With FD-OCT, 100 frames\sec can be obtained, with an automatic pullback of 20 mm/sec and a resolution of 500.000 pixel/frame during a single injection of contrast bolus. TD-OCT used a broadband light whereas FD-OCT employs a laser that emits near monochromatic light which allows higher frame rate and speed of data acquisition. Currently available frequency-domain OCT (FD-OCT) systems have much higher frame rates and scanning speeds, enabling the acquisition of long coronary segments very rapidly. OCT technology has been developing over time, moving from time domain to frequency domain OCT systems.
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Recently, non occlusive techniques that consist in flushing the coronary artery with contrast media to displace the blood pool during vessel’s scan that allow full vessel visualisation without occlusion have come forth (8). This result was previously achieved by relatively complex techniques such as occluding the coronary lumen with an inflated balloon and simultaneously flushing the vessel with saline through the balloon catheter. IVUS maximum tissue penetration, on the other hand, is 10 mm, thus allowing plaque volume measurement.įurthermore, red blood cells interfere with the propagation of infrared light, therefore it is necessary to displace the blood from vessel’s lumen during the OCT scan to avoid artifacts that may limit good visualisation of the coronary artery wall. Nevertheless, current maximum tissue penetration with OCT is approximately 1.5 mm-3 mm and consequently, some vessel structures, including the external elastic lamina, cannot be visualised by OCT in cases of coexisting large atherosclerotic plaque. OCT resolution is also superior to non-invasive coronary imaging techniques such as computer tomography coronary angiography (CTCA) and cardiac magnetic resonance (CMR). Axial resolution with OCT is 10-20 micron whereas it is typically only 100-200 micron with intravascular ultrasounds. It uses light in the infrared spectrum with central wavelength between 1,250 and 1,350 nm (3,4). Speed of light being greater than ultrasound, an interferometer is necessary to measure the backscattered light. The system then creates cross sections of the coronary artery allowing for real- and off-line analysis of each section.
OCTs measure the echo time delay and the signal intensity after its reflection or back-scattering from the coronary wall structures while simultaneously operating a pull-back along the coronary artery, and thus performing a scan of the segment of interest (1). OCT catheters contain a single optical fiber that emits infrared light.
Infrared light offers greater resolution but less tissue penetration It benefits both therapeutic and research purposes and is also proving able to fill gaps in conventional invasive coronary imaging. OCT in this area has grown and is spreading. In the last years, the need for more precise information regarding coronary artery disease to achieve optimal treatment has seen intravascular imaging becoming an area of primary importance in interventional cardiology.
Its general principle of operation is similar to IVUS, however OCT uses infrared light, not ultrasound. Optical coherence tomography (OCT) is a novel invasive imaging technique that produces high resolution intracoronary images.
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