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Low-Dose CT Angiography is as Safe and Accurate as Catheter Angiography

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Low-dose coronary CT angiography matched the sensitivity of catheter-based angiography, and is a potentially valid alternative to the gold-standard for triaging symptomatic patients suspected of coronary artery disease (CAD), researchers say.

Rcadia_CORONARY_analyzerLed by Dr. Moritz Wyler von Ballmoos, of the Department of Cardiac Surgery, Children’s Hospital Boston and Harvard Medical School, the researchers performed a meta-analysis of evidence from 16 studies compared a newer technique for CT angiography with that of catheter angiography. Their study appears in the March 15 issue of the Annals of Internal Medicine.

“Our systematic review and meta-analysis of currently available data indicate that coronary CT angiography with prospective ECG gating has a high specificity,” the researchers wrote, “and an excellent sensitivity for the detection of morphologically significant CAD, compared with catheter angiography. This CT technique is associated with a low effective radiation dose of 2.7 mSv (millisievert)."

The low-dose technique using prospective ECG gating, also known as step-and-shoot or sequential mode, involves applying radiation only at a predefined point in the cardiac cycle rather than over the entire cycle. It has been shown to reduce the radiation dose by up to 80 percent; however, many have questioned whether the limited available reconstruction phases of prospective ECG gating would significantly reduce the amount of information needed to accurately diagnose all of the CAD that may be present.

This study found that the technique did not result in any significant loss of information needed for accurate clinical diagnosis, in addition von Ballmoos’ team found this to be true regardless of type scanner used, or radiologists using it.

“The diagnostic performance on the patient level is highly consistent across the different CT scanners, centers, radiologists, and study populations that were included in our study,” von Ballmoos told The Hub in an e-mail interview. “This is a very important finding for it suggests that the excellent performance of CT angiography is not tied to one particular type of scanner, protocol, study population or radiologist, but is generally true.”

For the meta-analysis, the researchers considered 1,360 studies involving CT angiography, but winnowed that down to 16 studies that met all their inclusion criteria. Seven of the studies used a single-source 64-slice CT, four studies used dual-source 64-slice scanners, 2 were conducted with 320-slice CT, 1 used dual-source128-slice CT, 1 used a single-source 128-slice scanner, and one study used a single-source 256 CT scanner.

Overall, 2,622 coronary arteries and 11,518 coronary arterial segments were examined in the 960 patients included in the 16 studies. The mean prevalence of CAD for study patients was 60.1 percent, the mean BMI was 26.5 kg/m2, and the mean age was 63.4 years. All studies included only patients with sinus rhythm.

The patient-level pooled sensitivity across all studies was 1.00 (CI, 0.98 to 1.00) and the pooled specificity was 0.89 (CI, 0.85 to 0.92) for low-dose coronary CT angiography compared with catheter angiography.

The researchers found greater variation between studies in diagnostic performance at the vessel and segment levels than at the patient level. They thought this might have been due to random variation between studies or variation of study characteristics. When they re-analyzed the data accounting for variations in study characteristics, they found that body mass index and CAD prevalence were independently and significantly associated with the diagnostic performance of low-dose coronary CT angiography in both the vessel- and segment-level analyses.

“On the vessel level there was somewhat more variation than would be expected to occur by chance alone,” von Ballmoos said. “In our results and the discussion we offer possible explanations for the difference found between studies and the identified variables should be taken into consideration by radiologists and other clinicians that opt to use CT angiography for diagnosis of CAD.”

The researchers noted that the prospective ECG gating CT technique is associated with a low effective radiation dose of 2.7 mSv. This compares with radiation doses of about 12 mSv with retrospective ECG gating, the low-dose technique offers substantially reduced radiation exposure for patients.

The researchers concluded that at this low radiation dose the technique may be a suitable imaging test for ruling out CAD in patients with a low to intermediate pretest probability of CAD. However, they caution that their study is based on a small number of studies, many of which were done at a single site. Further studies are therefore needed before widespread diffusion of the technology can be recommended.

By: Michael O'Leary, contributing editor Health Imaging Hub

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