From the November 2012 issue of HealthCare Business News magazine


Previously, the minimum brightness level for a diagnostic monitor was held to be 170 candelas per square meter. But in new guidelines released this year, the American College of Radiology bumped these up to 350 cd/m2 for diagnostic monitors (and 420 cd/m2 for mammography).

The earlier number reflected technological limitations of older analog monitors that have largely been replaced with cold cathode fluorescent lamp (CCFL) and light-emitting diode (LED) backlights, Hirschorn said. And the difference is important.


“You could miss stuff at 200 you can see at 400,” Hirschorn said.

While the iPhone and iPad all have brightness levels above 400 cd/ m2, he said, the trick with mobile devices is calibration.

Testing
A problem inherent to all displays is checking that they are still as bright as they were when they left the factory.
For desktop medical monitors, calibration can be done with built-in sensors in the back that measure the light that’s emitted, and sensors in the front that gauge the light as it actually leaves the screen. External photometers, recommended for at least a yearly check-up of monitor brightness, also help ensure devices are living up to their factory specifications.

But mobile and tablet users can’t access video subsystems in their devices. “Apple and Samsung aren’t going to let you do that,” Hirschorn remarked.

So makers of mobile image viewing software came up with what Hirschorn considers a rather ingenious solution: the tap test. This requires radiologists to identify, and tap on, a certain target on an image. This ensures that the display settings are right, and that the environment is conducive for a reading. But it also, indirectly, assesses the radiologist, making sure, say, the doctor doesn’t need new glasses.

“In some ways it’s better than a photometer,” Hirschorn said. “Because the tap test doesn’t just test the device, it tests the human being.”



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