FDA seeking to make MRI safe for all

WASHINGTON – A mannequin skull sits in an MRI machine, about to be filled with a thick, brain-like gel.

MRIs are required tests for numerous disorders. But they are off-limits for millions of patients with certain implants, such as pacemakers or brain electrodes. The scanners can dangerously heat the metal parts.

“The MRI industry thinks it’s simple: ‘Don’t use’ ” in those patients, said the Food and Drug Administration’s Larry Kessler. “That’s not the end game.”

Instead, amid pressure from doctors, the agency wants to speed development of MRI-compatible implants. Hence the mannequin, part of a little-known FDA research program where 140 scientists probe the pitfalls and promises of medical devices.

Much of the work by Kessler’s $21 million Office of Science and Engineering Laboratories is aimed at helping the FDA better analyze new devices before approving their sale.

Because problems frequently arise later, these scientists also are giving new scrutiny to the usefulness of equipment already on the market – and whether they can spur improvements.

Consider the MRI dilemma.

Recently, a man was left temporarily comatose after an MRI scan was performed even though he had a “deep brain stimulator,” an implant increasingly used to fight Parkinson’s disease and other tremors. Two other brain-stimulator recipients died, not after MRIs but after a heat therapy called diathermy that emits the same radio-frequency energy as MRIs do.

The FDA is trying to find ways to make MRIs safe for people with these and other implants.

FDA scientist Howard Bassen filled the mannequin skull with a gel substance similar to the consistency of the brain. He attached electrodes from a deep brain stimulator and zapped the skull with the radio waves that MRIs and diathermy emit.

The electrodes’ temperature rose more than 20 degrees in 5 seconds, Bassen found. Heat concentrated at the tip where it literally can burn a hole in delicate brain tissue. The thinner the wire, the hotter it got; that is important for recognizing which devices are riskier.

Manufacturers are working to create MRI-compatible implants. Doctors are looking for ways that recipients of older implants can get scanned safely. Models like Bassen’s mannequin should help those attempts, Kessler said.

The FDA also is investigating just how well new computer-aided cancer tests really work. These programs promise to double-check radiologists by pointing out potentially suspicious spots on tests such as mammograms. But most computer recheckers use fewer X-ray views than radiologists do on their own, said FDA electrical engineer Nick Petrick.

“Do they help poorer radiologists become better?” Petrick asked, or give them the wrong cues. “If you blindly follow the computer, you’ll be biopsying every third or fourth patient.”

Also under review are worrisome hormone-mimicking chemicals that can leach from such equipment as dialysis filters and blood bags. But there are not good ways to measure how much of those chemicals patients absorb or whether patients are harmed.

Scientists from the FDA and George Washington University culled brain cells from rats to create a better test to measure patient exposure and are searching for genetic signs of toxicity.