images were fused with the view of the surgical field obtained by the endoscope's camera. Accuracy of CBCT image co-registration was tested using a custom-made grid with incorporated 3D spheres. Results Co-registration of the CBCT image on the endoscopic view was performed. Accuracy of the overlay, measured as mean target registration error (TRE), was 0.55 mm with a standard deviation of 0.24 mm and with a median value of 0.51mm and interquartile range of 0.39--0.68 mm. Conclusion We present a novel augmented reality surgical navigation system, with fusion of intraoperative CBCT on the endoscopic view. The system shows sub-millimeter accuracy.

Safe and accurate placement of pedicle screws remains a critical step in open and minimally invasive spine surgery. The diffuse reflectance spectroscopy (DRS) technique may offer the possibility of intra-operative guidance for pedicle screw placement. Currently, Magnetic Resonance Imaging (MRI) is one of the most accurate techniques used to measure fat concentration in tissues. Therefore, the purpose of this study is to compare the accuracy of fat content measured invasively in vertebrae using DRS and validate it against the Proton density fat fraction (PDFF) derived via MRI. Chemical shift-encoding-based water-fat imaging of the spine was first performed on six cadavers. PDFF images were computed and manually segmented. 23 insertions using a custom-made screw probe with integrated optical fibers were then performed under cone beam computer tomography (CBCT). DR spectra were recorded at several positions along the trajectory as the optical screw probe was inserted turn by turn into the vertebral body. Fat fractions determined via DRS and MRI techniques were compared by spatially correlating the optical screw probe position within the vertebrae on CBCT images with respect to the PDFF images. The fat fraction determined by DRS was found to have a high correlation with those determined by MRI, with a Pearson coefficient of 0.950 (P< 0.001) as compared with PDFF measurements calculated from the MRI technique. Additionally, the two techniques were found to be comparable for fat fraction quantification within vertebral bodies (R2 = 0.905).

OBJECTIVE: The goal of this study was to develop and validate a system for automatic segmentation of the spine, pedicle identification, and screw path suggestion for use with an intraoperative 3D surgical navigation system.METHODS: Cone-beam CT (CBCT) images of the spines of 21 cadavers were obtained. An automated model-based approach was used for segmentation. Using machine learning methodology, the algorithm was trained and validated on the image data sets. For measuring accuracy, surface area errors of the automatic segmentation were compared to the manually outlined reference surface on CBCT. To further test both technical and clinical accuracy, the algorithm was applied to a set of 20 clinical cases. The authors evaluated the system's accuracy in pedicle identification by measuring the distance between the user-defined midpoint of each pedicle and the automatically segmented midpoint. Finally, 2 independent surgeons performed a qualitative evaluation of the segmentation to judge whether it was adequate to guide surgical navigation and whether it would have resulted in a clinically acceptable pedicle screw placement.RESULTS: The clinically relevant pedicle identification and automatic pedicle screw planning accuracy was 86.1%. By excluding patients with severe spinal deformities (i.e., Cobb angle > 75° and severe spinal degeneration) and previous surgeries, a success rate of 95.4% was achieved. The mean time (± SD) for automatic segmentation and screw planning in 5 vertebrae was 11 ± 4 seconds.CONCLUSIONS: The technology investigated has the potential to aid surgeons in navigational planning and improve surgical navigation workflow while maintaining patient safety.

Pedicle screw placement accuracy during spinal fixation surgery varies greatly and severe misplacement has been reported in 1-6.5 % of screws. Diffuse reflectance (DR) spectroscopy has previously been shown to reliably discriminate between tissues in the human body. We postulate that it could be used to discriminate between cancellous and cortical bone. Therefore, the purpose of this study is to validate DR spectroscopy as a warning system to detect impending pedicle screw breach in a cadaveric surgical setting using typical clinical breach scenarios. DR spectroscopy was incorporated at the tip of an integrated pedicle screw and screw driver used for tissue probing during pedicle screw insertions on six cadavers. Measurements were collected in the wavelength range of 400-1600 nm and each insertion was planned to result in a breach. Measurements were labelled as cancellous, cortical or representing a pre-cortical zone (PCZ) in between, based on information from cone beam computed tomographies at corresponding positions. In addition, DR spectroscopy data was recorded after breach. Four typical pedicle breach types were performed, and a total of 45 pedicle breaches were recorded. For each breach direction, the technology was able to detect the transition of the screw tip from the cancellous bone to the PCZ (P < 0.001), to cortical bone (P < 0.001), and to a subsequent breach (P < 0.001). Using support vector machine (SVM) classification, breach could reliably be detected with a sensitivity of 98.3 % [94.3-100 %] and a specificity of 97.7 % [91.0-100%]. We conclude that DR spectroscopy reliably identifies the area of transition from cancellous to cortical bone in typical breach scenarios and can warn the surgeon of impending pedicle breach, thereby resulting in safer spinal fixation surgeries. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Study Design. Prospective observational study. Objective. The aim of this study was to evaluate the accuracy of pedicle screw placement using augmented reality surgical navigation (ARSN) in a clinical trial. Summary of Background Data. Recent cadaveric studies have shown improved accuracy for pedicle screw placement in the thoracic spine using ARSN with intraoperative 3D imaging, without the need for periprocedural x-ray. In this clinical study, we used the same system to place pedicle screws in the thoracic and lumbosacral spine of 20 patients. Methods. The study was performed in a hybrid operating room with an integrated ARSN system encompassing a surgical table, a motorized flat detector C-arm with intraoperative 2D/3D capabilities, integrated optical cameras for augmented reality navigation, and noninvasive patient motion tracking. Three independent reviewers assessed screw placement accuracy using the Gertzbein grading on 3D scans obtained before wound closure. In addition, the navigation time per screw placement was measured. Results. One orthopedic spinal surgeon placed 253 lumbosacral and thoracic pedicle screws on 20 consenting patients scheduled for spinal fixation surgery. An overall accuracy of 94.1% of primarily thoracic pedicle screws was achieved. No screws were deemed severely misplaced (Gertzbein grade 3). Fifteen (5.9%) screws had 2 to 4 mm breach (Gertzbein grade 2), occurring in scoliosis patients only. Thirteen of those 15 screws were larger than the pedicle in which they were placed. Two medial breaches were observed and 13 were lateral. Thirteen of the grade 2 breaches were in the thoracic spine. The average screw placement time was 5.2 ± 4.1 minutes. During the study, no device-related adverse event occurred. Conclusion. ARSN can be clinically used to place thoracic and lumbosacral pedicle screws with high accuracy and with acceptable navigation time. Consequently, the risk for revision surgery and complications could be minimized. Level of Evidence: 3

The use of pre-operative CT and MR images for navigation during endo-nasal skull-base endoscopic surgery is a well-established procedure in clinical practice. Fusion of CT and MR images on the endoscopic view can offer an additional advantage by directly overlaying surgical-planning information in the surgical view. Fusion of intraoperative images, such as cone beam computed tomography (CBCT), represents a step forward since these images can also account for intra-operative anatomical changes. In this work, we present a method for intra-operative CBCT image fusion on the endoscopic view for endo-nasal skull-base surgery, implemented on the Philips surgical navigation system. This is the first study which utilizes an optical tracking system (OTS) embedded in the flat-panel detector of the C-arm for endoscopic-image augmentation. In our method the OTS, co-registered in the same CBCT coordinate system, is used for tracking the endoscope. Accuracy in CBCT image registration in the endoscopic view is studied using a calibration board. Image fusion is tested in a realistic surgical scenario by using a skull phantom and inserts that mimic critical structures at the skull base. Overall performances tested on the skull phantom show a high accuracy in tracking the endoscope and registration of CBCT on endoscopic view. It can be concluded that the implemented system show potential for usage in endo-nasal skull-base surgery.

Safe and accurate placement of screws remains a critical issue in open and minimally invasive spine surgery. We propose to use diffuse reflectance (DR) spectroscopy as a sensing technology at the tip of a surgical instrument to ensure a safe path of the instrument through the cancellous bone of the vertebrae. This approach could potentially reduce the rate of cortical bone breaches, thereby resulting in fewer neural and vascular injuries during spinal fusion surgery. In our study, DR spectra in the wavelength ranges of 400 to 1600 nm were acquired from cancellous and cortical bone from three human cadavers. First, it was investigated whether these spectra can be used to distinguish between the two bone types based on fat, water, and blood content along with photon scattering. Subsequently, the penetration of the bone by an optical probe was simulated using the Monte-Carlo (MC) method, to study if the changes in fat content along the probe path would still enable distinction between the bone types. Finally, the simulation findings were validated via an experimental insertion of an optical screw probe into the vertebra aided by x-ray image guidance. The DR spectra indicate that the amount of fat, blood, and photon scattering is significantly higher in cancellous bone than in cortical bone (p < 0.01), which allows distinction between the bone types. The MC simulations showed a change in fat content more than 1 mm before the optical probe came in contact with the cortical bone. The experimental insertion of the optical screw probe gave similar results. This study shows that spectral tissue sensing, based on DR spectroscopy at the instrument tip, is a promising technology to identify the transition zone from cancellous to cortical vertebral bone. The technology therefore has the potential to improve the safety and accuracy of spinal screw placement procedures. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License.

BACKGROUND CONTEXT Several studies have shown that the use of a combination of intraoperative CT images and navigation, significantly improves pedicle screw placement accuracy. A new concept of surgical navigation system using augmented reality (AR) with intraoperative 3D cone beam CT (CBCT) was developed specifically for spinal surgery. PURPOSE To evaluate accuracy, efficiency, and safety of an AR-based surgical navigation system for pedicle screw placement. STUDY DESIGN/SETTING Prospective study. PATIENT SAMPLE Twenty patients. OUTCOME MEASURES Pedicle screw placement accuracy, procedural time, patients and occupational radiation doses. METHODS Twenty patients (1:1 male:female, 30±19 years) eligible for spine surgery with pedicle screw placement (13 scoliosis deformity cases and 7 other surgical indications) were prospectively enrolled and treated using surgical navigation with AR (Philips Healthcare, Best, the Netherlands). A total of 253 screws were placed in the patients using AR. The navigation system consists of optical video cameras integrated in a ceiling-mounted C-arm in a hybrid operating room (OR). An intraoperative CBCT was acquired from the C-arm to plan an optimal path for screw placement. The screws were navigated thanks to the planned paths augmented to the reality scene shown by the video cameras. An additional CBCT was performed to evaluate the accuracy of screw placement by independent reviewers using the Gertzbein scale. Total navigation time for screw placement, patient radiation dose as well as occupational staff dose was measured. RESULTS In average 13±6 screws per patient were placed with navigation. The accuracy of pedicle screw placement was 94% yielding 15/253 screws rated as grade 2 (2–4 mm pedicle breach) from which 13 were lateral breaches. Thirteen of these grade 2 screws had a diameter larger than the pedicle isthmus size where they were placed. The average navigation time was 5.2±4.1 minutes with a median value of 4 minutes from making the bone entry burr-hole to the final screw placement. Navigation time corresponded to an average of 16.8% of the total procedure time. The average patient radiation dose was 31±13 Gy cm2 (median 32, range: 14–51) with an average of 4 CBCT scans per procedure. During intraoperative 3D acquisitions, the OR staff was behind a leaded shield in the corner of the OR and did not wear apron lead protection during surgery. The average cumulative occupational dose of all staff member in the OR was 0.8±1.1 µSv (median 0.3, range: 0.0–3.2). CONCLUSIONS Surgical navigation using AR with intraoperative CBCT demonstrated clinical accuracy as high as 94% of pedicle screw placement with no related clinical complications. The average required time of navigation per screw placement was as short as 5.2 minutes. The use of navigation was a short fraction of the total procedure time. The CBCT intraoperative imaging available on the AR-based navigation system demonstrated negligible cumulative staff dose. Several studies have shown that the use of a combination of intraoperative CT images and navigation, significantly improves pedicle screw placement accuracy. A new concept of surgical navigation system using augmented reality (AR) with intraoperative 3D cone beam CT (CBCT) was developed specifically for spinal surgery. To evaluate accuracy, efficiency, and safety of an AR-based surgical navigation system for pedicle screw placement. Prospective study. Twenty patients. Pedicle screw placement accuracy, procedural time, patients and occupational radiation doses. Twenty patients (1:1 male:female, 30±19 years) eligible for spine surgery with pedicle screw placement (13 scoliosis deformity cases and 7 other surgical indications) were prospectively enrolled and treated using surgical navigation with AR (Philips Healthcare, Best, the Netherlands). A total of 253 screws were placed in the patients using AR. The navigation system consists of optical video cameras integrated in a ceiling-mounted C-arm in a hybrid operating room (OR). An intraoperative CBCT was acquired from the C-arm to plan an optimal path for screw placement. The screws were navigated thanks to the planned paths augmented to the reality scene shown by the video cameras. An additional CBCT was performed to evaluate the accuracy of screw placement by independent reviewers using the Gertzbein scale. Total navigation time for screw placement, patient radiation dose as well as occupational staff dose was measured. In average 13±6 screws per patient were placed with navigation. The accuracy of pedicle screw placement was 94% yielding 15/253 screws rated as grade 2 (2–4 mm pedicle breach) from which 13 were lateral breaches. Thirteen of these grade 2 screws had a diameter larger than the pedicle isthmus size where they were placed. The average navigation time was 5.2±4.1 minutes with a median value of 4 minutes from making the bone entry burr-hole to the final screw placement. Navigation time corresponded to an average of 16.8% of the total procedure time. The average patient radiation dose was 31±13 Gy cm2 (median 32, range: 14–51) with an average of 4 CBCT scans per procedure. During intraoperative 3D acquisitions, the OR staff was behind a leaded shield in the corner of the OR and did not wear apron lead protection during surgery. The average cumulative occupational dose of all staff member in the OR was 0.8±1.1 µSv (median 0.3, range: 0.0–3.2). Surgical navigation using AR with intraoperative CBCT demonstrated clinical accuracy as high as 94% of pedicle screw placement with no related clinical complications. The average required time of navigation per screw placement was as short as 5.2 minutes. The use of navigation was a short fraction of the total procedure time. The CBCT intraoperative imaging available on the AR-based navigation system demonstrated negligible cumulative staff dose.

STUDY DESIGN:Cadaveric laboratory study.OBJECTIVE:To assess the feasibility and accuracy of minimally invasive thoracolumbar pedicle screw placement using augmented reality (AR) surgical navigation.SUMMARY OF BACKGROUND DATA:Minimally invasive spine (MIS) surgery has increasingly become the method of choice for a wide variety of spine pathologies. Navigation technology based on AR has been shown to be feasible, accurate, and safe in open procedures. AR technology may also be used for MIS surgery.METHODS:The AR surgical navigation was installed in a hybrid operating room (OR). The hybrid OR includes a surgical table, a motorized flat detector C-arm with intraoperative 2D/3D imaging capabilities, integrated optical cameras for AR navigation, and patient motion tracking using optical markers on the skin. Navigation and screw placement was without any x-ray guidance. Two neurosurgeons placed 66 Jamshidi needles (two cadavers) and 18 cannulated pedicle screws (one cadaver) in the thoracolumbar spine. Technical accuracy was evaluated by measuring the distance between the tip of the actual needle position and the corresponding planned path as well as the angles between the needle and the desired path. Time needed for navigation along the virtual planned path was measured. An independent reviewer assessed the postoperative scans for the pedicle screws' clinical accuracy.RESULTS:Navigation time per insertion was 90 ± 53 seconds with an accuracy of 2.2 ± 1.3 mm. Accuracy was not dependent on operator. There was no correlation between navigation time and accuracy. The mean error angle between the Jamshidi needles and planned paths was 0.9° ± 0.8°. No screw was misplaced outside the pedicle. Two screws breached 2 to 4 mm yielding an overall accuracy of 89% (16/18).CONCLUSION:MIS screw placement directed by AR with intraoperative 3D imaging in a hybrid OR is accurate and efficient, without any fluoroscopy or x-ray imaging during the procedure.LEVEL OF EVIDENCE:N/A.

Spinal fusion is a common procedure to stabilize the spinal column by fixating parts of the spine. In such procedures, metal screws are inserted through the patients back into a vertebra, and the screws of adjacent vertebrae are connected by metal rods to generate a fixed bridge. In these procedures, 3D image guidance for intervention planning and outcome control is required. Here, for anatomical guidance, an automated approach for vertebra segmentation from C-arm CT images of the spine is introduced and evaluated. As a prerequisite, 3D C-arm CT images are acquired covering the vertebrae of interest. An automatic model-based segmentation approach is applied to delineate the outline of the vertebrae of interest. The segmentation approach is based on 24 partial models of the cervical, thoracic and lumbar vertebrae which aggregate information about (i) the basic shape itself, (ii) trained features for image based adaptation, and (iii) potential shape variations. Since the volume data sets generated by the C-arm system are limited to a certain region of the spine the target vertebra and hence initial model position is assigned interactively. The approach was trained and tested on 21 human cadaver scans. A 3-fold cross validation to ground truth annotations yields overall mean segmentation errors of 0.5 mm for T1 to 1.1 mm for C6. The results are promising and show potential to support the clinician in pedicle screw path and rod planning to allow accurate and reproducible insertions.

The displacement of the brain parenchyma during open brain surgery, known as ‘brain shift’, affects the applicability of pre-operative planning and affects the outcome of the surgery. In this article we investigated the accuracy of a novel method to intra-operatively determine the brain shift displacement field throughout the whole brain volume. The brain shift displacement was determined by acquiring contrast enhanced cone-beam CT before and during the surgery. The respective datasets were pre-processed, landmark enhanced, and elastically registered to find the displacement field. The accuracy of this method was evaluated by artificially creating post-operative data with a known ground truth deformation. The artificial post-operative data was obtained by applying the deformation field from one patient on the pre-operative data of another patient, which was repeated for three patients. The mean error that was found with this method ranged from 1 to 2 mm, while the standard deviation was about 1 mm.

BACKGROUND:Cerebrospinal fluid leakage and ventricular compression during open surgery may lead to brain deformation called brain shift. Brain shift may affect intraoperative navigation that is based on image-based preoperative planning. Tools to correct or predict these anatomic modifications can be important to maintain precision during open guided neurosurgery. OBJECTIVE:To obtain a reliable intraoperative volumetric deformation vector field describing brain shift during intracranial neurosurgical procedures. METHODS:We acquired preoperative and intraoperative cone-beam computed tomography enhanced with intravenous injection of iodine contrast. These data sets were preprocessed and elastically registered to obtain the volumetric brain shift deformation vector fields. RESULTS:We obtained the brain shift deformation vector field in 9 cases. The deformation fields proved to be highly nonlinear, particularly around the ventricles. Interpatient variability was considerable, with a maximum deformation ranging from 8.1 to 26.6 mm and a standard deviation ranging from 0.9 to 4.9 mm. CONCLUSION:Contrast-enhanced cone-beam computed tomography provides a feasible technique for intraoperatively determining brain shift deformation vector fields. This technique can be used perioperatively to adjust preoperative planning and coregistration during neurosurgical procedures.

Study Design.A cadaveric laboratory study.Objective.The aim of this study was to assess the feasibility and accuracy of thoracic pedicle screw placement using augmented reality surgical navigation (ARSN).Summary of Background Data.Recent advances in spinal navigation have shown improved accuracy in lumbosacral pedicle screw placement but limited benefits in the thoracic spine. 3D intraoperative imaging and instrument navigation may allow improved accuracy in pedicle screw placement, without the use of x-ray fluoroscopy, and thus opens the route to image-guided minimally invasive therapy in the thoracic spine.Methods.ARSN encompasses a surgical table, a motorized flat detector C-arm with intraoperative 2D/3D capabilities, integrated optical cameras for augmented reality navigation, and noninvasive patient motion tracking. Two neurosurgeons placed 94 pedicle screws in the thoracic spine of four cadavers using ARSN on one side of the spine (47 screws) and free-hand technique on the contralateral side. X-ray fluoroscopy was not used for either technique. Four independent reviewers assessed the postoperative scans, using the Gertzbein grading. Morphometric measurements of the pedicles axial and sagittal widths and angles, as well as the vertebrae axial and sagittal rotations were performed to identify risk factors for breaches.Results.ARSN was feasible and superior to free-hand technique with respect to overall accuracy (85% vs. 64%, P<0.05), specifically significant increases of perfectly placed screws (51% vs. 30%, P<0.05) and reductions in breaches beyond 4mm (2% vs. 25%, P<0.05). All morphometric dimensions, except for vertebral body axial rotation, were risk factors for larger breaches when performed with the free-hand method.Conclusion.ARSN without fluoroscopy was feasible and demonstrated higher accuracy than free-hand technique for thoracic pedicle screw placement.Level of Evidence: N/A

Purpose To compare the navigational accuracy and radiation dose during needle localization of targets for augmented reality (AR) with and without motion compensation (MC) versus those for cone-beam computed tomography (CT) with real-time fluoroscopy navigation in a pig model. Materials and Methods This study was approved by the Institutional Animal Care and Use Committee. Three operators each localized 15 targets (bone fragments) approximately 7 cm deep in the paraspinal muscles of nine Yorkshire pigs by using each of the three modalities (AR with and without MC and cone-beam CT with fluoroscopy). Target depth, accuracy (distance between needle tip and target), and radiation dose (dose-area product [DAP]) were recorded for each procedure. Correlation between accuracy and depth of target was assessed by using the Pearson correlation coefficient. Two-way analysis of variance was used for differentiating accuracy and DAPs across navigation techniques and operator backgrounds. Results There was no correlation between depth of target and accuracy. There was no significant difference in accuracy between modalities (mean distance, 3.0 mm ± 1.9 [standard deviation] for cone-beam CT with fluoroscopy, 2.5 mm ± 2.0 for AR, and 3.2 mm ± 2.7 for AR with MC [P = .33]). There was, however, a significant difference in fluoroscopy radiation dose (10.4 Gy · cm(2) ± 10.6 for cone-beam CT fluoroscopy, 2.3 Gy · cm(2) ± 2.4 for AR, and 3.3 Gy · cm(2) ± 4.6 for AR with MC [P < .05]) and therefore in total procedural radiation dose (20.5 Gy · cm(2) ± 13.4 for cone-beam CT fluoroscopy, 12.6 Gy · cm(2) ± 5.3 for AR, 13.6 Gy · cm(2) ± 7.4 for AR with MC [P < .05]). Conclusion Use of an AR C-arm system reduces radiation dose while maintaining navigational accuracy compared with cone-beam CT fluoroscopy during image-guided percutaneous needle placement in a pig model. (©) RSNA, 2016 Online supplemental material is available for this article.