Dual-Source CT Offers High Resolution, Less Radiation


CHICAGO — Dual-source computed tomography significantly reduces radiation exposure to patients undergoing heart scans, and eliminates the need for heart-slowing medications, according to a study presented at the annual meeting of the Radiological Society of North America.

Improved temporal resolution with dual-source CT improves diagnostic quality by significantly reducing cardiac motion artifacts, obviating the need for β-blockade, said Dr. U. Joseph Schoepf.

In addition, more effective ECG pulsing techniques and faster scan times available with dual-source CT (DSCT) significantly decrease radiation dose by an average of 10%, compared with conventional 64-slice CT, Dr. Schoepf said in an interview.

“Dual-source CT has built-in features that allow the operator to accurately tailor radiation dose to each patient,” said Dr. Schoepf, associate professor of radiology and medicine at the Medical University of South Carolina (MUSC) in Charleston.

In this study, the first 30 patients who underwent CT angiography with a DSCT scanner (SOMATOM Definition, Siemens Medical Solutions) were compared with the most recent 30 patients to undergo 64-slice CT angiography at MUSC.

“With the DSCT group, we were at the beginning of our learning curve, so by now we're even more facile in using the dual scanner than we were with the study patients,” Dr. Schoepf explained.

A fixed temporal resolution of 83 milliseconds, heart-rate adaptive pitch, and ECG pulsing were used with the DSCT in all cases. Temporal resolution at 64-slice CT was 165 milliseconds at a fixed pitch of 0.2.

With both scanners, the gantry rotation time was 330 milliseconds, collimation was 0.6 millimeters, and the injection protocol was triphasic.

A radiologist and a cardiologist who were blinded to the scanner type evaluated the coronary arteries for motion artifact using the American Heart Association segment model. Patient heart rate, radiation dose, and use of β-blockers were recorded.

“With the previous generation scanner, we still had to use β-blockers to slow heart rate to achieve good images,” Dr. Schoepf said in an interview. “We quickly learned that medications were not necessary with the DS scanner because of the faster shutter speed and better temporal resolution.”

The abandonment of ?-blockade simplifies procedural logistics, he said, explaining that the typical intravenous protocol requires having a nurse available and increases scan time because the drug is administered while the patient occupies the scanner table. “And it's always better to avoid giving drugs when you can,” he added.

The average computed tomography dose index (fundamental radiation dose parameter used in CT) volumes were 61 milligray (mGy) for patients aged 35–72 years and 53 mGy for patients aged 21–89 years, respectively (P < .001).

The average heart rates were 64 beats per minute among the control group and 73 beats per minute among those imaged with the dual scanner. β-Blockers were used in 12 of the 30 patients scanned with 64-slice CT; none were used in the DSCT group.

Cardiac motion artifacts were observed in 24% of coronary segments in 64-slice CT patients, compared with 9% of segments in the DSCT arm. In each group, data sets were completely void of motion artifacts in 3 of 30 and 12 of 30 patients, respectively.

“Overall, the diagnostic quality was better in the DSCT group despite the faster heart rates,” said Dr. Schoepf, who disclosed that he is a consultant to and has received research support from Siemens Medical Solutions and the imaging contrast divisions of Bayer, GE Healthcare, and Bracco Diagnostics. However, no outside funding was used for the current study or the scanners used in it, he said.

“With another step in the evolution of medical imaging, we're closing the gap from invasive to noninvasive diagnostic catheterization and getting to the point of being able to get the same diagnostic information, particularly for excluding coronary artery disease,” Dr. Schoepf said. “But the investment of around &dollar;2.6 million for a dual-source CT probably is only worth it if you want to exploit the particular capabilities of this device, which include the dedicated cardiac, vascular, and dual-energy applications.”

The SOMATOM Definition has been available in the United States since early 2006.

DSCT (right) of the pulmonary vein shows clearer delineation of all segments, compared with single-source 64-slice CT (left). Photos courtesy Dr. U. Joseph Schoepf

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