Minimizing Radiation Exposure a Priority in Pediatric Imaging

The following is a guest post by Robert Gould, ScD, Professor and Vice Chair-Technology at UCSF.

Imaging of premature infants is challenging in part because they are so small. The image of entire infant can easily fit on the smallest available detector size of 8”x10”. These images are done with portable radiographic equipment that has to be carefully positioned.  The infant is normally in an incubator with numerous lines for monitoring physiology that often have to be moved to acquire the image. The babies are very fragile and must be handled with great care.

In the Department of Radiology and Biomedical Imaging at UCSF, we have a limited number of technologists who take these images so that they are experienced and have a high degree of skill. Collimation (coning) – which means restricting the x-ray beam so that only the region of interest (for example, the chest) – is emphasized. UCSF Radiology uses a digital detector called computed radiography (CR), which is state-of-the-art for portable imaging and allows for a lower radiation dose to be used for such radiographs.  Radiologists specializing in pediatric imaging interpret the images. The radiologists review the quality of the images with the technologists on a weekly basis.

It should be noted that a recent New York Times article on pediatric imaging errors could be confusing, as it mixes various types of diagnostic imaging and even radiation therapy in the article. CT scans, which are rarely performed on premature babies, are not the same as portable radiographic imaging, which is common (daily in many cases) for premature infants to assess their chests, and the placement of tubes and lines. The amount of radiation needed for CT imaging is higher than for portable imaging and, while there are studies that showed that during the 1990s and perhaps the early 2000s there were CT scans done on children using adult techniques and consequently gave unnecessary radiation to the children, that practice has been largely discontinued for years throughout the country. Indeed, at UCSF, the settings for pediatric imaging have always been adjusted for patient size. The radiation dose for portable x-ray imaging is low in comparison to CT, and also depends on patient size. Since premature infants are extremely small, the amount of radiation needed for such radiographs is a tiny fraction of what is used for adult imaging or CT. This does not justify poor collimation and whole body imaging, but there was no indication in the NYT article of what the dose levels from these portable studies were or should have been. (Dose is defined as energy absorbed per unit mass and is to a point. The dose to an infant is not constant but varies significantly throughout the area being imaged).

Radiation therapy is a totally different application of radiation (for therapy vs. diagnosis). Levels of radiation required for therapy and the care that must be taken in delivering this radiation to the patient are not applicable to diagnostic imaging. For example, collimation of the radiation beam on therapy equipment is essential to both achieve a successful cure and to prevent normal tissue from being injured. Therapy equipment has x-ray beam collimating devices that are very precise, capable of millimeter accuracy. Diagnostic imaging equipment does not have such technically sophisticated collimators and does not need them.

In summary, the UCSF community can be assured that the department of Radiology and Biomedical Imaging takes seriously its obligation to image gently, with as low a radiation dose as possible and with the proper guidelines and techniques that minimizes radiation exposure to all its patients, particularly the pediatric population.