Image-guided surgery: what is the accuracy?

More than meets the eye: Augmented reality in surgical oncology

BACKGROUND AND OBJECTIVES

In the field of surgical oncology, there has been a desire for innovative techniques to improve tumor visualization, resection, and patient outcomes. Augmented reality (AR) technology superimposes digital content onto the real-world environment, enhancing the user's experience by blending digital and physical elements. A thorough examination of AR technology in surgical oncology has yet to be performed.

METHODS

A scoping review of intraoperative AR in surgical oncology was conducted according to the guidelines and recommendations of The Preferred Reporting Items for Systematic Review and Meta-analyzes Extension for Scoping Reviews (PRISMA-ScR) framework. All original articles examining the use of intraoperative AR during surgical management of cancer were included. Exclusion criteria included virtual reality applications only, preoperative use only, fluorescence, AR not specific to surgical oncology, and study design (reviews, commentaries, abstracts).

RESULTS

A total of 2735 articles were identified of which 83 were included. Most studies (52) were performed on animals or phantom models, while the remaining included patients. A total of 1112 intraoperative AR surgical cases were performed across the studies. The most common anatomic site was brain (20 articles), followed by liver (16), renal (9), and head and neck (8). AR was most often used for intraoperative navigation or anatomic visualization of tumors or critical structures but was also used to identify osteotomy or craniotomy planes.

CONCLUSIONS

AR technology has been applied across the field of surgical oncology to aid in localization and resection of tumors.

OneSLAM to map them all: a generalized approach to SLAM for monocular endoscopic imaging based on tracking any point

PURPOSE

Monocular SLAM algorithms are the key enabling technology for image-based surgical navigation systems for endoscopic procedures. Due to the visual feature scarcity and unique lighting conditions encountered in endoscopy, classical SLAM approaches perform inconsistently. Many of the recent approaches to endoscopic SLAM rely on deep learning models. They show promising results when optimized on singular domains such as arthroscopy, sinus endoscopy, colonoscopy or laparoscopy, but are limited by an inability to generalize to different domains without retraining.

METHODS

To address this generality issue, we propose OneSLAM a monocular SLAM algorithm for surgical endoscopy that works out of the box for several endoscopic domains, including sinus endoscopy, colonoscopy, arthroscopy and laparoscopy. Our pipeline builds upon robust tracking any point (TAP) foundation models to reliably track sparse correspondences across multiple frames and runs local bundle adjustment to jointly optimize camera poses and a sparse 3D reconstruction of the anatomy.

RESULTS

We compare the performance of our method against three strong baselines previously proposed for monocular SLAM in endoscopy and general scenes. OneSLAM presents better or comparable performance over existing approaches targeted to that specific data in all four tested domains, generalizing across domains without the need for retraining.

CONCLUSION

OneSLAM benefits from the convincing performance of TAP foundation models but generalizes to endoscopic sequences of different anatomies all while demonstrating better or comparable performance over domain-specific SLAM approaches. Future research on global loop closure will investigate how to reliably detect loops in endoscopic scenes to reduce accumulated drift and enhance long-term navigation capabilities.

Surgical Navigation in the Anterior Skull Base Using 3-Dimensional Endoscopy and Surface Reconstruction

Importance

Image guidance is an important adjunct for endoscopic sinus and skull base surgery. However, current systems require bulky external tracking equipment, and their use can interrupt efficient surgical workflow.

Objective

To evaluate a trackerless surgical navigation system using 3-dimensional (3D) endoscopy and simultaneous localization and mapping (SLAM) algorithms in the anterior skull base.

Design, Setting, and Participants

This interventional deceased donor cohort study and retrospective clinical case study was conducted at a tertiary academic medical center with human deceased donor specimens and a patient with anterior skull base pathology.

Exposures

Participants underwent endoscopic endonasal transsphenoidal dissection and surface model reconstruction from stereoscopic video with registration to volumetric models segmented from computed tomography (CT) and magnetic resonance imaging.

Main Outcomes and Measures

To assess the fidelity of surface model reconstruction and accuracy of surgical navigation and surface-CT model coregistration, 3 metrics were calculated: reconstruction error, registration error, and localization error.

Results

In deceased donor models (n = 9), high-fidelity surface models of the posterior wall of the sphenoid sinus were reconstructed from stereoscopic video and coregistered to corresponding volumetric CT models. The mean (SD; range) reconstruction, registration, and localization errors were 0.60 (0.24; 0.36-0.93), 1.11 (0.49; 0.71-1.56) and 1.01 (0.17; 0.78-1.25) mm, respectively. In a clinical case study of a patient who underwent a 3D endoscopic endonasal transsphenoidal resection of a tubercular meningioma, a high-fidelity surface model of the posterior wall of the sphenoid was reconstructed from intraoperative stereoscopic video and coregistered to a volumetric preoperative fused CT magnetic resonance imaging model with a root-mean-square error of 1.38 mm.

Conclusions and Relevance

The results of this study suggest that SLAM algorithm-based endoscopic endonasal surgery navigation is a novel, accurate, and trackerless approach to surgical navigation that uses 3D endoscopy and SLAM-based algorithms in lieu of conventional optical or electromagnetic tracking. While multiple challenges remain before clinical readiness, a SLAM algorithm-based endoscopic endonasal surgery navigation system has the potential to improve surgical efficiency, economy of motion, and safety.

The Role of Augmented Reality Neuronavigation in Transsphenoidal Surgery: A Systematic Review

In the field of minimally invasive neurosurgery, microscopic transsphenoidal surgery (MTS) and endoscopic transsphenoidal surgery (ETS) have been widely accepted as a safe approach for pituitary lesions and, more recently, their indications have been extended to lesions at various skull base regions. It is mandatory during transsphenoidal surgery (TS) to identify key anatomical landmarks in the sphenoid sinus and distinguish them from the lesion. Over the years, many intraoperative tools have been introduced to improve the neuronavigation systems aiming to achieve safer and more accurate neurosurgical interventions. However, traditional neuronavigation systems may lose the accuracy of real-time location due to the discrepancy between the actual surgical field and the preoperative 2D images. To deal with this, augmented reality (AR)-a new sophisticated 3D technology that superimposes computer-generated virtual objects onto the user's view of the real world-has been considered a promising tool. Particularly, in the field of TS, AR can minimize the anatomic challenges of traditional endoscopic or microscopic surgery, aiding in surgical training, preoperative planning and intra-operative orientation. The aim of this systematic review is to analyze the potential future role of augmented reality, both in endoscopic and microscopic transsphenoidal surgeries.

Image-to-Patient Registration in Computer-Assisted Surgery of Head and Neck: State-of-the-Art, Perspectives, and Challenges

Today, image-guided systems play a significant role in improving the outcome of diagnostic and therapeutic interventions. They provide crucial anatomical information during the procedure to decrease the size and the extent of the approach, to reduce intraoperative complications, and to increase accuracy, repeatability, and safety. Image-to-patient registration is the first step in image-guided procedures. It establishes a correspondence between the patient's preoperative imaging and the intraoperative data. When it comes to the head-and-neck region, the presence of many sensitive structures such as the central nervous system or the neurosensory organs requires a millimetric precision. This review allows evaluating the characteristics and the performances of different registration methods in the head-and-neck region used in the operation room from the perspectives of accuracy, invasiveness, and processing times. Our work led to the conclusion that invasive marker-based methods are still considered as the gold standard of image-to-patient registration. The surface-based methods are recommended for faster procedures and applied on the surface tissues especially around the eyes. In the near future, computer vision technology is expected to enhance these systems by reducing human errors and cognitive load in the operating room.

Robust H-K Curvature Map Matching for Patient-to-CT Registration in Neurosurgical Navigation Systems

Image-to-patient registration is a coordinate system matching process between real patients and medical images to actively utilize medical images such as computed tomography (CT) during surgery. This paper mainly deals with a markerless method utilizing scan data of patients and 3D data from CT images. The 3D surface data of the patient are registered to CT data using computer-based optimization methods such as iterative closest point (ICP) algorithms. However, if a proper initial location is not set up, the conventional ICP algorithm has the disadvantages that it takes a long converging time and also suffers from the local minimum problem during the process. We propose an automatic and robust 3D data registration method that can accurately find a proper initial location for the ICP algorithm using curvature matching. The proposed method finds and extracts the matching area for 3D registration by converting 3D CT data and 3D scan data to 2D curvature images and by performing curvature matching between them. Curvature features have characteristics that are robust to translation, rotation, and even some deformation. The proposed image-to-patient registration is implemented with the precise 3D registration of the extracted partial 3D CT data and the patient's scan data using the ICP algorithm.

Adverse Events Associated With Image-Guided Sinus Navigation in Endoscopic Sinus Surgery: A MAUDE Database Analysis

OBJECTIVE

The utilization of image-guided navigation during endoscopic sinus surgery (ESS) has increased significantly since its introduction. However, the most common associated complications are still unknown. This study describes and analyzes adverse events related to image-guided ESS.

STUDY DESIGN

Cross-sectional analysis.

SETTING

The Food and Drug Administration's 2018-2022 MAUDE database (Manufacturer and User Facility Device Experience).

METHODS

The MAUDE database was searched for all reports on adverse events involving sinus navigation systems used in ESS from 2018 to 2022. Reported events were reviewed and categorized.

RESULTS

During the study period, there were 1857 adverse events from 1565 reports, which were divided into device-related (n = 1834, 98.8%) and patient-related (n = 23, 1.2%) complications. The most common device-related complications were nonfunctionality of the system (n = 512, 27.9%), device imprecision (n = 427, 23.3%), and device sensing problems (n = 277, 15.1%). The most common patient-related complications were cerebrospinal fluid (CSF) leak (n = 14, 60.9%), intracranial injury (n = 4, 17.4%), and bleeding/hemorrhage (n = 3, 13.1%). Imprecision was associated with increased risk of navigation abortion by the surgeon (odds ratio, 1.50 [95% CI, 1.38-1.65]; P < .001) and increased risk of CSF leak (odds ratio, 16.5 [95% CI, 3.66-74.0]; P < .001) as compared with other device-related complications.

CONCLUSIONS

The most commonly reported device- and patient-related adverse events associated with image-guided sinus navigation systems were device nonfunction, imprecision, device sensing difficulties, and CSF leak. When imprecise navigation occurred, there was an increased likelihood of CSF leak and navigation abortion by the surgeon. Health care providers should be mindful of these possible complications when electing to use image-guided sinus navigation during ESS.

Accuracy and precision of navigated transcranial magnetic stimulation

Objective.Transcranial magnetic stimulation (TMS) induces an electric field (E-field) in the cortex. To facilitate stimulation targeting, image-guided neuronavigation systems have been introduced. Such systems track the placement of the coil with respect to the head and visualize the estimated cortical stimulation location on an anatomical brain image in real time. The accuracy and precision of the neuronavigation is affected by multiple factors. Our aim was to analyze how different factors in TMS neuronavigation affect the accuracy and precision of the coil-head coregistration and the estimated E-field.Approach.By performing simulations, we estimated navigation errors due to distortions in magnetic resonance images (MRIs), head-to-MRI registration (landmark- and surface-based registrations), localization and movement of the head tracker, and localization of the coil tracker. We analyzed the effect of these errors on coil and head coregistration and on the induced E-field as determined with simplistic and realistic head models.Main results.Average total coregistration accuracies were in the range of 2.2-3.6 mm and 1°; precision values were about half of the accuracy values. The coregistration errors were mainly due to head-to-MRI registration with average accuracies 1.5-1.9 mm/0.2-0.4° and precisions 0.5-0.8 mm/0.1-0.2° better with surface-based registration. The other major source of error was the movement of the head tracker with average accuracy of 1.5 mm and precision of 1.1 mm. When assessed within an E-field method, the average accuracies of the peak E-field location, orientation, and magnitude ranged between 1.5 and 5.0 mm, 0.9 and 4.8°, and 4.4 and 8.5% across the E-field models studied. The largest errors were obtained with the landmark-based registration. When computing another accuracy measure with the most realistic E-field model as a reference, the accuracies tended to improve from about 10 mm/15°/25% to about 2 mm/2°/5% when increasing realism of the E-field model.Significance.The results of this comprehensive analysis help TMS operators to recognize the main sources of error in TMS navigation and that the coregistration errors and their effect in the E-field estimation depend on the methods applied. To ensure reliable TMS navigation, we recommend surface-based head-to-MRI registration and realistic models for E-field computations.

Clinical Application of Augmented Reality in Computerized Skull Base Surgery

Cranial base tactics comprise the regulation of tiny and complicated structures in the domains of otology, rhinology, neurosurgery, and maxillofacial medical procedure. Basic nerves and veins are in the nearness of these buildings. Increased the truth is a coming innovation that may reform the cerebral basis approach by supplying vital physical and navigational facts brought together in a solitary presentation. In any case, the awareness and acknowledgment of prospective results of expanding reality frameworks in the cerebral base region are really poor. This article targets examining the handiness of expanded reality frameworks in cranial foundation medical procedures and emphasizes the obstacles that present innovation encounters and their prospective adjustments. A specialized perspective on distinct strategies used being produced of an improved realty framework is furthermore offered. The newest item offers an expansion in interest in expanded reality frameworks that may motivate more secure and practical procedures. In any case, a couple of concerns have to be cared to before that can be for the vast part fused into normal practice.

Marker-less augmented reality based on monocular vision for falx meningioma localization

BACKGROUND

The existing augmented reality (AR) based neuronavigation systems typically require markers and additional tracking devices for model registration, which causes excessive preparatory steps.

METHODS

For fast and accurate intraoperative navigation, this work proposes a marker-less AR system that tracks the head features with the monocular camera. After the semi-automatic initialization process, the feature points between the captured image and the pre-loaded keyframes are matched for obtaining correspondences. The camera pose is estimated by solving the Perspective-n-Point problem.

RESULTS

The localization error of AR visualization on scalp and falx meningioma is 0.417 ± 0.057 and 1.413 ± 0.282 mm, respectively. The maximum localization error is less than 2 mm. The AR system is robust to occlusions and changes in viewpoint and scale.

CONCLUSIONS

We demonstrate that the developed system can successfully display the augmented falx meningioma with enough accuracy and provide guidance for neurosurgeons to locate the tumour in brain.

Image-guided surgery in otolaryngology: A review of current applications and future directions in head and neck surgery

Image-guided surgery (IGS) has become a widely adopted technology in otolaryngology. Since its introduction nearly three decades ago, IGS technology has developed rapidly and improved real-time intraoperative visualization for a diverse array of clinical indications. As usability, accessibility, and clinical experiences with IGS increase, its potential applications as an adjunct in many surgical procedures continue to expand. Here, we describe the basic components of IGS and review both the current state and future directions of IGS in otolaryngology, with attention to current challenges to its application in surgery of the nonrigid upper aerodigestive tract.

International consensus statement on allergy and rhinology: rhinosinusitis 2021

I.

EXECUTIVE SUMMARY

BACKGROUND: The 5 years since the publication of the first International Consensus Statement on Allergy and Rhinology: Rhinosinusitis (ICAR-RS) has witnessed foundational progress in our understanding and treatment of rhinologic disease. These advances are reflected within the more than 40 new topics covered within the ICAR-RS-2021 as well as updates to the original 140 topics. This executive summary consolidates the evidence-based findings of the document.

METHODS

ICAR-RS presents over 180 topics in the forms of evidence-based reviews with recommendations (EBRRs), evidence-based reviews, and literature reviews. The highest grade structured recommendations of the EBRR sections are summarized in this executive summary.

RESULTS

ICAR-RS-2021 covers 22 topics regarding the medical management of RS, which are grade A/B and are presented in the executive summary. Additionally, 4 topics regarding the surgical management of RS are grade A/B and are presented in the executive summary. Finally, a comprehensive evidence-based management algorithm is provided.

CONCLUSION

This ICAR-RS-2021 executive summary provides a compilation of the evidence-based recommendations for medical and surgical treatment of the most common forms of RS.

Evolution and Stagnation of Image Guidance for Surgery in the Lateral Skull: A Systematic Review 1989-2020

Objective: Despite three decades of pre-clinical and clinical research into image guidance solutions as a more accurate and less invasive alternative for instrument and anatomy localization, translation into routine clinical practice for surgery in the lateral skull has not yet happened. The aim of this review is to identify challenges that need to be solved in order to provide image guidance solutions that are safe and beneficial for use during lateral skull surgery and to synthesize factors that facilitate the development of such solutions. Methods: Literature search was conducted via PubMed using terms relating to image guidance and the lateral skull. Data extraction included the following variables: image guidance error, imaging resolution, image guidance system, tracking technology, registration method, study endpoints, clinical target application, and publication year. A subsequent search of FDA 510(k) database for identified image guidance systems and extraction of the year of approval, intended use, and indications for use was performed. The study objectives and endpoints were subdivided in three time phases and summarized. Furthermore, it was analyzed which factors correlated with the image guidance error. Factor values for which an error ≤0.5 mm (μ_error + 3σ_error) was measured in more than one study were identified and inspected for time trends. Results: A descriptive statistics-based summary of study objectives and findings separated in three time intervals is provided. The literature provides qualitative and quantitative evidence that image guidance systems must provide an accuracy ≤0.5 mm (μ_error + 3σ_error) for their safe and beneficial application during surgery in the lateral skull. Spatial tracking accuracy and precision and medical image resolution both correlate with the image guidance accuracy, and all of them improved over the years. Tracking technology with accuracy ≤0.05 mm, computed tomography imaging with slice thickness ≤0.2 mm, and registration based on bone-anchored titanium fiducials are components that provide a sufficient setting for the development of sufficiently accurate image guidance. Conclusion: Image guidance systems must reliably provide an accuracy ≤0.5 mm (μ_error + 3σ_error) for their safe and beneficial use during surgery in the lateral skull. Advances in tracking and imaging technology contribute to the improvement of accuracy, eventually enabling the development and wide-scale adoption of image guidance solutions that can be used safely and beneficially during lateral skull surgery.

Image-guided cochlear access by non-invasive registration: a cadaveric feasibility study

Image-guided cochlear implant surgery is expected to reduce volume of mastoidectomy, accelerate recovery, and improve safety. The purpose of this study was to investigate the safety and effectiveness of image-guided cochlear implant surgery by a non-invasive registration method, in a cadaveric study. We developed a visual positioning frame that can utilize the maxillary dentition as a registration tool and completed the tunnels experiment on 5 cadaver specimens (8 cases in total). The accuracy of the entry point and the target point were 0.471 ± 0.276 mm and 0.671 ± 0.268 mm, respectively. The shortest distance from the margin of the tunnel to the facial nerve and the ossicular chain were 0.790 ± 0.709 mm and 1.960 ± 0.630 mm, respectively. All facial nerves, tympanic membranes, and ossicular chains were completely preserved. Using this approach, high accuracy was achieved in this preliminary study, suggesting that the non-invasive registration method can meet the accuracy requirements for cochlear implant surgery. Based on the above accuracy, we speculate that our method can also be applied to neurosurgery, orbitofacial surgery, lateral skull base surgery, and anterior skull base surgery with satisfactory accuracy.

Positional effect of preoperative neuronavigational magnetic resonance image on accuracy of posterior fossa lesion localization

OBJECTIVE

The aim of this study was to analyze the positional effect of MRI on the accuracy of neuronavigational localization for posterior fossa (PF) lesions when the operation is performed with the patient in the prone position.

METHODS

Ten patients with PF tumors requiring surgery in the prone position were prospectively enrolled in the study. All patients underwent preoperative navigational MRI in both the supine and prone positions in a single session. Using simultaneous intraoperative registration of the supine and prone navigational MR images, the authors investigated the images' accuracy, spatial deformity, and source of errors for PF lesions. Accuracy was determined in terms of differences in the ability of the supine and prone MR images to localize 64 test points in the PF by using a neuronavigation system. Spatial deformities were analyzed and visualized by in-house-developed software with a 3D reconstruction function and spatial calculation of the MRI data. To identify the source of differences, the authors investigated the accuracy of fiducial point localization in the supine and prone MR images after taking the surface anatomy and age factors into consideration.

RESULTS

Neuronavigational localization performed using prone MRI was more accurate for PF lesions than routine supine MRI prior to prone position surgery. Prone MRI more accurately localized 93.8% of the tested PF areas than supine MRI. The spatial deformities in the neuronavigation system calculated using the supine MRI tended to move in the posterior-superior direction from the actual anatomical landmarks. The average distance of the spatial differences between the prone and supine MR images was 6.3 mm. The spatial difference had a tendency to increase close to the midline. An older age (> 60 years) and fiducial markers adjacent to the cervical muscles were considered to contribute significantly to the source of differences in the positional effect of neuronavigation (p < 0.001 and p = 0.01, respectively).

CONCLUSIONS

This study demonstrated the superior accuracy of neuronavigational localization with prone-position MRI during prone-position surgery for PF lesions. The authors recommend that the scan position of the neuronavigational MRI be matched with the surgical position for more precise localization.

Augmented reality-enhanced navigation in endoscopic sinus surgery: A prospective, randomized, controlled clinical trial

OBJECTIVE

Endoscopic sinus surgery represents the gold standard for surgical treatment of chronic sinus diseases. Thereby, navigation systems can be of distinct use. In our study, we tested the recently developed KARL STORZ NAV1 SinusTracker navigation software that incorporates elements of augmented reality (AR) to provide a better preoperative planning and guidance during the surgical procedure.

METHODS

One hundred patients with chronic sinus disease were operated on using either a conventional navigation software (n = 52, non-AR, control group) or a navigation software incorporating AR elements (n = 48, AR, intervention group). Incidence of postoperative complications, duration of surgery, surgeon-reported benefit from the navigation system and patient-reported postoperative rehabilitation were assessed.

RESULTS

The surgeons reported a higher benefit during surgery, used the navigation system for more surgical steps and spent longer time with preoperative image analysis when using the AR system as compared with the non-AR system. No significant differences were seen in terms of postoperative complications, target registration error, operation time and postoperative rehabilitation.

CONCLUSION

The AR enhanced navigation software shows a high acceptance by sinus surgeons in different stages of surgical training and offers potential benefits during surgery without affecting the duration of the operation or the incidence of postoperative complications.

LEVEL OF EVIDENCE

1b.

Image-Guided Surgery and Intraoperative Imaging in Rhinology: Clinical Update and Current State of the Art

INTRODUCTION

Image-guided surgery (IGS) has gained widespread acceptance in otorhinolaryngology for its applications in sinus and skull base surgery. Although the core concepts of IGS have not changed, advances in image guidance technology, including the incorporation of intraoperative imaging, have the potential to enhance surgical education, allow for more rigorous preoperative planning, and aid in more complete surgery with improved outcomes.

OBJECTIVES

Provide a clinical update regarding the use of image guidance and intraoperative imaging in the field of rhinology and endoscopic skull base surgery with a focus on current state of the art technologies.

METHODS

English-language studies published in PubMed, Cochrane, and Embase were searched for articles relating to image-guided sinus surgery, skull base surgery, and intraoperative imaging. Relevant studies were reviewed and critical appraisals were included in this clinical update, highlighting current state of the art advances.

CONCLUSIONS

As image guidance and intraoperative imaging systems have advanced, their applications in sinus and skull base surgery have expanded. Both technologies offer invaluable real-time feedback on the status and progress of surgery, and thus may help to improve the completeness of surgery and overall outcomes. Recent advances such as augmented and virtual reality offer a window into the future of IGS. Future advancements should aim to enhance the surgeon's operative experience by improving user satisfaction and ultimately lead to better surgical results.

Fusion of augmented reality imaging with the endoscopic view for endonasal skull base surgery; a novel application for surgical navigation based on intraoperative cone beam computed tomography and optical tracking

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.

Optical and Optoacoustic Imaging

The present chapter summarizes progress with optical methods that go beyond human vision. The focus is on two particular technologies: fluorescence molecular imaging and optoacoustic (photoacoustic) imaging. The rationale for the selection of these two methods is that in contrast to optical microscopy techniques, both fluorescence and optoacoustic imaging can achieve large fields of view, i.e., spanning several centimeters in two or three dimensions. Such fields of views relate better to human vision and can visualize large parts of tissue, a necessary premise for clinical detection. Conversely, optical microscopy methods only scan millimeter-sized dimensions or smaller. With such operational capacity, optical microscopy methods need to be guided by another visualization technique in order to scan a very specific area in tissue and typically only provide superficial measurements, i.e., information from depths that are of the order of 0.05-1 mm. This practice has generally limited their clinical applicability to some niche applications, such as optical coherence tomography of the retina. On the other hand, fluorescence molecular imaging and optoacoustic imaging emerge as more global optical imaging methods with wide applications in surgery, endoscopy, and non-invasive clinical imaging, as summarized in the following. The current progress in this field is based on a volume of recent review and other literature that highlights key advances achieved in technology and biomedical applications. Context and figures from references from the authors of this chapter have been used here, as it reflects our general view of the current status of the field.

Identifying the Sources of Error When Using 3-Dimensional Printed Head Models with Surgical Navigation

OBJECTIVES

The evaluation of sources of error when preparing, printing, and using 3-dimensional (3D) printed head models for training purposes.

METHODS

Two 3D printed models were designed and fabricated using actual patient imaging data with reference marker points embedded artificially within these models that were then registered to a surgical navigation system using 3 different methods. The first method uses a conventional manual registration, using the actual patient's imaging data. The second method is done by directly scanning the created model using intraoperative computed tomography followed by registering the model to a new imaging dataset manually. The third is similar to the second method of scanning the model but eventually uses an automatic registration technique. The errors for each experiment were then calculated based on the distance of the surgical navigation probe from the respective positions of the embedded marker points.

RESULTS

Errors were found in the preparation and printing techniques, largely depending on the orientation of the printed segment and postprocessing, but these were relatively small. Larger errors were noted based on a couple of variables: if the models were registered using the original patient imaging data as opposed to using the imaging data from directly scanning the model (1.28 mm vs. 1.082 mm), and the accuracy was best using the automated registration techniques (0.74 mm).

CONCLUSION

Spatial accuracy errors occur consistently in every 3D fabricated model. These errors are derived from the fabrication process, the image registration process, and the surgical process of registration.

Cone-Beam Computed Tomography Allows Accurate Registration to Surgical Navigation Systems: A Multidevice Phantom Study

Background

Cone-beam computed tomography (CBCT) is a fast imaging technique with a substantially lower radiation dosage than conventional multidetector computed tomography (MDCT) for sinus imaging. Surgical navigation systems are increasingly being used in endoscopic sinus and skull base surgery, reducing perioperative morbidity.

Objective

To investigate CBCT as a low-radiation imaging modality for use in surgical navigation.

Methods

The required field of view was measured from the tip of the nose to the posterior clinoid process anteroposteriorly and the nasolabial angle to the roof of the frontal sinus superoinferiorly on 50 consecutive MDCT scans (male = 25; age = 17–85 years). A phantom head was manufactured by 3-dimensional printing and imaged using 3 CBCT scanners (Carestream, J Morita, and NewTom), a conventional MDCT scanner (Siemens), and highly accurate laser scanner (FARO). The phantom head was registered to 3 surgical navigation systems (Brainlab, Stryker, and Medtronic) using scans from each system.

Results

The required field of view (mean ± standard deviation) was measured as 107 ± 7.6 mm anteroposteriorly and 90.3 ± 9.6 mm superoinferiorly. Image error deviations from the laser scan (median ± interquartile range) were comparable for MDCT (0.19 ± 0.09 mm) and CBCT (CBCT 1: 0.15 ± 0.11 mm; CBCT 2: 0.33 ± 0.18 mm; and CBCT 3: 0.13 ± 0.13 mm) scanners. Fiducial registration error and target registration error were also comparable for MDCT- and CBCT-based navigation.

Conclusion

CBCT is a low-radiation preoperative imaging modality suitable for use in surgical navigation.

Patient-specific templates for image-guided intervention - a phantom study

Purpose: To evaluate the in vitro accuracy of a new device and method for simultaneous stereotactic CT-guided punctures.Material and methods: 240 needle paths were planned in 1 mm, 1.5 mm and 3 mm slice thickness with a custom-designed software. The data were transferred to a three-axis tabletop CNC machine that then drilled the hole pattern for the needles into square plastic plates. Kirschner wires were slid through the holes of the two parallel fixed plates to aim at the chosen targets inside the phantom. The accuracy was calculated by taking control CTs and measuring the Euclidean distance and the normal distance between the wire and the entry and target point.Results: The mean Euclidean distance of the wire tip to the target for the 1 mm, 1.5mm and 3 mm slice thickness were 2.5 mm (SD ± 0.64), 2.71mm (SD ± 0.78) and 2.8 mm (SD ± 1.0). The mean normal distance was 1.42 mm (SD ± 0.65), 1.43mm (SD ± 0.75) and 1.9 mm (SD ± 1.1), respectively.Conclusion: The system yields satisfactory accuracy comparable to other image-guided intervention systems. Involuntary movements of the patient need to be taken into account in a clinical setting.

On the accuracy of optically tracked transducers for image-guided transcranial ultrasound

PURPOSE

Transcranial focused ultrasound (FUS) is increasingly being explored to modulate neuronal activity. To target neuromodulation, researchers often localize the FUS beam onto the brain region(s) of interest using spatially tracked tools overlaid on pre-acquired images. Here, we quantify the accuracy of optically tracked image-guided FUS with magnetic resonance imaging (MRI) thermometry, evaluate sources of error and demonstrate feasibility of these procedures to target the macaque somatosensory region.

METHODS

We developed an optically tracked FUS system capable of projecting the transducer focus onto a pre-acquired MRI volume. To measure the target registration error (TRE), we aimed the transducer focus at a desired target in a phantom under image guidance, heated the target while imaging with MR thermometry and then calculated the TRE as the difference between the targeted and heated locations. Multiple targets were measured using either an unbiased or bias-corrected calibration. We then targeted the macaque S1 brain region, where displacement induced by the acoustic radiation force was measured using MR acoustic radiation force imaging (MR-ARFI).

RESULTS

All calibration methods enabled registration with TRE on the order of 3 mm. Unbiased calibration resulted in an average TRE of 3.26 mm (min-max: 2.80-4.53 mm), which was not significantly changed by prospective bias correction (TRE of 3.05 mm; 2.06-3.81 mm, p = 0.55). Restricting motion between the transducer and target and increasing the distance between tracked markers reduced the TRE to 2.43 mm (min-max: 0.79-3.88 mm). MR-ARFI images showed qualitatively similar shape and extent as projected beam profiles in a living non-human primate.

CONCLUSIONS

Our study describes methods for image guidance of FUS neuromodulation and quantifies errors associated with this method in a large animal. The workflow is efficient enough for in vivo use, and we demonstrate transcranial MR-ARFI in vivo in macaques for the first time.

Missed paranasal sinus compartments in sinus surgery with and without image-guidance systems: a pilot feasibility study

PURPOSE

Image-guidance systems (IGS) have gained widespread use in endoscopic sinus surgery (ESS) and have been thoroughly analysed. In this study, we looked for a new parameter to determine if patients could directly benefit from the use of IGS during primary ESS. We questioned if IGS could improve the quality of ESS in chronic rhinosinusitis (CRS) patients via allowing a more comprehensive treatment of all involved sinus compartments.

METHODS

In a pilot feasibility study, we evaluated uncomplicated CRS patients following primary ESS with and without IGS between January 2011 and June 2012 using preoperative and postoperative CT scans. The preoperative CT scans identified the sinus compartments requiring surgery. The postoperative CT scans were used to evaluate the treatment effect in these compartments. From these data, we calculated a missing ratio (missed compartments/compartments requiring surgery) for each patient.

RESULTS

Of the 169 ESS patients who were treated, ten patients were retrospectively identified as complying with the inclusion and exclusion criteria following ESS with IGS. Ten patients treated without IGS were then randomly chosen. The median missing ratio for non-IGS patients was 36%, and for IGS patients, the median missing ratio was 0% (p = 0.046). However, the missing ratio was depended on the number of compartments requiring surgery. Stratification of the number of compartments requiring surgery resulted in an exact p value of 0.13.

CONCLUSIONS

IGS could help the surgeon to more completely address diseased sinus compartments. For better scientific merit, a comparative study of ESS with and without IGS seems feasible, using the proposed failing score missed compartments/compartments requiring surgery as the primary outcome parameter.

Influence of patient-specific anatomy on medical computed tomography and risk evaluation of minimally invasive surgery at the otobasis

PURPOSE

With the increasing use of new minimally invasive approaches in temporal bone surgery, the need arises for evaluation of the risk of injury to sensitive anatomical structures. The factors that influence the measurement uncertainty (variation in representation of position and shape of anatomical structures) of imaging are of relevance. We investigate the effect of patients' anatomy on the measurement uncertainty of medical CT.

METHODS

Six formalin-fixed temporal bones were used, fiducial markers were bone-implanted, and 20 CT scans of each temporal bone were generated. Surgically threatened anatomical structures of importance were defined. Manual segmentation was performed to create 3D surface models, and different Gaussian filters were applied. Analysis points were established along the border of the superior semicircular canal to determine the deviation between the 3D images of the labyrinth. The standard uncertainty was calculated, and one-way analysis of variance was performed (significance level = 5%) to evaluate the effect of certain factors (patient, side, Gaussian filter) on the measurement uncertainty.

RESULTS

The influence of patient-specific anatomy on the measurement uncertainty of medical CT (p = 0.049) was demonstrated for the first time. The applied Gaussian filter (p = 0.622) and the patient's side (p = 0.341) showed no significant effect.

CONCLUSION

The applied method and the results of the statistical analysis suggest that the patient's individual anatomical conditions affect the measurement uncertainty of medical CT. Thus, the patient's anatomy must be considered as an important influencing factor during risk evaluation concerning minimally invasive and image-guided surgery.

Toward Holographic-Guided Surgery

The implementation of augmented reality (AR) in image-guided surgery (IGS) can improve surgical interventions by presenting the image data directly on the patient at the correct position and in the actual orientation. This approach can resolve the switching focus problem, which occurs in conventional IGS systems when the surgeon has to look away from the operation field to consult the image data on a 2-dimensional screen. The Microsoft HoloLens, a head-mounted AR display, was combined with an optical navigation system to create an AR-based IGS system. Experiments were performed on a phantom model to determine the accuracy of the complete system and to evaluate the effect of adding AR. The results demonstrated a mean Euclidean distance of 2.3 mm with a maximum error of 3.5 mm for the complete system. Adding AR visualization to a conventional system increased the mean error by 1.6 mm. The introduction of AR in IGS was promising. The presented system provided a solution for the switching focus problem and created a more intuitive guidance system. With a further reduction in the error and more research to optimize the visualization, many surgical applications could benefit from the advantages of AR guidance.

Head-mounted display augmented reality to guide pedicle screw placement utilizing computed tomography

PURPOSE

Augmented reality has potential to enhance surgical navigation and visualization. We determined whether head-mounted display augmented reality (HMD-AR) with superimposed computed tomography (CT) data could allow the wearer to percutaneously guide pedicle screw placement in an opaque lumbar model with no real-time fluoroscopic guidance.

METHODS

CT imaging was obtained of a phantom composed of L1-L3 Sawbones vertebrae in opaque silicone. Preprocedural planning was performed by creating virtual trajectories of appropriate angle and depth for ideal approach into the pedicle, and these data were integrated into the Microsoft HoloLens using the Novarad OpenSight application allowing the user to view the virtual trajectory guides and CT images superimposed on the phantom in two and three dimensions. Spinal needles were inserted following the virtual trajectories to the point of contact with bone. Repeat CT revealed actual needle trajectory, allowing comparison with the ideal preprocedural paths.

RESULTS

Registration of AR to phantom showed a roughly circular deviation with maximum average radius of 2.5 mm. Users took an average of 200 s to place a needle. Extrapolation of needle trajectory into the pedicle showed that of 36 needles placed, 35 (97%) would have remained within the pedicles. Needles placed approximated a mean distance of 4.69 mm in the mediolateral direction and 4.48 mm in the craniocaudal direction from pedicle bone edge.

CONCLUSION

To our knowledge, this is the first peer-reviewed report and evaluation of HMD-AR with superimposed 3D guidance utilizing CT for spinal pedicle guide placement for the purpose of cannulation without the use of fluoroscopy.

A proposal for limited criminal liability in high-accuracy endoscopic sinus surgery

The aim of the present study is to propose legal reform limiting surgeons' criminal liability in high-accuracy and high-risk surgery such as endoscopic sinus surgery (ESS). The study includes a review of the medical literature, focusing on identifying and examining reasons why ESS carries a very high risk of serious complications related to inaccurate surgical manoeuvers and reviewing British and Italian legal theory and case-law on medical negligence, especially with regard to Italian Law 189/2012 (so called "Balduzzi" Law). It was found that serious complications due to inaccurate surgical manoeuvers may occur in ESS regardless of the skill, experience and prudence/diligence of the surgeon. Subjectivity should be essential to medical negligence, especially regarding high-accuracy surgery. Italian Law 189/2012 represents a good basis for the limitation of criminal liability resulting from inaccurate manoeuvres in high-accuracy surgery such as ESS. It is concluded that ESS surgeons should be relieved of criminal liability in cases of simple/ordinary negligence where guidelines have been observed.

Navigation accuracy after automatic- and hybrid-surface registration in sinus and skull base surgery

Objective

Computer-aided-surgery in ENT surgery is mainly used for sinus surgery but navigation accuracy still reaches its limits for skull base procedures. Knowledge of navigation accuracy in distinct anatomical regions is therefore mandatory. This study examined whether navigation accuracy can be improved in specific anatomical localizations by using hybrid registration technique.

Study design

Experimental phantom study.

Setting

Operating room.

Subjects and methods

The gold standard of screw registration was compared with automatic LED-mask-registration alone, and in combination with additional surface matching. 3D-printer-based skull models with individual fabricated silicone skin were used for the experiments. Overall navigation accuracy considering 26 target fiducials distributed over each skull was measured as well as the accuracy on selected anatomic localizations.

Results

Overall navigation accuracy was <1.0 mm in all cases, showing the significantly lowest values after screw registration (0.66 ± 0.08 mm), followed by hybrid registration (0.83± 0.08 mm), and sole mask registration (0.92 ± 0.13 mm).On selected anatomic localizations screw registration was significantly superior on the sphenoid sinus and on the internal auditory canal. However, mask registration showed significantly better accuracy results on the midface. Navigation accuracy on skull base localizations could be significantly improved by the combination of mask registration and additional surface matching.

Conclusion

Overall navigation accuracy gives no sufficient information regarding navigation accuracy in a distinct anatomic area. The non-invasive LED-mask-registration proved to be an alternative in clinical routine showing best accuracy results on the midface. For challenging skull base procedures a hybrid registration technique is recommendable which improves navigation accuracy significantly in this operating field. Invasive registration procedures are reserved for selected challenging skull base operations where the required high precision warrants the invasiveness.

Next-Generation Surgical Navigation Systems in Sinus and Skull Base Surgery

Over the past 25 years, rhinologists have adopted surgical navigation technology for endoscopic sinus and skull base procedures. Navigation systems often produce a wide target registration error (TRE). Ideally, next-generation systems will include a leap in target registration error reduce TRE through innovative hardware and software. Incorporation of microsensors will be another important innovation. Future systems are likely to include augmented reality, which can project overlays of critical anatomy on real-world endoscopic images. Recent trends in surgical navigation suggest a phase of rapid evolution.

Advances in Microdebrider Technology: Improving Functionality and Expanding Utility

Since its application in nasal surgery, the microdebrider has revolutionized the practice of endoscopic sinus surgery. As the demands and breadth of procedures performed endoscopically have increased, so has the need for improvement in the microdebrider and related technologies. This article addresses how use of the microdebrider has impacted endonasal surgery and discusses current advances, which include creation of specialty hand pieces and blades, increases in instrument rotational speed, incorporation of navigation and energy, adaptation for intracranial use, and disposable instrumentation designed for in office use. Advances in microdebrider technology have improved functionality and expanded the utility of these devices.

Accuracy and reproducibility of virtual cutting guides and 3D-navigation for osteotomies of the mandible and maxilla

Background

We set out to determine the accuracy of 3D-navigated mandibular and maxillary osteotomies with the ultimate aim to integrate virtual cutting guides and 3D-navigation into ablative and reconstructive head and neck surgery.

Methods

Four surgeons (two attending, two clinical fellows) completed 224 unnavigated and 224 3D-navigated osteotomies on anatomical models according to preoperative 3D plans. The osteotomized bones were scanned and analyzed.

Results

Median distance from the virtual plan was 2.1 mm unnavigated (IQR 2.6 mm, ≥3 mm in 33%) and 1.2 mm 3D-navigated (IQR 1.1 mm, ≥3 mm in 6%) (P<0.0001); median pitch was 4.5° unnavigated (IQR 7.1°) and 3.5° 3D-navigated (IQR 4.0°) (P<0.0001); median roll was 7.4° unnavigated (IQR 8.5°) and 2.6° 3D-navigated (IQR 3.8°) (P<0.0001).

Conclusion

3D-rendering enables osteotomy navigation. 3 mm is an appropriate planning distance. The next steps are translating virtual cutting guides to free bone flap reconstruction and clinical use.

Intraoperative evaluation of device placement in spine surgery using known-component 3D-2D image registration

Intraoperative x-ray radiography/fluoroscopy is commonly used to assess the placement of surgical devices in the operating room (e.g. spine pedicle screws), but qualitative interpretation can fail to reliably detect suboptimal delivery and/or breach of adjacent critical structures. We present a 3D-2D image registration method wherein intraoperative radiographs are leveraged in combination with prior knowledge of the patient and surgical components for quantitative assessment of device placement and more rigorous quality assurance (QA) of the surgical product. The algorithm is based on known-component registration (KC-Reg) in which patient-specific preoperative CT and parametric component models are used. The registration performs optimization of gradient similarity, removes the need for offline geometric calibration of the C-arm, and simultaneously solves for multiple component bodies, thereby allowing QA in a single step (e.g. spinal construct with 4-20 screws). Performance was tested in a spine phantom, and first clinical results are reported for QA of transpedicle screws delivered in a patient undergoing thoracolumbar spine surgery. Simultaneous registration of ten pedicle screws (five contralateral pairs) demonstrated mean target registration error (TRE) of 1.1  ±  0.1 mm at the screw tip and 0.7  ±  0.4° in angulation when a prior geometric calibration was used. The calibration-free formulation, with the aid of component collision constraints, achieved TRE of 1.4  ±  0.6 mm. In all cases, a statistically significant improvement (p  <  0.05) was observed for the simultaneous solutions in comparison to previously reported sequential solution of individual components. Initial application in clinical data in spine surgery demonstrated TRE of 2.7  ±  2.6 mm and 1.5  ±  0.8°. The KC-Reg algorithm offers an independent check and quantitative QA of the surgical product using radiographic/fluoroscopic views acquired within standard OR workflow. Such intraoperative assessment could improve quality and safety, provide the opportunity to revise suboptimal constructs in the OR, and reduce the frequency of revision surgery.

Minimally invasive, multi-port approach to the lateral skull base: a first in vitro evaluation

PURPOSE

The aim of the study was to validate a minimally invasive, multi-port approach to the internal auditory canal at the lateral skull base on a cadaver specimen.

METHODS

Fiducials and a custom baseplate were fixed on a cadaver skull, and a computed tomography image was acquired. Three trajectories from the mastoid surface to the internal auditory canal were computed with a custom planning tool. A self-developed positioning system with a drill guide was attached to the baseplate. After referencing on a high precision coordinate measuring machine, the drill guide was aligned according to the planned trajectories. Drilling of three trajectories was performed with a medical stainless steel drill bit.

RESULTS

The process of planning and drilling three trajectories to the internal auditory canal with the presented workflow and tools was successful. The mean drilling error of the system (Euclidian distance between the planned trajectory and centerline of the actual drilled canal) was [Formula: see text] mm at the entry point and [Formula: see text] mm at the target. The inaccuracy of the drill process itself and its physical limitations were identified as the main contributing factors.

CONCLUSION

The presented system allows the planning and drilling of multiple minimally invasive canals at the lateral skull base. Further studies are required to reduce the drilling error and evaluate the clinical application of the system.

Prospects and limitations of different registration modalities in electromagnetic ENT navigation

The present study examined electromagnetic tracking technology for ENT navigation. Five different registration modalities were compared and navigation accuracy was assessed. Four skull models were individually fabricated with a three-dimensional printer, based on patients' computer tomography datasets. Individual silicone masks were fitted for skin and soft tissue simulation. Five registration modalities were examined: (1) invasive marker, (2) automatic, (3) surface matching (AccuMatch), (4) anatomic landmarks, and (5) oral splint registration. Overall navigation accuracy and accuracy on selected anatomic locations were assessed by targeting 26 titanium screws previously placed over the skull. Overall navigation accuracy differed significantly between all registration modalities. The target registration error was 0.94 ± 0.06 mm (quadratic mean ± standard deviation) for the invasive marker registration, 1.41 ± 0.04 mm for the automatic registration, 1.59 ± 0.14 mm for the surface matching registration, and 5.15 ± 0.66 mm (four landmarks) and 4.37 ± 0.73 mm (five landmarks) for the anatomic landmark registration. Oral splint registration proved itself to be inapplicable to this navigation system. Invasive marker registration was superior on most selected anatomic locations. However, on the ethmoid and sphenoid sinus the automatic registration process revealed significantly lower target registration error values. Only automatic and surface registration met the accuracy requirements for noninvasive registration. Particularly, the automatic image-to-world registration reaches target registration error values on the anterior skull base which are comparable with the gold standard of invasive screw registration.

Surface matching for high-accuracy registration of the lateral skull base

PURPOSE

The accuracy achievable when utilizing image guidance depends to a large extent on the accuracy with which the patient can be registered to preoperative image data. This work proposes a method for the registration of the temporal bone based on surface matching and investigates the achievable accuracy of the technique.

METHODS

Fourteen human temporal bones were utilized for evaluation; incisions were made, fiducial screws were implanted to act as a ground truth, and imaging was performed. The positions of the fiducials and surface of the mastoid were extracted from image data and reference positions defined at the round window and the mastoid surface. The surface of the bone was then digitized using a tracked pointer within the region exposed by the incisions and the physical and image point clouds registered, with the result compared to the fiducial-based registration.

RESULTS

Results of one case were excluded due to a problem with the ground truth registration. In the remaining cases an accuracy of [Formula: see text] and [Formula: see text] mm was observed relative to the ground truth at the surface of the mastoid and round window, respectively.

CONCLUSIONS

A technique for the registration of the temporal bone was proposed, based on surface matching after exposure of the mastoid surface, and evaluated on human temporal bone specimens. The results reveal that high-accuracy patient-to-image registration is possible without the use of fiducial screws.

New Protocol for Skin Landmark Registration in Image-Guided Neurosurgery: Technical Note

BACKGROUND

Newer versions of the commercial Medtronic StealthStation allow the use of only 8 landmark pairs for patient-to-image registration as opposed to 9 landmarks in older systems. The choice of which landmark pair to drop in these newer systems can have an effect on the quality of the patient-to-image registration.

OBJECTIVE

To investigate 4 landmark registration protocols based on 8 landmark pairs and compare the resulting registration accuracy with a 9-landmark protocol.

METHODS

Four different protocols were tested on both phantoms and patients. Two of the protocols involved using 4 ear landmarks and 4 facial landmarks and the other 2 involved using 3 ear landmarks and 5 facial landmarks. Both the fiducial registration error and target registration error were evaluated for each of the different protocols to determine any difference between them and the 9-landmark protocol.

RESULTS

No difference in fiducial registration error was found between any of the 8-landmark protocols and the 9-landmark protocol. A significant decrease (P &lt; .05) in target registration error was found when using a protocol based on 4 ear landmarks and 4 facial landmarks compared with the other protocols based on 3 ear landmarks.

CONCLUSION

When using 8 landmarks to perform the patient-to-image registration, the protocol using 4 ear landmarks and 4 facial landmarks greatly outperformed the other 8-landmark protocols and 9-landmark protocol, resulting in the lowest target registration error.

High-resolution imaging of the central nervous system: how novel imaging methods combined with navigation strategies will advance patient care

This narrative review captures a subset of recent advances in imaging of the central nervous system. First, we focus on improvements in the spatial and temporal profile afforded by optical coherence tomography, fluorescence-guided surgery, and Coherent Anti-Stokes Raman Scattering Microscopy. Next, we highlight advances in the generation and uses of imaging-based atlases and discuss how this will be applied to specific clinical situations. To conclude, we discuss how these and other imaging tools will be combined with neuronavigation techniques to guide surgeons in the operating room. Collectively, this work aims to highlight emerging biomedical imaging strategies that hold potential to be a valuable tool for both clinicians and researchers in the years to come.

An analysis of tracking error in image-guided neurosurgery

PURPOSE

This study quantifies some of the technical and physical factors that contribute to error in image-guided interventions. Errors associated with tracking, tool calibration and registration between a physical object and its corresponding image were investigated and compared with theoretical descriptions of these errors.

METHODS

A precision milled linear testing apparatus was constructed to perform the measurements.

RESULTS

The tracking error was shown to increase in linear fashion with distance normal to the camera, and the tracking error ranged between 0.15 and 0.6 mm. The tool calibration error increased as a function of distance from the camera and the reference tool (0.2-0.8 mm). The fiducial registration error was shown to improve when more points were used up until a plateau value was reached which corresponded to the total fiducial localization error ([Formula: see text]0.8 mm). The target registration error distributions followed a [Formula: see text] distribution with the largest error and variation around fiducial points.

CONCLUSIONS

To minimize errors, tools should be calibrated as close as possible to the reference tool and camera, and tools should be used as close to the front edge of the camera throughout the intervention, with the camera pointed in the direction where accuracy is least needed during surgery.

Accuracy assessment of a marker-free method for registration of CT and stereo images applied in image-guided implantology: a phantom study

To assess the accuracy of a proposed marker-free registration method as opposed to the conventional marker-based method using an image-guided dental system, and investigating the best configurations of anatomical landmarks for various surgical fields in a phantom study, a CT-compatible dental phantom consisting of implanted targets was used. Two marker-free registration methods were evaluated, first using dental anatomical landmarks and second, using a reference marker tool. Six implanted markers, distributed in the inner space of the phantom were used as the targets; the values of target registration error (TRE) for each target were measured and compared with the marker-based method. Then, the effects of different landmark configurations on TRE values, measured using the Parsiss IV Guided Navigation system (Parsiss, Tehran, Iran), were investigated to find the best landmark arrangement for reaching the minimum registration error in each target region. It was proved that marker-free registration can be as precise as the marker-based method. This has a great impact on image-guided implantology systems whereby the drawbacks of fiducial markers for patient and surgeon are removed. It was also shown that smaller values of TRE could be achieved by using appropriate landmark configurations and moving the center of the landmark set closer to the surgery target. Other common factors would not necessarily decrease the TRE value so the conventional rules accepted in the clinical community about the ways to reduce TRE should be adapted to the selected field of dental surgery.

Minimally invasive multiport surgery of the lateral skull base

OBJECTIVE

Minimally invasive procedures minimize iatrogenic tissue damage and lead to a lower complication rate and high patient satisfaction. To date only experimental minimally invasive single-port approaches to the lateral skull base have been attempted. The aim of this study was to verify the feasibility of a minimally invasive multiport approach for advanced manipulation capability and visual control and develop a software tool for preoperative planning.

METHODS

Anatomical 3D models were extracted from twenty regular temporal bone CT scans. Collision-free trajectories, targeting the internal auditory canal, round window, and petrous apex, were simulated with a specially designed planning software tool. A set of three collision-free trajectories was selected by skull base surgeons concerning the maximization of the distance to critical structures and the angles between the trajectories.

RESULTS

A set of three collision-free trajectories could be successfully simulated to the three targets in each temporal bone model without violating critical anatomical structures.

CONCLUSION

A minimally invasive multiport approach to the lateral skull base is feasible. The developed software is the first step for preoperative planning. Further studies will focus on cadaveric and clinical translation.

A projected landmark method for reduction of registration error in image-guided surgery systems

PURPOSE

Image-guided surgery systems are limited by registration error, so practical and effective methods to improve accuracy are necessary. A projection point-based method for reducing the surface registration error in image-guided surgery was developed and tested.

METHODS

Checkerboard patterns are projected on visible surfaces to create projected landmarks over a region of interest. Surface information thus becomes available in the form of point clouds of surface point coordinates with submillimeter resolution. The reconstructed 3D point cloud is registered using iterative closest point (ICP) approximation to a 3D point cloud extracted from preoperative CT images of the same region of interest. The projected landmark surface registration method was compared with two other methods using a facial surface phantom: (a) landmark registration using anatomical features, and (b) surface matching based on an additional 40 surface points.

RESULTS

The mean error for the projected landmark surface registration method was 0.64 mm, which was 47.4 and 35.3 % lower relative to mean errors of the anatomical landmark registration and the surface-matching methods, respectively. After applying the proposed method, using target registration error as a gold standard, the resulting mean error was 1.1 mm or a reduction of 61.2 % compared to the anatomical landmark registration.

CONCLUSION

Optical checkerboard pattern projection onto visible surfaces was used to acquire surface point clouds for image-guided surgery registration. A projected landmark method eliminated the effects of unwanted and overlapping points by acquiring the desired points at specific locations. The results were more accurate than conventional landmark or surface registration.

A region-based anatomical landmark configuration for sinus surgery using image guided navigation system: a phantom-study

PURPOSE

To evaluate the current beliefs about the ways to reduce target registration error (TRE) values in image guided Sinus surgery by rearranging the fiducial configuration, and investigating the best configurations for various surgical fields in a phantom study.

METHODS

A new CT-compatible skull phantom consisting of implanted targets was designed to enable direct measurement of TRE in four fields of sinus surgery, Frontal, Ethmoid, Sphenoid and Maxillary. The effects of different landmark configurations on TRE values, measured by the Parsiss-IV navigation system were investigated to find the best landmark arrangement for each region, and compared to the TRE prediction formula to assess the clinically accepted landmark selection approaches based on this formula.

RESULTS

It was shown that smaller values of TRE could be attained by arranging the center of the fiducials to be more focused on the surgery target. The addition of more fiducials and keeping non-linear arrangement of landmark would not necessarily decrease the TRE value.

CONCLUSION

Optimizing the landmark configuration is important for increasing the localization accuracy in image guided sinus surgery. The common beliefs accepted in the clinical community about the ways to reduce the TRE are very general and should be adapted to specific field of image guided surgery.

Real-time imaging with the o-arm for skull base applications: a cadaveric feasibility study

Introduction Although intraoperative imaging/navigation has established its critical role in neurosurgery, its role in cranial base surgery is currently limited. Due to issues such as poor bony resolution and accuracy, surgeons have to rely on anatomic landmarks that can be distorted by pathology when drilling out critical structures. Though originally developed for spinal application, we hypothesized that the O-Arm could address the above issues for use in cranial base procedures. Methods A cadaveric study was performed in which heads underwent a preprocedure scan via the O-Arm, a fluoroscopic device capable of providing three-dimensional images through the use of cone-beam technology. Preprocedure scans were taken and then registered to a Stealth S7 machine (Medtronic, Inc., Minneapolis, MN, USA). Key cranial base landmarks were identified on these scans and then subsequently identified under direct visualization after (1) endoscopic endonasal dissection and (2) a middle fossa approach. We then quantified the difference in distance between the preplanned and identified structure during surgery. This difference was considered the error. Results For anterior cranial fossa structures, the mean error was 0.25 mm (anterior septum), 0.27 mm (left septum), and 0.32 mm (right septum). For middle fossa structures, the errors were: 0.11 mm (foramen spinosum), 0.44 mm (foramen rotundum), and 0.21 mm (foramen ovale). Conclusion Based on this preliminary cadaveric study, we feel the O-Arm can provide the necessary imaging resolution at the skull base to be employed for intraoperative navigation during cranial base approaches (open and endoscopic). This study warrants further investigation into its clinical use in patients undergoing similar surgical procedures.