Effects of Augmented Reality on Thoracolumbar Pedicle Screw Instrumentation Across Different Levels of Surgical Experience.

OBJECTIVE: Augmented reality (AR) is an emerging technology that may accelerate skill acquisition and improve accuracy of thoracolumbar pedicle screw placements. We aimed to quantify the relative assistance of AR compared with freehand (FH) pedicle screw accuracy across different surgical experience levels. METHODS: A spine fellowship-trained and board-certified attending neurosurgeon, postgraduate year 4 neurosurgery resident, and second-year medical student placed 32 FH and 32 AR-assisted thoracolumbar pedicle screws in 3 cadavers. A cableless, voice-activated AR system was paired with a headset. Accuracy was assessed using χ2 analysis and the Gertzbein-Robbins scale. Angular error, distance error, and time per pedicle screw were collected and compared. RESULTS: The attending neurosurgeon had 91.6% (11/12) clinically acceptable (Gertzbein-Robbins scale A or B) insertion in both FH and AR groups; the resident neurosurgeon had 100% (9/9) FH and AR in both cases; the medical student had 72.3% (8/11) FH accuracy and 81.8% (9/11) AR accuracy. The medical student displayed significantly lower ideal (Gertzbein-Robbins scale A) FH accuracy compared with the resident neurosurgeon (P = 0.017) and attending neurosurgeon (P = 0.005), but no difference when using AR. FH screw placement was faster by both the attending neurosurgeon (median 46 seconds vs. 94.5 seconds, P = 0.0047) and the neurosurgery resident neurosurgeon (median 144 seconds vs. 140 seconds, P = 0.05). Total clinically acceptable AR and FH accuracy was 90.6% (29/32) and 87.5% (28/32), respectively (P = 0.69). CONCLUSIONS: AR screw placement allowed an inexperienced medical student to double their accuracy in 1 training session. With subsequent iterations, this promising technology could serve as an important tool for surgical training.

Improved Accuracy and Lowered Learning Curve of Ventricular Targeting Using Augmented Reality-Phantom and Cadaveric Model Testing.

BACKGROUND: Augmented reality (AR) has demonstrated significant potential in neurosurgical cranial, spine, and teaching applications. External ventricular drain (EVD) placement remains a common procedure, but with error rates in targeting between 10% and 40%. OBJECTIVE: To evaluate Novarad VisAR guidance system for the placement of EVDs in phantom and cadaveric models. METHODS: Two synthetic ventricular phantom models and a third cadaver model underwent computerized tomography imaging and registration with the VisAR system (Novarad). Root mean square (RMS), angular error (γ), and Euclidian distance were measured by multiple methods for various standard EVD placements. RESULTS: Computerized tomography measurements on a phantom model (0.5-mm targets showed a mean Euclidean distance error of 1.20 ± 0.98 mm and γ of 1.25° ± 1.02°. Eight participants placed EVDs in lateral and occipital burr holes using VisAR in a second phantom anatomic ventricular model (mean RMS: 3.9 ± 1.8 mm, γ: 3.95° ± 1.78°). There were no statistically significant differences in accuracy for postgraduate year level, prior AR experience, prior EVD experience, or experience with video games ( P > .05). In comparing EVDs placed with anatomic landmarks vs VisAR navigation in a cadaver, VisAR demonstrated significantly better RMS and γ, 7.47 ± 0.94 mm and 7.12° ± 0.97°, respectively ( P ≤ .05). CONCLUSION: The novel VisAR AR system resulted in accurate placement of EVDs with a rapid learning curve, which may improve clinical treatment and patient safety. Future applications of VisAR can be expanded to other cranial procedures.

Augmented Reality Spine Surgery Navigation: Increasing Pedicle Screw Insertion Accuracy for Both Open and Minimally Invasive Spine Surgeries.

STUDY DESIGN: Collectively, seven cadavers were instrumented with 124 thoracolumbar pedicle screws using VisAR augmented reality/guidance. Sixty-five screws were inserted into four donors using open dissection spine surgery. Fifty-nine screws were positioned in three donors with a minimally invasive spine surgery (MISS) procedure. For both open and MISS, VisAR was used exclusively for pedicle screw navigation. OBJECTIVE: The objective of this study was to determine the accuracy of pedicle screw placement using VisAR for open spine and MISS procedures. SUMMARY OF BACKGROUND DATA: Pedicle screw placement can be challenging depending on anatomical location and a surgeon's experience. AR may minimize fluoroscopy use and speed screw insertion. METHODS: Prior to computed tomography (CT) a series of four image visible April Tag optical fiducials were attached to the backs' of the donors. Resulting images were used preoperatively for planned virtual pedicle screw pathways including entry point, trajectory, and depth. The study link was encrypted on a quick response (QR) code, printed, and viewed in the operating room (OR) by the surgeon using VisAR (HoloLens 2 headset). Viewing the code wirelessly uploads and launches the study, converting the DICOM data to holographic images which register to the fiducials on the donor's back. The annotated pathways for each pedicle were called up by voice command and the surgeon positioned each screw by aligning with the virtual guidance hologram. RESULTS: Overall, 124 pedicle screws were inserted with VisAR navigation with 96% accuracy (Gertzbein-Robbins grades A and B). The combined angle of error was 2.4° and the distance error was 1.9 mm. CONCLUSION: Augmented reality is a highly accurate, emerging technology for navigating both open and minimally invasive spine surgery techniques with off-the-shelf headset hardware. LEVEL OF EVIDENCE: N/A.

The application of augmented reality-based navigation for accurate target acquisition of deep brain sites: advances in neurosurgical guidance.

OBJECTIVE: The objective of this study is to quantify the navigational accuracy of an advanced augmented reality (AR)-based guidance system for neurological surgery, biopsy, and/or other minimally invasive neurological surgical procedures. METHODS: Five burr holes were drilled through a plastic cranium, and 5 optical fiducials (AprilTags) printed with CT-visible ink were placed on the frontal, temporal, and parietal bones of a human skull model. Three 0.5-mm-diameter targets were mounted in the interior of the skull on nylon posts near the level of the tentorium cerebelli and the pituitary fossa. The skull was filled with ballistic gelatin to simulate brain tissue. A CT scan was taken and virtual needle tracts were annotated on the preoperative 3D workstation for the combination of 3 targets and 5 access holes (15 target tracts). The resulting annotated study was uploaded to and launched by VisAR software operating on the HoloLens 2 holographic visor by viewing an encrypted, printed QR code assigned to the study by the preoperative workstation. The DICOM images were converted to 3D holograms and registered to the skull by alignment of the holographic fiducials with the AprilTags attached to the skull. Five volunteers, familiar with the VisAR, used the software/visor combination to navigate an 18-gauge needle/trocar through the series of burr holes to the target, resulting in 70 data points (15 for 4 users and 10 for 1 user). After each attempt the needle was left in the skull, supported by the ballistic gelatin, and a high-resolution CT was taken. Radial error and angle of error were determined using vector coordinates. Summary statistics were calculated individually and collectively. RESULTS: The combined angle of error of was 2.30° ± 1.28°. The mean radial error for users was 3.62 ± 1.71 mm. The mean target depth was 85.41 mm. CONCLUSIONS: The mean radial error and angle of error with the associated variance measures demonstrates that VisAR navigation may have utility for guiding a small needle to neural lesions, or targets within an accuracy of 3.62 mm. These values are sufficiently accurate for the navigation of many neurological procedures such as ventriculostomy.

Use of augmented reality for image-guided spine procedures.

PURPOSE: Because of its ability to superimpose imaging data on a patient, while anchoring the user's view to the immediate surroundings, augmented reality (AR) has the potential to dramatically improve the accuracy and reduce the time required for preoperative planning and performance of minimally invasive spine surgeries and procedures. Described and reported herein is the direct clinical application of AR navigation on a series of common percutaneous image-guided spine procedures. MATERIALS AND METHODS: AR, including a "virtual needle" (VN) asset, was used to guide and navigate a total of 18 procedures performed on 10 patients. Comparative control data were generated using a phantom model (n = 32). These data are used to determine the accuracy of AR for federal drug administration submissions. Optical codes were implemented to allow automatic and real-time registration. A manual process was used when the use of optical codes was not available. Target error, distance to the target and target size were measured for both phantom and clinical groups. Mean errors between the two groups were compared. RESULTS: Target error between the control and clinical data sets showed no significant difference. Moreover, the distance to the target site and the target size had no effect on target acquisition. CONCLUSIONS: This data set suggests that AR navigation, utilizing a VN, is an emerging, accurate, valuable additive method for surgical and procedural planning for percutaneous image-guided spinal procedures and has potential to be applied to a broad range of clinical and surgical applications.

Outcomes of Yttrium-90 Radioembolization for Unresectable Combined Biphenotypic Hepatocellular-Cholangiocarcinoma.

PURPOSE: To evaluate outcomes of yttrium-90 radioembolization in patients with combined biphenotypic hepatocellular-cholangiocarcinoma (cHCC-CC). MATERIALS AND METHODS: A retrospective review of patients with biopsy-confirmed cHCC-CC treated with yttrium-90 radioembolization between 2012 and 2018 was performed. Twenty-two patients with cHCC-CC (mean age 65.6 y, 17 men, 5 women) underwent 29 radioembolization treatments (5 resin, 24 glass microspheres). Survival data were available in 21 patients, and hepatic imaging response data were available in 20 patients. Hepatic imaging response to radioembolization was assessed on follow-up CT or MR imaging using modified Response Evaluation Criteria In Solid Tumours criteria. Univariate stepwise Cox regression analysis was used to evaluate the association between demographic and clinical factors and survival. Logistic regression evaluated associations between clinical factors and response to treatment, overall response, and disease control. RESULTS: Hepatic imaging response was as follows: 15% complete response, 40% partial response, 10% stable disease, and 35% progressive disease (55% response rate, 65% disease control rate). Two patients were downstaged or bridged to transplant, and 1 patient was downstaged to resection. Median overall survival was 9.3 mo (range, 2.5-31.0 mo) from time of radioembolization. Nonreponse to treatment, bilobar disease, presence of multiple tumors, and elevated carbohydrate antigen 19-9 before treatment were associated with reduced survival after radioembolization. CONCLUSIONS: Radioembolization is a viable option for locoregional control of cHCC-CC with good response and disease control rates.

The use of a binary chelate formulation: Could gadolinium based linear contrast agents be rescued by the addition of zinc selective chelates?

Tissue and bone retention of gadolinium based contrast agents (GBCAs) has become a clinical concern because of the potential short and long term toxic effects of free gadolinium. This is a critical problem for most open-chain agents that more readily transmetallate in vivo, in comparison to macrocyclic compounds. Gadolinium diethylene tri-aminepentaacetic acid bis-glucosamide (Gd-DTPA-BIGA) is an experimental, open-chain contrast agent which has a significantly increased relaxivity coefficient in comparison to other GBCAs. This results in greater signal intensity and improved contrast enhancement. These superior imaging qualities initiated a search for a solution to the transmetallation of this agent. Plasma zinc is a well-known GBCA transmettalation agent. Since the base chelate of Gadodiamide (Gd-DPTA-Bis-Methylamide or Omniscan), DTPA-Bis-Methylamide (DTPA-BMA), readily transmettalates with and binds serum zinc, we hypothesized that a plasma "zinc sink," may significantly reduce transmetallation of linear agents. 5% DTPA-BMA was added to a formulation of Gd-DTPA-BIGA, which was tested against the original formulation of Gd-DTPA-BIGA with 0.2% of the base chelate DTPA-BIGA. These formulations, including gadodiamide, were labeled with 153GdCl3 followed by infusion into cohorts of Sprague Dawley rats which were sacrificed at 1, 30 and 60 days. Internal organs were harvested, along with blood, skin and femur, and analyzed for residual gadolinium. A subset of tissues were also interrogated with ICP-MS. Labeled Gadodiamide and saline where used as controls. Conclusion: The addition of 5% DTPA-BMA, as a zinc binding agent, reduced the transmetallation of the linear agent Gd-DTPA-BIGA, in comparison to its original formulation supplemented with 0.2% BIGA. This result indicates that supplementing linear GBCAs with ancillary chelates may hold promise for reducing, or eliminating the biological archiving of gadolinium in tissues. In addition, this paper provides valuable animal data on the long term retention of gadolinium from linear based contrast agents.

Whole-Body Computed Tomography-Based Body Mass and Body Fat Quantification: A Comparison to Hydrostatic Weighing and Air Displacement Plethysmography.

OBJECTIVE: We correlate and evaluate the accuracy of accepted anthropometric methods of percent body fat (%BF) quantification, namely, hydrostatic weighing (HW) and air displacement plethysmography (ADP), to 2 automatic adipose tissue quantification methods using computed tomography (CT). METHODS: Twenty volunteer subjects (14 men, 6 women) received head-to-toe CT scans. Hydrostatic weighing and ADP were obtained from 17 and 12 subjects, respectively. The CT data underwent conversion using 2 separate algorithms, namely, the Schneider method and the Beam method, to convert Hounsfield units to their respective tissue densities. The overall mass and %BF of both methods were compared with HW and ADP. RESULTS: When comparing ADP to CT data using the Schneider method and Beam method, correlations were r = 0.9806 and 0.9804, respectively. Paired t tests indicated there were no statistically significant biases. Additionally, observed average differences in %BF between ADP and the Schneider method and the Beam method were 0.38% and 0.77%, respectively. The %BF measured from ADP, the Schneider method, and the Beam method all had significantly higher mean differences when compared with HW (3.05%, 2.32%, and 1.94%, respectively). CONCLUSIONS: We have shown that total body mass correlates remarkably well with both the Schneider method and Beam method of mass quantification. Furthermore, %BF calculated with the Schneider method and Beam method CT algorithms correlates remarkably well with ADP. The application of these CT algorithms have utility in further research to accurately stratify risk factors with periorgan, visceral, and subcutaneous types of adipose tissue, and has the potential for significant clinical application.

Volumetric analysis of central body fat accurately predicts incidence of diabetes and hypertension in adults.

BACKGROUND: Central adipose tissue is appreciated as a risk factor for cardiometabolic disorders. The purpose of this study was to determine the efficacy of a volumetric 3D analysis of central adipose tissue in predicting disease. Full body computerized tomography (CT) scans were obtained from 1225 female (518) and male (707) subjects, aged 18-88. Percent central body fat (%cBF) was determined by quantifying the adipose tissue volume from the dome of the liver to the pubic symphysis. Calcium score was determined from the calcium content of coronary arteries. Relationships between %cBF, BMI, and several cardiometabolic disorders were assessed controlling for age, sex, and race. RESULTS: Higher %cBF was significantly greater for those with type 2 diabetes and hypertension, but not stroke or hypercholesterolemia. Simple anthropometric determination of BMI equally correlated with diabetes and hypertension as central body fat. Calcium scoring significantly correlated with all measurements of cardiovascular health, including hypertension, hypercholesterolemia, and heart disease. CONCLUSIONS: Central body fat and BMI equally and highly predict incidence of hypertension and type 2 diabetes.

Comparison of Gd(DTPA-BMA) (Omniscan) versus Gd(HP-DO3A) (ProHance) relative to gadolinium retention in human bone tissue by inductively coupled plasma mass spectroscopy.

OBJECTIVE: The objective of this study was to determine the gadolinium (Gd) concentration remaining in human bone tissue after administration of standard clinical doses of 2 Gd-based contrast agents: ProHance and Omniscan. MATERIALS AND METHODS: After administration of 0.1 mmol/kg of Gd chelate to patients undergoing hip replacement surgery, bone specimens were collected and analyzed, and compared with an age-matched control population without a history of Gd chelate administration. Bone specimens were collected fresh, refrigerated, and subsequently frozen. After grinding and freeze-drying, tissue digestion was performed using Teflon bombs and concentrated nitric acid. A method for analysis of Gd in bone specimens was developed and validated using inductively coupled plasma mass spectroscopy (ICP-MS). RESULTS: Results were compared with a previous study using a different technique for analysis of the same tissue specimens. Tissue retention was 1.77+/-0.704 microg Gd/g bone (n=9) for Omniscan and 0.477+/-0.271 microg Gd/g bone (n=10) for ProHance measured by ICP-MS. These findings confirmed results from the previous ICP-AES study. CONCLUSION: Omniscan (Gd[DTPA-BMA]) left approximately 4 times (previous study 2.5 times) more Gd behind in bone than did ProHance (Gd[HP-DO3A]).

Basic principles of magnetic resonance imaging.

We have come full circle from spinning quarks to 3D medical images. The bulk of MRI is now performed using slice-selective gradients, during which RF energy is applied to excite the hydrogen nuclei. By stepping a phase-encoding gradient during each TR and using a frequency-encoding gradient as the data are sampled, the 3D human object can be reduced to many individual points or voxels. By acquiring multiple slices at once, the time efficiency of imaging can be vastly improved. Many newer strategies use variations of this technique to acquire multiple lines of data during a single echo, enshrining spin warp imaging as the most important method of signal acquisition for MRI.

Comparison of Gd DTPA-BMA (Omniscan) versus Gd HP-DO3A (ProHance) retention in human bone tissue by inductively coupled plasma atomic emission spectroscopy.

RATIONALE AND OBJECTIVES: Human bone tissue was collected following administration of a clinical dose of gadolinium chelate (0.1 mmol per kg) to patients undergoing hip joint replacement surgery to determine if measurable differences in Gd deposition occur between 2 widely available magnetic resonance contrast agents. MATERIALS AND METHODS: Gd HP-DO3A (ProHance), Gd DTPA-BMA (Omniscan), and an age-matched control population without history of gadolinium chelate administration were compared. Bone samples were collected fresh, placed in refrigeration, and subsequently frozen. Tissue digestion was performed using a microwave tissue digester and concentrated nitric acid. A method of tissue analysis was created for gadolinium using inductivity coupled plasma atomic emission spectroscopy (ICP-AES). RESULTS: Tissue retention was 1.18 +/- .787 microg Gd/g bone (N = 10) for Omniscan and 0.466 +/- .387 microg Gd/g bone (N = 8) for ProHance measured by ICP-AES. CONCLUSION: Omniscan (Gd DTPA-BMA) left 2.5 times more Gd behind in bone than did ProHance (Gd HP-DO3A).