Biomedical Science and Research Journals | Characterization of Atherosclerotic Plaques by NIRS-IVUS System
Characterization of Atherosclerotic Plaques by NIRS-IVUS System
Introduction
Nowadays, the pathologies of the cardiovascular system
represent the main cause of mortality in our country: about
45% of all deaths are, in fact, attributable to cardiovascular
diseases. In particular, of the 250,000 cases of annual death due
to cardiovascular diseases, two-thirds are attributable to coronary
heart disease. Atherosclerosis is the vascular pathology with the
greatest clinical impact because it is responsible for myocardial
infarction and cerebrovascular accidents that represent the
main cause of death and morbidity in industrialized countries.
Coronary atherosclerosis is a multifactorial pathology that, to
become clinically manifest, requires the formation of a fibro-lipid
plaque inside the wall of an artery that reduces blood flow; it is a
dynamic degenerative disease that can have a sudden transition
from a chronic condition to clinical instability following a process
of plaque rupture and thrombotic overlap. The primary objective of
the research remains the early identification of the lesion at risk of
instability in order to prevent the clinical event. This lesion on the
path of instability is described as a “vulnerable plaque”, i.e. a lesion
with a high probability of becoming responsible for an acute event
in the future.
The desire to identify and treat vulnerable plaques before
major adverse events stimulated the development of invasive and
non-invasive high-resolution imaging techniques.
Carotid ultrasonography was the first technique used to identify
asymptomatic subjects a critical subclinical pathology or very
early alterations, such as an abnormal thickening of the intimate
and medium coats. Over the years these simpler techniques have
been accompanied by other more complex methods such as
computerized multi-layer tomography (MSCT), magnetic resonance
imaging (MRI) or other invasive evaluations, such as angiography,
intracoronary ultrasound (IVUS, Intravascular Ultrasound),
optical coherence tomography (OCT), to capture even the finest
characteristics of atherosclerotic plaques and try to assess the
risk of progression or instability more precisely. A critical analysis
of these different diagnostic methods is appropriate as these are
techniques useful for identifying patients with high atherosclerotic
load or instruments aimed at identifying plaques at greater risk of
rupture and therefore cause of acute coronary events [1,4].
To date, no imaging technique can accurately identify the risk
of plaque rupture. It is therefore essential to develop alternative
imaging techniques capable of obtaining a correct typing of the
atherosclerotic plaque to identify the «vulnerable», with a high risk
of breakage
In several studies it was analyzed the possibility of using
near-infrared spectroscopy (NIRS, Near Infrared Spectroscopy),
a routine technique used in physics to determine the chemical
composition of substances, to identify the chemical components of
coronary plates as a means to evaluate their vulnerability. The goal
of intracoronary NIR spectroscopy is to produce a “chemogram”
of the artery wall that will serve as a vulnerability index. Studies
conducted by different groups have definitively documented that,
in the absence of difficulties posed by cardiac movement and the
presence of blood, NIR spectroscopy, can accurately identify the
important characteristics of atherosclerotic plaques suspected of
representing plaque vulnerability [5,7].
In 2009, Waxman et al. [8] conducted the first human studies to
test the safety and efficacy of NIRS spectroscopy in the detection of
coronary plaques with lipid core.
NIR spectroscopy applied to the coronary arteries is a promising
diagnostic imaging modality that plays a key role in interventional
cardiology practice, allowing a better and early diagnosis of
coronary diseases. The identification of the composition is
important because the coronary arteries can contain plaques
with lipid core that can lead to heart attacks and complications in
stenting procedures.
Stenting is traditionally guided by an X-ray angiography
that identifies the general position of the lumen narrowing but
cannot reveal the composition of the vessel wall. To overcome
the limitations of angiography, doctors turn to various advanced
imaging solutions to optimize not only their stenting strategy, but
also the care their interventional cardiology patients must undergo.
Several studies have compared different intracoronary imaging
technologies for the detection of atherosclerotic plaques (Table 1).
Table 1: Imaging technologies for the detection of atherosclerotic plaques.
Table 2: Imaging methods for the detection of an introvascular plaque.
The ideal invasive device for the characterization of coronary
plaques should provide a complete roadmap of the atherosclerotic
load throughout the coronary artery and detect specific lesion
data that characterizes the structure, composition and biological
dynamics of each plaque (Table 2).
Imaging techniques, such as angiography, IVUS, OCT, and
angioscopy, provide valuable insights into structure and function,
but are unable to provide accurate and easily obtainable information
regarding plaque composition.
Unlike IVUS and OCT, which detect a lipid core based on signal
loss, NIRS spectroscopy allows the direct detection of the lipid core
since cholesterol has a unique spectral identity in the NIR spectrum
that allows its differentiation from other biological components.
Since NIRS spectroscopy provides only composition data, it can be
used to supplement the structural data provided by angiography,
IVUS and OCT.
While the devices previously available were able to achieve
many of these objectives in a reproducible, safe and economically
advantageous way, different characteristics were not detectable,
such as the ability to accurately identify an LRP (Lipid-Rich Plaque)
and to quantify the degree of inflammation. These additional
characteristics are, instead, available combining the intracoronary
IVUS and the NIRS, since a combination of these provides a complete
characterization of the structure and composition of the vessel
through the system’s ability to detect plaques with a high lipid load.
This complete characterization of the vessel promotes optimal
clinical decision-making and supports more effective treatment
strategies; for example, the NIRS will be able to confirm the
presence of LCP if the high plaque load and the hypoechoic regions
are detected by the IVUS, which could indicate lesions with a high
risk of distal embolization during balloon dilation and stenting [9].
Intravascular ultrasound imaging (IVUS) provides an image of
the structure of the wall but has limited ability to determine the
composition of the plaques. An important feature of NIRS is that
light can penetrate into the tissues and can therefore identify and
differentiate different types of tissue, despite the presence of blood
between the detector and the target tissue. This is an important
advantage for coronary artery imaging.
NIR spectroscopy rapidly, specifically, and reliably identifies
the lipid core plates and the aforementioned information combined
with those related to the vessel structure obtained by IVUS allow a
true vessel characterization to be performed.
This complete characterization of the vessel promotes optimal
clinical decision-making and supports more effective treatment
strategies; for example, the NIRS will be able to confirm the presence of LCP if the high plaque load and the hypoechoic regions
are detected by the IVUS, which could indicate lesions with a high
risk of distal embolization during balloon dilation and stenting.
For the reduction of coronary risk, early identification and
stabilization of atherosclerotic plaques is of primary importance;
the imaging of atherosclerosis has therefore an important clinical
role today, far superior to its very great scientific utility and
the combination of near-infrared spectroscopy and coronary
intravascular ultrasound, allowing a better and early diagnosis
of coronary diseases, represents one of the most promising
technologies in monitoring and identifying the vulnerability of
atherosclerotic plaques to future interventional cardiology.
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