Introducing PneuStep

MRI-safe motor enables robotic biopsies

Engineers at the Baltimore-based Johns Hopkins University Urology Robotics Lab report the invention of a motor without metal or electricity that can safely power remote-controlled, robotic medical devices used for cancer biopsies and MR-guided therapies.

"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," says 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."

A description of the new motor, made entirely out of plastics, ceramics and rubber, and driven by light and air, was published in a recent issue of the IEEE/ASME Transactions on Mechanotronics.

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, says Stoianovici.

The team used six of the motors to power the first-ever MRI-compatible robot to access the prostate gland. The robot is currently 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," says Stoianovici.

The new Johns Hopkins motor, dubbed "PneuStep," consists of three pistons connected to a series of gears. The gears are turned by airflow, which is then 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," says Stoianovici.

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

"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," says 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.

—Johns Hopkins Medical Institutions