18-20 Week Screening Pregnancy Ultrasound
What is an 18-20 week screening pregnancy ultrasound? An 18–20 week pregnancy screening ultrasound is part of the routine care…Read more
Coronary artery scoring is a CT scanning technique for identifying and quantifying calcium deposits in the coronary arteries reflecting underlying atherosclerosis. It relies on the ability of the CT scanner to detect small areas of calcium within atheromatous plaques. As there is no intravenous contrast medium given to the patient to enhance intravascular blood (as in CT angiography), this examination cannot show coronary artery anatomy or pathology.
Coronary artery calcium scores are of most use in those patients with intermediate risk of cardiovascular disease, where the result will either lower or raise the risk profile and, potentially, provide a change in management.
Potential clinical cardiovascular risk for any patient can be assessed1 and calculated into low-, medium- or high-risk categories.2
Those at low risk (such as an asymptomatic 35-year-old male non-smoker who exercises and has no significant family history) and those at high risk (such as a 60-year-old obese male long-term smoker with chest pain on exertion) would not benefit from this study.
Review of risk classification in asymptomatic intermediate-risk patients (aged 35–75 years) without known coronary heart disease.
Intermediate-risk patients have been defined as:3
Asymptomatic intermediate-risk patients: women aged between 35 and 70 years and men aged between 40 and 60 years.
In these intermediate-risk patients, the test is valid for main ethnic groups; however, the result is most accurate in patients of Caucasian origin.
It must be stressed that there is potential for a technically false negative result. A score of zero does not exclude the possibility of myocardial infarction in the future.
Any contraindication to X-ray exposure, of which pregnancy is the most common.
Any patient with a high risk of a coronary event and symptoms should have appropriate investigation and treatment urgently. These patients are not suitable for coronary artery scoring.
The information from a coronary calcium score study will not be of any benefit to anyone who has already had a myocardial infarction or coronary revascularisation.
Coronary artery calcium scoring in patients on dialysis and with established long-term diabetes is not recommended, due to the high likelihood of a high score and the current scientific uncertainty over the interpretation of the result.
All scanners have physical limitations due to table weight limits and the diameter of the scanner aperture. Older scanners are able to scan patients up to 150 kg. Newer scanners can in some cases accommodate patient weights of 220–250 kg. Some obese patients have large abdominal girths. Most scanners have a gantry diameter of about 68 cm, with newer scanners up to 78 cm. If you are concerned that your patient may exceed any of these limits, it is best to contact the hospital or practice to find out whether this may preclude scanning.
Radiation risks are discussed in detail in another information item on InsideRadiology (see Radiation risk of medical imaging for adults and children). Radiation dose used in low-dose CT examinations are significantly lower than most other CT studies. Current examination techniques would deliver a radiation dose equivalent to approximately two breast mammogram examinations.
Alternative strategies exist to assess the personal risk of a cardiovascular event. Risk stratification techniques to assess a 10-year individual risk of a cardiovascular event include:
These are in wide use, but tend to have a heavy weighting to the patient’s age and may not adequately take into account lifestyle factors, such as smoking, diet, exercise and body mass index.
Alternative non-angiographic methods of imaging or testing to better stratify the individual’s risk include:
In those patients who fit into high-risk categories or who are symptomatic, then detailed imaging of the coronary arteries may be required. This will require either CT coronary angiography or direct catheter angiography.
Page last modified on 13/6/2018.
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