MRI-safe motor developed for robotic biopsies
Engineers at the Johns Hopkins Urology Robotics Lab have invented a motor without metal or electricity that is able to power remote-controlled robotic medical devices used for MRI-guided cancer biopsies and therapies. The motor is so steady that it is actually more precise than a human hand, according to the researchers. A description of the new motor, made entirely out of plastics, ceramics and rubber, and driven by light and air, was published in the February issue of the IEEE/ASME Transactions on Mechanotronics.
 “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 the robotics lab. “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.”
Developing the robot was a challenge because of MRI’s strong magnetic interference. Metals are unsafe in MRI because the machine relies on a strong magnet, and electric currents distort MR images, said Stoianovici.
Six of the motors were used to power an 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,” said Stoianovici.
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 MR scanner and is controlled remotely by observing the images.
“The robot moves slowly but precisely, and our experiments show that the needle always comes within a millimeter of the target,” said Stoianovici. The device should 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 John 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.