This PDF file contains the front matter associated with SPIE Proceedings Volume 10855, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Coronary arteries are covered by a thin layer of endothelial cells (ECs). Impairment of ECs is at the origin of coronary atherosclerosis and its clinical manifestations. However, the study of ECs in humans remains elusive because of a lack of an imaging tool with sufficient resolution. We have developed a light-based 1-µm-resolution microscopic imaging technology termed micro-optical coherence tomography (µOCT) that can be implemented in a coronary catheter. In this study, we investigated the capability of µOCT to visualize EC morphology. We stripped the endothelium from 36 fresh swine coronary segments with cyanoacrylate glue. Histology showed that the stripping procedure successfully removed ECs from the swine coronary arteries. Coronary segments were then imaged in 3D with µOCT, and were processed for histology and scanning electron microscopy (SEM). µOCT images of stripped vs. intact sites were volume rendered in 3D and visually compared. 3D-µOCT allowed visualization of EC pavementing on intact artery surfaces that was strongly correlated to that seen by SEM. EC pavementing disappeared, and surface roughness calculated by computed root mean squared error diminished significantly at the sites with stripped EC compared with intact sites. µOCT was also utilized in human cadaver coronary arteries, showing its capability of identifying EC morphology of human coronary plaque harboring leukocyte adhesion, EC stent strut tissue coverage, and lack of ECs at lesions with necrotic core or superficial nodular calcifications. In conclusion, µOCT enables EC visualization in coronary arteries, suggesting that it could be useful in patients with coronary artery disease to better understand the role of ECs in the pathogenesis of coronary artery disease.

We demonstrate megahertz intravascular Doppler Optical Coherence Tomography (OCT). The OCT system relies on a 1.1 mm diameter motorized catheter and a 1.5 MHz Fourier Domain Mode Locked (FDML) laser. By resolving the phase shift between adjoint A-lines, the flow pattern image can be reconstructed. Imaging experiments were carried out in swine coronary artery in vitro at a speed of 600 frames/s. The MHz sweep rate not only allows us to investigate flow velocity of up to 37.5 cm/s without phase-unwrapping, but also enables dynamic flow imaging at high frame rate.

Intravascular optical coherence tomography (IV-OCT) provides micrometer-order resolution images for interventional guidance, visualizing artery wall geometry and composition. We developed an ultrafast IV-OCT system, called Heartbeat OCT, providing accurate imaging of a coronary artery by completing a scan during the filling phase between two consecutive ventricular contractions. In this study we aim to quantify the imaging accuracy of the Heartbeat OCT by comparing the stents imaging results with a commercial OCT and a micro-CT. Two metal stents (Biotronik Orsiro) were implanted in the LAD artery of two male pigs. After 28 days, in vivo images were acquired using Heartbeat OCT and a commercial OCT system (Ilumien Optis, St. Jude Medical). After sacrificing the pigs, we acquired ex vivo images of the stents using a micro-CT, creating reference datasets for comparison. We conducted quantitative image processing studies in three steps. We first manually segmented the stents in OCT images. In the second step, a reference planar reconstruction of the stents was created based on the micro-CT images. In the third step, we counted, for each OCT pullback, the percentage of stents pixels that are located at < 80 µm from the reference structure. The results show that, in the two images acquired with Heartbeat OCT, 60% and 49% of stent strut locations matched with the reference micro-CT data. In the data from the commercial OCT system 48% and 51% spots matched with the reference data. In conclusion, Heartbeat OCT shows an 3D geometric imaging accuracy comparable or superior to that of the commercial OCT.

With intravascular Optical Coherence Tomography (IVOCT), phantom models are invaluable for system characterization and clinical training. However, accurately simulating 3D tissue geometries and heterogeneous optical properties has been challenging with phantom fabrication methods used to date. Anatomical phantom models typically require mesoscale structures integrated with heterogenous materials to simulate optical scattering and absorption by vascular tissue. In this study, we showed that two photon polymerisation (2PP) 3D printing offers the potential to generate complex tissue phantom scaffolds with sub-micron resolution (<200 nm), and that microinjection of tissue mimicking materials into these scaffolds allows for creation of realistic mesoscale anatomical phantom models of both healthy and diseased tissues. We developed three types of IVOCT phantom models: a free-standing wire model, a vessel side-branch model and an arterial plaque model. The free-standing wires ranged in diameter from 5 to 34 microns. Integration of tissue mimicking materials was performed using micropipettes with a tip diameter of 50 to 60 microns. Healthy vascular tissue was simulated using a mixture of PDMS, silicone oil and TiO2. Coconut oil was used to simulate a pathological lipid inclusion. All models were examined using optical microscopy and scanning electron microscopy, prior to imaging with a commercial IVOCT system. To our knowledge, this is the first phantom study to use 2PP 3D printing for OCT phantoms. The combination of optically-generated 3D scaffolds and microinjection of tissue mimicking materials will enable complex imaging phantoms for a wide range of microscopic and mesoscale optical imaging techniques.

The polymerization dynamics and microstructure of the fibrin network is vital to hemostasis. During cardiac surgery, heparin is administered to prevent bleeding and reversed using protamine at the end of surgery. Residual heparin and inadequate reversal following surgery impair fibrin integrity, likely associated with major postoperative blood loss. In this study, we apply a recent approach, SECM, to evaluate fibrin integrity in blood clots during heparin administration and protamine reversal in cardiac surgery patients. SECM’s capability for video rate microscopy over large fields of view with a spatial resolution of 0.4x1.0µm permits the dynamic assessment of fibrin polymerization and 3D microstructure. Plasma from 10 patients was collected during cardiac surgery at baseline and following protamine reversal. In addition, the dose-dependent response of heparin was studied by spiking 6 normal plasma samples at heparin doses of 0.1-2USP/mL. All samples were tested using SECM and clot polymerization parameters including fibrin time (FT) and fibrin density (FD) were derived. In cardiac surgical patients, FD was lower after protamine reversal (p<0.05) compared to baseline despite similar FT, suggesting that fibrin microstructure is not restored immediately after surgery. In spiked samples, fibrin polymerization was delayed with higher FT (p<0.05), fibrin strands were longer, and the FD was lower (p<0.05) with increasing heparin dose. Similar to surgical samples, FD was not restored following protamine reversal (p<0.01) in spiked samples. These studies show that the loss of fibrin integrity following cardiac surgery can be quantified using SECM, which may provide new insights on mechanisms of postoperative bleeding.

A fiber-based, label-free multispectral fluorescence lifetime imaging and intravascular ultrasound (FLIm/IVUS) system was evaluated as a new tool for monitoring variations in biochemical and structural composition of vascular biomaterials, including native arteries and engineered vascular grafts both in vitro and in vivo. Fiber-based FLIm was adapted to assess the hollow geometry of vasculature, allowing for imaging of the luminal surface of vessels. The capacity of FLIm to resolve tissue cellular location (i.e. scaffold reendothelialization) and collagen to elastin ratio on the vessel wall was investigated. Quantitative imaging parameters derived from spectrally- and temporally-resolved autofluorescence (i.e. intensity ratios and fluorescence lifetime) provide benchmark indicators to identify areas of recellularized tissue, and to distinguish wall matrix compositions within and across biomaterials. In addition, fiber-based FLIm was complemented with intravascular ultrasound (IVUS) for simultaneous in vivo evaluation of biochemical and structural tissue properties. Here, we performed an in vitro evaluation of pig carotid arteries and show correlations between FLIm parameters and biochemical composition in different anatomical locations. We discuss the spectral and lifetime differences between native pig carotid artery, acellular antigen removed bovine pericardium grafts, and reendotheliarized grafts. Finally, we translate the findings to an in vivo clinical FLIm/IVUS imaging study with antigen removed bovine pericardium grafted on healthy pig native carotid artery. Upon implantation, the graft is expected to repopulate with cells, and change composition as cells remodel it. These experiments demonstrate the feasibility of fiber-based FLIm/IVUS to examine vascular engineered tissue in research and clinical settings.

Tissue engineered vascular graft (TEVG) are used when native vessels are not available to repair vascular damage. At the time of implantation in human body, these constructs present poor cellularity. To understand the cellularization kinetics under physiological conditions in a setting suitable for experimentation, bioreactors are often used in laboratory setting because of its controllable culture parameters including seeding conditions, flow type, pressure and temperature. Therefore, a non-destructive, label-free imaging modality that is capable of evaluating cell migration on luminal surfaces of TEVGs inside bioreactors is valuable for studying cellularization kinetics and providing a potential quality control method for manufacturing mature TEVGs. A multispectral Fluorescence Lifetime Imaging (ms-FLIm) using 355 nm excitation was configured to accommodate a rotating side-firing scanning probe for intraluminal imaging of tubular-shaped bovine pericardium (BP) scaffolds. The scanning was realized by reciprocal rotation and pullback of the fiber probe. Mesenchymal stem cells were seeded on BP-based TEVGs and cultured in the prototype bioreactor for up to one week. Distinct experimental conditions including the seeding side (i.e. BP serious and fibrous side) and media flow (i.e. static and dynamic pulsatile flow) were evaluated. Using ms-FLIm, the migration of cells on antigen removed BP TEVGs was periodically examined over a week; and the migration rates under different conditions were analyzed. Current results suggest helical ms-FLIm has potential to monitor in situ tissue recellularization process in bioreactors.

Coronary artery disease (CAD) remains the world’s leading cause of death, causes widespread adverse effects on quality of life, and perpetuates massive healthcare spending. The involvement of lipid core plaques (LCPs) in CAD development, its progression, and acute coronary events has been well known for decades, yet detecting lipid core plaques in a living patient remains challenging. Detection of LCPs during the coronary catheterization procedure may lead to secondary prevention, reduction in procedural complications, and eventually the development of reliable non-invasive methods for primary prevention. Near infrared spectroscopy (NIRS) is widely used across numerous industries for rapid, non-destructive, remote identification of chemical compounds. Intravascular NIRS was developed for use during the coronary catheterization procedure and has been rigorously prospectively validated for a unique and novel diagnostic FDA claim for the detection of lipid core plaque. An additional important property of an LCP that is thought to significantly affect its vulnerability to rupture is the strength of the overlying collagen cap. New developments with intravascular NIRS suggest that it may additionally be useful for detection of structurally deficient collagen in LCP plaques, which are those that are most likely weak and more vulnerable to rupture. Updates will be given for the ongoing clinical utility of intravascular NIRS and the progress in the prospective validation of its capability to detect structurally deficient plaque caps.

The role of biomechanical signaling is well accepted as a modulator of cardiac cell behavior and a requirement for cardiac morphogenesis. However, the small, fragile nature of the embryonic heart makes it difficult to determine transient mechanical homeostasis during heart development and search for causal links between biomechanical forces and cardiac cell behavior in vivo. Toward this problem, we have developed a set of methods for live dynamic optical coherence tomography (OCT) imaging of the developing heart in cultured mouse embryos, starting at earliest stages. To manipulate cardiodynamics in live embryo culture, we have successfully established cardiac optogenetics to control heartbeat frequency in the embryonic mouse heart for the first time. By coupling OCT imaging with optogenetic control, we can generate 4D (3D+time) images of the heart and extract structural and functional information such as heart wall dynamics and blood flow velocity during optogenetic manipulation. As a way to quantify organization of structural fibers in early embryonic hearts, we implemented second harmonic generation, an unbiased imaging approach to detect collagen. Using optogenetic cardiac pacing and second harmonic generation imaging, we will look at how changes in heart biomechanics are consequential in the deposition and organization of cardiac collagen. This work is bringing us closer to understanding how mechanical stimuli from heart contraction regulate mechanical homeostasis and cardiac differentiation in vivo, potentially contributing to management of congenital heart defects.

Radiofrequency ablation is widely used in cardiology as an effective minimally invasive treatment for atrial fibrillation. However, radiofrequency noise, electronic interference, low resolution and poor tissue contrast complicate real-time lesion monitoring using conventional imaging modalities such as magnetic resonance imaging or ultrasound imaging based on electronic transducers. Recently, a bench-top all-optical ultrasound imaging system, where ultrasound is both generated and detected using light, was presented (doi:10.1364/BOE.9.003481) that achieved high-resolution, video-rate 2D images. In this system, pulsed excitation light was focussed onto a nanocomposite membrane, where it was converted into ultrasound via the photoacoustic effect. Using scanning optics, the resulting optical ultrasound source was translated to synthesise a 1D source aperture comprising irregularly spaced ultrasound sources. Back-scattered ultrasound was detected using a single fibre-optic Fabry-Pérot cavity. Here, this system (which is inherently insensitive to electromagnetic interference) was used to achieve the first video-rate, depth-resolved 2D images acquired during RF ablation using an all-optical ultrasound imaging setup. We used this system to monitor the formation of radiofrequency ablation lesions (max 30 W, 65°C, 60 s) in ex vivo chicken breast samples, at a frame rate of 9 Hz, resolution of 100 µm, an imaging depth >15 mm, and a contrast of up to 30 dB. With its high miniaturisation potential, all-optical ultrasound imaging shows great promise for guiding interventional procedures, where real-time ablation lesion visualisation could improve lesion delivery and patient outcome.

An important parameter that affects the quality of radiofrequency ablation lesions that are produced is the contact angle and contact orientation. Both are challenging to determine in vivo, and a method to classify that information and provide feedback in real time could potentially titrate the energy dose and increase the success rates of this treatment. In our work, a grin lens-terminated single mode fiber was integrated into a commercial RFA catheter to allow for M-mode OCT imaging at the catheter tip. Ventricular wedges were dissected from four fresh swine hearts and submerged in whole blood. M-mode imaging was performed in four different orientations: non-contact, 30 degrees, 60 degrees, and 90 degrees. One contact classifier with two sub-classifiers was developed to classify whether the catheter is in proper contact with the tissue and the angle of the catheter when it is in contact. This classifier is based on convolutional neural networks and used keras as developing framework with tensorflow backend. We achieved 98.51% accuracy in the "contact" or "noncontact" classifier and 91.21% in the orientation classifier with 30 degrees, 60 degrees and 90 degrees as outputs. We successfully tested the contact quality classifier in real time and achieved high accuracy in 0.0053 seconds for a group of 20 A-lines. These results support the potential of having the guidance of catheter placement during the RFA therapy using OCT image and pre-trained classifiers. Future experiments will further test M-mode OCT and our processing algorithm within a larger sample size and demonstrate the utility in vivo.

Acute myocardial infarction is one of the major diseases leading to death and disability worldwide. A rapid, noninvasive and direct diagnostic method of ischemic heart disease is helpful to improve the condition. Photons propagation at 850nm by Monte Carlo simulation and photon distribution in thoracic tissues were studied firstly based on the Visible Chinese Human Dataset (VCH). Quantitative results of absorption photons and light fluence distribution indicated partial photons could reach to myocardium. In simulation result, 32% photons were absorbed by the myocardium. The light fluence intensity declined with the tissue depth. When light reaches the heart, the light intensity decreases 10,000 times. The feasibility of near-infrared light applied in the heart and transmission to the myocardium was verified firstly by mathematical simulation, which may provide a novel method for monitoring myocardial hemodynamics.