Individual exam dose may decrease, but gross levels will go up

Individual dose levels in x-ray based imaging exams are decreasing. But exam frequency and total coverage are increasing, so per capita radiation dose levels are on the rise, according to a presentation Friday.

Prof. Willi Kalender, Ph.D., of the University of Erlangen in Germany, described the dynamics at work as multidetector CT gains ground as a common imaging study. Although a number of techniques being developed by vendors are reducing dose levels, the growing use of radiation-based imaging studies will ultimately increase the total dose exposure to the overall population.

Vendors have been working to improve image quality, and some of the innovations have allowed them to reduce dose. Overbeaming, for example, has been reduced with the advent of multidetector scanners, which allow wider arrays with less radiation loss, Kalender said.

Similarly, tube current modulation and noise-reducing image reconstruction techniques can improve image quality at lower dose levels. Ultimately, automatic exposure control in CT scanning promises to adjust and lower dose levels while preserving image quality, Kalender said.

But the superior images produced by newer scanners are increasing their popularity. More scans will translate to higher per capita dose levels, Kalender said.

His comments came during a special focus session in which experts discussed strategies for reducing radiation dose.

Digital technology should permit lower dose levels if radiologists, technologists, and physicists make the effort to find out how low dose settings can go and still allow images to be adequate for interpretation, said Prof. Jan Persliden, head of medical physics at Orebro University Hospital in Sweden.

Better communication among those groups will allow them to find the best trade-off between low-dose, high-noise images and ones that are still diagnostically useful.

"You should be known in the radiology department so you will know what is happening all of the time," Persliden told a crowd made up largely of physicists and technologists.

A visiting professor came to Persliden's facility who produced high-quality images that really impressed the staff. The professor had reset all the imaging parameters to increase dose and limit noise. While the images were better, there was no gain in diagnostic accuracy, Persliden said.

Prof. Eliseo Vano, a professor of radiology at San Carlos University Hospital in Madrid, cautioned that more training may be needed to reflect an increase in the use of imaging equipment by specialists outside radiology, including cardiologists and urologists.

Those who perform interventional procedures should be aware that larger patients produce more scatter radiation. Vano advised the use of personal dosimeters, suspended screens, curtains under the table, and other personal shielding tools.