Cardiac CT scan overview

Cardiac CT is a noninvasive diagnostic imaging technique that employs x-rays to obtain images of the heart.

During a cardiac CT scan, an x-ray source and opposing detector move continuously around the patient in a circular path while the patient table moves slowly through the scanner allowing imaging on many different planes. The x-rays passing through the patient’s tissues are captured by a receiver on the opposite side of the body and sent to a computer that reconstructs an image of the heart, viewable from different perspectives.

Each unit on the reconstructed image appears as a shade of gray depending on the transmission of x-rays through that part of the body – a property known as attenuation, which is measured in Hounsfield (H) units. Bone, calcium, and metal, for example, have a high attenuation and appear as white. Water and fat have intermediate attenuation and appear as gray, and air has a low attenuation and appears as black.

In some cases, an attenuating iodine-based contrast agent may be administered intravenously to highlight the blood vessels and inspect them for abnormalities, a technique commonly referred to as cardiac CT angiography (CTA). Scanning is relatively rapid and cardiac CT allows for a visual evaluation of the entire heart in less than 30 seconds.

Cardiac CT scan overview

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Review Date: 5/5/2025

Reviewed By: Michael A. Chen, MD, PhD, Associate Professor of Medicine, Division of Cardiology, Harborview Medical Center, University of Washington Medical School, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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