SPECT postprocessing for epileptogenic focus localization: SISCOM versus ISAS.

OBJECTIVE: Ictal SPECT can be used as an estimate for the epileptogenic zone in people with focal epilepsy. Subtraction of ictal and interictal SPECT scans reveals the area with significant ictal hyperperfusion. Some methods use a control database to also correct for physiological variance. This control database is ideally scanner specific, but it is not trivial to obtain such a database because of ethical issues. In this study, we used a publicly available control database to compare ictal-interictal SPECT analyzed by SPM (ISAS) with the most commonly used subtraction ictal SPECT co-registered to MRI (SISCOM). METHODS: Ictal and interictal SPECTs of 26 patients (age range: 7-50 years, 15 adults, 11 children) with focal drug resistant epilepsy in workup for epilepsy surgery were retrospectively analyzed using both SISCOM and ISAS. The control database for ISAS was obtained from the ISAS website. Two groups of blinded reviewers determined the location of ictal hyperperfusion in all datasets. Results were compared between subtraction algorithms and with the resected area (if available) or the suspected epileptogenic zone. The number of significant clusters and the locations of maximum hyperperfusion were compared between algorithms. RESULTS: The location of ISAS and SISCOM hyperperfusion was the same in 14 patients (54%). ISAS localized in 6 patients where SISCOM did not. Compared to the resected area or suspected epileptogenic zone, SISCOM correctly localized in 55%, while ISAS did in 65% (not significantly different). ISAS shows significantly less clusters than SISCOM. The maximum hyperperfusion was in the reviewer's location in 65% for ISAS and 38% for SISCOM. SIGNIFICANCE: ISAS using a publicly available control database gives comparable or better results than SISCOM. ISAS results are easier to interpret than SISCOM results. We show that ISAS is a reliable alternative for SISCOM, which could easily be implemented in epilepsy surgery clinics. PLAIN LANGUAGE SUMMARY: We explored the effectiveness of ISAS as an alternative to the widely used SISCOM for assessing SPECT scans in epilepsy surgery candidates. Utilizing a publicly available control database, we compared the two methods in 26 patients. The results indicate that ISAS might offer increased accuracy and interpretability, making it a promising option, especially for centers without access to a specific control dataset.

Establishing a Biomarker for the Prediction of Short-Term Graft Detachment After Descemet Membrane Endothelial Keratoplasty.

PURPOSE: The purpose of this study was to investigate the predictive value of pachymetry mapping 1 day after Descemet membrane endothelial keratoplasty (DMEK) as a biomarker for early graft detachment. METHODS: This was a post hoc analysis of 65 pseudophakic subjects with Fuchs endothelial dystrophy who underwent DMEK surgery between December 2018 and April 2021 as part of the Advanced Visualization In Corneal Surgery Evaluation international multicenter randomized controlled trial. One eye per patient was included. Preoperatively and 1 day postoperatively, patients underwent anterior segment optical coherence tomography imaging. Using a grid consisting of 25 zones (ie, pachymetry map), corneal thickness and presence of a graft detachment were mapped for each patient. Detachments of any size were considered, regardless of subsequent clinical interventions. Missing data were imputed and subsequently divided into a training and test set. Two prediction methods were evaluated: one model based on absolute corneal thickness and a regression model. RESULTS: A total of 65 eyes were included for analysis of which 33 developed any form of graft detachment. Preoperatively, no significant differences were observed between the groups ( P = 0.221). Corneal thickness in the corneal zones with a detached graft was significantly increased compared with corneal zones with an attached graft ( P < 0.001). The regression prediction model had an area under the curve of 0.87 (sensitivity: 0.79 and specificity: 0.75), whereas the absolute thickness cutoff model only reached 0.65. CONCLUSIONS: Pachymetry mapping 1 day after DMEK was predictive for early graft detachment, and the prediction model had a good to excellent performance. This aids in identifying patients at risk for graft detachment and subsequent tailored postoperative care.

The spatial relationship between the MRI lesion and intraoperative electrocorticography in focal epilepsy surgery.

MRI and intraoperative electrocorticography are often used in tandem to delineate epileptogenic tissue in resective surgery for focal epilepsy. Both the resection of the MRI lesion and tissue with high rates of electrographic discharges on electrocorticography, e.g. spikes and high-frequency oscillations (80-500 Hz), lead to a better surgical outcome. How MRI and electrographic markers are related, however, is currently unknown. The aim of this study was to find the spatial relationship between MRI lesions and spikes/high-frequency oscillations. We retrospectively included 33 paediatric and adult patients with lesional neocortical epilepsy who underwent electrocorticography-tailored surgery (14 females, median age = 13.4 years, range = 0.6-47.0 years). Mesiotemporal lesions were excluded. We used univariable linear regression to find correlations between pre-resection spike/high-frequency oscillation rates on an electrode and its distance to the MRI lesion. We tested straight lines to the centre and the edge of the MRI lesion, and the distance along the cortical surface to determine which of these distances best reflects the occurrence of spikes/high-frequency oscillations. We conducted a moderator analysis to investigate the influence of the underlying pathology type and lesion volume on our results. We found spike and high-frequency oscillation rates to be spatially linked to the edge of the MRI lesion. The underlying pathology type influenced the spatial relationship between spike/high-frequency oscillation rates and the MRI lesion (P spikes < 0.0001, P ripples < 0.0001), while the lesion volume did not (P spikes = 0.64, P ripples = 0.89). A higher spike rate was associated with a shorter distance to the edge of the lesion for cavernomas [F(1,64) = -1.37, P < 0.0001, η 2 = 0.22], focal cortical dysplasias [F(1,570) = -0.25, P < 0.0001, η 2 = 0.05] and pleomorphic xanthoastrocytomas [F(1,66) = -0.18, P = 0.01, η 2 = 0.09]. In focal cortical dysplasias, a higher ripple rate was associated with a shorter distance [F(1,570) = -0.35, P < 0.0001, η 2 = 0.05]. Conversely, low-grade gliomas showed a positive correlation; the further an electrode was away from the lesion, the higher the rate of spikes [F(1,75) = 0.65, P < 0.0001, η 2 = 0.37] and ripples [F(1,75) = 2.67, P < 0.0001, η 2 = 0.22]. Pathophysiological processes specific to certain pathology types determine the spatial relationship between the MRI lesion and electrocorticography results. In our analyses, non-tumourous lesions (focal cortical dysplasias and cavernomas) seemed to intrinsically generate spikes and high-frequency oscillations, particularly at the border of the lesion. This advocates for a resection of this tissue. Low-grade gliomas caused epileptogenicity in the peritumoural tissue. Whether a resection of this tissue leads to a better outcome is unclear. Our results suggest that the underlying pathology type should be considered when intraoperative electrocorticography is interpreted.

Automatic evaluation of graft orientation during Descemet membrane endothelial keratoplasty using intraoperative OCT.

Correct Descemet Membrane Endothelial Keratoplasty (DMEK) graft orientation is imperative for success of DMEK surgery, but intraoperative evaluation can be challenging. We present a method for automatic evaluation of the graft orientation in intraoperative optical coherence tomography (iOCT), exploiting the natural rolling behavior of the graft. The method encompasses a deep learning model for graft segmentation, post-processing to obtain a smooth line representation, and curvature calculations to determine graft orientation. For an independent test set of 100 iOCT-frames, the automatic method correctly identified graft orientation in 78 frames and obtained an area under the receiver operating characteristic curve (AUC) of 0.84. When we replaced the automatic segmentation with the manual masks, the AUC increased to 0.92, corresponding to an accuracy of 86%. In comparison, two corneal specialists correctly identified graft orientation in 90% and 91% of the iOCT-frames.

Vital Role of In-House 3D Lab to Create Unprecedented Solutions for Challenges in Spinal Surgery, Practical Guidelines and Clinical Case Series.

For decades, the advantages of rapid prototyping for clinical use have been recognized. However, demonstrations of potential solutions to treat spinal problems that cannot be solved otherwise are scarce. In this paper, we describe the development, regulatory process, and clinical application of two types of patient specific 3D-printed devices that were developed at an in-house 3D point-of-care facility. This 3D lab made it possible to elegantly treat patients with spinal problems that could not have been treated in a conventional manner. The first device, applied in three patients, is a printed nylon drill guide, with such accuracy that it can be used for insertion of cervical pedicle screws in very young children, which has been applied even in semi-acute settings. The other is a 3D-printed titanium spinal column prosthesis that was used to treat progressive and severe deformities due to lysis of the anterior column in three patients. The unique opportunity to control size, shape, and material characteristics allowed a relatively easy solution for these patients, who were developing paraplegia. In this paper, we discuss the pathway toward the design and final application, including technical file creation for dossier building and challenges within a point-of-care lab.

fMRI Resting-State Connectivity between Language and Nonlanguage Areas as Defined by Intraoperative Electrocortical Stimulation in Low-Grade Glioma Patients.

BACKGROUND AND OBJECTIVES: It remains to be determined whether noninvasive functional imaging techniques can rival the clinical potential of direct electrocortical stimulation (DES). In this study, we compared the results of resting-state functional magnetic resonance imaging (rs-fMRI) to those of DES for language mapping. Our goals were twofold: (1) to replicate a previous study that demonstrated that resting-state connectivity (RSC) was significantly larger between positive DES language sites than between negative DES language sites and (2) to compare the spatial resolution of rs-fMRI to that of DES. METHODS: We conducted a retrospective study of nine low-grade glioma patients. Language sites were identified by intraoperative DES. We compared RSC values between and within groups of DES-positive and DES-negative regions of interest (ROIs). Both close-negative sites (i.e., DES-negative sites <1 cm apart from and on the same gyrus as DES-positive sites) and far-negative sites (i.e., purely randomly chosen sites not in the vicinity of the tumor or of the DES-positive sites but on the same lobe) were included. Receiver operating characteristics were used to quantify comparisons. RESULTS: Functional connectivity between all positive language sites was on average significantly higher than between all close-negative sites and between all far-negative sites. The functional connectivity between the positive language ROIs and their respective close-negative control sites was not smaller than between all positive language sites. CONCLUSION: rs-fMRI likely reflects similar neural information as detected with DES, but in its current form does not reach the spatial resolution of DES.

The potential of spring distraction to dynamically correct complex spinal deformities in the growing child.

PURPOSE: Current treatment of progressive early onset scoliosis involves growth-friendly instrumentation if conservative treatment fails. These implants guide growth by passive sliding or repeated lengthenings. None of these techniques provide dynamic correction after implantation. We developed the spring distraction system (SDS), by using one or multiple compressed springs positioned around a standard sliding rod, to provide active continuous distraction of the spine to stimulate growth and further correction. The purpose of this study was to determine feasibility and proof of concept of the SDS. METHODS: We developed a versatile, dynamic spring distraction system for patients who would benefit from active continuous distraction. This prospective case series evaluates four patients with exceptional and progressive congenital spine deformities. RESULTS: Four patients had a mean age of 6.8 years at surgery with a mean follow-up of 36 months (range 25-45). The mean progressive thoracic lordosis, which was the reason for initiating surgical treatment in two patients, changed from 32° lordosis preoperatively to 1° kyphosis post-operatively. During follow-up, this further improved to 32° thoracic kyphosis. In the two other patients, with cervicothorcacic scoliosis, the main coronal curve improved from 79° pre-operatively to 56° post-operatively and further improved to 42°. The mean T1-S1 spine growth during follow-up for all patients was 1.3 cm/year. There was one reoperation because of skin problems and no device-failures. CONCLUSION: These early results show the feasibility and the proof of concept of spring-based distraction as a dynamic growth-enhancing system with the potential of further correction of the deformity after implantation.

Distance Control and Virtual Drilling Improves Anatomical Orientation During Anterior Petrosectomy.

BACKGROUND: A combined drill distance control and virtual drilling image guidance feedback method was developed. OBJECTIVE: To investigate whether first-time usage of the proposed method, during anterior petrosectomy (AP), improves surgical orientation and surgical performance. The accuracy of virtual drilling and the clinical practicability of the method were also investigated. METHODS: In a simulated surgical setting using human cadavers, a trial was conducted with 5 expert skull base surgeons from 3 different hospitals. They performed 10 AP approaches, using either the feedback method or standard image guidance. Damage to critical structures was assessed. Operating time, drill cavity sizes, and proximity of postoperative drill cavities to the cochlea and the acoustic meatus, were measured. Questionnaires were obtained postoperatively. Errors in the virtual drill cavities as compared with actual postoperative cavities were calculated. In a clinical setup, the method was used during AP. RESULTS: Surgeons rated their intraoperative orientation significantly better with the feedback method compared with standard image guidance. During the cadaver trial, the cochlea was harmed on 1 occasion in the control group, while surgeons drilled closer to the cochlea and meatus without injuring them in the group using feedback. Virtual drilling under- and overestimation errors were 2.2 ± 0.2 and -3.0 ± 0.6 mm on average. The method functioned properly during the clinical setup. CONCLUSION: The proposed feedback method improves orientation and surgical performance in an experimental setting. Errors in virtual drilling reflect spatial errors of the image guidance system. The feedback method is clinically practicable during AP.

Implications of Extracranial Distortion in Ultra-High-Field Magnetic Resonance Imaging for Image-Guided Cranial Neurosurgery.

BACKGROUND: Ultra-high-field magnetic resonance imaging (MRI) of the brain is attractive for image guidance during neurosurgery because of its high tissue contrast and detailed vessel visualization. However, high-field MRI is prone to distortion artifacts, which may compromise image guidance. Here we investigate intra- and extracranial distortions in 7-T MRI scans. METHODS: Five patients with and 5 patients without skin-adhesive fiducials received magnetization-prepared T1-weighted 7-T MRI and standard 3-T MRI scans. The 7- and 3-T images were rigidly coregistered and compared. Intracranial distortions were evaluated qualitatively, whereas shifts at the skin surface and shifts of the center positions of skin-adhesive fiducials were measured quantitatively. Moreover, we present an illustrative case of an ultra-high-field image-guided skull base meningioma resection. RESULTS: We found excellent intracranial correspondence between 3- and 7-T MRI scans. However, the average maximum skin shift was 6.8 ± 2.0 mm in group A and 5.2 ± 0.9 mm in group B. The average maximum difference between the skin-adhesive fiducial positions was 5.6 ± 3.1 mm in group B. In our tumor resection case, the meningioma blood supply could be targeted early thanks to 7-T image guidance, which made subsequent tumor removal straightforward. CONCLUSIONS: There are no visible intracranial distortions in magnetization-prepared T1-weighted 7-T MRI cranial images. However, we found considerable extracranial shifts. These shifts render 7-T images unreliable for patient-to-image registration. We recommend performing patient-to-image registration on a routine (computed tomography scan or 3-T magnetic resonance) image and subsequently fusing the 7-T magnetic resonance image with the routine image on the image guidance machine, until this issue is resolved.

Challenges in the design and regulatory approval of 3D-printed surgical implants: a two-case series.

BACKGROUND: Additive manufacturing or three-dimensional (3D) printing of metal implants can provide novel solutions for difficult-to-treat conditions, yet legislation concerning patient-specific implants complicates the implementation of these techniques in daily practice. In this Article, we share our acquired knowledge of the logistical and legal challenges associated with the use of patient-specific 3D-printed implants to treat spinal instabilities. METHODS: Two patients with semiurgent cases of spinal instability presented to our hospital in the Netherlands. In case 1, severe kyphotic deformity of the thoracic spine due to neurofibromatosis type 1 had led to incomplete paralysis, and a strong metallic strut extending from C6 to T11 was deemed necessary to provide long-term anterior support. In case 2, the patient presented with progressive paralysis caused by cervicothoracic dissociation due to vanishing bone disease. As the C5-T1 vertebral bodies had mostly vanished, an implant spanning the anterior spine from C4 to T2 was required. Because of the complex and challenging nature of both cases, conventional approaches were deemed inadequate; instead, patient-specific implants were designed with use of CT scans and computer-aided design software, and 3D printed in titanium with direct metal printing. For each implant, to ensure patient safety, a comprehensive technical file (describing the clinical substantiation, technical and design considerations, risk analysis, manufacturing process, and labelling) was produced in collaboration with a university department certified for the development and manufacturing of medical devices. Because the implants were categorised as custom-made or personalised devices under the EU Medical Device Regulation, the usual procedures for review and approval of medical devices by a notified body were not required. Finite-element analyses, compression strength tests, and cadaveric experiments were also done to ensure the devices were safe to use. FINDINGS: The planning, design, production, and insertion of the 3D-printed personalised implant took around 6 months in the first patient, but, given the experience from the first case, only took around 6 weeks in the second patient. In both patients, the surgeries went as planned and good positioning of each implant was confirmed. Both patients were discharged home within 1 week after the surgery. In the first patient, a fatigue fracture occured in one of the conventional posterior fusion rods after 10 months, which we repaired, without any deformation of the spine or signs of failure of the personalised implant observed. No other adverse events occurred up to 25 months of follow-up in case 1 and 6 months of follow-up in case 2. INTERPRETATION: Patient-specific treatment approaches incorporating 3D-printed implants can be helpful in carefully selected cases when conventional methods are not an option. Comprehensive and efficient interactions between medical engineers and physicians are essential to establish well designed frameworks to navigate the logistical and regulatory aspects of technology development to ensure the safety and legal validity of patient-specific treatments. The framework described here could encourage physicians to treat (once untreatable) patients with novel personalised techniques. FUNDING: Interreg VA Flanders-The Netherlands programme, Applied and Engineering Sciences research programme, the Netherlands Organisation for Scientific Research, and the Dutch Arthritis Foundation VIDEO ABSTRACT.

Benchmarking Distance Control and Virtual Drilling for Lateral Skull Base Surgery.

BACKGROUND: Novel audiovisual feedback methods were developed to improve image guidance during skull base surgery by providing audiovisual warnings when the drill tip enters a protective perimeter set at a distance around anatomic structures ("distance control") and visualizing bone drilling ("virtual drilling"). OBJECTIVE: To benchmark the drill damage risk reduction provided by distance control, to quantify the accuracy of virtual drilling, and to investigate whether the proposed feedback methods are clinically feasible. METHODS: In a simulated surgical scenario using human cadavers, 12 unexperienced users (medical students) drilled 12 mastoidectomies. Users were divided into a control group using standard image guidance and 3 groups using distance control with protective perimeters of 1, 2, or 3 mm. Damage to critical structures (sigmoid sinus, semicircular canals, facial nerve) was assessed. Neurosurgeons performed another 6 mastoidectomy/trans-labyrinthine and retro-labyrinthine approaches. Virtual errors as compared with real postoperative drill cavities were calculated. In a clinical setting, 3 patients received lateral skull base surgery with the proposed feedback methods. RESULTS: Users drilling with distance control protective perimeters of 3 mm did not damage structures, whereas the groups using smaller protective perimeters and the control group injured structures. Virtual drilling maximum cavity underestimations and overestimations were 2.8 ± 0.1 and 3.3 ± 0.4 mm, respectively. Feedback methods functioned properly in the clinical setting. CONCLUSION: Distance control reduced the risks of drill damage proportional to the protective perimeter distance. Errors in virtual drilling reflect spatial errors of the image guidance system. These feedback methods are clinically feasible.

Thulium laser-assisted endoscopic third ventriculostomy: Determining safe laser settings using in vitro model and 2 year follow-up results in 106 patients.

BACKGROUND AND OBJECTIVE: Endoscopic third ventriculostomy is used to treat hydrocephalus. Different laser wavelengths have been proposed for laser-assisted endoscopic third ventriculostomies over the last decades. The aim of this study was to evaluate Thulium laser endoscopic third ventriculostomy heat penetration in the surrounding environment of the floor of the third ventricle in an in vitro setting with visualization of thermal distribution. Subsequently 106 Thulium laser endoscopic third ventriculostomy procedures were retrospectively analyzed to demonstrate safety. METHODS: The in vitro visualization was based on the color Schlieren method. The heat penetration was measured beneath a tissue phantom of the floor of the third ventricle with a fiber of 365 µm in diameter at different energy settings; 1.0W (956 J/cm2 ), 2.0W (1,912 J/cm2 ), 4.0W (3,824 J/cm2 ), and 7.0W (6,692 J/cm2 ), with a pulse duration of 1.0 second. All experiments were repeated five times. In addition, 106 Thulium laser endoscopic third ventriculostomy procedures between 2005 and 2015 were retrospectively analysed for etiology, sex, complications, and laser parameters. RESULTS: In the energy settings from 1.0 to 4.0 W, heat penetration depth beneath the phantom of the third ventricle did not exceed 1.5 mm. The heat penetration depth at 7 W, exceeded 6 mm. The clinical overall success rate was 80% at the 2-year follow-up study. Complications occurred in 5% of the procedures. In none of the 106 investigated clinical patients bleeding or damage to the basilar artery was encountered due to Thulium laser ablation. CONCLUSIONS: The in vitro experiments show that under 4.0W the situation is considered safe, due to low penetration of heat, thus the chance of accidentally damaging critical structures like the basilar artery is very small. The clinical results show that the Thulium laser did not cause any bleeding of the basilar artery, and is a safe technique for laser endoscopic third ventriculostomy. Lasers Surg. Med. © 2017 Wiley Periodicals, Inc.

In vitro comparison of renal stone laser treatment using fragmentation and popcorn technique.

OBJECTIVE: To study the effectiveness of two laser techniques clinically used to fragment renal stones: fragmenting technique (FT) and popcorn technique (PT). METHODS: Phantom stones were placed in a test tube filled with water, mimicking a renal calyx model. A Holmium:YAG laser was used for fragmentation using both techniques. Four series of experiments were performed with two parameters: the technique (FT or PT) and the number of stones in the test tube (one or four). The mass decrease of the phantom stones was measured before, during, and after the experiment to quantify the effect of both techniques. RESULTS: Visualization of PT showed that the main effect of PT takes place, when the stone moves in front of the laser fiber and is subject to direct radiant exposure. Both FT and PT resulted in a decrease in stone weight; the mass decrease of the stones subjected to FT exceeded that of the stones subjected to PT, even with less laser energy applied. This difference in mass decrease was evident in both the experiments with one and four stones. CONCLUSIONS: PT was less effective in decreasing stone weight compared with FT. The FT is more effective regarding the applied energy than PT, even in a shorter time period and regardless of the number of stones. This study suggests that FT is to be preferred over PT, when stones are accessible by the laser fiber. Lasers Surg. Med. 49:698-704, 2017. © 2017 Wiley Periodicals, Inc.

Evaluation of the ScopeControl endoscope test system in six hospitals in The Netherlands.

As rigid endoscopes are re-used after minimal invasive surgery, they degrade over time. To guarantee the optical quality of a rigid endoscope, the ScopeControl has been developed to measure key optical parameters such as, light transmission (LT), color correctness (CC), focus (FC), fiber transmission (FT), viewing angle (VA) and field of view (FV). To evaluate the performance of the ScopeControl, five ScopeControls SV (study version) have been tested in six hospitals in the Netherlands. Aspects such as robustness, precision, usability of the measured data, acceptation criteria and ergonomic aspects have been assessed. The ScopeControl maintains its stability over time and can measure LT, CC and FC with 5% precision, VA and FV with 2% accuracy and FT with 10% precision. The final thresholds above which an endoscope could still be considered to be in good condition, appeared to be: VA at 75%, CC, FC and FV at 70%, LT at 65% and FT at 35% of that of the best endoscope of that type ever found. The ScopeControl SV fits the workflow of the sterilization department as it is easy to use and can easily be cleaned. The time to perform a measurement is 2-3 min (one minute is spent to select the correct endoscope). The ScopeControl PV (launched in November 2013), has been used clinically from April to November 2014. It proves to be more stable, well accepted by personnel from the sterilization department and be of large value of preventing defect endoscopes on the surgery table.

Imaging the seizure during surgery with a hyperspectral camera.

An epilepsy patient with recurring sensorimotor seizures involving the left hand every 10 min, was imaged with a hyperspectral camera during surgery. By calculating the changes in oxygenated, deoxygenated blood, and total blood volume in the cortex, a focal increase in oxygenated and total blood volume could be observed in the sensory cortex, corresponding to the seizure-onset zone defined by intracranial electroencephalography (EEG) findings. This probably reflects very local seizure activity. After multiple subpial transections in this motor area, clinical seizures abated.

Real-time bladder lesion registration and navigation: a phantom study.

BACKGROUND: Bladder cancer is the fourth most common malignancy in men, with a recurrence rate of 33-64%. Tumor documentation during cystoscopy of the bladder is suboptimal and might play a role in these high recurrence rates. OBJECTIVE: In this project, a bladder registration and navigation system was developed to improve bladder tumor documentation and consequently increase reproducibility of the cystoscopy. MATERIALS/METHODS: The bladder registration and navigation system consists of a stereo-tracker that tracks the location of a newly developed target, which is attached to the endoscope during cystoscopy. With this information the urology registration and navigation software is able to register the 3D position of a lesion of interest. Simultaneously, the endoscopic image is captured in order to combine it with this 3D position. To enable navigation, navigational cues are displayed on the monitor, which subsequently direct the cystoscopist to the previously registered lesion. To test the system, a rigid and a flexible bladder phantom was developed. The system's robustness was tested by measuring the accuracy of registering and navigating the lesions. Different calibration procedures were compared. It was also tested whether system accuracy is limited by using a previously saved calibration, to avoid surgical delay due to calibration. Urological application was tested by comparing a rotational camera (fixed to the rotating endoscope) to a non-rotational camera (dangling by gravity) used in standard urologic practice. Finally, the influence of volume differences on registering and navigating was tested. RESULTS/CONCLUSION: The bladder registration and navigation system has an acceptable accuracy for bladder lesion registration and navigation. Limitations for patient determinants included changes in bladder volume and bladder deformation. In vivo studies are required to measure the effect of these limitations and functionality in urological practice as a tool to increase reproducibility of the cystoscopy.

The use of near-infrared light for safe and effective visualization of subsurface blood vessels to facilitate blood withdrawal in children.

Obtaining access to blood vessels can be difficult, especially in children. Visualization of subsurface blood vessels might be a solution. Ultrasound and visible light have been used to this purpose, but have some drawbacks. Near-infrared light might be a better option since subsurface blood vessels can be visualized in high contrast due to less absorption and scattering in tissue as compared to visible light. Our findings with a multispectral imaging system support this theory. A device, the VascuLuminator, was developed, based on transillumination of the puncture site with near-infrared light. The VascuLuminator was designed to meet the requirements of compact and safe use. A phantom study showed that the maximum depth of visibility (5.5mm for a 3.6mm blood vessel) is sufficient to visualize blood vessels in typical locations for peripheral venous and arterial access. A quantitative comparison of the VascuLuminator and to two other vessel imaging devices, using reflection of near-infrared light instead of transillumination, was conducted. The VascuLuminator is able to decrease failure at first attempt in blood withdrawal in pediatric patients from 10/80 (13%) to 1/45 (2%; P=.05).

Validation of exposure visualization and audible distance emission for navigated temporal bone drilling in phantoms.

BACKGROUND: A neuronavigation interface with extended function as compared with current systems was developed to aid during temporal bone surgery. The interface, named EVADE, updates the prior anatomical image and visualizes the bone drilling process virtually in real-time without need for intra-operative imaging. Furthermore, EVADE continuously calculates the distance from the drill tip to segmented temporal bone critical structures (e.g. the sigmoid sinus and facial nerve) and produces audiovisual warnings if the surgeon drills in too close vicinity. The aim of this study was to evaluate the accuracy and surgical utility of EVADE in physical phantoms. METHODOLOGY/PRINCIPAL FINDINGS: We performed 228 measurements assessing the position accuracy of tracking a navigated drill in the operating theatre. A mean target registration error of 1.33±0.61 mm with a maximum error of 3.04 mm was found. Five neurosurgeons each drilled two temporal bone phantoms, once using EVADE, and once using a standard neuronavigation interface. While using standard neuronavigation the surgeons damaged three modeled temporal bone critical structures. No structure was hit by surgeons utilizing EVADE. Surgeons felt better orientated and thought they had improved tumor exposure with EVADE. Furthermore, we compared the distances between surface meshes of the virtual drill cavities created by EVADE to actual drill cavities: average maximum errors of 2.54±0.49 mm and -2.70±0.48 mm were found. CONCLUSIONS/SIGNIFICANCE: These results demonstrate that EVADE gives accurate feedback which reduces risks of harming modeled critical structures compared to a standard neuronavigation interface during temporal bone phantom drilling.

Determination of a facial nerve safety zone for navigated temporal bone surgery.

BACKGROUND: Transtemporal approaches require surgeons to drill the temporal bone to expose target lesions while avoiding the critical structures within it, such as the facial nerve and other neurovascular structures. We envision a novel protective neuronavigation system that continuously calculates the drill tip-to-facial nerve distance intraoperatively and produces audiovisual warnings if the surgeon drills too close to the facial nerve. Two major problems need to be solved before such a system can be realized. OBJECTIVE: To solve the problems of (1) facial nerve segmentation and (2) calculating a safety zone around the facial nerve in relation to drill-tip tracking inaccuracies. METHODS: We developed a new algorithm called NerveClick for semiautomatic segmentation of the intratemporal facial nerve centerline from temporal bone computed tomography images. We evaluated NerveClick's accuracy in an experimental setting of neuro-otologic and neurosurgical patients. Three neurosurgeons used it to segment 126 facial nerves, which were compared with the gold standard: manually segmented facial nerve centerlines. The centerlines are used as a central axis around which a tubular safety zone is built. The zone's thickness incorporates the drill tip tracking errors. The system will warn when the tracked tip crosses the safety zone. RESULTS: Neurosurgeons using NerveClick could segment facial nerve centerlines with a maximum error of 0.44 ± 0.23 mm (mean ± standard deviation) on average compared with manual segmentations. CONCLUSION: Neurosurgeons using our new NerveClick algorithm can robustly segment facial nerve centerlines to construct a facial nerve safety zone, which potentially allows timely audiovisual warnings during navigated temporal bone drilling despite tracking inaccuracies.

The effect of zirconia and titanium implant abutments on light reflection of the supporting soft tissues.

OBJECTIVES: To determine the difference in light reflection of oral mucosa covering titanium (Ti) or zirconia (ZrO(2)) abutments as it relates to the thickness of the covering mucosa. MATERIAL AND METHODS: Fifteen anterior implants (Astra Osseo speed(®)) in 11 patients were fitted with a Ti or a ZrO(2) abutment (cross-over, within-subject comparison). Hyper-spectral images were taken with a camera fitted on a surgical microscope. High-resolution images with 70 nm interval between 440 and 720 nm were obtained within 30 s (1392 × 1024 pixels). Black- and white-point reference was used for spatial and spectral normalization as well as correction for motion during exposure. Reflection spectra were extracted from the image on a line mid-buccal of the implant, starting 1 mm above the soft tissue continuing up to 3 mm apically. RESULTS: Median soft tissue height is 2.3 mm (min: 1.2 mm and max: 3.1 mm). The buccal mucosa rapidly increases in the thickness, when moving apically. At 2.2 mm, thickness is 3 mm. No perceivable difference between the Ti and ZrO(2) abutment can be observed when the thickness of the mucosa is 2±0.1 mm (95% confidence interval) or more. CONCLUSION: It is expected that the difference in light reflection of soft tissue covering Ti or ZrO(2) abutments is no longer noticeable for the human eye when the mucosa thickness exceeds 2 mm. Haemoglobin peaks in the reflection spectrum can be observed and make hyper-spectral imaging a practical and useful tool for measuring soft tissue health.