Evaluation of the precision of navigation-assisted endoscopy according to the navigation tool setup and the type of endoscopes.

OBJECT: Preoperative image-based neuronavigation-assisted endoscopy during intracranial procedures is gaining great interest. This study aimed to analyze the precision of navigation-assisted endoscopy according to the navigation setup, the type of optic and its working angulation. METHODS: A custom-made box with four screws was referenced. The navigation-assisted endoscope was aligned on the screws (targets). The precision on the navigation screen was defined as the virtual distance-to-target between the tip of the endoscope and the center of the screws. Three modifiers were assessed: (1) the distance D between the box and the reference array (CLOSE 13 cm - MIDDLE 30 cm - FAR 53 cm), (2) the distance between the tip of the endoscope and the navigation array on the endoscope (close 5 cm - middle 10 cm - far 20 cm), (3) the working angulation of the endoscope (0°-endoscope and 30°-endoscope angled at 90° and 45° with the box). RESULTS: The median precision was 1.3 mm (Q1: 1.1; Q3: 1.7) with the best setting CLOSE/close. The best setting in surgical condition (CLOSE/far) showed a distance-to-target of 2.3 mm (Q1: 1.9; Q3: 2.5). The distance D was correlated to the precision (Spearman rho = 0.82), but not the distance d (Spearman rho = 0.04). The type of optic and its angulation with the box were also correlated to the precision (Spearman rho = - 0.37). The best setting was the use of a 30°-endoscope angled at 45° (1.4 mm (Q1: 1.0; Q3: 1.9)). CONCLUSION: Navigated-assisted endoscopy is feasible and offers a good precision. The navigation setup should be optimized, reducing the risk of inadvertent perifocal damage.

Evaluation of the effect of standard neuronavigation and augmented reality on the integrity of the perifocal structures during a neurosurgical approach.

OBJECTIVE: Intracranial minimally invasive procedures imply working in a restricted surgical corridor surrounded by critical structures, such as vessels and cranial nerves. Any damage to them may affect patient outcome. Neuronavigation systems may reduce the risk of such complications. In this study, the authors sought to compare standard neuronavigation (NV) and augmented reality (AR)-guided navigation with respect to the integrity of the perifocal structures during a neurosurgical approach using a novel model imitating intracranial vessels. METHODS: A custom-made box, containing crisscrossing hard metal wires, a hidden nail at its bottom, and a wooden top, was scanned, fused, and referenced for the purpose of the study. The metal wires and an aneurysm clip applier were connected to a controller, which counted the number of contacts between them. Twenty-three naive participants were asked to 1) use NV to define an optimal entry point on the top, perform the smallest craniotomy possible on the wooden top, and to use a surgical microscope when placing a clip on the nail without touching the metal wires; and 2) use AR to preoperatively define an ideal trajectory, navigate the surgical microscope, and then perform the same task. The primary outcome was the number of contacts made between the metal wires and the clip applier. Secondary outcomes were craniotomy size, and trust in NV and AR to help avoid touching the metal wires, as assessed by a 9-level Likert scale. RESULTS: The median number of contacts tended to be lower with the use of AR than with NV (AR, median 1 [Q1: 1, Q3: 2]; NV, median 3 [Q1: 1, Q3: 6]; p = 0.074). The size of the target-oriented craniotomy was significantly lower with the use of AR compared with NV (AR, median 4.91 cm2 [Q1: 4.71 cm2, Q3: 7.55 cm2]; and NV, median 9.62 cm2 [Q1: 7.07 cm2; Q3: 13.85 cm2]). Participants had more trust in AR than in NV (the differences posttest minus pretest were mean 0.9 [SD 1.2] and mean -0.3 [SD 0.2], respectively; p < 0.05). CONCLUSIONS: The results of this study show a trend favoring the use of AR over NV with respect to reducing contact between a clip applier and the perifocal structures during a simulated clipping of an intracranial aneurysm. Target-guided craniotomies were smaller with the use of AR. AR may be used not only to localize surgical targets but also to prevent complications associated with damage to structures encountered during the surgical approach.

Evaluation of the precision of operative augmented reality compared to standard neuronavigation using a 3D-printed skull.

OBJECTIVE: Augmented reality (AR) in cranial surgery allows direct projection of preregistered overlaid images in real time on the microscope surgical field. In this study, the authors aimed to compare the precision of AR-assisted navigation and standard pointer-based neuronavigation (NV) by using a 3D-printed skull in surgical conditions. METHODS: A commercial standardized 3D-printed skull was scanned, fused, and referenced with an MR image and a CT scan of a patient with a 2 × 2-mm right frontal sinus defect. The defect was identified, registered, and integrated into NV. The target was physically marked on the 3D-printed skull replicating the right frontal sinus defect. Twenty-six subjects participated, 25 of whom had no prior NV or AR experience and 1 with little AR experience. The subjects were briefly trained in how to use NV, AR, and AR recalibration tools. Participants were asked to do the following: 1) "target the center of the defect in the 3D-printed skull with a navigation pointer, assisted only by NV orientation," and 2) "use the surgical microscope and AR to focus on the center of the projected object" under conventional surgical conditions. For the AR task, the number of recalibrations was recorded. Confidence regarding NV and AR precision were assessed prior to and after the experiment by using a 9-level Likert scale. RESULTS: The median distance to target was statistically lower for AR than for NV (1 mm [Q1: 1 mm, Q3: 2 mm] vs 3 mm [Q1: 2 mm, Q3: 4 mm] [p < 0.001]). In the AR task, the median number of recalibrations was 4 (Q1: 4, Q3: 4.75). The number of recalibrations was significantly correlated with the precision (Spearman rho: -0.71, p < 0.05). The trust assessment after performing the experiment scored a median of 8 for AR and 5.5 for NV (p < 0.01). CONCLUSIONS: This study shows for the first time the superiority of AR over NV in terms of precision. AR is easy to use. The number of recalibrations performed using reference structures increases the precision of the navigation. The confidence regarding precision increases with experience.