Engineers at the Johns Hopkins
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 therapies guided by magnetic resonance
imaging. 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, an associate professor of urology in the
School of Medicine 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
A description of the new motor, made entirely of
plastics, ceramics and rubber, and driven by light and air,
was published in the February issue of the IEEE/ASME
Transactions on Mechanotronics.
The challenge for his 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,
Stoianovici said. The team used six of the motors to power
the first-ever MRI-compatible robot to access the prostate
The robot currently is undergoing preclinical
"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 new Johns Hopkins motor, dubbed PneuStep, consists
of three pistons connected to a series of gears. The gears
are turned by airflow, 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,"
The robot goes alongside the patient in the MRI
scanner and is controlled remotely by observing the images
on the MR. The motor is rigged with fiber optics, which
feed 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 said.
Li-Ming Su, an associate professor of urology and
director of laparoscopic and robotic urologic surgery at
the Brady Urological Institute at Johns Hopkins, said,
"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
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
Authors on the paper are Stoianovici, Alexandru
Patriciu, Doru Petrisor, Dumitru Mazilu and Louis Kavoussi,
all of Johns Hopkins.