Optical Coherence Tomography
2018; Lippincott Williams & Wilkins; Volume: 49; Issue: 4 Linguagem: Inglês
10.1161/strokeaha.117.019818
ISSN1524-4628
AutoresChing‐Jen Chen, Jeyan S. Kumar, Stephanie H. Chen, Dale Ding, Thomas J. Buell, Samir Sur, Natasha Ironside, Evan Luther, Michael Ragosta, Min Soo Park, M. Yashar S. Kalani, Kenneth C. Liu, Robert M. Starke,
Tópico(s)Intracranial Aneurysms: Treatment and Complications
ResumoHomeStrokeVol. 49, No. 4Optical Coherence Tomography Free AccessReview ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessReview ArticlePDF/EPUBOptical Coherence TomographyFuture Applications in Cerebrovascular Imaging Ching-Jen Chen, MD, Jeyan S. Kumar, MD, Stephanie H. Chen, MD, Dale Ding, MD, Thomas J. Buell, MD, Samir Sur, MD, Natasha Ironside, MBChB, Evan Luther, MD, Michael RagostaIII, MD, Min S. Park, MD, M. Yashar Kalani, MD, PhD, Kenneth C. Liu, MD and Robert M. Starke, MD, MSc Ching-Jen ChenChing-Jen Chen From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). , Jeyan S. KumarJeyan S. Kumar From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). , Stephanie H. ChenStephanie H. Chen From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). , Dale DingDale Ding From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). , Thomas J. BuellThomas J. Buell From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). , Samir SurSamir Sur From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). , Natasha IronsideNatasha Ironside From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). , Evan LutherEvan Luther From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). , Michael RagostaIIIMichael RagostaIII From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). , Min S. ParkMin S. Park From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). , M. Yashar KalaniM. Yashar Kalani From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). , Kenneth C. LiuKenneth C. Liu From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). and Robert M. StarkeRobert M. Starke From the Department of Neurological Surgery (C.-J.C., J.S.K., T.J.B., M.S.P., M.Y.K.) and Division of Cardiovascular Medicine (M.R.), University of Virginia Health System, Charlottesville; Department of Neurological Surgery, University of Miami, FL (S.C., S.S., E.L., R.M.S.); Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ (D.D.); Department of Neurosurgery, Auckland City Hospital, New Zealand (N.I.); and Department of Neurosurgery, Milton S. Hershey Medical Center, PA (K.C.L.). Originally published28 Feb 2018https://doi.org/10.1161/STROKEAHA.117.019818Stroke. 2018;49:1044–1050Other version(s) of this articleYou are viewing the most recent version of this article. Previous versions: January 1, 2018: Previous Version 1 Cross-sectional imaging of biological tissue microstructure using optical backscattering was first demonstrated in 1991.1 The technique, known as optical coherence tomography (OCT), uses low-coherence interferometry to produce a 2-dimensional image of optical scattering from tissues in a way that resembles pulse-echo imaging in ultrasound. Huang et al1 revealed promising clinical and research applications with their in vitro demonstrations of this novel imaging technique in both the peripapillary area of the retina and the coronary arteries. The first in vivo clinical application of OCT was reported in 1993, when it permitted detailed, noninvasive imaging of the anterior eye chamber, as well as other structures, such as the fovea and the optic disc of the retina.2–5 Collaboration between this pioneering group and the New England Eye Center has led to its routine use in ophthalmologic diagnostics and its subsequent commercial availability in 1996.6Recent advancements in OCT technology have broadened its application to retinal vasculature and nontransparent tissues.7–10 OCT angiography has permitted noninvasive evaluation of retinal vascular abnormalities ranging from detecting neovascularization to quantifying ischemia.11 OCT use in areas ranging from developmental biology research to clinical applications in the fields of gastroenterology, urology, and neurosurgery have now been investigated.8,12–23 Optimization of OCT technology as an imaging modality has been achieved with the use of real-time imaging yielding greater image acquisition rates and laser light sources, which have improved image resolution.12,24–27 The recent US Food and Drug Administration approval of OCT for intravascular imaging has provided an unprecedented level of detail, on the micron level, in the evaluation of vascular pathologies that involve individual vessel wall layers.28 This has also sparked interest in the translation of the technology into the field of neuroendovascular surgery, where OCT data have the potential to revolutionize the diagnosis and management of stroke, aneurysms, and other cerebrovascular pathologies.Comparison of OCT and Intravascular UltrasoundIntravascular ultrasound (IVUS) is a well-established clinical imaging modality for the evaluation of vascular pathologies and is somewhat analogous to OCT. Images in ultrasound are formed based on the backscattering or reflection of sound waves detected by the probe from tissues with different acoustic properties. Axial image resolution in ultrasound is determined primarily by the frequency of the sound waves. Typical sound wave frequencies used in clinical settings are in the 10- to 40-MHz range, yielding axial resolutions as fine as 100 μm.6 When compared with ultrasound, OCT systems have axial resolutions ranging from 12 to 100 μm and transverse resolutions between 20 and 90 μm.29 Although higher axial image resolutions can be achieved using higher frequency sound waves in ultrasound, attenuation of high-frequency sound waves significantly limits the depth of imaging to a few millimeters. Because it is more difficult to focus sound waves than light waves, transverse image resolution using ultrasound is inherently lower than for OCT.6 Although image contrast in OCT is produced by differences in refraction index of optical scattering in tissues, contrast in ultrasound is obtained via differences in acoustic impedance mismatch of sound wave scattering in tissues.6Despite an imaging depth of only a few millimeters, OCT produces significantly higher resolution images than ultrasound. In addition, IVUS may be limited by large acoustic shadows when imaging implants with fine structures and low porosity (ie, flow diverters [FDs]). Therefore, with the development of Fourier-domain OCT (FD-OCT) systems, OCT may closely rival, if not surpass IVUS as the superior modality for intravascular imaging.OCT in Coronary ArteriesMuch of the work on intravascular OCT imaging has been performed in coronary arteries. The focus of intravascular imaging remains vessel lumen geometry, which forms the primary basis for disease severity evaluation (Figure [A]) and procedural treatment guidance. An accurate evaluation of the lumen vessel/stent interface is essential for critical measurements, which include minimal luminal area, fraction of luminal obstruction, percent neointimal hyperplasia, degree of stent apposition or expansion, minimal stent cross-sectional area, luminal gain/loss, and degree of restenosis.29 OCT has become an increasingly popular intravascular imaging modality during the past decade, providing clear delineation of the boundaries between lumen and vessel wall. Furthermore, the absence of signal interference from calcium in vessel walls enables its application in guiding complex interventional procedures in vasculatures with abundant superficial calcification.29 In addition to evaluating native vasculature, OCT has demonstrated utility in assessing intracoronary stent placement (Figure [B] and [C]). The ability to capture high-resolution images and the versatility of the physical properties of light offered by OCT will continue to improve our understanding of vascular pathologies.Download figureDownload PowerPointFigure. In vivo human optical coherence tomography images of coronary and internal carotid arteries. A, Axial image of stable fibrous plaque (white arrows) within coronary artery acquired using optical coherence tomography. B, Axial image of well-apposed stent within coronary artery acquired using optical coherence tomography. Stent struts are indicated by white arrows. C, Axial image of malapposed stent (white arrows) within coronary artery acquired using optical coherence tomography. D, Axial image of arterial dissection (white arrows) within petrous segment of internal carotid artery acquired using optical coherence tomography.OCT in Extracranial Athero-Occlusive DiseaseBeyond its intracoronary applications, OCT has recently been used for the evaluation of extracranial vascular pathologies, including atherosclerosis, stent placement, and dissection (Figure [D]). Yoshimura reported the first application of OCT imaging in the internal carotid artery (ICA) in a case report describing the detection of intraluminal thrombus by OCT, not seen on IVUS, in a patient with symptomatic carotid stenosis.30 This finding led to a change in management from the planned carotid artery stenting (CAS) procedure to a carotid endarterectomy. The specimen demonstrated a soft plaque with intraluminal thrombus, which correlated with the preoperative OCT findings. Furthermore, Reimers et al31 were able to obtain high-resolution images with information on stent geometry and plaque coverage from their preliminary experience of OCT imaging in 7 patients with symptomatic and asymptomatic carotid stenosis who underwent CAS. Although both occlusive and nonocclusive techniques were used in the study, images obtained using the occlusive technique were superior in quality and more suitable for analysis. The use of OCT resulted in the prolongation of procedural time by 16±12 minutes, and only 1 patient experienced transient loss of consciousness for ≈3 minutes during OCT and ICA flow occlusion without lasting neurological sequela. In a subsequent study comparing OCT and IVUS for CAS, Yoshimura et al reported superior detection rates of intraluminal thrombus and neovascularization using OCT. The authors also demonstrated excellent interobserver and intraobserver variability in reporting OCT diagnoses of thrombus, neovascularization, ulceration, and lipid pool.To validate the in vivo TD-OCT data with ex vivo TD-OCT and conventional histopathology, Matthews et al32 attempted to correlate the structural compositions of the common carotid artery and ICA in human and animal subjects. The common carotid artery of 3 pigs demonstrated excellent correlation in vessel structural compositions between in vivo TD-OCT, ex vivo TD-OCT, and histopathology. In vivo images of cavernous and petrous segments of the ICA in human cadavers were found to be comparable with ex vivo images and histopathology and demonstrated the vessel layers in clear detail. An area of high signal in the luminal side of the vessel walls, noted on both in vivo and ex vivo TD-OCT, corresponded to the elastin and smooth muscle layers of the tunica media seen on histopathology, demonstrating that in vivo TD-OCT imaging closely correlated with the structural information visualized on histological examination.Previously, a major challenge in obtaining high-resolution images with the use of OCT in the large-caliber, high-flow carotid arteries has been inadequate blood clearance, necessitating proximal vessel occlusion for satisfactory image acquisition. Faster pullback speed associated with the development of FD-OCT enables adequate blood clearance during the shortened imaging acquisition period and obviating the need for proximal occlusion. Its wider field of view also facilitates the imaging of larger arteries, such as the ICA. Jones et al33 reported that 97% of all cross-sectional images obtained via FD-OCT in 4 patients with asymptomatic carotid disease were suitable for analysis. Similarly, Attizzani et al,28 using FD-OCT without proximal balloon occlusion, were able to obtain satisfactory images for analysis in 2 patients with late vascular response after CAS.Therefore, FD-OCT represents a promising imaging modality of the carotid vasculature that does not require complex technical adaptations for blood clearance or carotid flow interruption. However, clinicians should be aware that although no safety issues beyond those associated with conventional carotid angiography have been reported, the risks associated with OCT remain incompletely defined while awaiting appropriately powered studies.33 Despite the larger field of view associated with FD-OCT systems, extensive lipid deposition precludes the accurate interpretation and quantification of the underlying layers of the vessel wall. Finally, although histopathologic correlations with OCT for the coronary vasculature have been extensively studied, such correlation in the carotid circulation has yet to be investigated.OCT in Intracranial Pathology and Athero-Occlusive DiseaseDiagnosis and Assessment of Cerebral AneurysmsOCT has been a proposed imaging modality for the diagnosis, treatment, and surveillance of cerebral aneurysms. Currently, catheter digital subtraction angiography remains the gold standard for the diagnosis of cerebral aneurysms, providing information on aneurysm morphology, size, and location, as well as aiding the decision-making process for management strategies. However, additional factors, such as wall thickness and histopathologic characteristics, may offer a new treatment paradigm, leading to fewer potentially dangerous interventions for low-risk aneurysms. Saccular aneurysms are believed to arise from acquired or congenital defects at vessel branch points. One of these defects is the absence of internal elastic lamina layer, referred to as medial cushion defects. Matthews et al,32 who compared normal and elastase-treated common carotid artery segments of pigs and aorta of rabbits, evaluated these samples using ex vivo TD-OCT. The presence or absence of elastin in the tunica media, seen in normal or elastase-treated vessels, respectively, could be clearly distinguished using TD-OCT and subsequently corroborated with histopathology. To assess the ability of OCT to evaluate cerebral aneurysms, Hoffman et al34 developed silicone phantom aneurysm models based on patients' 3-dimensional angiographic datasets. The authors found that the ability to capture the entire aneurysm geometry was dependent on the catheter position in the vessel, aneurysm diameter, height, and ostium size. In the second part of the study, the circle of Willis of 3 cadavers was explanted and ex vivo OCT imaging was performed. All 3 layers of the vessel wall could be visualized, with accurate assessment of their respective thicknesses along with the origins of the perforating arteries. This underscores the ability of OCT to analyze the intracranial vasculature with accuracy and reproducibility and may play an important role in characterizing the rupture risk of aneurysms.To achieve blood clearance in OCT image acquisition, several techniques have been used, including contrast boluses or balloon occlusion. However, these strategies can cause intravascular pressure elevations and increase wall stress, which could theoretically rupture aneurysms. Current OCT catheters are only able to image sidewall aneurysms because the light exits perpendicular to the catheter axis.34 Because most aneurysms arise at vessel bifurcations or branch points, alterations in current OCT catheter design (ie, a forward-facing OCT probe) would be required to image these aneurysms completely. Additionally, the current OCT devices are only able to provide a limited evaluation of large or wide-necked aneurysms. Hence, improvements in the field of view may allow more complete imaging of these aneurysms, including their domes.Coil Embolization of Cerebral AneurysmsAfter coil embolization of aneurysms, catheter angiography is often used to monitor for recanalization. Rates of recurrent hemorrhage and the need for repeat treatments is not insignificant following initial coiling, particularly for ruptured, large, and wide-necked aneurysms, thus highlighting the need for imaging modalities that can better assess aneurysm healing and occlusion after embolization.35 The first ex vivo OCT animal model to assess aneurysm healing was developed by Thorell et al36 using surgically created sidewall aneurysms in canine carotid arteries. These experimental aneurysms were treated with platinum Guglielmi detachable or biopolymer-coated Matrix coils, and the animals were euthanized at various time points after follow-up angiography. At each time point, OCT was able to demonstrate tissue growth (healing by fibrosis or endothelialization), not visible on conventional angiography, over the aneurysm neck in this canine model, which correlated with subsequent histopathologic analysis. In vivo OCT imaging findings in patients with treated cerebral aneurysms were first reported by Su et al37 in a proof-of-concept study that used an OCT catheter with a smaller profile design to access the tortuous intracranial vessels.Flow Diversion for Cerebral AneurysmsThe use of OCT in the assessment of flow-diverting stents for the treatment of cerebral aneurysms has been explored by several studies. Proper apposition of FDs is critical for promoting neoendothelialization across the aneurysm neck, as well as to prevent endoleak between the stent and vessel wall, which can lead to incomplete aneurysm occlusion.38,39 Stent malapposition can also lead to delayed thromboembolic complications. To this end, van der Marel et al40 sought to compare OCT with high-resolution contrast-enhanced cone-beam computed tomography (VasoCT) to evaluate stent apposition in an experimental canine aneurysm model. Sidewall aneurysms, created in the common carotid artery and treated using FDs, were subsequently evaluated by VasoCT and OCT using the grading of regional apposition after FD treatment method. After image postprocessing, the Euclidian distances were calculated between the FD and vessel walls, with potential areas of malapposition being further investigated with raw cross-sectional images. The authors found that VasoCT and OCT performed equally well in detecting areas of malapposition using the grading of regional apposition after FD treatment scoring system; however, both modalities were limited by false positives from artifacts induced by motion or the metallic properties of the FD, which were easily resolved after further confirmation with the cross-sectional images. Occasional negative distances were observed on the OCT maps, and analysis of the cross-sectional images at these points demonstrated thrombus at the distal end of the FD, as well as a side branch with intensity features similar to vessel wall. When compared with VasoCT, OCT, with its superior spatial resolution, was better able to image individual struts of the FD and more precisely localize the arterial wall, allowing for malapposition detection beyond 0.25 mm. In addition, microthrombi on the surface of FDs that are often unseen on conventional 2-dimensional digital subtraction angiography can be detected using OCT, thus potentially guiding more targeted treatments.41 OCT may also possess an advantage in FD imaging at the skull base, where artifact from surrounding bone limits modalities, such as VasoCT. It is important to note that the study was limited by the use of a straight segment of an extracranial vessel for evaluation, which does not accurately represent the tortuosity and complexity of the intracranial vasculature.In a feasibility study, Lopes et al42 described their initial experience with intracranial navigation of the OCT catheter and image acquisition within a deployed FD stent in a human cadaver. Perforating vessels from the middle cerebral and posterior cerebral arteries, not seen on conventional catheter angiography, could be visualized with OCT. Subsequently, after an FD was deployed in the basilar artery, all of the stent's struts and their relation to the vessel wall could be visualized. Furthermore, the struts' relation to perforator orifices at their takeoffs from the basilar artery could also be evaluated. Information on perforator size, location, and density provided by OCT may allow for better stent selection (ie, ideal strut density) and placement, minimizing the risk of infarction from perforator occlusion. In a follow-up study, the authors implanted 3 different models of FD stents in pigs and used OCT to monitor neointimal formation.43 OCT was able to reliably measure neointimal information, corroborated by histopathology, and provide a valuable metric in following patients with FD stents. Additionally, the accuracy of measurement using OCT may enable improved selection of an appropriate FD size, reducing the risk of thromboembolic events resulting from high-density metal coverage, as well as the need for multiple stents.40Most recently, Given et al44 describe the first report of in vivo application of OCT in the intracranial vasculature in a patient treated with balloon angioplasty and stent placement for vertebrobasilar insufficiency. Immediately after the procedure, the patient was asymptomatic; however, the patient developed right-sided hemiplegia, nystagmus, and respiratory distress 15 hours after the procedure. Because of concerns for residual stenosis, the patient underwent repeat angiography, which demonstrated a nonocclusive thrombus at the proximal stent, and was treated with pharmacological thrombolysis. FD-OCT imaging was then used to visualize the stent and vertebrobasilar vasculature to determine whether any flow limiting stenosis or vessel pathology, such as dissection, was present. They were able to obtain a clear visualization of the stent with excellent apposition, minimal tissue prolapse through the stent, and a maximal 28% residual stenosis. This case illustrated one of the future applications of OCT in the management of patients with complex intracranial vascular pathology. Table 1 summarizes the current literature investigating the use of OCT in cerebrovascular imaging.Table 1. Current Literature Evaluating the Use of OCT in Cerebrovascular ImagingStudyYearTypeObjectiveResultsMatthews et al322011Ex vivo and in vivo human, ex vivo and in vivo pigTo determine the feasibility of catheter-based OCT, and to compare OCT images with histological preparations and benchtop OCT of nondiseased blood vessels.Successful acquisition of in vivo human OCT images of intracranial vasculature. Segments of common carotid arteries in pigs and petrous/cavernous segments of internal carotid arteries of humans could be captured at high resolution. OCT images correlated well with histological sectioning.Hoffman et al342016Silicone phantomTo investigate the ability of OCT in characterizing intracranial aneurysms using silicone phantom with aneurysms from patient data.For sidewall aneurysms with maximum heights less than the maximum imaging diameter of the OCT system, additional information of the aneurysm wall can be obtained. Evaluation is limited for bifurcation and larger aneurysms.Thorell et al362005Ex vivo canineBenchtop OCT evaluation of experimentally created sidewall aneurysms treated with coil embolization at varying time points.Visualization of fibrosis and endothelialization across aneurysm necks. Excellent correlation with histological preparations.van der Marel et al402017In vivo canineAssessment of FD implanted in canine model with experimentally created sidewall aneurysms using OCT and VasoCT.Detection of malapposition of stents and acute thrombus formation, with comparable rates to VasoCT.Lopes et al422011Ex vivo humanOCT catheter evaluation basilar artery stent in human cadaver.High-resolution images of perforators and stent struts can be acquired.Patel et al452017In vivo humanOCT evaluation of left vertebral artery stent in a patient with vertebral artery stenosis.First in vivo human study with high-resolution images of stent malapposition.FD indicates flow diverter; and OCT, optical coherence tomography.Future DirectionsThe potential of OCT for evaluating the intracranial vasculature and its diseases is just beginning to be realized. There exist possibilities for using OCT to assess both extracranial and intracranial stents. OCT has been used to successfully identify the proximal starting point of an ICA dissection before initiating CAS. Additionally, OCT can rapidly identify stent strut apposition to the parent vessel, endoleaks, patency of perforating arties, in-stent stenosis or thrombosis, and tissue prolapse during the stenting procedure. On follow-up angiography, OCT may demonstrate neointimal growth, restenosis, and stent fracture, foreshort
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