This article may be too technical for most readers to understand.(September 2016) |
Endoscopic optical coherence tomography | |
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Endoscopic optical coherence tomography, also intravascular optical coherence tomography is a catheter-based imaging application of optical coherence tomography (OCT). [1] It is capable of acquiring high-resolution images from inside a blood vessel using optical fibers and laser technology.
One of its main applications is for coronary arteries, which are often treated by endoscopic, minimally invasive surgical procedures. [2] Other applications for peripheral arteries and for neurovascular procedures have been proposed and are being investigated. Neurovascular applications required significant technological developments, due to the highly tortuous anatomy of the cerebrovasculature.
Intravascular OCT rapidly creates three-dimensional images at a resolution of approximately 15 micrometers, an improved resolution with respect to intravascular ultrasound and coronary angiogram, the other imaging techniques. [3] This offers additional information that can be used to optimize the treatment and management of vascular disease.
OCT is analogous to medical ultrasound, measuring the backreflection of infrared light rather than sound. The time for light to be reflected back from the tissue under inspection is used to measure distances. However, due to the high speed of light, the backreflection time cannot be measured directly, but is instead measured using interferometry. [4]
OCT is measured using either time domain (TD-OCT) or frequency domain techniques (FD-OCT). Commercially available coronary OCT technology is based on frequency domain techniques, resulting in rapid acquisition procedures (1 to 2 seconds). Intracoronary OCT uses near-infrared light at 1300 nm and can visualize the microstructure of the arterial wall, its size, and therapeutic devices with high accuracy.
Intravascular OCT was developed for the imaging of arterial disease at a resolution higher than the other techniques available, such as x-ray angiography and intravascular ultrasounds. OCT allows to assess atherosclerotic plaques characteristics at a resolution of approximately 15 μm (or better) and found applications for the guidance of catheter-based coronary interventions (ie, percutaneous coronary interventions). The first report of endoscopic OCT appeared in 1997 in the journal Science exploring various applications including gastroenterology and airways. [5] The first intravascular in vivo use in a preclinical model was reported in 1994 [6] and first in human, clinical imaging in 2003. [7] The first OCT imaging catheter and system was commercialized by LightLab Imaging, Inc., a company based in Massachusetts formed following a technology transfer in 1997 from Fujimoto's lab (MIT). [8]
Early on, time-domain OCT technology required slow acquisitions (>10 seconds long) requiring the use of balloon occlusion techniques to displace the blood from the arterial lumen, opaque to near-infrared light. This prevented a broader adoption for several years. Aroun 2008-2009, the advent of rapid sweep source lasers allowed for the development of intravascular Fourier-Domain OCT (FD-OCT). [9] [10] This enabled for the first-time rapid acquisitions of a long coronary segment in a couple of seconds, allowing non occlusive brief contrast injections to clear the arterial lumen from blood. Initial demonstration of FD-OCT for coronary imaging was achieved in 2008-2009 [11] [3] which significantly accelerated clinical adoption starting in 2009.
Following regulatory clearances in the major geographies between 2009 and 2012 of fast acquisition Fourier domain OCT, the use of intracoronary OCT rapidly increased. It is used to help coronary disease diagnosis, planning of the intervention, assess procedural results, and prevent complications.
In the last decade, clinical benefits of coronary OCT have been systematically investigated. Several studies have linked the use of intravascular imaging such as IVUS and OCT to better stent expansion, a metric strongly correlated to better clinical outcomes in patients suffering from coronary artery disease and myocardial infarction. [12] [13] [14]
Larger randomized clinical trials have been undertaken. In 2023, a double-blind prospective trial demonstrated improvement in morbidity and mortality in coronary bifurcation interventions: "Among patients with complex coronary-artery bifurcation lesions, OCT-guided PCI was associated with a lower incidence of MACE at 2 years than angiography-guided PCI." [15] Although not every study showed significant results, [16] to date, several studies demonstrated the benefits in patient outcomes of using intravascular imaging during coronary arteries interventions. [17] [18] The use of intravascular imaging for coronary intervention is reported on the current cardiology guidelines.
Data published in late 2016 showed that over 150,000 intracoronary optical coherence tomography procedures are performed every year, and its adoption is rapidly growing at a rate of ~10-20% every year. [19]
Assessment of artery lumen morphology is the cornerstone of intravascular imaging criteria to evaluate disease severity and guide intervention. The high-resolution of OCT imaging allows to assess with high accuracy vessel lumen area, wall microstructure, intracoronary stent apposition and expansion. [20] [21] OCT has an improved ability with respect to intravascular ultrasound to penetrate and delineate calcium in the vessel wall that makes it well suited to guide complex interventional strategies in vessels with superficial calcification. OCT has the capability of visualize coronary plaque erosion and fibrotic caps overlying lipid plaques. [22]
In the last decade, significant advances have been made in the endovascular treatment of stroke, including brain aneurysms, intracranial atherosclerosis and ischemic stroke. [23] Intravascular OCT has been proposed has a key technology that can improve current procedure and treatments. [24] However, current intracoronary OCT catheters are not designed for navigation and reliable imaging of tortuous cerebrovascular arteries. [25]
Recently, different (wire-like) OCT catheters have been proposed and were specifically designed for the human cerebrovasculature, [26] named neuro optical coherence tomography (nOCT). A first clinical study to investigate safety, feasibility, and clinical potential has been conducted. [27] Initial applications for the treatment of brain aneurysms and intracranial atherosclerosis have been demonstrated [28] [29] [30] showing future potential. [31] [32]
The most critical technological advance was the catheter and the development of fast wavelength sweeping near-infrared lasers. The fiber optic catheter/endoscope required rapid alignment of two optical fibers with 8 μm cores (one rotating) across free space. The distal end has a focusing component (GRIN or ball lens, typically).
State-of-the-art intracoronary optical coherence tomography uses a swept-source laser to make OCT images at high-speed (i.e., approximately 80,000 kHz - A-scan lines per second) to complete acquisition of a 3D OCT volume of coronary segments in a few-seconds. [33] The first intravascular FD-OCT was introduced to the market in 2009 (EU and Asia) and in 2012 (US). In 2018, two intracoronary OCT catheters are clinically available for use in the coronary arteries, having a size in diameter between 2.4F and 2.7F. [ citation needed ]
The axial resolution of state-of-the-art commercial systems is less than 20 micrometers, which is decoupled from the catheter lateral resolution. The highest resolution of OCT allows for the in vivo imaging of vessel microstructural features at an unprecedented level, enabling visualization of vessel wall atherosclerosis, pathology, and interaction with therapeutic devices at a microscopic level. [34]
Recent developments included the combination of OCT with spectroscopy and fluorescence in a single imaging catheter [35] [36] and miniaturization of the imaging catheter. [37]
Safety of intravascular imaging, including intracoronary OCT and intravascular ultrasound, has been investigated by several studies. Recent clinical trials reported a very low rate of self-limiting, minor complications on over 3,000 patients where in all cases no harm or prolongation of hospital stay was observed. Intracoronary optical coherence tomography was demonstrated to be safe among heterogeneous groups of patients presenting varying clinical setting. [38]
Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is performed by injecting a radio-opaque contrast agent into the blood vessel and imaging using X-ray based techniques such as fluoroscopy. With time-of-flight (TOF) magnetic ressonance it is no longer necessary to use a contrast.
Optical coherence tomography (OCT) is an imaging technique that uses interferometry with short-coherence-length light to obtain micrometer-level depth resolution and uses transverse scanning of the light beam to form two- and three-dimensional images from light reflected from within biological tissue or other scattering media. Short-coherence-length light can be obtained using a superluminescent diode (SLD) with a broad spectral bandwidth or a broadly tunable laser with narrow linewidth. The first demonstration of OCT imaging was published by a team from MIT and Harvard Medical School in a 1991 article in the journal Science. The article introduced the term "OCT" to credit its derivation from optical coherence-domain reflectometry, in which the axial resolution is based on temporal coherence. The first demonstrations of in vivo OCT imaging quickly followed.
Restenosis is the recurrence of stenosis, a narrowing of a blood vessel, leading to restricted blood flow. Restenosis usually pertains to an artery or other large blood vessel that has become narrowed, received treatment to clear the blockage, and subsequently become re-narrowed. This is usually restenosis of an artery, or other blood vessel, or possibly a vessel within an organ.
An atheroma, or atheromatous plaque, is an abnormal accumulation of material in the inner layer of an arterial wall.
Intravascular ultrasound (IVUS) or intravascular echocardiography is a medical imaging methodology using a specially designed catheter with a miniaturized ultrasound probe attached to the distal end of the catheter. The proximal end of the catheter is attached to computerized ultrasound equipment. It allows the application of ultrasound technology, such as piezoelectric transducer or CMUT, to see from inside blood vessels out through the surrounding blood column, visualizing the endothelium of blood vessels.
Percutaneous coronary intervention (PCI) is a minimally invasive non-surgical procedure used to treat narrowing of the coronary arteries of the heart found in coronary artery disease. The procedure is used to place and deploy coronary stents, a permanent wire-meshed tube, to open narrowed coronary arteries. PCI is considered 'non-surgical' as it uses a small hole in a peripheral artery (leg/arm) to gain access to the arterial system; an equivalent surgical procedure would involve the opening of the chest wall to gain access to the heart area. The term 'coronary angioplasty with stent' is synonymous with PCI. The procedure visualises the blood vessels via fluoroscopic imaging and contrast dyes. PCI is performed by an interventional cardiologists in a catheterization laboratory setting.
A drug-eluting stent (DES) is a tube made of a mesh-like material used to treat narrowed arteries in medical procedures both mechanically and pharmacologically. A DES is inserted into a narrowed artery using a delivery catheter usually inserted through a larger artery in the groin or wrist. The stent assembly has the DES mechanism attached towards the front of the stent, and usually is composed of the collapsed stent over a collapsed polymeric balloon mechanism, the balloon mechanism is inflated and used to expand the meshed stent once in position. The stent expands, embedding into the occluded artery wall, keeping the artery open, thereby improving blood flow. The mesh design allows for stent expansion and also for new healthy vessel endothelial cells to grow through and around it, securing it in place.
The history of invasive and interventional cardiology is complex, with multiple groups working independently on similar technologies. Invasive and interventional cardiology is currently closely associated with cardiologists, though the development and most of its early research and procedures were performed by diagnostic and interventional radiologists.
Fractional flow reserve (FFR) is a diagnostic technique used in coronary catheterization. FFR measures pressure differences across a coronary artery stenosis to determine the likelihood that the stenosis impedes oxygen delivery to the heart muscle.
Intima–media thickness (IMT), also called intimal medial thickness, is a measurement of the thickness of tunica intima and tunica media, the innermost two layers of the wall of an artery. The measurement is usually made by external ultrasound and occasionally by internal, invasive ultrasound catheters. Measurements of the total wall thickness of blood vessels can also be done using other imaging modalities.
A coronary stent is a tube-shaped device placed in the coronary arteries that supply blood to the heart, to keep the arteries open in patients suffering from coronary heart disease. The vast majority of stents used in modern interventional cardiology are drug-eluting stents (DES). They are used in a medical procedure called percutaneous coronary intervention (PCI). Coronary stents are divided into two broad types: drug-eluting and bare metal stents. As of 2023, drug-eluting stents were used in more than 90% of all PCI procedures. Stents reduce angina and have been shown to improve survival and decrease adverse events after a patient has suffered a heart attack—medically termed an acute myocardial infarction.
Coronary artery aneurysm is an abnormal dilatation of part of the coronary artery. This rare disorder occurs in about 0.3–4.9% of patients who undergo coronary angiography.
Spontaneous coronary artery dissection (SCAD) is an uncommon but potentially lethal condition in which one of the coronary arteries that supply the heart, spontaneously develops a blood collection, or hematoma, within the artery wall due to a tear in the wall. SCAD is one of the arterial dissections that can occur.
Coronary flow reserve (CFR) is the maximum increase in blood flow through the coronary arteries above the normal resting volume. Its measurement is often used in medicine to assist in the treatment of conditions affecting the coronary arteries and to determine the efficacy of treatments used.
Coronary CT angiography is the use of computed tomography (CT) angiography to assess the coronary arteries of the heart. The patient receives an intravenous injection of radiocontrast and then the heart is scanned using a high speed CT scanner, allowing physicians to assess the extent of occlusion in the coronary arteries, usually in order to diagnose coronary artery disease.
Cardiac imaging refers to minimally invasive imaging of the heart using ultrasound, magnetic resonance imaging (MRI), computed tomography (CT), or nuclear medicine (NM) imaging with PET or SPECT. These cardiac techniques are otherwise referred to as echocardiography, Cardiac MRI, Cardiac CT, Cardiac PET and Cardiac SPECT including myocardial perfusion imaging.
Giovanni J. Ughi, engineer and scientist, is one of the inventors of multimodality optical coherence tomography (OCT) and Laser-induced fluorescence molecular imaging, pioneering a first-in-man study of coronary arteries during his work at Massachusetts General Hospital and Harvard Medical School. The results of his work, combining two imaging technologies, may better identify dangerous coronary plaques, responsible for coronary artery disease and myocardial infarction.
Intravascular imaging is a catheter based system that allows physicians such as interventional cardiologists to acquire images of diseased vessels from inside the artery. Intravascular imaging provides detailed and accurate measurements of vessel lumen morphology, vessel size, extension of diseased artery segments, vessel size and plaque characteristics. Examples of intravascular imaging modalities are intravascular ultrasound (IVUS) and intracoronary optical coherence tomography.
Intravascular fluorescence is a catheter-based molecular imaging technique that uses near-infrared fluorescence to detect artery wall autofluorescence (NIRAF) or fluorescence generated by molecular agents injected intravenously (NIRF). No commercial systems based on intravascular fluorescence are currently on the market, however, significant steps forwards in intravascular fluorescence imaging technology have been made between 2010-2016. It is typically used to detect functional state of artery wall including some known high-risk features of atherosclerosis. It is usually combined with structural imaging modalities such as Intravascular ultrasound and/or Intracoronary optical coherence tomography, to provide functional information in a morphological context.
Optical coherence elastography (OCE) is an emerging imaging technique used in biomedical imaging to form pictures of biological tissue in micron and submicron level and maps the biomechanical property of tissue.