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April 15 - New Cardiac CT Technique Lowers Radiation Exposure

A new cardiac CT technique, prospective gated 64-channel cardiac CT, has a significantly lower radiation dose and produces CT coronary angiograms with better image quality than the standard retrospective electrocardiogram (ECG) gating, according to a recent study conducted by researchers at the University of Washington in Redmond, Wash.

“Standard retrospective gated cardiac CT uses continual scanner table motion and spiral acquisition with overlap of the radiation beam on each spiral—so each piece of tissue gets scanned 4 or 5 times. Retrospective gated CT scans with a broader beam and only one rotation per table location; the table is not moving during scanning and each piece of tissue gets scanned only once. Rather, the table moves every other heartbeat, when the radiation beam is turned off,” says William Shuman, MD, lead author of the study. “With retrospective gating, the X-ray beam is on all throughout the entire scan. With prospective gating, the beam is on for only 25% of the scan—like a snapshot.”

The researchers compared 50 CT coronary angiograms using both the new prospective gated 64-channel cardiac CT and standard retrospective ECG gating in patients matched for body size, heart rate, diagnosis, age, and sex. The researchers noted image quality and evaluated patient radiation dose.

“We image the coronary arteries in segments,” says Shuman. “Of the 621 segments we viewed on prospective gated 64-channel cardiac CT, we rated 70% as excellent, 29% as good, and 1% as adequate. On retrospective ECG, 632 segments were rated with 54% noted as excellent, 36% as good, and 10% as adequate. Radiation dose for the prospective gated CT exams was 76% lower than the standard retrospective technique.”

“While cardiac CT technology has made the easy imaging of the coronary arteries possible in only 5 seconds and without catheters, there is substantial radiation involved with the usual retrospective CT technique,” says Shuman. “This new prospective technique results in the same image quality but with a 76% lower radiation dose. This means cardiac CT may be a reasonable test in more patients to find coronary artery plaque or congenital heart disease.”

“With this new technique, very useful information about a patient’s heart and coronary arteries is quickly available with much less radiation,” says Shuman.

The full results of this study will be presented on Wednesday, April 16, 2008 during the American Roentgen Ray Society’s annual meeting in Washington, D.C.

Source: American Roentgen Ray Society

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