High-resolution angioscopic imaging during endovascular neurosurgery

A Novel Method for Angioscopic Imaging and Visualizing the Skull Base Using Complementary Metal Oxide Semiconductor Cameras

BACKGROUND AND OBJECTIVES

Complementary metal oxide semiconductor (CMOS) electrode arrays are a novel technology for miniaturized endoscopes; however, its use for neurointervention is yet to be investigated. In this proof-of-concept study, we aimed to demonstrate the feasibility of CMOS endoscopes in a canine model by providing direct visualization of the endothelial surface, deploying stents and coils, and accessing the spinal subdural space and skull base.

METHODS

Using 3 canine models, standard guide catheters were introduced into the internal carotid and vertebral arteries through the transfemoral route using fluoroscopy. A 1.2-mm CMOS camera was delivered through the guide catheter to inspect the endothelium. Next, the camera was introduced alongside standard neuroendovascular devices including coils and stents to provide direct visualization of their deployment within the endothelium during fluoroscopy. One canine was used for skull base and extravascular visualization. A lumbar laminectomy was performed, and the camera was navigated within the spinal subdural space until the posterior circulation intracranial vasculature was visualized.

RESULTS

We successfully visualized the endothelial surface and performed several endovascular procedures such as deployment of coils and stents under direct endovascular, angioscopic vision. We also demonstrated a proof of concept for accessing the skull base and posterior cerebral vasculature using CMOS cameras through the spinal subdural space.

CONCLUSION

This proof-of-concept study demonstrates the feasibility of CMOS camera technology to directly visualize endothelium, perform common neuroendovascular procedures, and access the base of the skull in a canine model.

Large field-of-view short-wave infrared metalens for scanning fiber endoscopy

SIGNIFICANCE

The scanning fiber endoscope (SFE), an ultrasmall optical imaging device with a large field-of-view (FOV) for having a clear forward view into the interior of blood vessels, has great potential in the cardiovascular disease diagnosis and surgery assistance, which is one of the key applications for short-wave infrared biomedical imaging. The state-of-the-art SFE system uses a miniaturized refractive spherical lens doublet for beam projection. A metalens is a promising alternative that can be made much thinner and has fewer off-axis aberrations than its refractive counterpart.

AIM

We demonstrate a transmissive metalens working at 1310 nm for a forward viewing endoscope to achieve a shorter device length and better resolution at large field angles.

APPROACH

We optimize the metalens of the SFE system using Zemax, fabricate it using e-beam lithography, characterize its optical performances, and compare them with the simulations.

RESULTS

The SFE system has a resolution of ∼ 140    μ m at the center of field (imaging distance 15 mm), an FOV of ∼ 70    deg , and a depth-of-focus of ∼ 15    mm , which are comparable with a state-of-the-art refractive lens SFE. The use of the metalens reduces the length of the optical track from 1.2 to 0.86 mm. The resolution of our metalens-based SFE drops by less than a factor of 2 at the edge of the FOV, whereas the refractive lens counterpart has a ∼ 3 times resolution degradation.

CONCLUSIONS

These results show the promise of integrating a metalens into an endoscope for device minimization and optical performance improvement.

The Scanning Fiber Endoscope: A Novel Surgical and High-Resolution Imaging Device for Intracranial Neurosurgery

BACKGROUND

The scanning fiber endoscope (SFE) is a novel medical imaging device that has been used in various vascular beds as a form of angioscopy, as well as in tracts and duct systems for endoluminal imaging. Owing to its miniaturized form, high resolution, and flexibility, it has demonstrated success in imaging across a wide range of diagnostic applications.

OBJECTIVE

To demonstrate, by performing a third ventriculostomy and visualizing the cranial nerves and brainstem anatomy, that, without modification, the SFE can be used through a transcranial approach in a therapeutic intraventricular neurosurgical application.

METHODS

A 3.7 French SFE system was used without modification on a live porcine model to perform a third ventriculostomy and acquire high-resolution images of the animal's ventricular system, cranial nerves, and brainstem. A side-by-side comparison was made with one of the current standard-of-care rigid endoscopes as a context for size and image quality.

RESULTS

High-resolution video-rate imaging was used to assist the successful, uncomplicated performance of a third ventriculostomy. High-resolution endoscopic images of the brainstem and cranial nerves were acquired.

CONCLUSION

Although the SFE has been shown to be a superior device for imaging, here we demonstrate its first use as a potential therapeutic device in intracranial neurosurgery.

Optimization Study of the Hemodynamics of Saline Flushing in Endoscopic Imaging of Chronic Total Occlusions (CTOs)

PURPOSE

In this study, in vitro experiments and computational fluid dynamic (CFD) simulations are used to expand the understand of the physics of saline flushing of a blocked artery to enable optical imaging. This process involves saline injection, mixing with blood, and advection of the mixture away from the region of interest to provide a clear optical path for imaging.

METHODS

CFD simulations are used as a rapid turn-around tool for the evolutionary design process of an endovascular catheter that combines imaging forward-viewing element with saline flushing lumens.

RESULTS

A novel design and control technique is developed that provides the method to regulate the pressure in a blocked artery during saline flushing, so only small deviations from physiological pressure values are exerted on the damaged artery wall at any time, minimizing risk of rupture. In vitro experiments demonstrate the optical clearing process in phantoms simulating chronic total occlusions (CTOs) in coronary arteries with an opaque blood surrogate being removed by saline flushing. With the CFD compared by the experiments, parametric analyses of artery diameter and curvature, and flushing lumen diameter size were conducted to understand their impact on flushing times and pressures. Different plaque morphologies were studied to explore the feasibility of saline flushing in different CTO conditions.

CONCLUSIONS

A new catheter design is demonstrated to safely and effectively produce saline flushing, leading to a clear optical imaging field, and an improved technique is outlined that overcomes some practical challenges and limitations commonly encountered in angioscopy.

A new set of eyes: development of a novel microangioscope for neurointerventional surgery

BACKGROUND

Endovascular technological advances have revolutionized the field of neurovascular surgery and have become the mainstay of treatment for many cerebrovascular pathologies. Digital subtraction angiography (DSA) is the 'gold standard' for visualization of the vasculature and deployment of endovascular devices. Nonetheless, with recent technological advances in optics, angioscopy has emerged as a potentially important adjunct to DSA. Angioscopy can offer direct visualization of the intracranial vasculature, and direct observation and inspection of device deployment. However, previous iterations of this technology have not been sufficiently miniaturized or practical for modern neurointerventional practice.

OBJECTIVE

To describe the evolution, development, and design of a microangioscope that offers both high-quality direct visualization and the miniaturization necessary to navigate in the small intracranial vessels and provide examples of its potential applications in the diagnosis and treatment of cerebrovascular pathologies using an in vivo porcine model.

METHODS

In this proof-of-concept study we introduce a novel microangioscope, designed from coherent fiber bundle technology. The microangioscope is smaller than any previously described angioscope, at 1.7 F, while maintaining high-resolution images. A porcine model is used to demonstrate the resolution of the images in vivo.

RESULTS

Video recordings of the microangioscope show the versatility of the camera mounted on different microcatheters and its ability to navigate external carotid artery branches. The microangioscope is also shown to be able to resolve the subtle differences between red and white thrombi in a porcine model.

CONCLUSION

A new microangioscope, based on miniaturized fiber optic technology, offers a potentially revolutionary way to visualize the intracranial vascular space.

Perspective review on applications of optics in cerebral endovascular neurosurgery

Cerebral endovascular neurosurgery has transformed the way we manage cerebrovascular disease. Several landmark trials have demonstrated the effectiveness of endovascular techniques leading to continued technological development and applications for various diseases. The utilization of optical technologies and devices is already underway in the field of endovascular neurosurgery. We discuss the contemporary paradigms, challenges, and current optical applications for the most common cerebrovascular diseases: carotid atherosclerotic disease, cerebral aneurysms, intracranial atherosclerosis, and dural arteriovenous fistulas. We also describe needs-based opportunities for future optical applications, with the goal of providing researchers a sense of where we feel optical technologies could impact the way we manage cerebral disease.

Electromechanical Model-Based Design and Testing of Fiber Scanners for Endoscopy

Forward-viewing catheters and scopes for diagnosing disease and guiding interventions in small ducts (less than 3 mm diameter) require wide-field high-quality imaging since scope tip bending is difficult and ineffective. A high-fidelity electromechanically coupled finite element (FE) model of a piezoelectric actuated resonant fiber scanner is presented, which enables improvement on the general design of fiber-optic scanner geometry to increase scan frequency and field of view (FOV). Using the proposed model, parametric sweeps on the specific design variables achieved by acid etching of glass fiber are analyzed to identify their effect on scanner performance and to choose improved designs. The resulting complex fiber scanner design requires development of unique microfabrication techniques. Comparison of three model simulations and their experimental testing show that our proposed coupled model has prediction error of ≤12% with respect to experimental data, while other uncoupled models have up to 39% error. The model and microfabrication techniques presented in this paper have significance for fiber scanning-based systems in that they demonstrate reliability for model-driven design and also flexibility for fiber scanner design of complex geometries, allowing for improvement on medical imaging performance.

High-Resolution Scanning Fiber Angioscopy as an Adjuvant to Fluoroscopy During Endovascular Interventions

PURPOSE

To demonstrate the feasibility and potential utility of high-resolution angioscopy during common endovascular interventions.

METHODS

A 3.7-F scanning fiber angioscope was used in 6 Yorkshire pigs to image branch vessel selection, subintimal dissection, wire snaring, and stent placement. The angioscope was introduced in a coaxial fashion within a standard 6-F guide catheter. A clear field of view was provided using continuous heparinized saline flush through the outer guide catheter. The flush flow rate was manually adjusted to provide clear imaging depending on the diameter of the vessel and local blood flow conditions.

RESULTS

The scanning fiber angioscope was compatible with off-the-shelf catheters and devices commonly used in peripheral and aortic interventions. Video-rate, high-resolution images were obtained during all the interventions tested and provided information that was complementary to simultaneously acquired fluoroscopy. The scanning fiber angioscope was able to detect subintimal dissection and branch vessel stent coverage with higher resolution than fluoroscopy alone.

CONCLUSION

Endoluminal imaging with the scanning fiber angioscope is feasible with current endovascular devices and provides additional relevant information that cannot be assessed fluoroscopically. The scanning fiber angioscope represents a novel optical platform on which new endovascular techniques may be developed that will minimize radiation and contrast doses for patients.

Challenges and opportunities in clinical translation of biomedical optical spectroscopy and imaging

Medical devices face many hurdles before they enter routine clinical practice to address unmet clinical needs. This is also the case for biomedical optical spectroscopy and imaging systems that are used here to illustrate the opportunities and challenges involved. Following initial concept, stages in clinical translation include instrument development, preclinical testing, clinical prototyping, clinical trials, prototype-to-product conversion, regulatory approval, commercialization, and finally clinical adoption and dissemination, all in the face of potentially competing technologies. Optical technologies face additional challenges from their being extremely diverse, often targeting entirely different diseases and having orders-of-magnitude differences in resolution and tissue penetration. However, these technologies can potentially address a wide variety of unmet clinical needs since they provide rich intrinsic biochemical and structural information, have high sensitivity and specificity for disease detection and localization, and are practical, safe (minimally invasive, nonionizing), and relatively affordable.

Multimodal laser-based angioscopy for structural, chemical and biological imaging of atherosclerosis

The complex nature of atherosclerosis demands high-resolution approaches to identify subtle thrombogenic lesions and define the risk of plaque rupture. Here, we report the proof-of-concept use of a multimodal scanning fiber endoscope (SFE) consisting of a single optical fiber scanned by a piezoelectric drive that illuminates tissue with red, blue, and green laser beams, and digitally reconstructs images at 30 Hz with high resolution and large fields-of-view. By combining laser-induced reflectance and fluorescence emission of intrinsic fluorescent constituents in arterial tissues, the SFE allowed us to co-generate endoscopic videos with a label-free biochemical map to derive a morphological and spectral classifier capable of discriminating early, intermediate, advanced, and complicated atherosclerotic plaques. We demonstrate the capability of scanning fiber angioscopy for the molecular imaging of vulnerable atherosclerosis by targeting proteolytic activity with a fluorescent probe activated by matrix metalloproteinases. We also show that the SFE generates high-quality spectral images in vivo in an animal model with medium-sized arteries. Multimodal laser-based angioscopy could become a platform for the diagnosis, prognosis, and image-guided therapy of atherosclerosis.

Application of emerging technologies to improve access to ischemic stroke care

During the past 20 years, the traditional supportive treatment for stroke has been radically transformed by advances in catheter technologies and a cohort of prominent randomized controlled trials that unequivocally demonstrated significant improvement in stroke outcomes with timely endovascular intervention. However, substantial limitations to treatment remain, among the most important being timely access to care. Nonetheless, stroke care has continued its evolution by incorporating technological advances from various fields that can further reduce patients' morbidity and mortality. In this paper the authors discuss the importance of emerging technologies—mobile stroke treatment units, telemedicine, and robotically assisted angiography—as future tools for expanding access to the diagnosis and treatment of acute ischemic stroke.

Multimodal laser-based angioscopy for structural, chemical and biological imaging of atherosclerosis

The complex nature of atherosclerosis demands high-resolution approaches to identify subtle thrombogenic lesions and define the risk of plaque rupture. Here, we report the proof-of-concept use of a multimodal scanning fiber endoscope (SFE) consisting of a single optical fiber scanned by a piezoelectric drive that illuminates tissue with red, blue, and green laser beams, and digitally reconstructs images at 30 Hz with high resolution and large fields-of-view. By combining laser-induced reflectance and fluorescence emission of intrinsic fluorescent constituents in arterial tissues, the SFE allowed us to co-generate endoscopic videos with a label-free biochemical map to derive a morphological and spectral classifier capable of discriminating early, intermediate, advanced, and complicated atherosclerotic plaques. We demonstrate the capability of scanning fiber angioscopy for the molecular imaging of vulnerable atherosclerosis by targeting proteolytic activity with a fluorescent probe activated by matrix metalloproteinases. We also show that the SFE generates high-quality spectral images in vivo in an animal model with medium-sized arteries. Multimodal laser-based angioscopy could become a platform for the diagnosis, prognosis, and image-guided therapy of atherosclerosis.

Diagnostic and Interventional Optical Angioscopy in Ex Vivo Carotid Arteries

BACKGROUND: Angioscopy – or endovascular endoscopy – is a catheter-based technique employing a flexible fiberoptic angioscope to directly visualize arterial lumen. Poor resolution and excessive stiffness of pre-existent angioscopes limited their use clinically. Recent advances resulted in novel fused optical fiber bundle angioscopes with improved flexibility and imaging resolution. Use of these devices in endovascular neurosurgery is still largely unexplored.

OBJECTIVE: To evaluate image quality and feasibility of optical angioscopes for diagnostic and interventional neuro-angioscopy in carotid arteries of human cadavers.

METHODS: A 5-F optical angioscope was used in human cadaveric carotid arteries to inspect integrity of arterial walls, identify atherosclerotic plaques and associated lesions prone to thrombogenicity, place intravascular occlusion coils, and deploy endovascular stents with real-time visualization.

RESULTS: Angioscopy provided key information about endoluminal anatomy such as presence and characteristics of atherosclerotic plaques and thrombogenic lesions not detected by conventional diagnostic methods. Direct real-time visualization of vascular lumen during endovascular interventions provided information on spatial distribution of coils, coil loop herniation, and apposition of stent cells against carotid artery wall complementary to angiography.

CONCLUSIONS: Fused optical fiber bundle angioscopes provide good-quality endoluminal images in human carotid arteries. Their use can feasibly assist in navigation of extracranial carotid arteries to inspect integrity of the arterial wall and identify atherosclerotic plaques and associated lesions vulnerable to thrombogenicity, allow placement of intravascular occlusion coils, and assess apposition of stents to vessel wall. Further in Vivo validation needs to be conducted along with additional research to improve image quality, flexibility, and size of angioscopes.

Wall Apposition Is a Key Factor for Aneurysm Occlusion after Flow Diversion: A Histologic Evaluation in 41 Rabbits

BACKGROUND AND PURPOSE

Robust wall apposition for flow-diverter stents may be important for endothelialization. Using a large series of experimental aneurysms treated with the Pipeline Embolization Device, the objectives of this study were to 1) assess interobserver agreement for the evaluation of wall apposition on posttreatment DSA and evaluate its association with aneurysm occlusion, and 2) measure the relationship between wall apposition assessed with histology and aneurysm occlusion rate after treatment.

MATERIALS AND METHODS

Saccular aneurysms were created in 41 rabbits and treated with the Pipeline Embolization Device. DSA was performed just after the deployment of the device and at follow-up. Three investigators independently graded wall apposition on posttreatment DSA as good or poor. A histopathologist blinded to the angiographic results graded the wall apposition on histologic samples. We examined the correlation between angiographic occlusion and wall apposition with histology and angiography.

RESULTS

Wall apposition evaluated on histology was strongly associated with saccular aneurysm occlusion. Sensitivity and specificity of wall apposition to predict complete occlusion at follow-up were 76.9% and 84.0%, respectively, with an overall accuracy of 81.6%. In this experimental study, DSA was suboptimal to assess flow-diverter apposition, with moderate interobserver agreement and low accuracy.

CONCLUSIONS

Good wall apposition is strongly associated with complete occlusion after flow-diverter therapy. In this study, DSA was suboptimal for assessing wall apposition of flow-diverter stents. These findings suggest that improved tools for assessing flow diverter-stent wall apposition are highly relevant.

Design and Fabrication of a Disposable Dental Handpiece for Clinical Use of a New Laser-Based Therapy-Monitoring System

Dental caries, the breakdown of tooth enamel by bacteria infection that causes cavities in the enamel, is the most common chronic disease in individuals 6–19 years of age in the U.S. Optical detection of caries has been shown to be sensitive to the presence of bacteria and the resulting demineralization of enamel. The scanning fiber endoscope (SFE) is a miniature camera system that can detect early stages of caries by performing high-quality imaging and laser fluorescence spectroscopy with 405 nm excitation. Because optical imaging of caries does not involve radiation risk, repeated imaging of the teeth is acceptable during treatment of the bacterial infection to monitor healing. A disposable handpiece was designed and fabricated to position the flexible fiber optic SFE probe for quantitative measurements. Plastic 3D-printed handpiece prototypes were tested with the SFE and a fluorescence calibration standard to verify mechanical fit and absence of signal contamination. Design feedback was provided by pediatric dentists and staff engineers to guide iterations. The final design configuration was based on the need to image interproximal regions (contact surfaces between adjacent teeth), ergonomics, and probe safety. The final handpiece design: (1) is safe for both the patient and the probe, (2) allows easy SFE insertion and removal, (3) does not interfere with spectral measurements, (4) standardizes the SFE's positioning during imaging by maintaining a consistent distance from the target surface, and (5) is significantly less expensive to produce and use than purchasing sanitary endoscope sheaths. The device will be used to help determine if new medicinal therapies can arrest caries and repair early interproximal demineralization under the clinical monitoring program. Ultimately, we anticipate that this handpiece will help us move closer toward widespread implementation of a dental diagnostic laser system that is safer and more sensitive than conventional methods for early caries detection.

Imaging Inflammation in Cerebrovascular Disease

Imaging inflammation in large intracranial artery pathology may play an important role in the diagnosis of and risk stratification for a variety of cerebrovascular diseases. Looking beyond the lumen has already generated widespread excitement in the stroke community, and the potential to unveil molecular processes in the vessel wall is a natural evolution to develop a more comprehensive understanding of the pathogenesis of diseases, such as ICAD and brain aneurysms.

Self-Contained Image Recalibration in a Scanning Fiber Endoscope Using Piezoelectric Sensing

The scanning fiber endoscope (SFE) is a new ultrathin (1.2 mm diameter) medical imaging device that utilizes a unique mechanical scanning technique to image large (120 deg) fields of view (FOVs). A single 80 μm optical fiber is circularly vibrated by a piezo-electric tube to illuminate a field while the reflected light is collected to construct an image pixel-by-pixel. Accurate scanning of the optical fiber is paramount to image quality. Previously, an optical calibration chamber in the base station was used to calibrate the scanning of the optical fiber. This analytical and experimental work eliminates the use of the calibration chamber by implementing a new piezoelectric sensing approach enabling self-contained recalibration to maintain high-image quality during long medical procedures and also reducing the cost, size, and power consumption of the SFE. This work provides a major step toward self-calibration through adaptive control without additional sensors.

Cerebrovascular neurosurgery 2014

Continued advances in our understanding of the management of cerebrovascular disease were made in 2014. A randomized trial for management of unruptured brain arteriovenous malformation (ARUBA) (Mohr et al. Lancet 2014;383:614-21.) and the Scottish intracranial vascular malformation study (Al-Shahi Salman et al. JAMA 2014;311:1661-9) were published and contrasted with reports based on extensive surgical experience. We highlight the results from the simvastatin in aneurysmal subarachnoid hemorrhage study (STASH) (Kirkpatrick et al. Lancet Neurol 2014;13:666-75) which unfortunately did not demonstrate a benefit of simvastatin on outcome in patients with aneurysmal subarachnoid hemorrhage. The 10 year follow-up of the international subarachnoid aneurysm trial (ISAT) (Molyneux et al. Lancet 2014 [E-pub]) and the 3 year follow-up results from the stenting and aggressive medical management for preventing recurrent stroke in intracranial stenosis (SAMMPRIS) (Derdeyn et al. Lancet 2014;383:333-41) were also reported. Results from the Japan adult Moyamoya trial (JAM) (Miyamoto et al. Stroke 2014;45:1415-21) are also briefly reviewed. Furthermore, benefits of familial screening for relatives of intracranial aneurysm and arteriovenous malformation patients, a promising angioscopic experience for endovascular procedures, as well as a modified bypass technique for management of complex aneurysms are outlined. The largest literature series to date for coiling large and giant aneurysms together with the midterm results of the Solitaire stent (ev3, Irvine, CA, USA) aneurysm remodeling study in coiling wide-necked aneurysms (SOLARE) are also presented (Gory et al. Neurosurgery 2014;75:215-9).

High-resolution angioscopic imaging during endovascular neurosurgery

BACKGROUND

Endoluminal optical imaging, or angioscopy, has not seen widespread application during neurointerventional procedures, largely as a result of the poor imaging resolution of existing angioscopes. Scanning fiber endoscopes (SFEs) are a novel endoscopic platform that allows high-resolution video imaging in an ultraminiature form factor that is compatible with currently used distal access endoluminal catheters.

OBJECTIVE

To test the feasibility and potential utility of high-resolution angioscopy with an SFE during common endovascular neurosurgical procedures.

METHODS

A 3.7-French SFE was used in a porcine model system to image endothelial disruption, ischemic stroke and mechanical thrombectomy, aneurysm coiling, and flow-diverting stent placement.

RESULTS

High-resolution, video-rate imaging was shown to be possible during all of the common procedures tested and provided information that was complementary to standard fluoroscopic imaging. SFE angioscopy was able to assess novel factors such as aneurysm base coverage fraction and side branch patency, which have previously not been possible to determine with conventional angiography.

CONCLUSION

Endovascular imaging with an SFE provides important information on factors that cannot be assessed fluoroscopically and is a novel platform on which future neurointerventional techniques may be based because it allows for periprocedural inspection of the integrity of the vascular system and the deployed devices. In addition, it may be of diagnostic use for inspecting the vascular wall and postprocedure device evaluation.