Trimming slice count to cut pediatric CT dose

A limited sequence of axial head CT slices has been demonstrated to reduce radiation exposure by 92 percent compared with standard CT scans in children who need repeated imaging of excessive fluid in the brain, according to a study published online Sept. 20 in the Journal of Neurosurgery.

The slimmed down sequence was able to reduce dose while also providing adequate and accurate diagnostic information. “The traditional thinking has been that fewer slices would, by definition, mean less clarity and less accuracy, rendering a CT scan suboptimal, but our findings show otherwise,” said lead investigator Jonathan Pindrik, MD, of Johns Hopkins University School of Medicine, in a press release.

Children with excessive fluid on the brain, or hydrocephalus, are at increased risks of radiation toxicity due to their immature tissue and the fact they require frequent scanning during treatment with brain shunts.

To see if see if a CT sequence of seven slices, rather than the more common 32 or 40, would be able to provide the necessary information at a reduced dose, Pindrik and colleagues took two previously performed standard head CT scans from each of 50 hydrocephalus patients age 17 or younger. The scans were retrospectively reviewed in both limited-sequence form and, four months later, as the original full series.

Results showed that in all 50 patients, the limited sequence produced 100 percent accurate images of the brain ventricles, reported the authors. However, there were two errors to the sequence capturing changes in ventricle size due to visual ambiguity.

There were no false negatives and three false-positives in the low-dose images. The minimal error rate demonstrated the sequence was adequate and would not have compromised treatment outcomes, according to Pindrik and colleagues.

“Techniques including minimization of axial slice quantity and modification of CT scanner parameters can achieve significant dose reduction, maintaining a balance between diagnostic utility and patient safety,” wrote the authors.