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Purpose: Up to date, there has been a lack of software infrastructure to connect 3D Slicer to any augmented reality (AR) device. This work describes a novel connection approach using Microsoft HoloLens 2 and OpenIGTLink, with a demonstration in pedicle screw placement planning. Methods: We developed an AR application in Unity that is wirelessly rendered onto Microsoft HoloLens 2 using Holographic Remoting. Simultaneously, Unity connects to 3D Slicer using the OpenIGTLink communication protocol. Geometrical transform and image messages are transferred between both platforms in real time. Through the AR glasses, a user visualizes a patient’s computed tomography overlaid onto virtual 3D models showing anatomical structures. We technically evaluated the system by measuring message transference latency between the platforms. Its functionality was assessed in pedicle screw placement planning. Six volunteers planned pedicle screws' position and orientation with the AR system and on a 2D desktop planner. We compared the placement accuracy of each screw with both methods. Finally, we administered a questionnaire to all participants to assess their experience with the AR system. Results: The latency in message exchange is sufficiently low to enable real-time communication between the platforms. The AR method was non-inferior to the 2D desktop planner, with a mean error of 2.1 ± 1.4 mm. Moreover, 98% of the screw placements performed with the AR system were successful, according to the Gertzbein–Robbins scale. The average questionnaire outcomes were 4.5/5. Conclusions: Real-time communication between Microsoft HoloLens 2 and 3D Slicer is feasible and supports accurate planning for pedicle screw placement.

Purpose: Augmented Reality (AR) has the potential to simplify ultrasound (US) examinations which usually require a skilled and experienced sonographer to mentally align narrow 2D cross-sectional US images in the 3D anatomy of the patient. This work describes and evaluates a novel approach to track retroreflective spheres attached to the US probe using an inside-out technique with the AR glasses HoloLens 2. Finally, live US images are displayed in situ on the imaged anatomy. Methods: The Unity application UltrARsound performs spatial tracking of the US probe and attached retroreflective markers using the depth camera integrated into the AR glasses—thus eliminating the need for an external tracking system. Additionally, a Kalman filter is implemented to improve the noisy measurements of the camera. US images are streamed wirelessly via the PLUS toolkit to HoloLens 2. The technical evaluation comprises static and dynamic tracking accuracy, frequency and latency of displayed images. Results: Tracking is performed with a median accuracy of 1.98 mm/1.81${}^{\circ }$\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ $$\end{document}for the static setting when using the Kalman filter. In a dynamic scenario, the median error was 2.81 mm/1.70${}^{\circ }$\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ $$\end{document}. The tracking frequency is currently limited to 20 Hz. 83% of the displayed US images had a latency lower than 16 ms. Conclusions: In this work, we showed that spatial tracking of retroreflective spheres with the depth camera of HoloLens 2 is feasible, achieving a promising accuracy for in situ visualization of live US images. For tracking, no additional hardware nor modifications to HoloLens 2 are required making it a cheap and easy-to-use approach. Moreover, a minimal latency of displayed images enables a real-time perception for the sonographer.

ABSTRACTCurrent approaches for surgical correction of craniosynostosis are highly dependent on the experience of the surgeon and inaccuracies during cranial vault remodelling can compromise the surgical outcome. The objective of this study is the evaluation of a novel augmented reality system to guide surgeons during fronto-orbital advancement procedures. A smartphone software application was developed to overlay virtual models on the surgical field using augmented reality technology. Intraoperative markers and 3D photography are used to ensure accurate alignment between the virtual data and patient anatomy. The system was evaluated through simulations on patient-specific phantoms and the workflow was tested on two real surgeries. Results of this study demonstrate the accuracy of the AR visualisation to guide osteotomy and remodelling during fronto-orbital advancement. Feedback from 9 surgeons supports the integration of this technology on the surgical workflow for the treatment of craniosynostosis to accurately translate the virtual plan into the operating room.

Purpose: 3D-printed patient-specific instruments have become a useful tool to improve accuracy in pelvic tumour resections. However, their correct placement can be challenging in some regions due to the morphology of the bone, so it is essential to be aware of the possible placement errors in each region. In this study, we characterize these errors in common pelvic osteotomies. Methods: We conducted an experiment with 9 cadaveric specimens, for which we acquired a pre-operative computed tomography scan. Small PSIs were designed for each case following a realistic surgical approach for four regions of the pelvis: iliac crest (C), supra-acetabular (S), ischial (I), and pubic (P). Final surgical placement was based on a post-operative scan. The resulting positions were compared with pre-operative planning, obtaining translations, rotations, and maximum osteotomy deviations in a local reference frame defined based on the bone’s morphology. Results: Mean translations and rotations in the direction of the osteotomy plane were as follows: C= 5.3 mm, 6.7°; S= 1.8 mm, 5.1°; I= 1.5 mm, 3.4°; P= 1.8 mm, 3.5°. Mean translations in the remaining axes were below 2 mm. Maximum osteotomy deviations (75% of cases) were below 11.8 mm in C(7.8 mm for half-length), 7.8 mm in S(5.5 mm for half-length), 5.5 mm in I, and 3.7 mm in P. Conclusion: We have characterized placement errors for small PSIs in four regions of the pelvis. Our results show high errors in Cand SPSIs in the direction of the resection plane’s normal, and thus large osteotomy deviations. Deviations in short osteotomies in S, Iand Pand placement errors in the remaining directions were low. The PSIs used in this study are biocompatible and can be produced with a desktop 3D printer, thus minimizing manufacturing cost.

Purpose: Surgical correction of metopic craniosynostosis typically involves open cranial vault remodeling. Accurate translation of the virtual surgical plan into the operating room is challenging due to the lack of tools for intraoperative analysis of the surgical outcome. This study aimed to evaluate the feasibility of using a hand-held 3D photography device for intraoperative evaluation and guidance during cranial vault surgical reconstruction. Methods: A hand-held structured light scanner was used for intraoperative 3D photography during five craniosynostosis surgeries, obtaining 3D models of skin and bone surfaces before and after the remodeling. The accuracy of this device for 3D modeling and morphology quantification was evaluated using preoperative computed tomography imaging as gold-standard. In addition, the time required for intraoperative 3D photograph acquisition was measured. Results: The average error of intraoperative 3D photography was 0.30 mm. Moreover, the interfrontal angle and the transverse forehead width were accurately measured in the 3D photographs with an average error of 0.72 degrees and 0.62 mm. Surgeon’s feedback indicates that this technology can be integrated into the surgical workflow without substantially increasing surgical time. Conclusion: Hand-held 3D photography is an accurate technique for objective quantification of intraoperative cranial vault morphology and guidance during metopic craniosynostosis surgical reconstruction. This noninvasive technique does not substantially increase surgical time and does not require exposure to ionizing radiation, presenting a valuable alternative to computed tomography imaging. The proposed methodology can be integrated into the surgical workflow to assist during cranial vault remodeling and ensure optimal surgical outcomes.

The pattern of brain metabolic changes produced by olanzapine has yet to be described, despite the theoretical and clinical interest of this new antipsychotic. We studied a group of 17 schizophrenic patients who underwent two 18fluoro-deoxyglucose-positron emmission tomography (FDG-PET) studies under two different conditions a baseline scan during treatment with either conventional antipsychotics (n15) or risperidone (n2) and a second scan performed 17–24 weeks after switching to olanzapine. PET scans were obtained while performing a standard cognitive paradigm (Continuous Performance Test) and analysed by means of Statistical Parametric Mapping. No significant metabolic changes were found in the comparison between pre- and post-olanzapine conditions. A brain map of the statistical power of our design showed that changes up to 3 in the frontal and up to 8 in the occipital region were not likely to exist (1–0.8). The degree of improvement in positive symptoms was related to the amount of activity decrease in the right orbital region and to the amount of activity increase in the primary visual area. Improvement in negative symptoms was associated with an activity increase in the dorsal prefrontal cortex, and a higher baseline activity in both temporal poles. These correlation patterns suggest that the functional mechanism of action of olanzapine may share traits from both typical and atypical neuroleptics.

The interpretation of the huge number of results in schizophrenia research using neuroimaging is uncertain. However, the simultaneous use of complimentary data obtained with these techniques may yield more relevant information in this regard. In this paper, we present a series of studies performed by our group in two schizophrenic samples with the use of structural (magnetic resonance imaging (MRI), functional [glucose positron emission tomography (PET) and N-acetylaspartate (NAA) magnetic resonance spectroscopy] and neurophysiological techniques (the P300 event-related potential). Transversal and longitudinal measurements were performed. The integrated vision of the results so obtained allows us to propose the hypothesis of a neurodevelopmentally determined state of prefrontal disinhibition, in which the degree of atrophy would directly relate to the metabolic rate. This state would already be present in the first stages of illness and could have neurotoxic consequences in the long term. This would explain the findings of an association between sulcal cerebrospinal fluid (CSF) and illness duration and decreased NAA levels in chronic but not in recent-onset cases. The prefrontal disinhibition would over stimulate the limbic system and the hippocampus would become over activated, the metabolic rate at this level being inversely related to P300 amplitude. Clozapine showed a more selective and intense action on that hyperactive metabolic tone than haloperidol.