Optical Coherence Tomography for Health Professionals

OCT clinical study and results analyzed by UH Harrington Heart & Vascular Institute physicians now FDA approved

University Hospitals Harrington Heart & Vascular Institute physicians and scientists have been involved in the clinical trials for Optical Coherence Tomography (OCT) and have just used it in the first case at University Hospitals Case Medical Center following U.S. Food and Drug Administration approval in May 2010.

As part of the Cardiovascular Imaging Core Laboratory, our physicians and scientists have participated in the creation, testing, deployment and evolution of multiple imaging capabilities. Our invasive cardiovascular imaging modalities include quantitative coronary analysis and intravascular ultrasound in addition to OCT, while our non-invasive imaging tools include computed tomography and magnetic resonance.

Optical Coherence Tomography

UH physicians and scientists have been involved with the development of OCT technology for nearly 10 years and have fostered multiple international collaborations in Europe and Asia, where product developer LightLab, Inc.’s C7-XR Imaging System and companion C7 Dragonfly Imaging Catheter are already approved in over 35 countries. Our clinical database houses more than 750 OCT images from multiple hospitals worldwide, making our team the most experienced in interpreting OCT images across the globe. Our physicians are the leading experts using this technology in the U.S. and provide training sessions on how to perform OCT in our experimental lab for other physicians across the country and world. We will continue to lead and train other U.S. and international physicians on how best to practice OCT to improve patient care.

This novel therapy, as pioneered by LightLab, Inc., was tested in a clinical trial at three U.S. sites with UH Case Medical Center Cardiovascular Imaging Core Laboratory physicians responsible as the core laboratory for analyzing the results.

OCT technology is a major improvement in catheter-based imaging as it allows near-microscopic examination of living tissues. The technology is unique because it allows direct photographic examination of soft tissues, which cannot be easily accomplished using other modalities.

OCT uses light rather than ultrasound, producing high-resolution in vivo images of coronary arteries and deployed stents. Semi-automated imaging analyses of OCT systems allow accurate measurements of luminal architecture and provide insights regarding stent apposition, overlap, neointimal thickening, and, in the case of bioabsorbable stents, information regarding the timeline of stent dissolution.

Physics Principles

The principles of cardiovascular Optical Coherence Tomography are simple and elegant: a single fiberoptic wire both emits light and records its reflection while simultaneously rotating and being drawn back along the artery. The resulting cross-sectional tomographic image reveals startling definition, far superior to any other currently available in vivo modality. The potent combination of high spatial resolution (~15µm, a 10-fold improvement over intravascular ultrasound) and in vivo imaging capability have placed this technology at the forefront of intracoronary arterial evaluation of atherosclerotic disease, and provide real-time feedback to clinicians with easy-to-interpret images of vessel wall, stent and lumen architecture.

The coronary OCT light source uses a bandwidth in the near-infrared spectrum with central wavelengths ranging from 1,250-1,350 nm. The image is generated by the backscattering of light from the vessel wall or the time it takes for emitted light to travel between the target tissue and back to the lens, producing an “echo time delay” with a measurable signal intensity or “magnitude.” The axial resolution, determined by the light wavelength, ranges from 12-18 µm, compared to 150-200 µm for intravascular ultrasound. The lateral resolution and depth of focus are decoupled from the axial resolution and defined by the spot size focused by the lens in the sample arm. The lateral resolution in catheter-based OCT is typically 20-90 µm as compared to 150-300 µm for intravascular ultrasound.

Multiple axial scans (A-lines) are continuously acquired as the imagewire rotates and a full revolution creates a complete cross-section of the vessel. OCT imaging requires a blood free environment, and time domain OCT (TD-OCT) was physically limited by a moving mirror in the reference arm and a tradeoff between imaging speed and sensitivity. Newer generations of intravascular OCT systems circumvent this limitation by using a fixed mirror with a variable frequency light source or “swept-laser.” This method, termed Fourier-Domain or Frequency-Domain OCT (FD-OCT), allows the simultaneous detection of reflections from all echo time delays, making the system significantly faster. For example, the average axial scans per second on the LightLabTM M2/M3 (TD-OCT systems) is 5,000 – 10,000 as compared to ~50,000 in the LightLabTM C7 XR (FD-OCT system). This results in frame rates > 100 fps, allowing 10 times faster pullback speeds (~20 mm/s).

Besides its visual appeal, vascular OCT images have well-delineated boundaries, making image interpretation easy and enabling near real-time quantification – both essential features for the practicing physician. The current technology permits the evaluation of clinical (e.g., luminal measurements during PCI) and research (e.g., fibrous cap thickness and strut level analysis) parameters for the interventional cardiologist.