AJR: Minimal padding during CCTA can reduce dose by 45%

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Eliminating or reducing “padding” duration by 100 msec during ECG-triggered coronary CT angiography (CCTA) can reduce dose by 45 percent and still manage to maintain image quality and interpretability, according to a study published in the April issue of the American Journal of Roentgenology.

“During ECG-triggered CCTA, there is a mandatory time that the scanner must be on during each heartbeat, and there is typically extra time added before and after this which is referred to as padding,” wrote lead author Troy M. LaBounty, MD, of the New York Presbyterian Hospital in New York City, and colleagues.

LaBounty and colleagues assessed 886 patients at three centers to study the effect of padding duration on image interpretability and the incident effect on radiation dose. Fifty-eight percent of patients were male, and all participants underwent an ECG-triggered CCTA.

During the study, physicians controlled patient heart rates by administering oral or IV metoprolol (if needed) to obtain heart beats under 65 beats per minute—recorded heart rates averaged to be 55 beats per minute.

The study was performed on two scanner models--the LightSpeed VCT XT and the Discovery HD 750 (both from GE Healthcare). Scan rotation times were 350 msec and studies utilized tube voltages at 100-120 kVp and 250-800 mA.

The study looked at dose-length product (DLP) pre-test and post-test on 111 patients at two sites. The researchers also evaluated pretest projected DLP at both zero and 100 msec.

During the study, researchers evaluated three groups: 268 patients with no padding, 482 patients with a padding duration of one to 99 msec, and 136 patients with a padding duration of 100 msec to 150 msec.

In the aforementioned patient groups, mean radiation doses were reported at 2.3 mSv, 3.8 mSv and 5.5 mSv, respectively. Additionally, the researchers found an increased padding duration to be associated with an increased dose. When comparing the patient cohort exposed to no padding and those exposed to a 100 msec padding duration, radiation dose differed by 45 percent.

“Our data show that use of minimal or no padding can result in reduced radiation dose with preserved image interpretability in examinations of patients with excellent heart rate control,” the authors wrote.

According to the authors, a viable step in further reducing radiation dose would be to shorten tube current times using tube current modulation.

“Tailoring of scan parameters, including padding duration, on a patient-by-patient basis may allow reduction in radiation and ensure that CCTA examinations are performed with the lowest possible radiation exposure to the patient in accordance with the as low as reasonably achievable principle,” they concluded.