Assessment
Screening
A number of screening techniques are commonly used to assess the progression of atherosclerosis. These techniques fall into two categories, invasive and non-invasive:
Invasive imaging techniques:
Coronary angiography:
Coronary angiography uses X-rays to examine the blood vessels or chambers of the heart. A catheter is inserted into a blood vessel and the tip is positioned either in the heart or in the coronary arteries supplying the heart. A contrast medium or dye is injected into the artery which is then visible by X-ray. The X-ray images obtained are called coronary angiograms and enable visualisation of the lumen of the overall coronary bed.1
Intravascular ultrasound (IVUS):
The IVUS technique involves sending and receiving ultrasound waves, which are emitted from a catheter introduced into an artery. The catheter rotates, producing a detailed picture of the lumen and arterial wall, including the atheromatous plaques, at those sites visualized by the catheter. This technique may be used to examine arterial wall thickness (intima-media thickness or IMT). Assessments of IMT have proved extremely reliable as a surrogate marker for examining the progression of atherosclerosis and for assessing cardiovascular risk. Cholesterol-lowering efficacy can be assessed using this method by measuring changes in atheroma and lumen area, before and after treatment.1
Non-invasive imaging techniques:
Magnetic resonance imaging (MRI):
MRI produces extremely detailed pictures of tissues, organs, and blood vessels without the need for X-rays or contrast material (although a special medium may be given to make images even clearer). Electromagnetic energy released when exposing a patient to radio waves in a strong magnetic field is measured and analysed by a computer, which then forms a two- or three-dimensional image. Limitations to this method include the complex equipment required and the difficulty in obtaining precise images because of the continuous motion of the heart.2
Computed tomography (CT):
A traditional CT scan is an X-ray procedure that combines many X-ray images to produce a computer-generated cross-section of the body. Cardiac CT uses advanced CT technology with intravenous contrast dye to generate images of the heart and coronary blood vessels. The complex equipment required, and the difficulty in obtaining precise images due to continuous motion of the heart, are also limitations to this method.3
Ultrasound (B-mode):
High resolution B-mode (brightness mode) ultrasound (also referred to as quantitative carotid B-mode ultrasound), uses high-frequency sound waves and their echoes to create an image. The B-mode ultrasound makes it possible to non-invasively characterise arterial wall function in the carotid and brachial arteries by measuring IMT and wall stiffness. B-mode ultrasound has been used extensively in epidemiologic studies to quantify associations of risk factors with extracranial carotid atherosclerosis and atherosclerosis progression as well as associations of atherosclerosis (and atherosclerosis progression) with coronary events.4
References:
1. Nissen SE, Yock P. Circulation 2001;103:604–616.
2. Chu B et al. Stroke 2004;8:2444-2448.
3. Truong QA et al. JACC Cardiovasc Imaging 2008;1(6):772-781.
4. Kastelein JJP et al. Am Heart J 2005;149:234-239.