IEEE Spectrum February, 2014 - 18

DID you FeeL that? A wireless probe manipulated by a laparoscopic instrument should let
surgeons sense tumors by touch.

displacement of the three profile sensors,
which move up and down with the tissue
surface. The three surface sensors and the
spherical indenter work jointly to determine the indentation depth and the force
with which the tissue pushes back, making a
map of the tissue's stiffness. The probe has
not yet been tested in an animal.
Valdastri's and Althoefer's work builds
upon nearly two decades of remote palpation
research. Previous approaches have focused
largely on adding touch sensors to conventional surgical instruments. Many of the
technologies have been successfully demonstrated, but none have been commercialized.
The challenge is that the costs of the technologies simply outweigh the benefits to
surgeons, say researchers. "If you ask surgeons, they'll tell you that they need touch
feedback, but then they go and perform a
vast range of minimally invasive procedures
without it," says Howe. "Touch feedback
is in the nice-to-have, not the got-to-have
category," he says.

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Harvard University who developed some
of the first remote palpation technologies in
the early 1990s.
The novelty of Valdastri's probe, compared
with previous designs, is in its use of a magnetic field sensor to track its position, according to Russell Taylor, director of the Center for
Computer-Integrated Surgical Systems and
Technology at Johns Hopkins University, in
Baltimore. "It's a very clever way to do it, but
it's certainly not the only way to do it," he says.
Another group of researchers, this one
based at King's College London and led by
robotics expert Kaspar Althoefer, has devised an alternative. Like Valdastri's prototype, Althoefer's system tracks the probe's
spatial position, how deeply it indents the
tissue, and the reaction force of the tissue.
But his design is based on optical fiber technology, and the probe is able to roll over the
tissue surface with minimal friction.
Althoefer's probe consists of three surface-profile sensors equally spaced around a
spherical indenter. As the probe glides over
a tissue surface, the sphere, which floats on
a pocket of air, indents the tissue, and a pair
of optical fibers measures the indentation.
Another set of optical fibers measures the

But Valdastri's and Althoefer's
probes have some characteristics
that might be appealing to surgeons.
Because Valdastri's device is wireless, it is less likely to get in the way
of other surgical tools, it doesn't
require a separate incision, and it
may allow surgeons to reach places
they can't with a rigid or wired instrument. And because Althoefer's
probe glides over the tissue surface
with almost no friction, it is less
likely to damage the tissue.
But there are also practical hurdles
to address in the quest for perfect
palpation. Rajni Patel, a robotics researcher at the University of Western
Ontario, in Canada, has developed a
pressure sensing array to palpate the
delicate tissues of the lung. But one
major challenge, he says, has been
designing an array that can withstand
the surgical sterilization process.
Researchers integrating palpation technologies into surgical robots are also still
sorting out how to display the many layers of information to the robot's operator.
That has been a challenge for biomedical
engineer Tim Salcudean at the University
of British Columbia, in Vancouver. Using a
technique dubbed vibro-elastography, he
is generating 3-D elasticity maps by exciting tissue with vibration and measuring
the waves produced using an ultrasound
elastography probe. The probe is held by
a surgical robot, which tracks its position.
Keeping track of the elasticity map while
performing surgery is a lot of work for the
surgeon, he says: "How do we display? Is it
an overlay or an adjacent image? How do
we simplify controls? It is all very challenging, but seeing through the patient is the
future of surgery."
It might not be long before feeling around
inside the body during surgery is considered old-fashioned. "The new generation
of surgeons are not doing a lot of open surgery, so they're not used to palpation," says
Salcudean. For those surgeons, computergenerated tissue maps might be all they need
to "feel" a tumor. -emily wa ltz

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Table of Contents for the Digital Edition of IEEE Spectrum February, 2014