Radiofrequency ablation (RFA) is a minimally invasive procedure that is commonly used for the treatment of atrial fibrillation. However, it is associated with a significant risk of arrhythmia recurrence and complications owing to the lack of direct visualization of cardiac substrates and real-time feedback on ablation lesion transmurality. Within this manuscript, we present an automated deep learning framework for in vivo intracardiac optical coherence tomography (OCT) analysis of swine left atria. Our model can accurately identify cardiac substrates, monitor catheter-tissue contact stability, and assess lesion transmurality on both OCT intensity and polarization-sensitive OCT data. To the best of our knowledge, we have developed the first automatic framework for in vivo cardiac OCT analysis, which holds promise for real-time monitoring and guidance of cardiac RFA therapy..

Atrial fibrosis is an important cause of atrial fibrillation (AF) and is often targeted for radiofrequency ablation (RFA) treatment. However, fibrosis identification during an RFA procedure is indirect and not well established. Polarization-sensitive optical coherence tomography (PSOCT) provides high-resolution in-depth noninvasive structural and tissue birefringence images, which can be effective for detecting fibrosis. In this work, combining histology and optical mapping of atrial action potential activity, we demonstrated the identification of atrial fibrosis that caused abnormal impulse propagation in a pig model of AF with PSOCT. Results indicate that PSOCT may provide effective guidance for RFA procedures in the future.

Radiofrequency ablation (RFA) is commonly used to treat atrial fibrillation (AF). However, the outcome is often compromised due to the lack of direct real-time feedback to assess lesion transmurality. In this work, we evaluated the ability of polarization-sensitive optical coherence tomography (PSOCT) to measure cardiac wall thickness and assess RF lesion transmurality during left atrium (LA) RFA procedures. Quantitative transmural lesion criteria using PSOCT images were determined ex vivo using an integrated PSOCT-RFA catheter and fresh swine hearts. LA wall thickness of living swine was measured with PSOCT and validated with a micrometer after harvesting the heart. A total of 38 point lesions were created in the LA of 5 living swine with the integrated PSOCT-RFA catheter using standard clinical RFA procedures. For all lesions with analyzable PSOCT images, lesion transmurality was assessed with a sensitivity of 89% (17 of 19 tested positive) and a specificity of 100% (5 of 5 tested negative) using the quantitative transmural criteria. This is the first report of using PSOCT to assess LA RFA lesion transmurality in vivo. The results indicate that PSOCT may potentially provide direct real-time feedback for LA wall thickness and lesion transmurality.

Tissue segmentation on cardiac optical coherence tomography (OCT) images has a great potential for radiofrequency ablation. Our deep learning model achieves high performance on cardiac tissue identification from catheter-based in-vivo OCT images.

Transseptal puncture (TSP) is commonly conducted under the guidance of fluoroscopy and/or intracardiac echocardiography (ICE) at the fossa ovalis (FO) to gain percutaneous access to the left atrium for intracardiac procedures. Issues with traditional TSP include: additional vascular access through a sheath, and fluoroscopy exposes patients to ionizing radiation. TSP, if not done appropriately can result in serious complications. We studied the feasibility of optical coherence tomography (OCT) guidance of TSP with ex vivo and in vivo experiments. Results show that OCT can provide detailed structure information to identify FO allowing for safe TSP.

Pulmonary vein isolation with radiofrequency ablation (RFA) has become the most common procedure to treat Atrial Fibrillation (AF). However, current RFA lesion formation is guided only with indirect information (e.g. temperature, impedance, contact force), which does not guarantee transmural lesions. Non-transmural lesions are understood to contribute to AF recurrence. We have previously demonstrated that polarization-sensitive optical coherence tomography (PSOCT) can monitor RFA lesion transmurality in the left atrium (LA) of living swine. However, it requires expert interpretation. Here, we demonstrate quantitative image quality and lesion transmurality evaluation metrics applied to the in vivo LA RFA PSOCT lesion monitoring data.

Significance: Pulmonary vein isolation with catheter-based radiofrequency ablation (RFA) is carried out frequently to treat atrial fibrillation. However, RFA lesion creation is only guided by indirect information (e.g., temperature, impedance, and contact force), which may result in poor lesion quality (e.g., nontransmural) and can lead to reoccurrence or complications. Aim: The feasibility of guiding intracardiac RFA with an integrated polarization-sensitive optical coherence tomography (PSOCT)-RFA catheter in the right atria (RA) of living swine is demonstrated. Approach: In total, 12 sparse lesions were created in the RA of three living swine using an integrated PSOCT-RFA catheter with standard ablation protocol. PSOCT images were displayed in real time to guide catheter-tissue apposition. After experiments, post-processed PSOCT images were analyzed to assess lesion quality and were compared with triphenyltetrazolium chloride (TTC) lesion quality analysis. Results: Five successful lesions identified with PSOCT images were all confirmed by TTC analysis. In two ablations, PSOCT imaging detected gas bubble formation, indicating overtreatment. Unsuccessful lesions observed with PSOCT imaging were confirmed by TTC analysis. Conclusions: The results demonstrate that the PSOCT-RFA catheter provides real-time feedback to guide catheter-tissue apposition, monitor lesion quality, and possibly help avoid complications due to overtreatment, which may enable more effective and safer RFA treatment. (C) The Authors.

Optical coherence tomography (OCT) employs near-infrared light to image the microstructure of different tissues. Clinically, it has been used to image the walls of coronary arteries. In research settings, one of the applications for OCT is visualizing endocardial and subendocardial structures. The present experiment sought to determine whether OCT can identify native conduction tissues in adult porcine hearts. During the study, the right atrial endocardial surfaces of excised adult porcine hearts were exposed. The triangle of Koch was imaged with the OCT system and the conduction tissue was identified. The area was then prepared for histologic examination with Masson's trichrome stain. The results of histologic preparations and OCT images were then compared. Ultimately, nine porcine hearts were examined using this methodology. OCT imaging successfully identified subendocardial structures presumed to be the compact atrioventricular node. Histologic images of the preparations delineated the different tissue types and conduction tissue was easily identified. The location of distinctive hyporeflective areas in the OCT images correlated with the location of conduction tissue in the histology images. In light of the findings of this study, it is suggested that atrioventricular nodal tissue can be identified by OCT in freshly dissected unfixed porcine hearts. OCT images distinguished the differentiated conduction tissue in close proximity with the endocardium, myofibers, and fibrous tissue, and the success of this was verified with histology. This technology may be useful for the direct visualization of the native conduction system during procedures in the operating room and electrophysiology laboratory. Further studies with perfused tissue samples and live animal experiments are needed to better assess the efficacy of this novel application.

Cardiac arrhythmias are a major source of mortality in the United States. Ablation is the only curative therapy for cardiac arrhythmias, and catheter-based radiofrequency ablation (RFA) through percutaneous access has emerged as the standard care for many arrhythmias. However, current procedures only monitor temperature, impedance and pressure measurements during ablation, which results in incomplete lesion formation (e.g., high recurrence rate for atrial fibrillation patients) and complications. In our previous work, we have shown integration of a commercially available RFA catheter with polarization sensitive optical coherence tomography (PSOCT). This was accomplished by housing the PSOCT probe inside of the RFA catheter with a window at the catheter tip that allows for forward viewing PSOCT imaging. Data from ex vivo experiments have shown that the integrated RFA catheter can be used to confirm catheter tissue apposition and monitor tissue change during ablation by measuring retardance. It was also demonstrated that the PSOCT window does not interfere with normal lesion formation. However, only the catheter tip was integrated, enabling only in vitro experiments. Therefore, we have developed a fully integrated PSOCT RFA catheter based on a commercially available catheter to enable experiments in living swine via percutaneous access. By properly choosing a middle layer sheath to house the PSOCT probe, we reduced the non-uniform rotation distortion (NURD), reduced PSOCT probe tip longitudinal movement due to winding back, improved image quality and stability. Further validation of functionality by simulating RFA procedures in living swine through percutaneous access is ongoing.

Radiofrequency ablation (RFA) is an important standard therapy for cardiac arrhythmias, but direct monitoring of tissue treatment is currently lacking.We demonstrate an RFA catheter integrated with polarization sensitive optical coherence tomography (PSOCT) for directly monitoring the RFA process in real time.The integrated RFA/OCT catheter was modified from a standard clinical RFA catheter and includes a miniature forward-viewing cone-scanning OCT probe.The PSOCT system was validated with a quarter-wave plate while the RFA function of the integrated catheter was validated by comparing lesion sizes with those made with an unmodified RFA catheter.Additionally, the integrated catheter guided catheter-tissue apposition and monitored RFA lesion formation in cardiac tissue in real time.The results show that catheter-tissue contact can be characterized by observing the features of the blood and tissue in the acquired OCT images and that RFA lesion formation can be confirmed by monitoring the change in phase retardance in the acquired PSOCT images.This system demonstrates the feasibility of an integrated RFA/OCT catheter to deliver RF energy and image the cardiac wall simultaneously and justifies further research into use of this technology to aid RFA therapy for cardiac arrhythmias.

Purpose: To study the effect of decentration and tilt of the type I Boston keratoprosthesis (KPro) on image quality in both aphakic and pseudophakic eyes. Methods: An optical ray-tracing program was used to simulate the image projected onto the retina in an eye with a perfectly centered KPro, and in eyes with varying degrees of KPro decentration and tilt. Decentration was modeled along a typical white-to-white distance of 12.0 mm, and the corresponding tilt was calculated assuming a radius of curvature of 8.0 mm, the radius of curvature of the backplate of the KPro. Both aphakic and pseudophakic eyes were simulated, and the corresponding modulation transfer function curves, point spread functions, and astigmatism were analyzed. Results: The perfectly centered KPro produced a high-quality image with no induced astigmatism. Increasing decentration beyond approximately 0.5 mm resulted in poorer image quality with a more pronounced effect in the presence of an intraocular lens. Using models of the normal eye as a threshold, image degradation due to decentration becomes clinically significant at approximately 1.4 mm and 0.9 mm for the aphakic and pseudophakic cases, respectively. Astigmatism introduced by decentration is approximately 0.25 D cylinders at those thresholds. Conclusions: Decentration of up to 0.5 mm had no significant impact on image quality and an attempt at good intraoperative centration of the KPro within this range is important. Conversely, decentration of 0.9 mm or more during surgical implantation can result in significant degradation in retinal image quality including astigmatism. The effect is greater in the pseudophakic eye.

Congenital heart defects (CHDs) are the most common birth defect, affecting between 4 and 75 per 1,000 live births depending on the inclusion criteria. Many of these defects can be traced to defects of cardiac cushions, critical structures during development that serve as precursors to many structures in the mature heart, including the atrial and ventricular septa, and all four sets of cardiac valves. Epithelial-mesenchymal transition (EMT) is the process through which cardiac cushions become populated with cells. Altered cushion size or altered cushion cell density has been linked to many forms of CHDs, however, quantitation of cell density in the complex 3D cushion structure poses a significant challenge to conventional histology. Optical coherence tomography (OCT) is a technique capable of 3D imaging of the developing heart, but typically lacks the resolution to differentiate individual cells. Our goal is to develop an algorithm to quantitatively characterize the density of cells in the developing cushion using 3D OCT imaging. First, in a heart volume, the atrioventricular (AV) cushions were manually segmented. Next, all voxel values in the region of interest were pooled together to generate a histogram. Finally, two populations of voxels were classified using either K-means classification, or a Gaussian mixture model (GMM). The voxel population with higher values represents cells in the cushion. To test the algorithm, we imaged and evaluated avian embryonic hearts at looping stages. As expected, our result suggested that the cell density increases with developmental stages. We validated the technique against scoring by expert readers.

The coupling dynamics between a dispersion-managed soliton oscillator and a nonlinear amplifier in an all-photonic crystal fiber-based laser system is emphasized. The intracavity and output pulse evolution dynamics with the dispersion management by a pair of gratings in the oscillator are investigated numerically and experimentally in detail. Then the relationship between the net intracavity dispersion in the oscillator and properties of amplification pulses from the nonlinear amplifier is studied. We find that the best performance in the laser amplification system is significantly dependent on the time-bandwidth product of the seed pulses and the amplifier pump power. As a consequence, the optimized seed output from the DM soliton oscillator for the nonlinear amplifier should be as close to the transform-limited pulse as possible and the intracavity anomalous dispersion should be as large as possible. The narrowest pulse duration of 43fs without a pedestal and an average power of 28W, is obtained at a pump power of 60W. At a pump power of 70W, 50-fs pulses with a highest output power of 34W, corresponding to a peak power of 16.2MW, can also be obtained.

We experimentally investigate the polarization dynamics of three kinds of gain fiber, the single-polarizing photonic crystal fiber, double clad polarization-maintaining large mode area fiber and double clad large mode area nonpolarizing fiber, in a continuous wave fiber laser oscillator under different initial polarization directions and pumping powers. The comparison results demonstrate that there are some distinguishable differences for the polarization evolutions inside the three kinds of active fibers. The polarization operation status of the fiber oscillator strongly depends on not only the gain fiber’s kinds, but also the length of the fiber, initial polarization directions and pumping power. The results suggest that polarization instability in a fiber laser should be an inherent reason for the higher operation noise.

对不同抽运方式下光子晶体光纤飞秒脉冲放大器中的脉冲演变过程进行了数值模拟和实验验证。在数值模拟上,采用了速率方程和非线性薛定谔方程相结合的理论模型;该模型考虑到端面抽运引起光纤中的非均匀增益分布、群速度色散和自相位调制三者之间的相互作用。模拟结果表明,相比于前向抽运放大方式,采用背向抽运放大方式不仅输出功率高,而且放大脉冲具有更窄的时域和光谱宽度,即较小的时间带宽积和更少的非线性积累。在验证实验上,搭建了基于前向和背向抽运方式的光子晶体光纤飞秒激光放大器;获得的实验结果与数值模拟结论一致,并对放大脉冲演变过程的物理机制进行了讨论。

Ultrashort pulse laser with a repetition rate of below 10 MHz is suitable for a variety of micromachining applications to avoid plasma shielding effects. Besides, the parabolic pulse possesses clean wings, short pulse duration, and large peak power because only the linear chirp is accumulated during the propagation. Based on these two points, a similariton oscillator with a repetition rate of below 10 MHz is a most perfect seed source of an amplification system for micromachining. In this paper, an amplifier similariton oscillator with dispersion map based on a piece of 10 m Yb-doped large-mode-area single-polarization photonic crystal fiber is demonstrated. The semiconductor saturable absorber mirror is employed in the linear cavity as an end mirror to initiate and maintain the mode-locking operation. An adjustable slit is adopted between the end mirror and grating pair in another arm, as a central wavelength adjuster and the spectral filter to ensure the laser operational wavelength in accordance with the working wavelength of semiconductor saturable absorber mirror and the stability of mode-locking operation. The stable single-pulse mode-locking operation can be achieved by adjusting the intracavity dispersion and the operating wavelength. With the net cavity dispersion of -0.89 ps(2), a spectrum with steep and smooth edges is obtained, which means that the laser does not operate in the soliton regime but in the dispersion-mapped amplifier similariton regime. A highest output power of 820 mW is obtained with a pulse duration of 6.2 ps and spectral width of 3.84 nm under a pump power of 12.8 W. The repetition rate is 8.6 MHz, corresponding to a pulse energy of 95 nJ. It is the first time that the similariton with a repetition rate of lower than 10 MHz and a highest pulse energy of 95 nJ from a similariton laser has been achieved, to the best of our knowledge. Numerical simulation results confirm that the self-similar evolution is achieved in the gain fiber, and the parabolic-and gauss-shaped pulse can be emitted at the zero-order reflection of the grating and after the slit, respectively.

A femtosecond laser single-stage nonlinear amplification system composed of Yb-doped large-mode-area singlepolarization photonic crystal fibers is demonstrated. Effects of net cavity dispersion and pump power on oscillator output parameters and the evolution dynamics of the amplified pulse after compression are discussed for different seed pulse parameters. Under the experimental conditions in this paper, the longer and less chirped pulses are obtained with a larger negative net intracavity dispersion in the oscillator. When a nearly-transform-limited pulse is chosen as seed pulse nder the condition of oscillator pump power of 4.53 W, the shortest nearly-pedestal-free amplified pulse is achieved under the amplifier pump power of 60 W after the dispersion is compensated by a grating pair, in which the pulse duration is 45.7 fs with an average power of 28 W at a repetition frequency of 42 MHz. When the oscillator pump power is increased to 5.08 W and most nearly-transform-limited pulses under the pump condition are selected as the seed pulses, the maximum average power of 34.5 W with a duration of 53.5 fs is obtained at an amplifier pump power of 70 W.

A high-energy and low repetition rate dispersion-mapped amplifier similariton oscillator with a large net intracavity anomalous dispersion and a linear cavity configuration is demonstrated experimentally at 1 μm. The numerical results confirm that self-similar evolution is accomplished in the gain fiber, and both the parabolic- and Gauss-shaped pulses can be emitted at different ports of the cavity, respectively. The maximum output power of 820 mW at a repetition rate of 8.6 MHz under a pump power of 12.76 W, corresponding to a pulse energy as high as of 95 nJ has been obtained.

A comparative study of femtosecond pulse dynamics in a photonic crystal fiber amplifier with backward and forward pump schemes is demonstrated experimentally and numerically. The output power, pulse duration and spectrum width of the amplified soliton pulse at different pump powers under the two pump schemes are discussed. The results show that the evolution of the soliton pulse shape in the temporal and spectral domains is also dependent on the direction of pump besides the output power. A narrower pulse duration and spectral width (i.e. smaller time-bandwidth-product), the much less nonlinearity accumulation (i.e. smaller B-Integral value) and a higher output power can be obtained in the backward pump scheme compared to that in the forward pump scheme. The physical origin can be explained by the interaction among group-velocity dispersion, self-phase modulation and nonuniform gain distribution along the fiber due to different end-pump directions. The results provide convincing support to choose the backward pump scheme rather than the forward pump scheme in soliton amplification region in a femtosecond fiber amplifier.