Reading room design sheds light on prior problem

Ambient light takes on new importance in soft-copy interpretation

By: Deborah R. Dakins

Good design for reading soft-copy digital mammography follows the same ergonomic principles that apply to other interpretive environments, with a few twists.

Easy-to-use, comfortable workstations are essential, as are adequate air ventilation and appropriate ambient lighting. But areas must also be designed to incorporate both soft-copy display systems for digital images and alternators for comparing film-based priors. This presents both design and workflow challenges.

The design conundrum lies in finding an efficient way to use the alternator, with its high luminance, and the monitor, which demands dimmed light for best interpretive performance.

Researchers have established that the three variables with the greatest effect on soft-copy productivity are ambient light, monitor brightness, and the number of monitors available.

Ambient light becomes even more important in a soft-copy digital mammography environment. A typical soft-copy display monitor projects luminance of about 70 foot lamberts or 240 candelas per square meter-much lower than a typical viewbox at about 3000 candelas per square meter.

The FDA allows ambient light in the soft-copy reading area to be as high as 50 lux, but less than 5 lux is desirable. Achieving such low levels requires minimizing light from nearby viewboxes, alternators, doors, windows, and other computer screens.

Ambient room light greater than 15 lux degrades image contrast, affecting image interpretation. Soft-copy digital mammography in particular requires careful control of ambient light, diffuse and specular reflections, and veiling glare to ensure diagnostic accuracy.

Even when optimal light levels are achieved, radiologists face another challenge: comparing film-based priors alongside soft-copy displays.

When soft-copy images are loaded onto a multiviewer next to the soft-copy reading station, there is a time saving component in comparing the two, said Dr. R. James Brenner, director of breast imaging at St. John's Hospital in Santa Monica, CA.

"But visual adaptation might require a little time for accommodation, and there is risk of perception error in this effort," he said. "The alternative is to load each case onto small adjacent viewboards, which can increase the time of reading substantially."

At some sites, prior films are digitized so that both old and new cases can be read on soft-copy displays. But display characteristics of digitized films are not the same as digitally acquired images, said Bradley Hemminger, Ph.D., an adjunct professor of radiology at the University of North Carolina, Chapel Hill. Some mental adjustment is still necessary.

"It's a transition issue: How do you meld these two worlds of analog film and soft copy? Since mammography requires seeing priors, it is an important issue, although in five to 10 years it may be less of one," he said.

In the interim, some sites have temporarily abandoned attempts to shift to soft-copy digital mammography interpretation. At UNC, radiologists continue to print digital mammography images to compare with priors.

"We find it very difficult to sit with a monitor next to the film images and see to the same level of detail while comparing them," said Dr. Etta Pisano, chief of breast imaging at UNC. "I'm trying to get my staff to transition to all soft copy, but they are resistant-and the reason they are resistant is one that I can't argue with. They're worried they are missing things, and they want to be careful. I don't want to discourage that."

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Mammography Reading Room Checklist

- Room layout with good traffic flow

- Viewing equipment laid out linearly, including view boxes for review of film-based priors

- Ambient light below 10 lux

- Adjustable vicinity lighting

- Displays with high contrast

- Ergonomic chairs and adjustable table height

- Noise below 45 dB

- Adequate airflow

- Utility lighting

- Thermostat and temperature control