Coronary CT Angiography: Insights Into Patient Preparation and Scanning
Section snippets
Spatial Resolution and Image Noise
Imaging the coronary arteries is the most challenging task of imaging the heart using CT. Nowhere else in the field of CT is the attempt made to image a structure that is so small that is also moving with such high velocity. Most coronary arteries are 5 millimeters (mm) or less in diameter, and significant pathology often occurs in vessels that are smaller than 3 mm in diameter. To detect a 50% stenosis in such a vessel requires visualizing a column of contrast that is ≤ 1.5 mm in diameter.
Image Noise
Cardiac CT images are inherently noisy because of the sections are very thin and because of the use of ECG-gating. In most patients, image noise is not a clinically significant issue and can be reduced by increasing tube current when necessary to increase photon flux and maintain image quality. In especially heavy patients, reconstruction of images using slightly thicker sections (up to 1.0 mm), or the use of a reconstruction algorithm that will smooth the image are methods of improving image
Instructions to the Patient Before Arriving
The usual instructions given before a contrast-enhanced CT apply. The patient should have no solid food to eat for 4 hours before the scan. However, patients must not be dehydrated as this may unduly elevate heart rate, and so patients should be encouraged to drink water for up to 1 hour before scanning. The usual precautions regarding contrast allergy and renal insufficiency apply. Patients should not take sildenafil or similar medications for at least 48 hours before the examination, as they
Conclusions
The future of Cardiac CT will see even more technological improvement, and though the field is still new it is clear that it will continue to serve as a method of diagnosing and evaluating cardiac disease. As with any other test, patients must be appropriately selected for the examination to provide the most useful information to the clinician and greatest benefit to the patient. Understanding the limitations of the test will help guide that selection. In addition, the acquisition of high
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