Coherent Optical Reflectometry Research Articles

Cardiac Pulsed Field Ablation Lesion Durability Assessed by Polarization-Sensitive Optical Coherence Reflectometry.

Pulsed field ablation uses electrical fields to cause nonthermal cell death over several hours. Polarization-sensitive optical coherence reflectometry is an optical imaging technique that can detect changes in the tissue ultrastructure in real time, which occurs when muscular tissue is damaged. The objective of this study was to evaluate the ability of a polarization-sensitive optical coherence reflectometry system to predict the development of chronic lesions based on acute changes in tissue birefringence during pulsed field ablation. Superior vena cava isolation was performed in 30 swine using a biphasic, bipolar pulsed field ablation system delivered with a nonirrigated focal tip catheter. Acute changes in tissue birefringence and voltage abatement were analyzed for each individual lesion. A high-resolution electroanatomical map was performed at baseline and 4 to 12 weeks after ablation to locate electrical gaps in the ablated area. A total of 141 lesions were delivered and included in the analysis. Acute electrical isolation based on the electroanatomical map was achieved in 96% of the animals, but chronic isolation was only seen in 14 animals (46%). The mean voltage abatement of lesions that showed recovery was 82.8%±14.6% versus 84.4%±17.4% for those that showed fibrosis (P=0.7). The mean acute reduction in tissue birefringence in points demonstrating fibrosis was 63.8%±11.3% versus 9.1%±0.1% in the points that resulted in electrical gaps. A threshold of acute reduction of birefringence of ≥20% could predict chronic lesion formation with a sensitivity of 96% and a specificity of 83%. Acute tissue birefringence changes assessed with polarization-sensitive optical coherence reflectometry during pulsed field ablation can predict chronic lesion formation and guide the ablation procedure although limited by the tissue thickness.

Fundamental SNR Limits Imposed by ASE in Frequency-Shifting Loops

Recirculating frequency-shifting loops (FSLs) are a simple source of optical frequency combs with bandwidth compatible with microwave technologies. As such, they have demonstrated promising capabilities for telecommunications, remote sensing, and microwave photonics. In these systems, the coherent frequency comb is produced by recirculation of a single frequency laser in a fiber loop containing a frequency shifter. Due to the insertion of an optical amplifier in the loop to compensate for the losses, amplified spontaneous emission (ASE) is inevitably emitted and superimposes to the coherent output. In this paper, we quantify theoretically the contribution of the ASE background to the FSL output for different types of receivers used in FSL-based techniques: direct, self-heterodyne, and dual-comb detection. In particular, we focus on two important practical applications of FSL: coherent optical reflectometry and real-time Fourier transforms of radio-frequency signals. We provide for each of them numerical estimations of the signal-to-noise ratio and dynamic range. This work constitutes a compact framework for the general evaluation of techniques based on FSLs.

Applications of Mueller Matrix Polarimetry to Biological and Agricultural Diagnostics: A Review

The review contains a systematization of the main approaches to the practical implementation of Mueller matrix polarimetry and the prospects for its application in biology and agriculture. The most typical optical layouts for measuring the Mueller matrix of various objects, such as disperse systems, tissues and surface structures, are discussed. Mueller matrix measurements, being integrated into standard schemes of conventional optical methods, such as scatterometry, optical coherence tomography, fluorimetry, spectrophotometry and reflectometry, can significantly expand their capabilities in the characterization of biological systems and bioorganic materials. Additionally, microwave Mueller matrix polarimetry can be used for monitoring soil conditions and crop growth. The proposed systematization is aimed at outlining the conceptual directions for the development of non-invasive diagnostic tools based on measuring the Mueller matrix, primarily with a focus on biological research and agricultural practice.

External Modulation Optical Coherent Domain Reflectometry with Long Measurement Range.

Optical coherent domain reflectometry (OCDR) can achieve a high spatial resolution that is independent of the bandwidth of the receiver, but the measurement range is usually very limited. Here we propose an external modulation OCDR system, in which a pair of linear frequency-modulated pulses generated by one modulator are employed as the probe pulse and the reference, respectively. The spatial resolution is determined by the frequency modulation range of the pulse, and the measurement speed is boosted by orders because the proposed technology can simultaneously diagnose a section of fiber with each pair of pulses, while only a single point can be accessed at a time in typical OCDR. In the demonstrational experiment, a measurement range of up to 50 km is achieved with a spatial resolution of 1.4 m and a measuring time of less than 30 s.

Quasi-tomography by free space line field spectral domain optical coherence reflectometry

This paper reports the development of a new technique, free space line field spectral domain optical coherence reflectometry (LF-SD-OCR), which is able to produce tomographic like (quasi) images. Furthermore, the capabilities and cost benefits of the technique are demonstrated by constructing a handheld LF-SD-OCR device. For glossy paint systems and other suitable samples, the line field format produces quasi-tomographic (cross-sectional) imaging through the layers, with axial and lateral image resolutions of 1.3 µm and 40 µm respectively. From these, the clear coat thicknesses on the bonnet of cars were measured by graph search segmentation and maximum A-scan projection. In comparison with the widely used single point ultrasound and optical devices, our technique gives the user more confident interpretation of the results as it produces a cross-sectional image of the sample in a single-shot fashion without the need of any mechnical scanning. In addition, the produced device has higher resolution and lower cost (£1660 cost of the constructed one-off prototype as compared with over £10K for comparable universally capable ultrasonic devices), making the technique an economically viable alternative to ultrasound in the quality assurance of coating systems and other application areas such as plastic film manufacturing control.

Operational control method for train integrity monitoring based on optical coherent reflectometry data

The paper presents a novel method for wagon counting of moving trains. The method is based on optical coherent reflectometry data from an area of train track laying. A wagon number operational control in a train composition is widely used as one of the main methods of train integrity monitoring. In turn, train integrity is one of the main important factors in the security provision of railway traffic. The method proposed in the paper is simple, intuitive and easily realizable in practice. Its high economic efficiency is caused by the fact that the method does not require any additional equipment with exception of that already installed in the monitoring system of the train movement regulation on the base of optical coherent reflectometry. The proposed algorithm is built upon the joint application of the hidden Markov model and Viterbi-like method used for sequence of states evaluation of the hidden Markov model. The field-service tests performed at the real railroad haul have proved high practical efficiency of the approach.

Relation between denaturation time measured by optical coherence reflectometry and thermal lesion depth during radiofrequency cardiac ablation: Feasibility numerical study.

Radiofrequency (RF) catheter ablation is a minimally invasive medical procedure used to thermally destroy the focus of cardiac arrhythmias. Novel optical techniques are now being integrated into RF catheters in order to detect the changes in tissue properties. Loss of birefringence due to fiber denaturation at around 70°C is related to changes in accumulated phase retardation and can be measured by polarization-sensitive optical coherence reflectometry (PS-OCR). Since irreversible thermal lesions are produced when the tissue reaches 50°C, our goal was to seek the mathematical relationship between both isotherms. A two-dimensional model based on a coupled electric-thermal problem was built and solved using the finite element method. The model consisted of cardiac tissue, blood, and a non-irrigated electrode with a sensor embedded in its tip to maintain a specific target electrode temperature. Computer simulations were conducted by varying the tissue characteristics. Lesion depth was estimated by the 50°C isotherm, while the denaturation time (TD) was taken as the time at which the 70°C isotherm reached a depth of 0.75 mm (which corresponds to the optical depth reached by PS-OCR technology). A strong correlation (R2 > 0.83) was found between TD and lesion depth and an even stronger correlation (R2 > 0.96) was found between TD and the time required to achieve a specific lesion depth. For instance, the ablation time required to ensure a minimum lesion depth of 3 mm was 1.33 × TD + 3.93 × seconds. The computer results confirmed the strong relationship between denaturation time and lesion depth and suggest that measuring denaturation time by PS-OCR could provide information on the ablation time required to reach a specific lesion depth. Lasers Surg. Med. 50:222-229, 2018. © 2017 Wiley Periodicals, Inc.

Distributed spatial mode dispersion measurement along strongly coupled multicore fibers based on the correlation analysis of Rayleigh backscattering amplitudes.

We describe a method for measuring spatial mode dispersion (SMD) distribution along a strongly coupled multicore fiber (SC-MCF). The SMD has been defined for characterizing an SC-MCF, and it changes with respect to local fiber bending and twisting. However, conventional measurement methods characterize only the overall SMD, and cannot identify fiber portions where the environmental conditions affect the SMD. This paper demonstrates distributed SMD measurement along an SC-MCF by auto-correlating Rayleigh backscattering amplitudes obtained with coherent optical reflectometry. We confirm our method experimentally, and distinguish the difference between the SMD growth along twisted and non-twisted fiber sections in concatenated SC-MCFs.

Novel catheter enabling simultaneous radiofrequency ablation and optical coherence reflectometry.

A novel radiofrequency ablation catheter has been developed with integrated custom designed optics, enabling real-time monitoring of radiofrequency ablation procedures through polarization-sensitive optical coherence reflectometry. The optics allow for proper tissue illumination through a view-port machined in the catheter tip, thus providing lesion depth control over the RF ablation treatment. The system was verified in an in-vitro model of swine myocardium. Optical performance and thermal stability was confirmed after more than 25 procedures, without any damage to the optical assembly induced by thermal stress or material degradation. The use of this catheter in RF ablation treatments may make possible to assess lesion depth during therapy, thus translating into a reduction of potential complications on the procedure.

Scalable synthesis of djurleite copper sulphide (Cu1.94S) hexagonal nanoplates from a single precursor copper thiocyanate and their photothermal properties

Copper sulphide materials have received great attention due to their low bandgap semiconducting properties. As compared to other chalcogenides, few synthetic examples have been reported, and a simple and scalable synthetic method for preparing size- and shape-controlled copper sulphide nanoparticles is required for potential wide application of these materials. Herein, a facile one pot scalable synthetic route has been developed for preparing highly monodisperse djurleite Cu1.94S hexagonal nanoplates. The thermal decomposition of a single precursor CuSCN was found suitable for preparing a large quantity of highly monodisperse Cu1.94S hexagonal nanoplates; a multi-gram scale product could be obtained in a single step. Under the synthetic scheme developed, the width of Cu1.94S nanoplates with a thickness of ~ 10 nm could be easily tuned from 70 nm to 130 nm. Their optical properties were investigated and their photothermal effect was also studied by photothermal optical coherence reflectometry (PT OCR). Cu1.94S hexagonal nanoplates showed a considerable photothermal effect, which was found to depend on the nanoparticle concentration.

Photothermal spectral-domain optical coherence reflectometry for direct measurement of hemoglobin concentration of erythrocytes

A novel optical detection method for hemoglobin concentration is described. The hemoglobin molecules consisting mainly of iron generate heat upon their absorption of light energy at 532nm, which subsequently changes the refractive index of the blood. We exploit this photothermal effect to determine the hemoglobin concentration of erythrocytes without any preprocessing of blood. Highly sensitive measurement of refractive index alteration of blood samples is enabled by a spectral-domain low coherence reflectometric sensor with subnanometer-level optical path-length sensitivity. The performance and validity of the sensor are presented by comparing the measured results against the reference data acquired from an automatic hematology analyzer.

Integrated optical coherence tomography and reflectometry system for ocular anterior segment imaging and tear film thickness evaluation

We report an integrated optical coherence tomography (OCT) and reflectometry system for ophthalmology imaging. The dual-functional device provides a complementary high-resolution tear film evaluation by reflectometry and anterior segment imaging by OCT, offering a more comprehensive anterior segment examination. The imaging measurement capabilities have been demonstrated on a human eye as well as on a model eye. The minimum measured tear film thickness is 0.3 μm with measurement resolution of less than ±0.58% of film thickness yet the OCT anterior segment offers a depth resolution of 7 μm with a 45-nm bandwidth superluminescent light source at 840-nm center wavelength. The integrated system has demonstrated the capability for three-dimensional imaging in the anterior segment of the eye.

Spectral-domain optical coherence reflectometric sensor for highly sensitive molecular detection

We describe what we believe to be a novel use of spectral-domain optical coherence reflectometry (SD-OCR) for highly sensitive molecular detection in real time. The SD-OCR sensor allows identification of a sensor surface of interest in an OCR depth scan and monitoring the phase alteration due to molecular interaction at that surface with subnanometer optical thickness sensitivity. We present subfemtomole detection sensitivity for etching of SiO(2) molecules and demonstrate its application as a biosensor by measuring biotin-streptavidin binding in a microfluidic device.

New percutaneous approaches for chronic total occlusion of coronary arteries

Successful recanalization and percutaneous revascularization of coronary arteries with chronic total occlusion (CTO) is one of the ‘last frontiers’ in coronary interventions. Conquering this obstacle will enable complete percutaneous revascularization in an increasing number of patients. The introduction within the last few years of enhanced guidewires combined with increasing operator experience and creative procedural techniques, such as the retrograde approach and the re-entry subintimal tracking technique (STAR), have significantly reduced the number of CTOs that should now be considered unapproachable. In addition, novel devices have been developed over recent years that may increase the success rate, as well as the safety, of the procedure. The Safe-Cross radiofrequency combines optical coherence reflectometry that warns the operator when the wire tip moves to within 1 mm of the outer vessel wall, combined with radiofrequency energy pulses to facilitate the passage. The CROSSER catheter mechanically vibrates against the face of the CTO at 20 kHz at a stroke depth of approximately 20 µm, creating a channel through the CTO. The most novel approach is the biologic one, in which proteolytic enzymes that digest the CTO cap to facilitate mechanical passage. The success rates for otherwise refractory CTOs will continue to improve with the development and validation of new imaging modalities and active energy source catheters.

Recanalization of chronic total peripheral arterial occlusions using optical coherent reflectometry with guided radiofrequency energy: A single center experience

A forward-looking, fiberoptic guided device (Safe-Cross System, Intraluminal Therapeutics, Carlsbad, CA) has been used with guided radiofrequency energy to open chronic total occlusions (CTOs). This report describes the use of optical coherent reflectometry (OCR) system to assess safety and efficacy of opening CTOs in native peripheral arteries in the lower extremities: iliac, femoral, and popliteal. 18 CTOs in native peripheral arteries in 17 patients were treated with OCR after failed attempts with conventional wires (minimum 10 min of fluoroscopic time). When the CTO was crossed, routine angioplasty with or without stent was performed. Efficacy was defined as achievement of distal lumen position. Safety was defined as device success without perforation, dissection (> or =Grade C), or distal embolization. The mean patient age was 72 years with 8 females and 10 males. Lesion characteristics included a mean vessel diameter of 5.8 mm and a mean lesion length of 22.4 cm. Ankle-brachial indices was < or =0.8 in all patients. The OCR system was successful in crossing 100% of the CTOs in patients that failed conventional wire crossing, whereas clinical success occurred in 94% of these patients. Complications consisted of a single dissection > or =Grade C. No perforations or distal embolization occurred. The Safe-Cross OCR System is both efficacious and safe in the treatment of CTOs that failed crossing with conventional wires and indirect visualization of the intraluminal position by using OCR technology appears to minimize vessel trauma, dissection, perforation, and distal embolization.

Is Magnetic Resonance Image Guidance the Key to Opening Chronic Total Occlusions?

Through progressive plaque growth or fibrotic organization of occlusive thrombus, atherosclerosis may result in chronic total occlusion (CTO) of a major arterial conduit. If CTO develops slowly, collateral pathways may supply sufficient perfusion to retain tissue viability despite occlusion of the major inflow conduit. However, such collateral-mediated perfusion rarely matches that provided by an open main conduit, particularly during the peak demand of regional muscular activity. Although strategies to limit regional oxygen demand (eg, β-blockers for the treatment of angina pectoris) or to enhance collateral function (eg, a walking program for superficial femoral occlusion, experimental angiogenesis) may be of some benefit, these approaches generally offer less complete return of normal physiology and relief of ischemic symptoms than does direct revascularization of the occluded vessel. With surgical bypass, the nature of the occlusion (its length, duration, tortuosity, calcification) is less important than the presence of a suitable distal anastomotic target. On the other hand, with catheter-based techniques, success depends heavily on these lesion characteristics. In fact, crossing such occluded segments with a guidewire remains the dominant barrier to catheter-based treatments of occluded arterial segments. Once the guidewire has been passed successfully into the distal true lumen, the process of dilating and stenting the segment is usually straightforward and durable, at least with the use of drug-eluting stents in coronary CTOs.1,2 Article p 1101 Devices designed to cross CTOs should have 3 key features: an ability to distinguish a true luminal path from one created within (dissection) or through (perforation) the vessel wall of the occluded segment, an ability to change direction (steer) to correct deviations from the desired path through the occlusion, and an ability to penetrate the frequently fibrotic and focally calcific substance of the occlusion through the use of either mechanical stiffness or an alternative energy modality (laser, …

Novel Approaches for the Treatment of Chronic Total Coronary Occlusions

Despite major advancements in the technology used for the percutaneous treatment of coronary artery disease, chronic total occlusions (CTOs) persist as a major challenge to the interventional cardiologist with relatively low success rates. CTOs are evident in 20% of patients undergoing cardiac catheterization and are responsible for the majority of cases that are referred to bypass surgery. There is growing evidence that patients may benefit from recanalization of a CTO by alleviation of angina, improving left ventricular function, and potentially long-term survival. The major obstacle to percutaneous recanalization of CTOs is the inability to cross the occlusion with coronary guidewires. Even when crossed, the operator has to deal with the exact location of the distal wire (e.g., dissection or true lumen) and the existence of relatively long lesion requiring multiple stents with high restenosis rates. New technologies for CTO revascularization have been focused mainly on a mechanical approach including specialized guidewires and more recently, specific devices using highly sophisticated technology such as laser guidewire, optical coherence reflectometry, and a blunt microdissection catheter. An alternate biological approach involves the local administration of enzymes such as plasminogen activators (urokinase) or collagenase, which can act locally to specifically degrade the collagen content of the CTO, thereby "softening" the occlusion and allowing easier guidewire crossing. In conclusion, CTOs emerge as a great technical challenge and are the focus of novel series of mechanical and biological approaches.

Usefulness of optical coherent reflectometry with guided radiofrequency energy to treat chronic total occlusions in peripheral arteries (the GRIP trial)

Optical coherent reflectometry, a forward-looking, fiberoptic-guided device was used in 72 patients to direct radiofrequency energy across the central intraluminal portion of 75 chronic total occlusions in peripheral arteries (iliac, femoral, and popliteal) that failed attempts with conventional guidewires. The system was successful in crossing 76% of the chronic total occlusions with no clinical perforations or distal embolizations, and complications consisted of a single dissection greater than or equal to grade C.

Utility of the Safe-Cross–guided radiofrequency total occlusion crossing system in chronic coronary total occlusions (Results from the Guided Radio Frequency Energy Ablation of Total Occlusions Registry Study)

The Safe-Cross radiofrequency guidewire (IntraLuminal Therapeutics, Carlsbad, California) combines 3 capabilities: (1) steerability of a conventional 0.014-in intermediate-stiffness guidewire, (2) optical coherence reflectometry to warn the operator when the wire tip approaches within 1 mm of the vessel wall, and (3) delivery of radiofrequency energy pulses to the wire tip to facilitate passage through an occluded segment. The Guided Radio Frequency Energy Ablation of Total Occlusions Registry was a prospective, nonrandomized, multicenter registry that enrolled 116 patients who had long-term coronary total occlusions and in whom a >10-minute good-faith attempt to cross the occlusion using conventional guidewires had failed. The median known duration of occlusion was 22 months (32%; >1 year), and the median length of the occluded segment was 25 mm (25%; >30 mm). Device success was achieved in 63 of 116 of patients (54.3%), and major adverse events occurred in 6.9%, consisting predominantly of isolated increases in cardiac enzymes with no procedure-related deaths, Q-wave myocardial infarctions, or emergency bypass operations. Clinical perforation occurred in 2.6% of patients; of these, perforation in only 1 patient (0.9%) was adjudicated to be directly related to the Safe-Cross radiofrequency wire rather than to the stiff and/or hydrophilic wires used after an inability to advance with the Safe-Cross. Based on these data, the device has been approved in Europe and was recently (January 2004) granted 510K clearance by the Food and Drug Administration.

Improved recanalization of chronic total coronary occlusions using an optical coherence reflectometry-guided guidewire.

Successful percutaneous therapy of chronic total occlusions is limited predominantly by the inability to cross the lesion. We report our experience of 29 chronic total occlusions (CTOs) that could not be crossed with conventional wires and subsequently underwent attempted recanalization facilitated using a wire navigated with optical coherence reflectometry. Mean length of occlusion was 22.1 mm (range, 4.5-88.7 mm). Successful recanalization was achieved in a further 15 (51.7%), with no complications of tamponade, myocardial infarction, or death. These results demonstrate that this wire can be a useful tool in addition to conventional wires in the treatment of CTO.