At the American Roentgen Ray Society (ARRS) 2010 annual meeting, held this week in San Diego, CA, researchers described a range of techniques that could help achieve this goal. Here's a selection of some of the studies presented.
• Sobhi Abadi from the University Health Network in Toronto, Canada, showed how protocol optimization during CT coronary angiography (CTCA) can limit the dose delivered to the breast. Abadi and colleagues scanned an adult female thoracic phantom using eight CTCA protocols that varied in detector configuration, electrocardiogram (ECG) gating method, X-ray tube activation and tube current modulation, and the use of breast shields.
"As cardiac CTCA has significant potential for the non-invasive imaging of coronary artery disease, its utilization is continuously increased, particularly among young women," explained Abadi. "Therefore, the radiation dose delivered to the female's breasts should be addressed."
The highest breast dose (82.9 mGy) was seen with retrospective ECG gating and 64 × 0.5 mm detectors without dose modulation. The use of prospective ECG gating (scanning only during a certain phase of the cardiac cycle) with a 320 × 0.5 mm detector configuration reduced this dose by 82% to 15.2 mGy. Employing surface breast shields during the exam resulted in an additional 38% reduction in breast dose, at the cost of increased image noise.
• Adaptive image filters allow the use of lower radiation dose during chest and abdominal CT scans, while significantly improving image quality, concluded a study headed up at Massachusetts General Hospital (Boston, MA). Twelve patients received CT scans at four dose levels in the chest (150 mAs, plus low-dose levels of 100, 75 and 40 mAs) and abdomen (200 mAs, plus 150, 100 and 50 mAs). All of the low-dose images were then processed with 2D adaptive filters.
All 18 lesions (most of which were smaller than 1 cm) could be seen on both unprocessed and processed CT exams. However, the quantitative average noise in the post-processed low-dose chest and abdomen CT images was significantly lower than in the unprocessed low-dose images.
The diagnostic confidence of post-processed low-dose images was fully confident at 40 mAs for chest CT, and at 100 mAs for abdominal CT exams. "Regardless of radiation dose, post-processing with image filters improved subjective noise for both chest and abdominal CT," said lead author Sarabjeet Singh.
• In a separate presentation from Massachusetts General Hospital, Priyanka Prakash described how applying automatic exposure control (AEC) to chest CT scans can cut radiation exposure by up to 20%.
The team evaluated 98 patients who were scanned using AEC to adjust radiation dose simultaneously for age, weight and clinical indication. This technique resulted in a dose reduction of between 6 and 20% compared to previous weight-based AEC protocols, and a 40–50% reduction when compared to fixed scans without AEC.
The researchers concluded that dose reduction in chest CT must be performed on an individualized basis using age-, weight- and clinical indication-based AEC protocols. "Thus, every patient gets scanned at a radiation dose that is appropriate for them," said Prakash.
• A team at Penn State Hershey Medical Center (Hummelstown, PA) detailed the use of z-axis dose modulation to decrease the radiation dose associated with unenhanced CT scans of the head. The study included two series of 100 unenhanced CT head examinations: 100 performed with z-axis modulation and 100 performed without.
With z-axis dose modulation, the weighted volume CT dose index and dose-length product were reduced by 35.8% and 35.2%, respectively. Image quality and noise were unaffected.
"As radiologists, we are constantly looking for ways to reduce the radiation dose associated with advanced imaging exams such as CT," said Thomas Zacharia, who presented this work to the AARS delegates. "Utilization of the z-axis modulation technique for CT head examinations offers significant radiation dose reduction while image quality is optimally obtained."
• While reducing CT dose is essential, tracking a patient's overall CT-delivered dose could also prove critical in minimizing a patient's lifetime radiation exposure. George Shih from Weill Cornell Medical Center (New York, NY) told meeting delegates about Valkyrie – an automated system that extracts radiation dose information from CT dose reports, and which can be integrated with any existing CT scanner.
In a study performed at Weill Cornell and Columbia University Medical Center (New York, NY), the Valkyrie system processed a random selection of 518 CT dose reports. Initial tests showed that Valkyrie accurately extracted dose information from all 518 reports. Work is currently underway to enable the system to automatically calculate an individualized corrected dose based on patient age, gender and size.
"While the system is functional, it is still in a development phase. We hope that eventually all hospitals will use Valkyrie or something equivalent for all CT studies," said Shih. "The fact that Valkyrie works with older CT equipment is important. This is an immediate solution for almost all hospitals, many of which may not be able to upgrade their CT technology in the short or medium term."