Technology supports low-dose pediatric strategy

Provision of radiology services to young children is demanding because of their small size, uncooperative nature, and exquisite sensitivity to radiation. Improvements to equipment in the past few years, however, have made an enormous contribution to pediatric radiologists' daily practice and to safety and efficacy levels, said Dr. Catherine Owens, director of imaging at Great Ormond Street Hospital for Sick Children (GOSHSC) in London.

The dose delivered to pediatric patients during imaging is a significant issue. A child receiving a high dose of ionizing radiation has many years in which to potentially develop malignancies associated with those x-rays. Staff at GOSHSC have devised a series of strategies in which modern equipment helps minimize their patients' radiation burden. Owens would now like to see all 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 told attendees at a British Institute of Radiology seminar in May.

Retrospective analysis of 2500 patients examined in a sealed fluoroscopy unit at Great Ormond Street found that children receive a far lower x-ray dose than U.K. guidelines specify. For upper gastrointestinal studies and micturating cystograms, for example, doses were five to 25 times lower than current national reference doses.

Those reference doses should be revised to reflect this statistic, according to Owens.

"These are useful data to try 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 in the battle to minimize children's radiation burden. A comprehensive audit during the system's first year of operation revealed a decrease in administered dose compared with the department's guideline doses for the single-slice system it replaced. Dose values for chest CT examinations fell by 34% to 41%, depending on the weight of the child, while abdominal CT doses fell by 24% to 66%.

"Our biggest fear was that with the press of a button, you could do a radiotherapy-type examination on patients, so we were very, very careful to set up very cautious doses for our children," Owens said. "But, paradoxically, we haven't gone up; we have actually gone down."

Modalities with no associated radiation risk also play a role in pediatric imaging. Ultrasound can be useful in assessing children's joints following trauma. Undisplaced supracondylar elbow fractures, for example, do not always show up on x-rays and can be a cause of litigation, she said. Ultrasound shows the presence of effusions at the elbow, as well as avulsion injuries and apophyseal tears, which are more common in children than in adults.

Ultrasound is also used to guide some interventional procedures at GOSHSC. Real-time ultrasound guidance can help clinicians perform anti-inflammatory injections more precisely in children with rheumatological conditions such as juvenile idiopathic arthritis.

The advent of ultrafast sequences and parallel imaging has benefited the hospital's pediatric MRI program. Shorter acquisition times reduce the likelihood of motion artifacts from a restless child. Work is under way to assess the use of MRI, rather than serial CT examinations, to monitor pulmonary nodules. The change to MRI would have considerable advantages in terms of dose reduction.

More than 200 children have undergone cardiac MRI at GOSHSC. One promising application is the use of MR 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 eventually develop primary stenoses.

MR angiography performed with a 1.5T scanner in 16 patients with a mean age of 10 provided diagnostic quality images of the coronaries in 72% of the cases. The technique proved very easy for patients older than 11, Owens said.