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.
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.