Cardiac imagers are accentuating positive aspects of an international multicenter study of cardiac multislice CT imaging, despite a wide variation in the amount of radiation exposure among 1965 patients and the generally infrequent use of available dose reduction strategies.
Dr. Jörg Hausleiter of the German Heart Center Munich reported results in the Feb. 4 issue of the Journal of the American Medical Association. He and 10 coauthors found the median dose length product (DLP) to be 885 mGy/cm, a whole-body measurement of absorbed radiation that is equivalent to 12 mSv or 600 chest x-rays. Dose was highly variable among facilities. The per-center median DLP ranged from 331 mGy/cm to 2146 mGy/cm.
Dose reduction strategies worked well where they were applied. Tube current modulation helped reduce DLP by 25% in the 73% of cases where it was applied. Turning down the tube setting to 100 kV from the standard 120-kV setting cut DLP by an average 46% but was used in only 5% of the cases. Sequential scanning, which exposes patients to radiation only during specific parts of diastole, reduced patient exposure by 78%, but it was used in just 6% of cases.
The trial (PROTECTION I) established for the first time how MSCT clinical protocols are applied with a variety of equipment in differing practice settings, said senior researcher Dr. Stephan Achenbach, director of cardiac imaging research at the University of Erlangen in Germany. About 96% of the exams were performed on 64-slice scanners, and about 4% with 16-slice technology.
Researchers were relieved that the 12 mSv median dose was low enough to avoid stirring controversy, he said. “This study shows that many sites are examining their patients [using] low doses,” Achenbach said. Making a comparison between the radiation exposure of one cardiac CT scan and 600 chest x-ray was misleading, he said.
“Chest x-rays these days involve almost no radiation,” he said.
Coauthor Cynthia McCollough, Ph.D., a medical physicist at Mayo Clinic in Rochester, MN, was encouraged by the widespread use of ECGgated tube current modulation. She blamed the infrequent use of tube current reduction and prospective ECGtriggered sequential scanning on a lack of published scientific literature.
The study establishes a baseline for prudent cardiac CT, said Dr. U. Joseph Schoepf, director of cardiac imaging research at the Medical College of South Carolina.
“The story of learning curves in the adoption of new technology runs like a red thread through this paper,” he said.
In an accompanying JAMA editorial, Dr. Andrew J. Einstein of the Columbia University College of Physicians and Surgeons wrote that the results underscore the need for a patient-specific benefit-risk analysis before performing high-dose cardiac CTA. The potential value of dose-reduction methods should serve as a wake-up call to cardiac CT laboratories that do not routinely use these methods, he said.
