High-end technology aids pediatric low-dose strategy

Advances in imaging technology are improving the safety and efficacy of pediatric radiology, according to Dr. Catherine Owens, director of imaging at Great Ormond Street Hospital for Sick Children in London.

Radiation dose is a significant issue for pediatric patients. Radiology personnel at Great Ormond Street have devised strategies to minimize radiation burden, based on modern-day imaging equipment. Owens would like to see other pediatric radiologists share their experiences of best practice.

"We need to work together in terms of our protocols for imaging children, because we can make mistakes with settings and doses, especially with these new scanners that are very easy to use," she said at the British Institute of Radiology conference in May.

Retrospective analysis of 2500 patients examined on a sealed fluoroscopy unit at Great Ormond Street has shown that children are receiving x-ray doses far lower than those suggested in U.K. guidelines. For upper gastrointestinal studies and micturating cystograms, for example, doses were five to 25 times lower than current national reference doses. The reference doses should be revised to reflect this finding, Owens said.

"These are useful data to persuade hospital managers to update equipment. These are the lowest doses for pediatric imaging recorded in the literature at this time," she said.

Installation of a 16-slice CT scanner has also helped minimize radiation burden. An audit during the scanner's first year of operation revealed a drop in administered dose, compared with the department's guideline doses for the single-slice system it replaced. Dose values for chest CT exams fell by 34% to 41%, depending on the child's weight, while abdominal CT doses fell by 24% to 66%.

Modalities with no associated radiation risk also play a role in pediatric imaging. Ultrasound is useful for assessing children's joints following trauma, Owens said. Undisplaced supracondylar elbow fractures, for example, do not always show up on plain-film x-ray and can be a cause of litigation. Ultrasound shows the presence of any effusion at the elbow. Avulsion injuries and apophyseal tears, which are more common in children than in adults, can also be seen on ultrasound.

Many children treated at the hospital have rheumatologic conditions such as juvenile idiopathic arthritis. Real-time ultrasound guidance can help clinicians inject anti-inflammatory therapies more precisely.

Ultrafast MRI sequences and parallel imaging have benefited the hospital's pediatric MRI program, Owens said. Shorter acquisition times reduce the likelihood of motion artifacts. Work is under way to evaluate the use of MRI instead of serial CT exams in monitoring pulmonary nodules.

More than 200 children have undergone cardiac MRI at the hospital. One promising application is the use of MRI to define the anatomy of coronary arteries following arterial switch operations. Coronary imaging is not usually performed in pediatric patients because they are unlikely to have atheromatous disease. In this case, however, patients can go on to have primary stenoses. A study in the February issue of Radiology found that pediatric patients older than 11 can easily undergo MR angiography for asymptomatic follow-up of arterial switch cases.