FUNDACION CNIC CARLOS III
Melchor Fernández Almagro, 3
Postal Code: 28029, Madrid, Spain
Phone: (+34) 91 4531200
Fax: (+34) 91 4531245
Imaging tests
Ankle Brachial Pressure Index (ABPI). This simple, cheap and highly reproducible test can be carried out during routine medical visit, and is very useful for diagnosing peripheral artery disease (PAD) and detecting subjects at high cardiovascular risk.
The ABPI test is a non-invasive estimate of the difference between the arterial pressure measured at the level of the ankle and the arm. Blood pressure is estimated from doppler ultrasound readings taken in both ankles and arms, and the ABPI is calculated as the ratio of the higher systolic ankle pressure reading to the higher systolic arm pressure reading.
An ABPI below 0.9 indicates the presence of an obstruction in the vasculature of the legs, and constitutes a diagnosis of PAD. Nonetheless, more than 80% of people testing positive show no other symptoms. Moreover, low ABPI is associated with a higher incidence of coronary and cerebrovascular complications and a higher risk of death of cardiovascular origin.
Carotid Ultrasound Imaging. Carotid ultrasound imaging, also known as carotid doppler, is a non-invasive diagnostic imaging procedure that does not cause discomfort. High frequency ultrasound waves are used to image the artery and monitor the circulation. The echoes reflected from the anatomical structures are computer processed to generate images of the carotid arteries, the large vessels in the neck that supply blood to the brain. The technique can detect, for example, plaques that reduce the vessel diameter and impede blood flow, a finding that would indicate a high risk of a cerebrovascular accident.
Unlike angiography, carotid ultrasound imaging does not use X rays, and thus does not expose subjects to ionizing radiation and does not require preparation of the patient.
Cardiac Ultrasound.
This non-invasive technique uses ultrasound to produce images of the heart, providing information about its size and shape and the function of the heart chambers and valves. The technique can also be used to detect heart problems in children.
The test identifies areas of heart muscle that do not contract properly as a consequence of limited blood supply or damage caused by a myocardial infarction.
It can also be used to detect the formation of thrombi (blood clots) in the heart, accumulation of liquid in the pericardium and problems in the aorta.
Computed Axial Tomography (CAT).
This diagnostic procedure combines the use of X rays with rotating electronic detectors. The sequences of radiographic images obtained are computer processed to yield a series of progressive transverse sections that build up a three-dimensional picture of the region being studied. The transverse, multidimensional images are displayed on a monitor.
The latest CAT scanners are so fast they can scan sectors of the body in a few seconds.
Cardiac CAT scans provide information about the presence, location and extent of an atheroma (or calcified plaque) in the coronary arteries—the blood vessels that supply oxygenated blood to the heart muscle. The presence of such a plaque (generated from deposits of cholesterol and other substances beneath the inner lining of the artery) is a sign of atherosclerosis and of a heightened risk of suffering a cardiovascular event.
The results of a cardiac CAT scan are expressed as a calcium score, and this test is also known as coronary artery calcium scoring.
CAT scans are painless and do not require injection of contrast material. Subjects just need to stay still and breathe shallowly for a short time so that images can be captured with precision.
Magnetic Resonance Imaging (MRI).
This is another non-invasive technique that provides detailed images of the heart, including its cavities and valves, without the need for catheterization. MRI therefore tends to be used in patients in whom traditional angiography is not possible.
Unlike radiographic techniques such as CAT, which uses X rays, MRI produces images through the combined use of powerful magnets and radio waves. The magnetic field of the MRI machine excites hydrogen atoms in the body which produce small radio signals. These are captured and processed into images displayed on a monitor.
MRI is very useful for obtaining clear information about the state of blood vessels without exposing the patient to ionizing radiation. In some cases, diagnostic definition can be improved by injection of a harmless contrast agent to highlight the vessels. This contrast agent is injected into the arm during one or two minutes before the scan.
MRI is frequently used together with other imaging techniques, such as PET or CAT, to achieve a more precise definition.
Depending on the area to be studied, the patient might be asked not to eat for four to six hours before the scan. In general, no other preparation is necessary.
Positron Emission Tomography (PET).
This non-invasive imaging technique uses small amounts of a radioactive substance called a radiotracer. The scanner is linked to a computer program that measures the amount of radiotracer absorbed by the area being studied. The images obtained give detailed information about the structure and function of tissues and organs.
Applied to the heart, PET provides information about size, shape and position, and enables physicians to detect whether the heart is functioning properly of if there is a circulatory defect. PET detects the flow of blood to the cardiac muscle and reveals the effects of a myocardial infarction on areas of the heart; for example, the presence of scar tissue, a sign of a previous lesion.
Today PET is often used in combination with CAT or MRI, since these approaches combine information about anatomy and function and allow more precise diagnosis than the use of the techniques applied separately.