In vitro characterization of cardiac radiofrequency ablation lesions using optical coherence tomography.

Currently, cardiac radiofrequency ablation (RFA) is guided by indirect signals. We demonstrate optical coherence tomography (OCT) characterization of RFA lesions within swine ventricular wedges. Untreated tissue exhibited a consistent birefringence artifact within OCT images due to the organized myocardium, which was not present in treated tissue. Birefringence artifacts were detected by filtering with a Laplacian of Gaussian (LoG) to quantify gradient strength. The gradient strength distinguished RFA lesions from untreated sites (p=5.93 x 10(-15)) with a sensitivity and specificity of 94.5% and 86.7% respectively. This study demonstrates the potential of OCT for monitoring cardiac RFA, confirming lesion formation and providing feedback to avoid complications.

Quantification of cardiac fiber orientation using optical coherence tomography.

Heterogeneity in cardiac tissue microstructure is a potential mechanism for the generation and maintenance of arrhythmias. Abnormal changes in fiber orientation increase the likelihood of arrhythmia. We present optical coherence tomography (OCT) as a method to image myofibers in excised intact heart preparations. Three-dimensional (3-D) image sets were gathered from the rabbit right ventricular free wall (RVFW) using a microscope-integrated OCT system. An automated algorithm for fiber orientation quantification in the plane parallel to the wall surface was developed. The algorithm was validated by comparison with manual measurements. Quantifying fiber orientation in the plane parallel to the wall surface from OCT images can be used to help understand the conduction system of the specific sample being imaged.

Bimodal biophotonic imaging of the structure-function relationship in cardiac tissue.

The development of systems physiology is hampered by the limited ability to relate tissue structure and function in intact organs in vivo or in vitro. Here, we show the application of a bimodal biophotonic imaging approach that employs optical coherence tomography and fluorescent imaging to investigate the structure-function relationship at the tissue level in the heart. Reconstruction of cardiac excitation and structure was limited by the depth penetration of bimodal imaging to approximately 2 mm in atrial tissue, and approximately 1 mm in ventricular myocardium. The subcellular resolution of optical coherence tomography clearly demonstrated that microscopic fiber orientation governs the pattern of wave propagation in functionally characterized rabbit sinoatrial and atrioventricular nodal preparations and revealed structural heterogeneities contributing to ventricular arrhythmias. The combination of this bimodal biophotonic imaging approach with histology and/or immunohistochemistry can span multiple scales of resolution for the investigation of the molecular and structural determinants of intact tissue physiology.

Ultrahigh-resolution optical coherence tomography at 1.15 mum using photonic crystal fiber with no zero-dispersion wavelengths.

We report a broad-band continuum light source with high power, low noise and a smooth spectrum centered at 1.15 mum for ultrahigh-resolution optical coherence tomography (OCT). The continuum is generated by self-phase modulation using a compact 1.059 mum femtosecond laser pumping a novel photonic crystal fiber, which has a convex dispersion profile with no zero dispersion wavelengths. The emission spectrum is red-shifted from the pump wavelength, ranges from 800 to 1300 nm and results in a measured axial resolution of ~2.8 mum in air. We demonstrate ultrahigh-resolution OCT imaging of biological tissue using this light source. The results suggest PCF with this type of dispersion profile is advantageous for generating SC as a light source for ultrahigh-resolution OCT.

Extracting three-dimensional orientation and tractography of myofibers using optical coherence tomography.

Abnormal changes in orientation of myofibers are associated with various cardiac diseases such as arrhythmia, irregular contraction, and cardiomyopathy. To extract fiber information, we present a method of quantifying fiber orientation and reconstructing three-dimensional tractography of myofibers using optical coherence tomography (OCT). A gradient based algorithm was developed to quantify fiber orientation in three dimensions and particle filtering technique was employed to track myofibers. Prior to image processing, three-dimensional image data set were acquired from all cardiac chambers and ventricular septum of swine hearts using OCT system without optical clearing. The algorithm was validated through rotation test and comparison with manual measurements. The experimental results demonstrate that we are able to visualize three-dimensional fiber tractography in myocardium tissues.

Depth resolved detection of lipid using spectroscopic optical coherence tomography.

Optical frequency domain imaging (OFDI) can identify key components related to plaque vulnerability but can suffer from artifacts that could prevent accurate identification of lipid rich regions. In this paper, we present a model of depth resolved spectral analysis of OFDI data for improved detection of lipid. A quadratic Discriminant analysis model was developed based on phantom compositions known chemical mixtures and applied to a tissue phantom of a lipid-rich plaque. We demonstrate that a combined spectral and attenuation model can be used to predict the presence of lipid in OFDI images.

Toward guidance of epicardial cardiac radiofrequency ablation therapy using optical coherence tomography.

Radiofrequency ablation (RFA) is the standard of care to cure many cardiac arrhythmias. Epicardial ablation for the treatment of ventricular tachycardia has limited success rates due in part to the presence of epicardial fat, which prevents proper rf energy delivery, inadequate contact of ablation catheter with tissue, and increased likelihood of complications with energy delivery in close proximity to coronary vessels. A method to directly visualize the epicardial surface during RFA could potentially provide feedback to reduce complications and titrate rf energy dose by detecting critical structures, assessing probe contact, and confirming energy delivery by visualizing lesion formation. Currently, there is no technology available for direct visualization of the heart surface during epicardial RFA therapy. We demonstrate that optical coherence tomography (OCT) imaging has the potential to fill this unmet need. Spectral domain OCT at 1310 nm is employed to image the epicardial surface of freshly excised swine hearts using a microscope integrated bench-top scanner and a forward imaging catheter probe. OCT image features are observed that clearly distinguish untreated myocardium, ablation lesions, epicardial fat, and coronary vessels, and assess tissue contact with catheter-based imaging. These results support the potential for real-time guidance of epicardial RFA therapy using OCT imaging.

Real-time monitoring of cardiac radio-frequency ablation lesion formation using an optical coherence tomography forward-imaging catheter.

Radio-frequency ablation (rfa) is the standard of care for the treatment of cardiac arrhythmias; however, there are no direct measures of the successful delivery of ablation lesions. Optical coherence tomography (OCT) imaging has the potential to provide real-time monitoring of cardiac rfa therapy, visualizing lesion formation and assessing tissue contact in the presence of blood. A rfa-compatible forward-imaging conical scanning probe is prototyped to meet this need. The forward-imaging probe provides circular scanning, with a 2-mm scan diameter and 30-mum spot size. During the application of rf energy, dynamics are recorded at 20 frames per second with a 40-kHz A-line rate. Real-time monitoring of cardiac rfa lesion formation and imaging in the presence of blood is demonstrated ex vivo in a swine left ventricle with a forward, flexible, circular scanning OCT catheter.