|COMMENTARY AND HISTORY OF MEDICINE
|Year : 2019 | Volume
| Issue : 1 | Page : 35-36
Intravascular ultrasound versus optical coherence tomography
Department of Cardiology, Heart Hospital, Hamad Medical Corporation, Doha, Qatar
|Date of Web Publication||7-May-2019|
Sr. Consultant Cardiologist, Director of HH Publications, Executive Coordinator for Research, Director of Non-invasive Cardiology (1981.2014), Heart Hospital, Hamad Medical Corporation, Doha
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Hajar R. Intravascular ultrasound versus optical coherence tomography. Heart Views 2019;20:35-6
| Introduction|| |
Technology is continually evolving in ways that we never dreamed of. Forty years ago, ultrasound technology burst into the forefront of medicine and had developed and become a powerful tool for diagnosis and management of cardiac diseases. Now comes the light technology, and hopefully, it will revolutionize the way that medicine is practiced. This light technology is used in medical imaging and is termed optical coherence tomography or OCT for short.
| What Is Optical Coherence Tomography?|| |
OCT is an intravascular imaging modality akin to intravascular ultrasound (IVUS). It is an emerging technology for performing high-resolution cross-sectional imaging. It is like ultrasound imaging, but it uses light instead of sound.
| History|| |
It does not have a long history; it came to being only in the 1990s. It was first performed on the retina and coronary artery in 1991. OCT has become established as an imaging modality in clinical ophthalmology and is finding applications in gastrointestinal diseases and in dermatology. Its biggest application in cardiovascular medicine is in the coronary vasculature to aid in the assessment of coronary artery disease and recently in the assessment of grafts.
Numerous clinical studies have been performed by many groups in the last several years.
Optical coherence tomography versus ultrasound
Ultrasound imaging is a well-established clinical imaging modality and is used in a wide range of applications, especially in the heart. In ultrasound, with the use of an ultrasonic probe transducer, a high-frequency sound wave is launched into the material or tissue being imaged.,,,, The sound wave travels into the material or tissue and is reflected or backscattered from internal structures having different acoustic properties. The frequency of the sound wave determines the image resolution in ultrasound, with higher frequencies yielding higher resolutions. However, attenuation of the sound wave also occurs with propagation and higher frequencies have reduced imaging depths. The time behavior or echo structure of the reflected sound waves is detected by the ultrasonic probe, and the ranges and dimensions of internal structures are determined from the echo delay. This principle is also similar to that of used in radar range detection of aircraft.
When a beam of sound or light is directed onto tissue, it is back-reflected or backscattered from structures which have different acoustic or optical properties as well as from boundaries between structures. The dimensions of the different structures can be determined by measuring the “echo” time it takes for sound or light to be back-reflected or backscattered from the different structures at varying axial (longitudinal) distances. In ultrasound, the axial measurement of distance or range is referred to as “A” mode scanning.
Difference between intravascular ultrasound and optical coherence tomography
In cardiology, OCT and IVUS are modern tools that contribute to the understanding of coronary artery disease and percutaneous coronary intervention (PCI). Nevertheless, OCT and IVUS differ in several aspects. For instance, current coronary OCT systems use a central wavelength of approximately 1300 nm and tissue penetration of OCT is limited to 1–3 mm, compared with 4–8 mm with IVUS. Because the speed of light (3 × 108 m/s) is much greater than that of sound (1500 m/s), OCT as a fiber optic system offers 10 times greater resolution and 40 times faster image acquisition compared with IVUS. Because of the high attenuation of light by blood, complete removal of the blood during OCT examination is necessary.
| Current Optical Coherence Tomography Systems|| |
Originally, the first-generation OCT was time-domain OCT (TD-OCT). In that system, TD-OCT requires balloon occlusion in proximal vessels to create a blood-free imaging environment. Previous studies have confirmed the safety of TD-OCT with balloon occlusion in comparison with IVUS. Nevertheless, the former is a complex procedure and its application is limited to ostial coronary disease.,, Currently, new-generation OCT systems that implement frequency-domain OCT (FD-OCT) imaging methods have been developed to overcome such limitations.,,
| Uses of Optical Coherence Tomography in Cardiology|| |
OCT is a promising tool and its usefulness is only just emerging. Compared to IVUS, its use is not yet routine. Outcome data are not yet available even thoughin vivo atherosclerosis has been extensively studied using OCT for over a decade.
There are not yet definitive guidelines concerning its use, and therefore, OCT is recommended as a research tool.
Because of its unsurpassed resolution, such as stent coverage and neointimal material obtained, OCT is arguably the gold standard for stent assessment nowadays. Response to treatment can be evaluated with OCT. It can also provide valuable information concerning stent strut apposition, expansion, and complications such as dissections poststent implantation. OCT has also provided cardiologists with exceptional pictures concerning in-stent restenosis or thrombosis, allowing us to better understand the pathological processes in its evolution. There have also been publications using OCT in spontaneous coronary artery dissection, chronic thromboembolic hypertension, and cardiac allograft vasculopathy. It seems that OCT is useful in these situations.
| Conclusion|| |
OCT is a novel, promising imaging modality with characteristics that differ from those of traditional modalities such as IVUS. However, OCT does not yet have the established clinical profile or ease-of-use of IVUS. Most of the studies on OCT have come from Korea, Japan, China, and Europe, but the use of OCT is becoming more widespread. Through these studies, it is hoped that the clinical role of OCT in PCI will be clearer. Moreover, with FD-OCT imaging which is reportedly easier to use, definitive guidelines for its proper use will be available.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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