Dynamic MRI: How to beat the magnet

Image source: Passive controlled motion device with piezoelectric motors. Courtesy Ilan Elias, MD, PhD

Long considered the gold standard for soft tissue imaging, the static nature of MRI has meant that many functional injuries in athletes have remained invisible, a limit that may have been significantly outgunned by the recent invention of an MRI-safe method and device to recreate controlled passive motion of a patient's joint.

Tissue imaging with MR has provided physicians with unsurpassed images for an array of conditions since the 1980s. One of the non-ionizing modality’s major downsides, however, has been the restrictions MR’s strong magnetic field imposes on eligible patients—only recently has headway been made in being able to image the millions of patients around the world with pacemakers, for example.

“MRI is an excellent tool to depict anatomy, especially for soft tissue. However, there’s a functional aspect to joints, muscles and the spine, and we have to be able to visualize this on MRI,” explained Ilan Elias, MD, PhD, from the department of orthopedic surgery at the Rothman Institute, Thomas Jefferson University Hospital, in Philadelphia.

“Many musculoskeletal injuries are frequently not seen directly on conventional MR because of the nature of those injuries, for example, snapping or dislocated tendons in the foot and wrist, extruded menisci and cruciate ligament insufficient knees."
 
Elias observed many patients complaining of functional injuries or perceived dislocations of tendons or unstable joints in the knees, ankles, spine and feet; but it was difficult to render an exact diagnosis because the injuries were not depicted via MRI.

As the quality and speed of MR advanced in the mid-1990s, Elias increasingly sought an avenue to reproduce his patients' motion injuries on MR. Elias’ attempts to replicate patient movement via motor-controlled devices were, as expected, continuously rebuffed by MR’s forceful electromagnetic fields, however.

“The major obstacle when I first started was, of course, that the MR engineers said that I could not use a motor inside the MR because, per definition, with the motor, there is electricity, which creates artifacts. And they were right,” Elias said.

By 2000, though, Elias devised a method to work around the electromagnetic interference. He used piezoelectric motors—stress-induced electrical motors—with highly specific grounding to produce electricity inside the bore without disrupting the MR signals. By embedding ferrites (thick magnets) on the device’s cables, shielding all electrical parts and installing filters in the suite from adjacent MR exam rooms, Elias was able to operate the motorized device within the gantry without introducing any artifacts.

With the major hurdle overcome, Elias created a device with multiple heads that could fit different patient appendages and anatomy. Patients input their injured parts in the device, which then remotely operates in a controlled motion that reproduces the patient’s movement and symptoms for imaging on MR.

The controlled nature of the device adds an additional advantage—Elias is able to precisely track patients’ injuries over time by replicating the device’s motion, which renders greater initial and long-term certitude, he claimed.

The device would not have been possible until relatively recently, Elias added, because MR was not quick enough to produce the dynamic images which effectively offer a video of patients’ injuries.

“The first thing that comes to most people’s minds is imaging sports-related injuries,” Elias explained. “But degenerative arthritis and degenerative spine diseases with impingement of nerves or unstable discs would be diagnosed more thoroughly when evaluated under motion."

Elias has recently received patents in the U.S. and abroad for the device and has used it successfully on approximately 150 patients, he estimated, but is currently shopping for vendors to collaborate on the device to gain FDA 510(k) clearance.