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New Cardiac CT Technique Reduces Radiation Sevenfold in Children

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Anomalous right coronary artery in a 17-year-old patient.  (Image courtesy of Dr. Kelly Han, Minneapolis Heart  Institute)Beta blockade combined with newer multi-detector CT angiography (MDCTA) reduced radiation exposure sevenfold compared to older scanners a new study shows. The new method may be the safest for coronary imaging for certain pediatric patients.

In a retrospective study of all coronary CTAs performed on patients less than 18 years of age at Minneapolis Heart Institute®, researchers found that not only did newer CTA techniques use lower doses of radiation than early CTA, the heart rate reduction using beta blockers allowed radiation doses significantly lower than conventional cardiac catheterization.

Led by Dr. Kelly Han, a pediatric cardiologist at Minneapolis Heart Institute® at Abbott Northwestern Hospital, the researchers presented their findings at the Sixth Annual Scientific Meeting of the Society of Cardiovascular Computed Tomography (SCCT) in Denver, this week.

One barrier to applying coronary CTA in children has been their relatively high heart rates, which require a higher radiation dose. Han told The Hub that by slowing the heart rate you can use a lower radiation dose.

“The scan mode you use is dependent on the heart rate and the lower the heart rate, the lower the radiation dose per scan,” she said in a phone interview. “Using a combination of medication to slow the heart rate and the new scanner technology, we have been able to obtain excellent images of the coronary arteries in patients as young as five months of age."

In the study, Han’s team compared radiation exposure, anesthesia use and diagnostic accuracy between first generation single-source, standard-pitch spiral CT scanners and second generation high-pitch, dual-source CT scanners for image quality and radiation risk in a pediatric population.

At the time of the presentation they had reviewed 76 consecutive MDCTA scans from a single practice over a 2-year period (June 2007 through February 2011). Patients ranged in age from three days to 18 years.

Patients were separated by scan mode into three groups:

  •    Group one included 22 first-generation, dual-source CT scanner with retrospective ECG gating (spiral scan mode).
  •    Group two included 35 second-generation, dual-source CT scanner with prospective ECG gating (sequential scan mode).
  •    Group three included 19 second-generation, dual-source CT using prospective ECG gating with high pitch (flash scan mode).

Re-implanted right coronary artery in a 9 month old taken with sequential mode CT scan. (Image courtesy  of Dr. Kelly Han, Minneapolis Heart Institute)The researchers compared the imaging results in the three groups. Image quality was graded on a four-point scale, with 4 defined as excellent image quality. Groups were compared using the Kruskal Wallis test. There was no significant difference in image quality between the groups.

The difference is radiation dose, however, was significant. The age-adjusted radiation dose in group one (spiral mode) was 1.8 mSv, in group two (sequential mode) it was 1.05 mSv, and the age adjusted dose in group three (flash scan) was 0.34 mSv.

“That is a sevenfold reduction in radiation dose compared to the spiral mode and that’s why it is important to get the heart rate down whenever you can,” Han said. "For patients who need coronary artery imaging the important thing is try to obtain a diagnostic image with the least risk to the patient. In patients where you can use a flash mode you can get great pictures with high quality at very low doses. So when indicated it is a wonderful tool."

Han summarized the subset of pediatric patients for whom coronary CT imaging is indicated. Patients with an anomalous coronary artery, and patients with Kawasaki’s disease, which is an acquired disease of children where they have a chance of getting coronary artery aneurysms and stenosis may benefit from CT imaging. The third indication is for patients who have had a coronary artery implant as part of a surgical procedure because some of them can have coronary artery narrowing at the site of the surgery later in life. 

by Michael O'Leary, contributing writer, Health Imaging Hub

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