Report from SCCT: Low-dose 64-slice cardiac CTA vies with catheter angiography

Cardiac imagers could bring effective radiation doses from 64-slice CT angiography down to almost half of current levels, according to a study presented Saturday at the 2007 Society of Cardiovascular Computed Tomography meeting. Dose levels could at least match those of coronary catheter angiography.

Sixty-four-slice CTA scanning allows physicians to get improved temporal and spatial resolution and avoid more invasive diagnostic procedures. The trade-off has been effective radiation doses twice as high or even higher than those achieved by conventional angiography. The rapid expansion of 64-slice technology makes it imperative to keep radiation dose as low as reasonably possible, said principal investigator Dr. Sabha Bhatti from the University of Wisconsin Hospital and Clinics in Madison.

Bhatti and colleagues prospectively enrolled 27 and 15 patients with suspected coronary artery stenosis who respectively underwent cardiac 64-slice CTA and conventional angiography for comparison. The researchers originally based their cardiac CTA protocol on manufacturers' recommendations. Before the study's completion, however, the investigators learned about ways to reduce radiation doses. They put in place a revised protocol using reduced peak tube current and exposure times during ECG modulation. Eight additional patients went through CTA under the new protocol.

After comparing all groups, the researchers found that the early CTA group received a mean effective radiation dose of 26 mSv, which dropped to 12 mSv in the later group. The difference in effective radiation dose between the two CTA groups and that between the earlier CTA group and conventional angiography were both statistically significant (p<0.0001). There was no difference, however, between the late CTA group and conventional angiography (p = 0.58).

The researchers acknowledged that the value of their single-center, small population study was limited and needed validation with further studies. Yet they were able to quantify and recognize a considerably high CTA radiation dose and bring it down later to the benefit of new patients, said Bhatti, whose study received the 2007 SCCT best abstract award.

"You should know your program's effective radiation dose, as this may be more than expected. We were able to get our effective radiation dose down by about 45%," she said.

Future technologies such as prospective gating and dual-source CT scanners may help cut radiation doses even further in the future. Since these are not widely available, however, physicians should make the best use of what they have at this time, Bhatti said.