Apple’s much ballyhooed unveiling of the fifth edition of its iPhone put the tech world in a frenzy this fall, but while radiologists might buy one to swap images with colleagues or even play Fruit Ninja, they probably won’t make a habit out of readingX-rays off their phones, according to a medical informatics expert.

Mobile devices have a role as an occasional backup device for radiologists, but their small size likely prevents them from being used for routine primary diagnosis, Dr. David Hirschorn told attendees in early September at the New York Medical Imaging Informatics Symposium, which he helped organize.

Smartphones and tablets equipped with medical image viewers are, however, better suited to non-diagnostic image sharing with referring doctors and their patients, he said.

“For every one (radiologist) use case, (there are) probably 10,000 use cases for the ordering clinician,” he said during his talk, “A Tale of Two Displays: Desktop and Mobile for Medical Imaging,” held at the Marriot Marquis in Times Square.

Size matters
The primary drawback for mobile devices is how tiny their screens are, Hirschorn said, not necessarily their resolution.

Megapixel count is a popular point of marketing medical monitors, but for clinical utility, the size of the overall display and the size of the pixels in the display, which determines how far back you have to stand to see it clearly, are among the most important factors, explained Hirschorn, the director of radiology informatics at Staten Island University Hospital, which sponsored the event.

For routine primary diagnosis of CR images, for instance, you need a display at least 20 to 24 inches across diagonally. An iPad is 9.7 inches, he said, too small to safely let doctors render diagnoses for radiography.

“I don’t care how many pixels you do or do not cram into my phone, I’m not gonna read a chest X-ray off it,” he said.

But smaller pixel size images, such as from CT, MRI, ultrasound and angiography, might be appropriate to read, occasionally, on high-quality tablets. In fact, the Mobile MIM viewer, a medical imaging viewer for the iPad and other devices cleared by the Food and Drug Administration for diagnostic readings in 2011, and the first of its kind, is only approved for CT, MRI and nuclear medicine, and only when a workstation is unavailable.

Unlike in radiography, these modalities have much higher inherent contrast, Hirschorn said.

“If you’re a radiologist you understand this. They’re not eye tests.”

Luminance
Brightness is also a factor in displays; if monitors are too dim, radiologists can miss subtle findings.

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.”