Coronary CT Angiography: Insights Into Patient Preparation and Scanning

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Cardiac computed tomography (CT) and coronary CT angiography represent a breakthrough in cardiac diagnostic power and are already making an impact on clinical practice. Yet, technical limitations remain and patients must be appropriately selected for this new and exciting examination. An understanding of those limitations will help guide patient selection and maximize the clinical yield of the test. The most significant issues to deal with are those of inherently increased image noise, vulnerability to cardiac and respiratory motion and arrhythmia, and image artifacts that result from the presence of coronary calcification and stents. Fortunately, there are methods to overcome all of these limitations. These predominantly involve diligent and attentive patient preparation before the scan, focusing on clinical, hemodynamic, and basic eletrocardiographic parameters. With proper premedication to optimize heart rate, simple patient coaching, attention to detail during the acquisition, and the use of software tools to optimize the axial image reconstruction, cardiac CT should consistently yield very satisfying results.

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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