[ RadSafe ] Extremely low dose CT coronary angiography shows promise in assessing cardiac function

[ROY HERREN]

Public release date: 11-Apr-2008


Contact: Necoya Tyson
necoya at arrs.org
703-858-4304
American Roentgen Ray Society 

Extremely low dose CT coronary angiography shows promise in assessing cardiac function
Extremely low dose CT coronary angiography can be used to measure cardiac function and has the potential for use when other commonly used examinations are limited, a preliminary study indicates.
“CT coronary angiography provides a wealth of data about cardiac structure and function; however, CT coronary angiography uses a high radiation dose and other examinations, such as echocardiography and nuclear medicine examinations, can evaluate structure and function with no or low radiation dose,” said Gregory G. Gladish, MD, of MD Anderson Cancer Center in Houston, and the lead author of the study. “Our goal was to determine if we could reduce the amount of radiation in the CT examination so that it would be at the same level or lower than the level of radiation used in the nuclear medicine examination,” Dr. Gladish said.
A dynamic cardiac phantom was prepared and scanned with a 64-detector row CT scanner in both static and dynamic mode (with a simulated heart rate of 68 beats per minute). Various current settings were used, radiation dose was measured and two radiologists reviewed the images. “We were able to create useable images at 3mSV, which is about the dose of the nuclear medicine examination and is about an 85% reduction in dose compared to standard cardiac CT,” said Dr. Gladish. “Our most surprising results from this study was that we could make a reproducible measurement of function at the lowest tube current that the scanner could produce, and this suggests there may be room for further dose reduction” he added.
Echocardiography is limited in some patients by obesity and other factors; a gated blood pool nuclear medicine examination is limited in how well it can evaluate heart wall thickening and regional wall motion. Low dose cardiac CT may be appropriate for these patients, Dr. Gladish said. This study was conducted using a phantom; the next step is to conduct the study on patients. 
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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, DC.




   Public release date: 11-Apr-2008


Contact: Necoya Tyson
necoya at arrs.org
703-858-4304
American Roentgen Ray Society 

Patient' exposure to radiation significantly lower when using new cardiac CT technique
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 when compared with the standard retrospective ECG gating, according to a recent study conducted by researchers at the University of Washington in Redmond, WA. 
“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,” said 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,” he said. 
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,” said Dr. 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,” he said. 
“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,” said Dr. 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,” he said. 
“With this new technique, very useful information about a patient’s heart and coronary arteries is quickly available with much less radiation,” said Dr. Shuman. 
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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, DC. 




  


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