MRI-Safe Motor Propels Robot Biopsies

A motor without metal or electricity can safely power remote-controlled robotic medical devices used for cancer biopsies and therapies guided by magnetic resonance imaging (MRI). The motor that drives the devices can be so precisely controlled by computer that movements are steadier and more precise than a human hand.

"Lots of biopsies on organs such as the prostate are currently performed blind, because the tumors are typically invisible to the imaging tools commonly used," said Dan Stoianovici, PhD, an associate professor of urology at Johns Hopkins and director of its robotics lab, where the device was invented. "Our new MRI-safe motor and robot can target the tumors. This should increase accuracy in locating and collecting tissue samples, reduce diagnostic errors and also improve therapy."

The new motor is made entirely out of plastics, ceramics and rubber and is driven by light and air. The challenge for Stoianovici's engineering team was to overcome MRI's dependence on strong magnetic interference. Metals are unsafe in MRIs because the machine relies on a strong magnet and electric currents distort MR images, said Stoianovici. The team used six of the motors to power the first-ever MRI-compatible robot to access the prostate gland. The robot currently is undergoing preclinical testing.

"Prostate cancer is tricky because it only can be seen under MRI, and in early stages it can be quite small and easy to miss," Stoianovici said.

The motor, dubbed PneuStep, consists of three pistons connected to a series of gears. The gears are turned by air flow, which is in turn controlled by a computer located in a room adjacent to the MRI machine. "We're able to achieve precise and smooth motion of the motor as fine as 50 micrometers, finer than a human hair," said Stoianovici.

The robot goes alongside the patient in the MRI scanner and is controlled remotely by observing the images. The motor is rigged with fiber optics, which feeds information back to the computer in real time, allowing for both guidance and readjustment.

"The robot moves slowly but precisely, and our experiments show that the needle always comes within a millimeter of the target," Stoianovici said. This type of precision control will allow physicians to use instruments in ways that currently are not possible, he added.

"This remarkable robot has a lot of promise -- the wave of the future is image-guided surgery to better target, diagnose and treat cancers with minimally invasive techniques," said Li-Ming Su, MD, an associate professor of urology and director of laparoscopic and robotic urologic surgery at the Brady Urological Institute at Johns Hopkins.

A description of the new motor was published in the February issue of the IEEE/ASME Transactions on Mechanotronics. Authors on the paper are Stoianovici, Alexandru Patriciu, Doru Petrisor, Dumitru Mazilu nd Louis Kavoussi, all of Johns Hopkins. The research was funded by the National Institutes of Health, the Prostate Cancer Foundation and a grant from the Johns Hopkins Medicine Alliance for Science and Technology Development Industry Committee. Current experiments with the robot are supported by the Patrick C. Walsh Foundation.

For more information, visit: urology.jhu.edu/urobotics/projects/PneuStep