High resolution in vivo intra-arterial imaging with optical coherence tomography

Histology-Grounded Automated Plaque Subtype Segmentation in Intravascular Optical Coherence Tomography

Background

Intravascular optical coherence tomography (IVOCT) adoption has been limited by the complexity of image interpretation. The interpretation of histologic subtypes beyond lipid, calcium, and fibrous is challenging to human readers. To assist and standardize IVOCT image analysis, we demonstrate an artificial intelligence algorithm based on a histology data set that identifies lipid pools, fibrofatty, calcified lipid, and calcified fibrous in human coronary arteries for the first time.

Methods

Sixty-seven human coronary arteries were imaged with IVOCT within 24 hours after death and then underwent histologic examination. IVOCT images were coregistered and segmented into histologic subtypes: lipid pools, fibrofatty tissue, calcified lipid, and calcified fibrous tissue. Experiments regarding lipidic plaque included fibrofatty tissue, lipid pools, and calcified lipids. Experiments regarding calcium plaque included calcified fibrous and calcified lipid plaques. Optical coherence tomography images were lumen justified and cropped to a depth of 200 pixels (1 mm) to account for limited optical coherence tomography penetration depth. IVOCT segmentations from expert readers guided by histology were used to train segmentation neural networks.

Results

For each data set, in addition to testing each of these subtypes individually, we trained and tested the model on the combined grouping of subtypes. Combined lipid subtypes achieved validation and test Dice (Sørensen-Dice coefficient) of 0.63 and 0.40, respectively, whereas combined calcium subtypes achieved validation and test Dice of 0.66 and 0.62, respectively.

Conclusions

This histology-validated artificial intelligence algorithm driven by histologic subtypes can identify plaque subtypes not evident to a human reader. The reported algorithm can provide a fast solution to IVOCT image interpretation.

Optical Coherence Tomography in Myocardial Infarction Management: Enhancing Precision in Percutaneous Coronary Intervention

In acute myocardial infarction (AMI), the urgency of coronary revascularization through percutaneous coronary intervention (PCI) is paramount, offering notable advantages over pharmacologic treatment. However, the persistent risk of adverse events, including recurrent AMI and heart failure post-revascularization, underscores the necessity for enhanced strategies in managing coronary artery disease. Traditional angiography, while widely employed, presents significant limitations by providing only two-dimensional representations of complex three-dimensional vascular structures, hampering the accurate assessment of plaque characteristics and stenosis severity. Intravascular imaging, specifically optical coherence tomography (OCT), significantly addresses these limitations with superior spatial resolution compared to intravascular ultrasound (IVUS). Within the context of AMI, OCT serves dual purposes: as a diagnostic tool to accurately identify culprit lesions in ambiguous cases and as a guide for optimizing PCI procedures. Its capacity to differentiate between various mechanisms of acute coronary syndrome, such as plaque rupture and spontaneous coronary dissection, enhances its diagnostic potential. Furthermore, OCT facilitates precise lesion preparation, optimal stent sizing, and confirms stent deployment efficacy. Recent meta-analyses indicate that OCT-guided PCI markedly improves safety and efficacy in revascularization, subsequently decreasing the risks of mortality and complications. This review emphasizes the critical role of OCT in refining patient-specific therapeutic approaches, aligning with the principles of precision medicine to enhance clinical outcomes for individuals experiencing AMI.

Label-Free Optical Technologies for Middle-Ear Diseases

Medical applications of optical technology have increased tremendously in recent decades. Label-free techniques have the unique advantage of investigating biological samples in vivo without introducing exogenous agents. This is especially beneficial for a rapid clinical translation as it reduces the need for toxicity studies and regulatory approval for exogenous labels. Emerging applications have utilized label-free optical technology for screening, diagnosis, and surgical guidance. Advancements in detection technology and rapid improvements in artificial intelligence have expedited the clinical implementation of some optical technologies. Among numerous biomedical application areas, middle-ear disease is a unique space where label-free technology has great potential. The middle ear has a unique anatomical location that can be accessed through a dark channel, the external auditory canal; it can be sampled through a tympanic membrane of approximately 100 microns in thickness. The tympanic membrane is the only membrane in the body that is surrounded by air on both sides, under normal conditions. Despite these favorable characteristics, current examination modalities for middle-ear space utilize century-old technology such as white-light otoscopy. This paper reviews existing label-free imaging technologies and their current progress in visualizing middle-ear diseases. We discuss potential opportunities, barriers, and practical considerations when transitioning label-free technology to clinical applications.

Automatic bifurcation detection utilizing pullback characteristics of bifurcation in intravascular optical coherence tomography

Bifurcation detection in coronary arteries is significant since it influences the treatment strategy selection and optimization. Bifurcations are also reliable landmarks for image registration. Intravascular optical coherence tomography (IVOCT) is a high-resolution imaging modality that is very useful in percutaneous coronary intervention stenting optimization. We present a bifurcation identification method utilizing pullback characteristics for IVOCT, which can effectively identify the bifurcations with a small size. The longitudinal view of the pullback will appear as an outward discontinuity in the bifurcation area. By detecting this discontinuity, bifurcation can be identified with high accuracy. We also use the normal vectors method to extract the ostium of bifurcation. We compare the proposed method with the widely-used distance transformation method by clinical 5302 IVOCT images from 22 pullbacks. The average metrics of true positive rate (TPR), true negative rate (TNR), positive predictive value (PPV), and negative predictive value (NPV) for the proposed method are 86.97%, 98.50%, 85.56%, and 98.67%, respectively. TPR, PPV, and NPV by the proposed method are improved by 40.24%, 9.31%, 3.90%, and TNR is on par compared with the distance transformation method. Especially in the small bifurcation identification, TPR of the proposed method is 64.71% higher than the distance transformation method with a bifurcation area ratio less than 0.2.

Detection of Vulnerable Coronary Plaques Using Invasive and Non-Invasive Imaging Modalities

Acute coronary syndrome (ACS) mostly arises from so-called vulnerable coronary plaques, particularly prone for rupture. Vulnerable plaques comprise a specific type of plaque, called the thin-cap fibroatheroma (TFCA). A TCFA is characterized by a large lipid-rich necrotic core, a thin fibrous cap, inflammation, neovascularization, intraplaque hemorrhage, microcalcifications or spotty calcifications, and positive remodeling. Vulnerable plaques are often not visible during coronary angiography. However, different plaque features can be visualized with the use of intracoronary imaging techniques, such as intravascular ultrasound (IVUS), potentially with the addition of near-infrared spectroscopy (NIRS), or optical coherence tomography (OCT). Non-invasive imaging techniques, such as computed tomography coronary angiography (CTCA), cardiovascular magnetic resonance (CMR) imaging, and nuclear imaging, can be used as an alternative for these invasive imaging techniques. These invasive and non-invasive imaging modalities can be implemented for screening to guide primary or secondary prevention therapies, leading to a more patient-tailored diagnostic and treatment strategy. Systemic pharmaceutical treatment with lipid-lowering or anti-inflammatory medication leads to plaque stabilization and reduction of cardiovascular events. Additionally, ongoing studies are investigating whether modification of vulnerable plaque features with local invasive treatment options leads to plaque stabilization and subsequent cardiovascular risk reduction.

Automatic lumen segmentation using uniqueness of vascular connected region for intravascular optical coherence tomography

We present an automatic lumen segmentation method using uniqueness of connected region for intravascular optical coherence tomography (IVOCT), which can effectively remove the effect on lumen segmentation caused by blood artifacts. Utilizing the uniqueness of vascular wall on A-lines, we detect the A-lines shared by multiple connected regions, identify connected regions generated by blood artifacts using traversal comparison of connected regions' location, shared ratio and area ratio and then remove all artifacts. We compare these three methods by 216 challenging images with severe blood artifacts selected from clinical 1076 IVOCT images. The metrics of the proposed method are evaluated including Dice index, Jaccard index and accuracy of 94.57%, 90.12%, 98.02%. Compared with automatic lumen segmentation based on the previous morphological feature method and widely used dynamic programming method, the metrics of the proposed method are significantly enhanced, especially in challenging images with severe blood artifacts.

Impact of diabetes mellitus on vascular healing process after everolimus-eluting stent implantation: An optical coherence tomography study

BACKGROUND/PURPOSE

To study the impact of diabetes mellitus (DM) on vascular healing process after implantation of everolimus-eluting stent (EES).

METHODS/MATERIALS

Data from 3 prospective studies (HEAL-EES, REVER, and RESERVOIR), including patients with EES implantation and OCT follow-up, were merged. Differences in vascular healing process assessed by OCT were compared between DM and non-DM using generalized estimating equations. Neointimal proliferation, neointimal signal pattern (high, low, and layered), and uncovered/malapposed struts were evaluated.

RESULTS

A total of 96 lesions (61 DM lesions and 35 non-DM lesions) were included. Mean OCT follow-up time was 8.9 ± 1.5 months and comparable between groups. DM were older, high frequently female and acute coronary syndrome, and received smaller stent than non-DM. No differences were observed in quantitative vascular healing process between groups. However, DM exhibited higher low and layered signal pattern neointima compared to non-DM at lesion level (p = 0.030) and cross-section level (p < 0.001). Uncovered/malapposed struts were comparable between groups.

CONCLUSIONS

Quantitative vascular healing process was comparable between groups. However, DM was significantly associated with low signal pattern, which is characteristic of focal inflammation, after EES implantation. Further study might be required to study relationship between neointimal signal pattern and clinical events.

Early coronary healing in ST segment elevation myocardial infarction: sirolimus-eluting stents vs. drug-coated balloons after bare-metal stents. The PEBSI-2 optical coherence tomography randomized study

OBJECTIVES

Drug-coated balloons (DCBs) have theoretical advantages over drug-eluting stents (DESs) to facilitate stent healing. We studied whether, in patients undergoing primary coronary interventions (pPCIs), a strategy of DCB after bare-metal stent improves early healing as determined by optical coherence tomography (OCT) compared with new-generation DES.

METHODS

pPCI patients were randomized (1:1) to treatment with new-generation sirolimus-eluting stents (DES group) or DCB-strategy. Vessel healing was assessed by OCT at 90 days.

RESULTS

Fifty-three patients were randomized (26 DES vs. 27 DCB). At 90 days, both strategies showed a low rate of uncovered struts (3.2 vs. 3.2%, P = 0.64) and a very high and similar rate of covered and apposed struts (96.6 vs. 96.1%, respectively; P = 0.58). However, DCB group had a significantly lower rate of major coronary evaginations (68 vs. 37%, P = 0.026), and more frequently developed a thin homogeneous neointimal layer (20 vs. 70.4%, P = 0.001) suggesting distinct superior healing at 3 months compared to DES.

CONCLUSIONS

In pPCI both, sirolimus-DES and DCB-strategy, provide excellent strut coverage at 3 months. However, DCB ensures more advanced and optimal stent healing compared to sirolimus-DES. Further research is needed to determine whether, in patients undergoing pPCI, DCB offers superior long-term clinical and angiographic outcomes than new-generation DES (NCT03610347).

Optical Coherence Tomography for Ophthalmology Imaging

Optical coherence tomography (OCT) is a depth-resolved imaging modality, which is able to achieve micrometer-scale resolution within biological tissue noninvasively. In the past 30 years, researchers all around the world had made several essential efforts on techniques relevant to OCT. OCT has become a routine process for eye diseases with different types. In this chapter, the three important stages in the development of OCT are briefly illustrated, including the time domain OCT (TD-OCT), the frequency domain OCT (FD-OCT) and the optical coherence tomography angiography (OCTA). Each of the technique has made great progress for use on living human eye imaging in clinical applications. TD-OCT was first proposed and commercialized, which is able to achieve acceptable 2D depth-resolved cross-sectional images of human retina in vivo. FD-OCT was the upgraded OCT technique compared with TD-OCT. By capturing the coherent signal within the Fourier space, the FD-OCT could improve the image sensitivity compared with TD-OCT, and achieve dozens of kilo hertz imaging speed. OCTA is the newest developments of OCT technique, which is able to visualize the micro vasculature networks of human retina in vivo. With OCTA technique, the newest ophthalmologic OCT system is able to achieve detailed diagnosis for both micro-structure and vasculature abnormalities for clinical applications. The further development of OCT technique on imaging speed, contrast, resolution, field of view, and so on will make OCT to be a more powerful tool for clinical usages.

Towards ultrahigh resolution OCT based endoscopical pituitary gland and adenoma screening: a performance parameter evaluation

Ultrahigh resolution optical coherence tomography (UHR-OCT) for differentiating pituitary gland versus adenoma tissue has been investigated for the first time, indicating more than 80% accuracy. For biomarker identification, OCT images of paraffin embedded tissue are correlated to histopathological slices. The identified biomarkers are verified on fresh biopsies. Additionally, an approach, based on resolution modified UHR-OCT ex vivo data, investigating optical performance parameters for the realization in an in vivo endoscope is presented and evaluated. The identified morphological features-cell groups with reticulin framework-detectable with UHR-OCT showcase a promising differentiation ability, encouraging endoscopic OCT probe development for in vivo application.

Optical coherence tomography modeling incorporating scattering, absorption, and multiple reflections

A direct scattering optical coherence tomography forward model was developed to simulate A-scans for both idealized and real light sources on an arbitrary given sample structure. Previous models neglected absorption, scattering, and multiple reflections at interfacial layers, and so two extended models were developed to investigate the impact of these processes. The first model uses the Beer-Lambert law to incorporate both absorption and scattering optical processes, and the second model uses a recursive form to model multiple reflections. These models were tested on a structure representative of a multilayered skin sample. The results show that the absorption and scattering processes have significant impact on the height of the peaks in the simulated A-scans. Conversely, the incorporation of multiple reflections has very little impact on the height of these peaks. Neither of the above processes has any impact on the locations of the A-scan peaks, which are associated with the sample interfaces between layers.

Imaging modalities to diagnose carotid artery stenosis: progress and prospect

In the past few decades, imaging has been developed to a high level of sophistication. Improvements from one-dimension (1D) to 2D images, and from 2D images to 3D models, have revolutionized the field of imaging. This not only helps in diagnosing various critical and fatal diseases in the early stages but also contributes to making informed clinical decisions on the follow-up treatment profile. Carotid artery stenosis (CAS) may potentially cause debilitating stroke, and its accurate early detection is therefore important. In this paper, the technical development of various CAS diagnosis imaging modalities and its impact on the clinical efficacy is thoroughly reviewed. These imaging modalities include duplex ultrasound (DUS), computed tomography angiography (CTA) and magnetic resonance angiography (MRA). For each of the imaging modalities considered, imaging methodology (principle), critical imaging parameters, and the extent of imaging the vulnerable plaque are discussed. DUS is usually the initial recommended CAS diagnostic examination. However, for the therapeutic intervention, either MRA or CTA is recommended for confirmation, and for added information on intracranial cerebral circulation and aortic arch condition for procedural planning. Over the past few decades, the focus of CAS diagnosis has also shifted from pure stenosis quantification to plaque characterization. This has led to further advancement in the existing imaging tools and development of other potential imaging tools like Optical coherence tomography (OCT), photoacoustic tomography (PAT), and infrared (IR) thermography.

Optical Coherence Tomography for Intracranial Aneurysms: A New Method for Assessing the Aneurysm Structure

BACKGROUND

There is a lack of precise methods for predicting the risk of aneurysm rupture. Therefore, prophylactic treatment is used, which leads to unnecessary potential complications. A new modality enabling a more accurate risk assessment is needed. Optical coherence tomography (OCT) is a new-generation imaging technology that has astonishing resolution for vascular imaging. In this study, OCT was used for the evaluation of intracranial aneurysms.

METHODS

In vivo OCT imaging was performed for aneurysms induced in 6 rabbits and in 9 intracranial aneurysm patients. Catheters were cut short to prevent any extra length from damaging aneurysms and tissues. Images of both the parent artery and the aneurysm at multiple viewing angles were obtained using rotational OCT scanning.

RESULTS

The OCT images of rabbits correlated well with histologic sections. The 3-layered architecture of the parent arteries was explicitly shown. Ruptured intracranial aneurysms manifested complete breakdown of the wall structure; however, this was not observed in any unruptured aneurysms. The OCT images of unruptured intracranial aneurysms demonstrated a trend of degradation by showing the gradual disappearance of the demarcation between the layers or incomplete apoptosis in layer structures.

CONCLUSION

OCT is the most precise imaging modality because it provides detailed information regarding the aneurysm structures, thus enabling more distinct insight into the vascular construction of intracranial aneurysms.

Comprehensive intravascular imaging of atherosclerotic plaque in vivo using optical coherence tomography and fluorescence lifetime imaging

Comprehensive imaging of both the structural and biochemical characteristics of atherosclerotic plaque is essential for the diagnosis and study of coronary artery disease because both a plaque's morphology and its biochemical composition affect the level of risk it poses. Optical coherence tomography (OCT) and fluorescence lifetime imaging (FLIm) are promising optical imaging methods for characterizing coronary artery plaques morphologically and biochemically, respectively. In this study, we present a hybrid intravascular imaging device, including a custom-built OCT/FLIm system, a hybrid optical rotary joint, and an imaging catheter, to visualize the structure and biochemical composition of the plaque in an atherosclerotic rabbit artery in vivo. Especially, the autofluorescence lifetime of the endogenous tissue molecules can be used to characterize the biochemical composition; thus no exogenous contrast agent is required. Also, the physical properties of the imaging catheter and the imaging procedures are similar to those already used clinically, facilitating rapid translation into clinical use. This new intravascular imaging catheter can open up new opportunities for clinicians and researchers to investigate and diagnose coronary artery disease by simultaneously providing tissue microstructure and biochemical composition data in vivo without the use of exogenous contrast agent.

Nano-optic endoscope for high-resolution optical coherence tomography in vivo

Acquisition of high-resolution images from within internal organs using endoscopic optical imaging has numerous clinical applications. However, difficulties associated with optical aberrations and the trade-off between transverse resolution and depth-of-focus significantly limit the scope of applications. Here, we integrate a metalens, with the ability to modify the phase of incident light at sub-wavelength level, into the design of an endoscopic optical coherence tomography catheter (termed nano-optic endoscope) to achieve near diffraction-limited imaging through negating non-chromatic aberrations. Remarkably, the tailored chromatic dispersion of the metalens in the context of spectral interferometry is utilized to maintain high-resolution imaging beyond the input field Rayleigh range, easing the trade-off between transverse resolution and depth-of-focus. We demonstrate endoscopic imaging both in resected human lung specimens and in sheep airways in vivo. The combination of the superior resolution and higher imaging depth-of-focus of the nano-optic endoscope will likely increase the clinical utility of endoscopic optical imaging.

Clinical translation of handheld optical coherence tomography: practical considerations and recent advancements

Since the inception of optical coherence tomography (OCT), advancements in imaging system design and handheld probes have allowed for numerous advancements in disease diagnostics and characterization of the structural and optical properties of tissue. OCT system developers continue to reduce form factor and cost, while improving imaging performance (speed, resolution, etc.) and flexibility for applicability in a broad range of fields, and nearly every clinical specialty. An extensive array of components to construct customized systems has also become available, with a range of commercial entities that produce high-quality products, from single components to full systems, for clinical and research use. Many advancements in the development of these miniaturized and portable systems can be linked back to a specific challenge in academic research, or a clinical need in medicine or surgery. Handheld OCT systems are discussed and explored for various applications. Handheld systems are discussed in terms of their relative level of portability and form factor, with mention of the supporting technologies and surrounding ecosystem that bolstered their development. Additional insight from our efforts to implement systems in several clinical environments is provided. The trend toward well-designed, efficient, and compact handheld systems paves the way for more widespread adoption of OCT into point-of-care or point-of-procedure applications in both clinical and commercial settings.

Intravascular Optical Coherence Tomography for Characterization of Atherosclerosis with a 1.7 Micron Swept-Source Laser

The main cause of acute coronary events, such as thrombosis, is the rupture of atherosclerotic plaques. Typical intravascular optical coherence tomography (IVOCT) imaging systems that utilize a 1.3 μm swept source laser are often used for identifying fibrous cap thickness of plaques, yet cannot provide adequate depth penetration to resolve the size of the lipid pool. Here, we present a novel  IVOCT system with a 1.7 μm center wavelength swept light source that can readily penetrate deeper into the tissue because of the longer wavelength and allows for better identification of plaques due to the lipid absorption spectrum at 1.7 μm. Using this system, we have imaged a human coronary artery to evaluate the performance of the novel OCT system and verified the results by hematoxylin and eosin (H&E) histology. The significantly improved imaging depth and better identification sensitivity suggest that the 1.7 μm OCT system holds great potential  that can be further translated for in-vivo applications of atherosclerosis characterization.

Automated segmentation and quantification of airway mucus with endobronchial optical coherence tomography

We propose a novel suite of algorithms for automatically segmenting the airway lumen and mucus in endobronchial optical coherence tomography (OCT) data sets, as well as a novel approach for quantifying the contents of the mucus. Mucus and lumen were segmented using a robust, multi-stage algorithm that requires only minimal input regarding sheath geometry. The algorithm performance was highly accurate in a wide range of airway and noise conditions. Mucus was classified using mean backscattering intensity and grey level co-occurrence matrix (GLCM) statistics. We evaluated our techniques in vivo in asthmatic and non-asthmatic volunteers.

Endoscopic optical coherence tomography: technologies and clinical applications [Invited]

In this paper, we review the current state of technology development and clinical applications of endoscopic optical coherence tomography (OCT). Key design and engineering considerations are discussed for most OCT endoscopes, including side-viewing and forward-viewing probes, along with different scanning mechanisms (proximal-scanning versus distal-scanning). Multi-modal endoscopes that integrate OCT with other imaging modalities are also discussed. The review of clinical applications of endoscopic OCT focuses heavily on diagnosis of diseases and guidance of interventions. Representative applications in several organ systems are presented, such as in the cardiovascular, digestive, respiratory, and reproductive systems. A brief outlook of the field of endoscopic OCT is also discussed.

Intravascular optical coherence tomography [Invited]

Shortly after the first demonstration of optical coherence tomography for imaging the microstructure of the human eye, work began on developing systems and catheters suitable for intravascular imaging in order to diagnose and investigate atherosclerosis and potentially to monitor therapy. This review covers the driving considerations of the clinical application and its constraints, the major engineering milestones that enabled the current, high-performance commercial imaging systems, the key studies that laid the groundwork for image interpretation, and the clinical research that traces intravascular optical coherence tomography (OCT) from early human pilot studies to current clinical trials.

Fully integrated optical coherence tomography, ultrasound, and indocyanine green-based fluorescence tri-modality system for intravascular imaging

We present a tri-modality imaging system and fully integrated tri-modality probe for intravascular imaging. The tri-modality imaging system is able to simultaneously acquire optical coherence tomography (OCT), ultrasound (US), and fluorescence imaging. Moreover, for fluorescence imaging, we used the FDA-approved indocyanine green (ICG) dye as the contrast agent to target lipid-loaded macrophages. We conducted imaging from a male New Zealand white rabbit to evaluate the performance of the tri-modality system. In addition, tri-modality images of rabbit aortas were correlated with hematoxylin and eosin (H&E) histology to check the measurement accuracy. The fully integrated miniature tri-modality probe, together with the use of ICG dye suggest that the system is of great potential for providing a more accurate assessment of vulnerable plaques in clinical applications.

The role of intracoronary imaging in acute coronary syndromes: OCT in focus

Optical coherence tomography (OCT) has emerged as a powerful intravascular imaging modality in recent years. The introduction of frequency-domain OCT has simplified the procedure and enabled its safe utilisation in different clinical settings including acute coronary syndromes, where it can determine the mechanism of plaque disruption, thrombus burden, and guide percutaneous coronary intervention. In patients presenting with stent failure (stent thrombosis and instent restenosis), OCT can also be very useful in determining the underlying mechanism and guiding therapy thereafter. This article aims to review the role of OCT in acute coronary syndromes as well as its potential clinical applications.

Crossing chronic total occlusions with the Ocelot system: the initial European experience

AIMS

The aim of the study was to determine the safety, efficacy and feasibility of a new chronic total occlusion (CTO) device using optical coherence tomography (OCT) technology, the Ocelot catheter (Avinger, Inc., Redwood City, CA, USA), for crossing of SFA CTOs following guidewire failure.

METHODS AND RESULTS

Prospective, multicentre, market preference testing. Thirty-three patients with confirmed CTO (99-100% stenosis by visual estimate) of their superficial femoral artery (SFA) were treated between September 28, 2011, and December 9, 2011, at three European centres. Ocelot crossed 94% (31/33) of CTOs, allowing guidewire placement in the distal true lumen. All (100%) lesions were treated without any major adverse safety events. Procedural time and contrast dose were significantly reduced (p<0.0001) when compared with a similar, non-OCT-guided CTO crossing device (Wildcat catheter; Avinger, Inc.). Overall physician feedback on the catheter performance was positive with an 87% average rating of excellent or good across seven categories. Performance ratings of Ocelot's OCT imaging guidance were consistently positive with an 86% average rating of excellent or good across five OCT categories.

CONCLUSIONS

The Ocelot catheter combines advanced CTO crossing technology with real-time OCT guidance. When compared with a similar non-OCT-guided catheter, crossing efficacy and safety profile improved. Total procedure time and contrast volumes were significantly reduced. The Ocelot is a safe, efficient and effective tool for crossing CTOs.

Three dimensional mesoscale analysis of translamellar cross-bridge morphologies in the annulus fibrosus using optical coherence tomography

The defining characteristic of the annulus fibrosus (AF) of the intervertebral disc (IVD) has long been the lamellar structures that consist of highly ordered collagen fibers arranged in alternating oblique angles from one layer to the next. However, a series of recent histologic studies have demonstrated that AF lamellae contain elastin- and type VI collagen-rich secondary "cross-bridge" structures across lamellae. In this study, we use optical coherence tomography (OCT) to elucidate the three-dimensional (3-D) morphologies of these translamellar cross-bridges in AF tissues. Mesoscale volumetric images by OCT revealed a 3-D network of heterogeneously distributed cross-bridges. The results of this study confirm the translamellar cross-bridge is identifiable as a distinguishable structure, which lies in the interbundle space of adjacent lamellae and crisscrosses multiple lamellae in the radial direction. In contrast to previously proposed models extrapolated from 2-D sections, results from this current study show that translamellar cross-bridges exist as a complex, interconnected network. We also found much greater variation in lengths of cross-bridges within the interbundle space of lamellae (0.8-1.4 mm from the current study versus 0.3-0.6 mm from 2-D sections). OCT-based 3-D morphology of translamellar cross-bridge provides novel insight into the AF structure.

Current OCT Approaches Do Not Reliably Identify TCFAs

It is now clearly established that Thin-Capped Fibroatheromas (TCFAs) lead to most Acute Coronary Syndromes (ACSs). The ability to selectively intervene on TCFAs predisposed to rupture and ACSs would dramatically alter the practice of cardiology. While the ability of OCT to identify thin walled plaques at micron scale resolutions has represented a major advance, it is a misconception that it can reliably identify TCFAs. One major reason is that the 'diffuse border' criteria currently used to determine 'lipid plaque' is almost undoubtedly from high scattering in the intima and not because of core composition (necrotic core). A second reason is that, rather than looking at lipid collections, studies need to be focused on identifying necrotic cores with OCT. Necrotic cores are characteristic of TCFAs and not lipid collections. Numerous other OCT approaches are available which can potentially accurately assess TCFAs, but these have not been aggressively pursed which we believe likely stems in part from the misconceptions over the efficacy of 'diffuse borders'.

Practical Challenges of Current Video Rate OCT Elastography: Accounting for Dynamic and Static Tissue Properties

Optical coherence tomography (OCT) elastography (OCTE) has the potential to be an important diagnostic tool for pathologies including coronary artery disease, osteoarthritis, malignancies, and even dental caries. Many groups have performed OCTE, including our own, using a wide range of approaches. However, we will demonstrate current OCTE approaches are not scalable to real-time, in vivo imaging. As will be discussed, among the most important reasons is current designs focus on the system and not the target. Specifically, tissue dynamic responses are not accounted, with examples being the tissue strain response time, preload variability, and conditioning variability. Tissue dynamic responses, and to a lesser degree static tissue properties, prevent accurate video rate modulus assessments for current embodiments. Accounting for them is the focus of this paper. A top-down approach will be presented to overcome these challenges to real time in vivo tissue characterization. Discussed first is an example clinical scenario where OTCE would be of substantial relevance, the prevention of acute myocardial infarction or heart attacks. Then the principles behind OCTE are examined. Next, constrains on in vivo application of current OCTE are evaluated, focusing on dynamic tissue responses. An example is the tissue strain response, where it takes about 20 msec after a stress is applied to reach plateau. This response delay is not an issue at slow acquisition rates, as most current OCTE approaches are preformed, but it is for video rate OCTE. Since at video rate each frame is only 30 msec, for essentially all current approaches this means the strain for a given stress is changing constantly during the B-scan. Therefore the modulus can't be accurately assessed. This serious issue is an even greater problem for pulsed techniques as it means the strain/modulus for a given stress (at a location) is unpredictably changing over a B-scan. The paper concludes by introducing a novel video rate approach to overcome these challenges.

Identification of vessel wall degradation in ascending thoracic aortic aneurysms with OCT

Degradation of the wall of human ascending thoracic aorta has been assessed through Optical Coherence Tomography (OCT). OCT images of the media layer of the aortic wall exhibit micro-structure degradation in case of diseased aortas from aneurysmal vessels. The OCT indicator of degradation depends on the dimension of areas of the media layer where backscattered reflectivity becomes smaller due to a disorder on the morphology of elastin, collagen and smooth muscle cells (SMCs). Efficient pre-processing of the OCT images is required to accurately extract the dimension of degraded areas after an optimized thresholding procedure. OCT results have been validated against conventional histological analysis. The OCT qualitative assessment has achieved a pair sensitivity-specificity of 100%-91.6% in low-high degradation discrimination when a threshold of 4965.88µm(2) is selected. This threshold suggests to have physiological meaning. The OCT quantitative evaluation of degradation achieves a correlation of 0.736 between the OCT indicator and the histological score. This in-vitro study can be transferred to the clinical scenario to provide an intraoperative assessment tool to guide cardiovascular surgeons in open repair interventions.

Fiber-optic polarization diversity detection for rotary probe optical coherence tomography

We report a polarization diversity detection scheme for optical coherence tomography with a new, custom, miniaturized fiber coupler with single mode (SM) fiber inputs and polarization maintaining (PM) fiber outputs. The SM fiber inputs obviate matching the optical lengths of the X and Y OCT polarization channels prior to interference and the PM fiber outputs ensure defined X and Y axes after interference. Advantages for this scheme include easier alignment, lower cost, and easier miniaturization compared to designs with free-space bulk optical components. We demonstrate the utility of the detection system to mitigate the effects of rapidly changing polarization states when imaging with rotating fiber optic probes in Intralipid suspension and during in vivo imaging of human airways.

Clinical applications of optical coherence tomography in urology

Since optical coherence tomography (OCT) was first demonstrated in 1991, it has advanced significantly in technical aspects such as imaging speed and resolution, and has been clinically demonstrated in a diverse set of medical and surgical applications, including ophthalmology, cardiology, gastroenterology, dermatology, oncology, among others. This work reviews current clinical applications in urology, particularly in bladder, urether, and kidney. Clinical applications in bladder and urether mainly focus on cancer detection and staging based on tissue morphology, image contrast, and OCT backscattering. The application in kidney includes kidney cancer detection based on OCT backscattering attenuation and non-destructive evaluation of transplant kidney viability or acute tubular necrosis based on both tissue morphology from OCT images and function from Doppler OCT (DOCT) images. OCT holds the promise to positively impact the future clinical practices in urology.

Measurement of wavefront aberrations and lens deformation in the accommodated eye with optical coherence tomography-equipped wavefront system

To quantitatively approach the relationship between optical changes in an accommodated eye and the geometrical deformation of its crystalline lens, a long scan-depth anterior segment OCT equipped wavefront sensor was developed and integrated with a Badal system. With this system, accommodation was stimulated up to 6.0D in the left eye and also measured in the same eye for three subjects. High correlations between the accommodative responses of refractive power and the radius of the anterior lens surface were found for the three subjects (r>0.98). The change in spherical aberration was also highly correlated with the change in lens thickness (r>0.98). The measurement was very well repeated at a 2nd measurement session on the same day for the three subjects and after two weeks for one subject. The novelty of incorporating the Badal system into the OCT equipped wavefront sensor eliminated axial misalignment of the measurement system with the test eye due to accommodative vergence, as in the contralateral paradigm. The design also allowed the wavefront sensor to capture conjugated sharp Hartmann-Shack images in accommodated eyes to accurately analyze wavefront aberrations. In addition, this design extended the accommodation range up to 10.0D. By using this system, for the first time, we demonstrated linear relationships of the changes between the refractive power and the lens curvature and also between the spherical aberration and the lens thickness during accommodation in vivo. This new system provides an accurate and useful technique to quantitatively study accommodation.

Toward the guidance of transbronchial biopsy: identifying pulmonary nodules with optical coherence tomography

BACKGROUND

Solitary pulmonary nodules (SPNs) frequently require transbronchial needle aspiration (TBNA) or biopsy to determine malignant potential, but have variable diagnostic yields. Confirming needle placement within SPNs during TBNA could significantly increase diagnostic yield. Optical coherence tomography (OCT) provides nondestructive, high-resolution, microstructural imaging with potential to distinguish SPN from parenchyma. We have developed needle-based OCT probes compatible with TBNA. Before OCT can play any significant role in guiding clinical TBNA, OCT interpretation criteria for differentiating SPN from lung parenchyma must be developed and validated.

METHODS

OCT of SPN and parenchyma was performed on 111 ex vivo resection specimens. OCT criteria for parenchyma and SPN were developed and validated in a blinded assessment. Six blinded readers (two pulmonologists, two pathologists, and two OCT experts) were trained on imaging criteria in a 15-min training session prior to interpreting the validation data set.

RESULTS

OCT of lung parenchyma displayed evenly spaced signal-void alveolar spaces, signal-intense backreflections at tissue-air interfaces, or both. SPNs lacked both of these imaging features. Independent validation of OCT criteria by the six blinded readers demonstrated sensitivity and specificity of 95.4% and 98.2%, respectively.

CONCLUSIONS

We have developed and validated OCT criteria for lung parenchyma and SPN with sensitivity and specificity &gt; 95% in this ex vivo study. We anticipate that OCT could be a useful complementary imaging modality to confirm needle placement during TBNA to potentially increase diagnostic yield.

Optimization of K-edge imaging for vulnerable plaques using gold nanoparticles and energy resolved photon counting detectors: a simulation study

We investigated the effect of different imaging parameters, such as dose, beam energy, energy resolution and the number of energy bins, on the image quality of K-edge spectral computed tomography (CT) of gold nanoparticles (GNP) accumulated in an atherosclerotic plaque. A maximum likelihood technique was employed to estimate the concentration of GNP, which served as a targeted intravenous contrast material intended to detect the degree of the plaque's inflammation. The simulation studies used a single-slice parallel beam CT geometry with an x-ray beam energy ranging between 50 and 140 kVp. The synthetic phantoms included small (3 cm in diameter) cylinder and chest (33 × 24 cm(2)) phantoms, where both phantoms contained tissue, calcium and gold. In the simulation studies, GNP quantification and background (calcium and tissue) suppression tasks were pursued. The x-ray detection sensor was represented by an energy resolved photon counting detector (e.g., CdZnTe) with adjustable energy bins. Both ideal and more realistic (12% full width at half maximum (FWHM) energy resolution) implementations of the photon counting detector were simulated. The simulations were performed for the CdZnTe detector with a pixel pitch of 0.5-1 mm, which corresponds to a performance without significant charge sharing and cross-talk effects. The Rose model was employed to estimate the minimum detectable concentration of GNPs. A figure of merit (FOM) was used to optimize the x-ray beam energy (kVp) to achieve the highest signal-to-noise ratio with respect to the patient dose. As a result, the successful identification of gold and background suppression was demonstrated. The highest FOM was observed at the 125 kVp x-ray beam energy. The minimum detectable GNP concentration was determined to be approximately 1.06 µmol mL(-1) (0.21 mg mL(-1)) for an ideal detector and about 2.5 µmol mL(-1) (0.49 mg mL(-1)) for a more realistic (12% FWHM) detector. The studies show the optimal imaging parameters at the lowest patient dose using an energy resolved photon counting detector to image GNP in an atherosclerotic plaque.

Assessing near infrared optical properties of ceramic orthodontic brackets using cross-polarization optical coherence tomography

Secondary decay (caries) under ceramic orthodontic brackets remains a significant dental problem and near infrared cross-polarization optical coherence tomography (CP-OCT) has the potential to detect underlying demineralization. The purpose of this study was to determine the effect of crystalline structure and chemical composition of ceramic brackets on CP-OCT imaging. Four ceramic brackets types, which were divided into monocrystalline and polycrystalline, were examined using CP-OCT. The results of this study demonstrated that the crystallinity of the ceramic brackets affected the 1310 nm CP-OCT imaging with the greatest attenuation seen in polycrystalline alumina brackets. The alumina polycrystalline bracket materials had significantly higher attenuation and scattering than alumina monocrystalline brackets (p < 0.05, ANOVA, Bonferroni). Additionally, bracket base morphology and composition affected NIR light attenuation. There was considerable attenuation in bracket bases that contained additive zirconium spheres (∼30 µm) and this alteration was significantly greater than the jagged alumina crystallographic alterations found in the other bracket systems (p < 0.05, ANOVA, Bonferroni). Noninvasive, near infrared (NIR) cross-polarization optical coherence tomography (CP-OCT) has potential to effectively image through portions of ceramic brackets; however, further investigation into the optical effects of resin integration in the base portion of the brackets is warranted.

Intravascular optical coherence tomography measurement of size and apposition of metallic stents

Effect of beam size and catheter position on the apparent size and apposition of metallic stent struts in IVOCT images were examined. Micro-CT data was employed to determine light - stent strut interactions. Simulated results suggest that location of the reflecting regions depend on relative orientation and position of stent struts to the IVOCT beam. Erroneous stent apposition measurements can occur when the IVOCT catheter is at an eccentric position. A method that mitigates stent strut apposition measurement errors is proposed.

The invasive assessment of coronary atherosclerosis and stents using optical coherence tomography: a clinical update

Ischaemic heart disease (IHD) remains one of the leading causes of death. Atherosclerosis has been intensely researched given the IHD prevalence and the financial impacts on healthcare systems. More recently, in vivo characterisation of coronary atherosclerotic plaque and tissue responses following stent implantation in a coronary artery has been made possible by a novel technology called optical coherence tomography (OCT). OCT is a light-based, invasive, intracoronary imaging modality long applied to the field of ophthalmology and now in clinical use worldwide. It gives a unique view of within the coronary artery using near-infrared light with a resolution of 15 microns, 10 times higher than other invasive coronary imaging techniques like intravascular ultrasound. The technology is being adopted to comprehensively detect features that make plaques 'vulnerable' (eg, large lipid pool, thin, fibrous-cap atheroma), whether stents are implanted optimally within the artery, and visualise the small layers of tissue that form over stent metal surfaces over time, which in turn may provide surrogate markers for long-term stent safety and help guide the optimal duration of dual antiplatelet therapy, a topic of big discussion at the current point of time.

Intravascular near-infrared fluorescence catheter with ultrasound guidance and blood attenuation correction

Intravascular near-infrared fluorescence (NIRF) imaging offers a new approach for characterizing atherosclerotic plaque, but random catheter positioning within the vessel lumen results in variable light attenuation and can yield inaccurate measurements. We hypothesized that NIRF measurements could be corrected for variable light attenuation through blood by tracking the location of the NIRF catheter with intravascular ultrasound (IVUS). In this study, a combined NIRF-IVUS catheter was designed to acquire coregistered NIRF and IVUS data, an automated image processing algorithm was developed to measure catheter-to-vessel wall distances, and depth-dependent attenuation of the fluorescent signal was corrected by an analytical light propagation model. Performance of the catheter sensing distance correction method was evaluated in coronary artery phantoms and ex vivo arteries. The correction method produced NIRF estimates of fluorophore concentrations, in coronary artery phantoms, with an average root mean square error of 17.5%. In addition, the correction method resulted in a statistically significant improvement in correlation between spatially resolved NIRF measurements and known fluorophore spatial distributions in ex vivo arteries (from r = 0.24 to 0.69, p < 0.01, n = 6). This work demonstrates that catheter-to-vessel wall distances, measured from IVUS images, can be employed to compensate for inaccuracies caused by variable intravascular NIRF sensing distances.

Volumetric optical frequency domain imaging of pulmonary pathology with precise correlation to histopathology

BACKGROUND

Lung cancer is the leading cause of cancer-related mortality. Radiology and bronchoscopy techniques do not have the necessary resolution to evaluate lung lesions on the microscopic scale, which is critical for diagnosis. Bronchial biopsy specimens can be limited by sampling error and small size. Optical frequency domain imaging (OFDI) provides volumetric views of tissue microstructure at near-histologic resolution and may be useful for evaluating pulmonary lesions to increase diagnostic accuracy. Bronchoscopic OFDI has been evaluated in vivo, but a lack of correlated histopathology has limited the ability to develop accurate image interpretation criteria.

METHODS

We performed OFDI through two approaches (airway-centered and parenchymal imaging) in 22 ex vivo lung specimens, using tissue dye to precisely correlate imaging and histology.

RESULTS

OFDI of normal airway allowed visualization of epithelium, lamina propria, cartilage, and alveolar attachments. Carcinomas exhibited architectural disarray, loss of normal airway and alveolar structure, and rapid light attenuation. Squamous cell carcinomas showed nested architecture. Atypical glandular formation was appreciated in adenocarcinomas, and uniform trabecular gland formation was seen in salivary gland carcinomas. Mucinous adenocarcinomas showed alveolar wall thickening with intraalveolar mucin. Interstitial fibrosis was visualized as signal-dense tissue, with an interstitial distribution in mild interstitial fibrotic disease and a diffuse subpleural pattern with cystic space formation in usual interstitial pneumonitis.

CONCLUSIONS

To our knowledge, this study is the first demonstration of volumetric OFDI with precise correlation to histopathology in lung pathology. We anticipate that OFDI may play a role in assessing airway and parenchymal pathology, providing fresh insights into the volumetric features of pulmonary disease.

Influence of dental resin material composition on cross-polarization-optical coherence tomography imaging

The purpose of this study was to investigate cross-polarization-optical coherence tomography (CP-OCT) signal attenuation through different resin material compositions. Four distinct composite systems were used: Filtek supreme ultra (FSU) (3M ESPE), IPS empress direct (EMD) (Ivoclar Vivadent), estelite sigma quick (SQK) (Tokuyama Dental), and Z100 (3M ESPE). Cross-sectional images of different composite-demineralized phantoms (n=108) were collected using a 1310-nm intraoral cross-polarization swept source OCT (CP-OCT) imaging system. %T quantified the CP-OCT signal attenuation. Scanning electron microscopy, transmission electron microscopy, and energy-dispersive x-ray spectrometer chemical analysis was utilized to determine how different matrix/filler compositions affected attenuation of the near infrared (NIR) signal. CP-OCT imaging of dental resin composites showed enormous variation in signal attenuation. For each of our composite systems, there was not a consistent attenuation difference in the NIR signal for A to D shades. The four composites had similar measured backscattering values but attenuated the overall signal to different degrees. When comparing the A2 shades between the four different composite systems, the order of highest to lowest of %T was EMD>Z100, FSU>SQK (ANOVA, Tukey, p<0.0001). As a result, we demonstrate the importance of understanding how the constituents of composite materials affect CP-OCT signal attenuation.

GPU accelerated real-time multi-functional spectral-domain optical coherence tomography system at 1300 nm

We present a GPU accelerated multi-functional spectral domain optical coherence tomography system at 1300 nm. The system is capable of real-time processing and display of every intensity image, comprised of 512 pixels by 2048 A-lines acquired at 20 frames per second. The update rate for all four images with size of 512 pixels by 2048 A-lines simultaneously (intensity, phase retardation, flow and en face view) is approximately 10 frames per second. Additionally, we report for the first time the characterization of phase retardation and diattenuation by a sample comprised of a stacked set of polarizing film and wave plate. The calculated optic axis orientation, phase retardation and diattenuation match well with expected values. The speed of each facet of the multi-functional OCT CPU-GPU hybrid acquisition system, intensity, phase retardation, and flow, were separately demonstrated by imaging a horseshoe crab lateral compound eye, a non-uniformly heated chicken muscle, and a microfluidic device. A mouse brain with thin skull preparation was imaged in vivo and demonstrated the capability of the system for live multi-functional OCT visualization.

Enabling freehand lateral scanning of optical coherence tomography needle probes with a magnetic tracking system

We present a high-resolution three-dimensional position tracking method that allows an optical coherence tomography (OCT) needle probe to be scanned laterally by hand, providing the high degree of flexibility and freedom required in clinical usage. The method is based on a magnetic tracking system, which is augmented by cross-correlation-based resampling and a two-stage moving window average algorithm to improve upon the tracker's limited intrinsic spatial resolution, achieving 18 µm RMS position accuracy. A proof-of-principle system was developed, with successful image reconstruction demonstrated on phantoms and on ex vivo human breast tissue validated against histology. This freehand scanning method could contribute toward clinical implementation of OCT needle imaging.