OCTORS have
always relied on their sense of touch, for everything from palpating a
lump to tightening a suture. But in recent years, technology has been dividing
doctors from their patients. Minimally invasive (or "keyhole") surgery,
in which cameras and surgical instruments are threaded through tiny openings,
may drastically reduce patient trauma and recovery time, but it also eliminates
the direct contact with organs, bones and muscles that doctors have enjoyed
in open surgery.
What technology has taken away, however, technology has begun to give
back. Haptics, from the Greek verb meaning "to touch," is the science of
incorporating the sense of feel into computer interfaces. For decades,
touch has been recognized as the next step, after sight and sound, toward
a natural, all-involving computer environment, but it is only recently
that computers have become fast enough and cheap enough to make haptic
interfaces viable.
As a result, commercial haptic devices have started to appear, not only
in niche markets like computer-aided design and 3-D modeling, but on the
consumer desktop: The iFeel mouse by Logitech has a small motor that kicks
or vibrates as users roll over menus, icons and window boundaries. Some
experts predict that haptics will soon be as familiar a part of the computer
desktop as color graphics and stereo sound are today.
But nowhere is the promise more exciting than in medicine. Simple haptic
interfaces are already part of some medical equipment, and researchers
are working toward the ultimate goal, to make even the robotic surgery
of the future, where doctor and patient might be continents apart, feel
(to the surgeon, anyway) like the traditional open surgery of the past.
At M.I.T.'s laboratory for Human and Machine Haptics, Dr. Mandayam Srinivasan,
the lab's founder, is developing a simulator to show medical students how
a correctly inserted needle feels when injecting a spinal anesthetic. Finding
the correct spot below layers of skin and ligament is a delicate procedure,
and a misplaced needle can paralyze a patient.
"Nowadays it is done with expert supervision, but still the trainee
does it for the first time on a patient," Dr. Srinivasan said. "It seems
to me that having a simulator, even if it is not perfectly realistic, would
still be beneficial."
The simulator consists of a syringe attached to a desktop force-feedback
device — a freely movable stick equipped with motors so it can push back
— and a computer running the simulation software, and a mannequin back.
With a simulator, students can experience the full spectrum of cases, not
just the usual ones.
"You can simulate scenarios that occur in 1 in 10,000 patients," Dr.
Srinivasan said. "I have heard anesthesiologists say that there are things
that they didn't encounter even after they had done a thousand epidural
procedures."
Greg Merrill, the founder of HT Medical Systems of Gaithersburg, Md.,
said that 75 percent of complications arising from procedures like intravenous
catheterization occur in the first 30 cases of a doctor's career. It's
a statistic that speaks eloquently for his firm's medical training simulators,
like CathSim, which teaches how to insert catheters and needles. The device
consists of a small box with a protruding force-feedback syringe. The device's
haptic feedback includes the "pops" of the needle piercing the skin and
vein. Different software modules simulate adult, child and geriatric profiles,
including, for example, the tough, scarred veins of an intravenous drug
user.
Future generations of simulators, Mr. Merrill said, will use data from
individual patients. "You can have the patient come in, get scanned, and
the physician can do patient-specific pre-operative rehearsal," Mr. Merrill
said. "That's of tremendous benefit in learning the best approach to a
procedure, figuring out which medical devices work best for that patient."
For example, stents, tiny tubes inserted into diseased arteries to keep
them open after balloon angioplasty, have to be carefully matched to each
patient's particular arterial geometry. A rigid stent cannot easily be
threaded into a tightly twisted artery. Today, surgeons use trial and error;
if one stent can't be deployed, they will pull it out and try another.
"Wouldn't it be nice to determine which is the appropriate product prior
to trying it out on the patient?" Mr. Merrill asked. "The advantage of
haptic feedback is you can feel the resistance that it's going to take
to deploy that stent within that patient-specific anatomy."
Haptics may be a hot commodity in the world of medical simulation, but
it has barely entered the real world of the operating theater.
"It's probably the one thing that's held back minimally invasive surgery
the most," Mr. Merrill said. "The doctor is moving further and further
from the site of the interaction, and the problem is they lose the sense
of touch. The number of procedures making the transition from open to minimally
invasive is not as big as it probably should be for that reason."
One problem is that the haptic interfaces available today are all sticklike
force-feedback devices. They are useful, but feeling the world with a stick
doesn't begin to convey the experience of holding something in your hands.
What is missing is something like artificial skin — shaped like a glove,
perhaps, or at the very least, a thimble — that will deliver a virtual
approximation of the rich tactile experience we take for granted.
At Stanford University's Dextrous Manipulation Lab, Dr. Mark Cutkosky
is working on such a device, called CyberGlove. The glove controls a two-fingered
robotic arm — whatever the user does, the robot does — which in turn feeds
back what it "feels" to the glove's fingers.
"There's a funny thing that happens when you provide feedback to the
user," Dr. Cutkosky said. "Suddenly, it no longer feels like, I'm here
with my glove and I'm controlling that robot hand over there. Suddenly
you feel like, that's my hand over there, it's an extension of me."
Although the CyberGlove is about as advanced as haptics gets today,
it is still a relatively primitive instrument that feeds back force (Dr.
Cutkosky is experimenting with adding vibration) to just a single haptic
unit on each finger. That's a far cry from the detail that fingertips are
capable of resolving.
In some ways, the sense of touch is more complex than vision or hearing.
To satisfy the eye that an image is moving, for example, it is enough to
display 15 still pictures a second. The haptic equivalent — fooling the
fingertip into believing it is feeling a surface — takes a thousand impulses
a second. In addition, while eyes respond exclusively to light, fingertips
respond to force, vibration and temperature. Between today's devices and
a robot surgeon that feels like a natural extension of a human lie years
of research and development.
"I am always amazed at how people take touch for granted," Dr. Srinivasan
said. "It's an amazing system. No wonder we haven't been able to build
robots that are comparable to even a 2-year-old human baby."
