Metal-free motor makes robotic biopsies safe for use with MRI
17 April 2007
Engineers at the Johns Hopkins Urology Robotics Lab have
developed a motor without metal or electricity that can safely power
remote-controlled robotic surgical tools 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.
The motor is constructed of nonmagnetic and dielectric materials such as
plastics, ceramics, and rubbers and is electricity free. It is driven by
compressed air and fibre optic technology is used for communications, so
that all electric components are located away from the MRI scanner. Six of
the motors are used in a surgical robot designed to carry out precise
MRI-guided surgical procedures (see below).
An MRI-safe surgical robot driven by six of the new motors
“Lots of biopsies on organs such as the prostate are currently performed
blind because the tumours are typically invisible to the imaging tools
commonly used,” says Dan Stoianovici, Ph.D., an associate professor of
urology at Johns Hopkins and director of the robotics lab. “Our new MRI-safe
motor and robot can target the tumours. This should increase accuracy in
locating and collecting tissue samples, reduce diagnostic errors and also
improve therapy. 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.”
A report on the new motor 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,
The new 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,” says Stoianovici. The robot currently
is undergoing preclinical testing.
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 fibre
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 millimetre of the target,” says Stoianovici.
This type of precision control will allow physicians to use instruments in
ways that currently are not possible, he says.
“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, M.D., an associate
professor of urology and director of laparoscopic and robotic urologic
surgery at the Brady Urological Institute at Hopkins.
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