Use of infant warming mats during CT found to increase radiation dose, decrease image quality

Newborn infants are commonly placed on warming infant transport mattresses (ITM) during CT scans to counter the increased risk of cold stress or hypothermia. A small-scale study published in Academic Radiology, however, suggests the use of these mattresses may do more harm than good.

William F. Sensakovic, PhD, of Florida Hospital in Orlando, and colleagues wrote that approximately one in four English neonatal units use ITMs, but little information is available on how the mattresses impact radiation dose or image quality.

“Modern CT scanners implement several automatic exposure control technologies to reduce patient radiation dose and improve image quality,” the authors wrote. “Although these technologies typically lead to reduced patient radiation dose, it is possible that the presence of a foreign object could confuse the automatic exposure control algorithms leading to increased patient radiation dose. Further, a foreign object could alter beam characteristics and cause image artifacts.”

So Sensakovic et al. went to work, examining the effects of using an ITM on a three-week-old patient with congenital melanoma. Images from the patient were retrospectively collected and compared to phantom scans with and without the ITM. All scans were acquired with a 128-slice CT scanner.

Overall, the team found that the original scan of the patient and the ITM displayed a decreased mean Hounsfield unit (HU) and increased HU standard deviation. In the phantom scans, the ITM was found to increase volumetric CT dose index (CTDIvol) by 27 percent, decrease HU by 3.5 HU, and increase HU standard deviation by 4.6 HU.

Also, while looking at the original scan, Sensakovic and colleagues noticed an ITM-induced artifact in the “posterior aspect of the patient.” And then they noticed the same artifact in the phantom scans.

“Qualitatively, the ITM-induced artifact seen in the patient was also seen in the phantom at the posterior level of the ITM,” the authors wrote. “This artifact appeared as a laterally directed streak of increased noise and decreased gray-level intensity.”

The research team did conclude that “angular tube-current modulation, strong iterative reconstruction, thick slices, metal artifact reduction, and high mA” could help reduce the artifact, but they still don’t recommend using the mattresses unless absolutely necessary.

“We believe that the use of an ITM under normal conditions is not warranted given the increase in radiation dose and induction of image artifacts,” the authors wrote.

The authors noted that their study did have some limitations. For instance, the phantom was the smallest available at their hospital, but it was technically several centimeters larger than the actual patient. Also, the phantom was not anthropomorphic, so its shape did not match that of the patient. In addition, the ITM used in the phantom scans was similar in thickness to the one originally used with the patient, but the mattresses are gelatinous, so it was not an exact match.