A low-dose CT protocol using a tin filter as the sole diagnostic tool can accurately diagnose foreign body
aspiration (FBA) in children while reducing radiation dose and avoiding bronchoscopy.
In her Monday presentation, Lena Gordon Murkes, MD, Karolinska Institutet, Stockholm, Sweden, reported that the use of low-dose CT resulted in lower effective doses, and more accurate diagnoses of suspected FBA, compared to conventional radiographic methods.
According to Dr. Gordon Murkes, dealing with foreign body aspiration is a fairly common problem in many emergency rooms. And that problem is complicated by the fact that FBA is often just suspected — parents might not know for sure whether their children have actually ingested or inhaled a foreign object.
While bronchoscopy will allow a physician to evaluate the airways for a retained foreign body, that procedure requires putting children under general anesthesia, which, while usually safe, can result in complications.
Chest radiographs or fluoroscopy — or both — could also be used in diagnosing FBA in young children. However, these conventional imaging methods are not entirely accurate, Dr. Gordon Murkes said, "So you run the risk of missing the foreign body itself."
CT, on the other hand, is highly accurate. The problem with CT, though, is the possibility of exposing the affected child to a high effective dose of radiation. "But with a tin filter we've managed to minimize the dose so that it is lower than a combination of X-ray and fluoroscopy," she said.
For high-contrast exams, low-energy photons aren't needed and only contribute to radiation dose, Dr. Gordon Murkes explained. The tin filter shapes the X-ray spectrum, leaving mostly high-energy photons.
Protocol Decreases Risks for Patients
Dr. Gordon Murkes and her colleagues conducted a retrospective review comparing the diagnostic performance and effective doses of conventional radiographic methods (fluoroscopy and plain radiography) with low-dose CT using a tin filter. They evaluated 136 children, 75 of whom underwent examination with conventional radiographic methods, while the remainder were examined with CT.
Dr. Gordon Murkes and her colleagues determined that low-dose CT examinations resulted in lower effective doses compared to conventional radiographic methods, with median doses of 0.04 mSv and 0.1 mSv, respectively. Both sensitivity and specificity were higher for low-dose CT (100% and 98%) than for conventional imaging methods (33% and 96%), as were positive and negative predicted values (90% and 100% for CT and 60% and 91% for conventional methods, respectively).
"The CT low-dose protocol reduces the radiation dose and decreases the risk of misdiagnoses and negative bronchoscopy outcomes, thereby avoiding operative risks and costs," Dr. Gordon Murkes said.
While the use of CT exams for children has raised concerns about radiation exposure, this is a low-dose exam, fast and "a sure method," Dr. Gordon Murkes said. "Our ENTs (ear, nose, and throat physicians) are extremely pleased with it because they are confident we can tell them if there is a foreign body in the airway and where it is located."