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Bioengineer's sonic flashlight would let doctors 'see' what's under patient's skin

Monday, July 22, 2002

By Byron Spice, Science Editor, Post-Gazette

A Pittsburgh biomedical engineer has developed a disarmingly simple device that does the seemingly miraculous -- enable doctors to peer through the skin of a patient as they insert a needle or make an incision.

George Stetten, with the sonic flashlight. (Robin Rombach, Post-Gazette)

The skin and other tissues don't suddenly become translucent, of course. But the device creates that illusion by superimposing an ultrasound image of the same area over what the doctor sees.

"It's an illusion, but it's a very useful illusion," said its inventor, Dr. George Stetten, "because it takes advantage of hand-eye coordination." The physician concentrating on inserting a needle, for instance, need not look away from the patient to check a computer monitor that displays the ultrasound image; instead, the electronic image seems to merge with the patient.

The ultrasound image can show features up to six inches beneath the skin -- "a lot farther than you'd probably trust sticking a needle blindly," he added.

The device works by a process he calls real-time tomographic reflection. But Stetten, a biomedical engineer at the University of Pittsburgh and a research scientist at Carnegie Mellon University's Robotics Institute, has given the device a less tongue-twisting nickname: the sonic flashlight.

The name suggested itself, Stetten insists. "It looked just like a flashlight," is his explanation, though the thing looks more like the offspring of a Palm Pilot mated with a rearview mirror.

Nobody has as yet used the sonic flashlight to guide medical instruments in a patient; tests thus far have been restricted to butchered meat and cadavers. But a number of physicians at the University of Pittsburgh School of Medicine have expressed interest, suggesting it might help in assessing trauma victims, placing central intravenous lines in the chest, performing amniocentesis, anesthetizing the eye and finding lumps or other subsurface masses that need to be biopsied.

More on George Stetten and the sonic flashlight

In the spotlight: Biomedical engineer George Stetten

Online graphic
Sonic flashlight: A useful illusion


What Stetten calls an illusion is what other technologists have dubbed "augmented reality." An offshoot of virtual reality, augmented reality seeks to combine a scene as it normally appears to a viewer with other images that carry additional information, such as X-rays. Surgeons have been particularly intrigued about the possibility of augmenting their vision with diagnostic imaging that highlights important tissues, such as malignancies, that might not be obvious to the eye.

But attempts to achieve this vision often have involved elaborate contraptions that include head-mounted video cameras and special goggles. Often, video cameras capture the "real" scene and a computer combines these images with the augmented images so they can be played back to the user.

Augmented reality has not been a major focus of Stetten's research; he primarily puzzles about how to get computers to analyze images, a task that's easy for humans but tough for machines. But elements of his eclectic background -- electrical and computer engineer, physician, singer/songwriter -- combined to produce the sonic flashlight.

The scion of a family of physician/researchers, Stetten initially followed his first love, engineering, and earned his bachelor's degree from Harvard University in 1976. After working as a hardware and software engineer at Harvard and MIT, he went to work at Wood's Hole Oceanographic Institute in 1980, where he developed data processing and navigation systems for the deep-sea submersible Alvin.

He returned to school to earn a master's degree in biology from New York University in 1986 and then went on to medical school at the State University of New York in Syracuse. Meanwhile, he worked as a consultant to the Bronx Zoo, developing a radio telemetry system packed inside artificial eggs that could be used to monitor incubation among endangered birds.

"I thought I might enjoy medicine, but I didn't," he said. Though he started residency training as a radiologist at Duke University Medical Center in 1991, "it became clear I was destined for the lab."

He ended up earning his doctorate in biomedical engineering at the University of North Carolina three years ago and obtained a joint faculty appointment to Pitt and CMU.

The sonic flashlight "was just a silly idea I had one day" soon after his arrival in Pittsburgh. While listening to a presentation on a head-mounted augmented reality system, he realized that a similar effect could be achieved by viewing the patient through a partially silvered mirror.

If an ultrasound image of the same portion of the patient was projected on the mirror, he realized, the doctor could see both the patient and the image at the same time.

Two and a half years later, the latest version of the sonic flashlight is about a foot long, with a cylindrical ultrasound probe on one end and a 3-by-5 inch black-and-white ultrasound display on the other. In the middle, the rectangular, partial mirror juts up perpendicular to the sonic flashlight's body.

During a patent search, Stetten discovered his idea was one that Steven Hofstein of Princeton University had developed 20 years earlier.

Hofstein, who helped invent what is known as the field-effect transistor, had envisioned it as a way of viewing an ultrasound image for diagnostic purposes, not as a means of guiding medical instruments.

Hofstein's version was much larger than the sonic flashlight, which is small and light enough to be held in one hand. It is tethered to a computer but, with increasing miniaturization, ultrasound devices could soon be the size of a cell phone, noted Stetten, who has applied for a patent on his device.

Dr. Louis Lobes, a clinical associate professor of ophthalmology at Pitt, says the device might help eye surgeons when they anesthetize the eye before surgery. To anesthetize pain-sensing nerves at the back of the eye, doctors must slip a needle underneath the eyeball -- taking care not to puncture the eyeball or mistakenly inject the optic nerve, either of which could result in blindness.

Lobes has experimented with the device on a cadaver and found it let him to see the needle tip as he worked it around the eyeball. "It's easy since the same person is handling both the needle and the ultrasound," he said.

Dr. Juan C. Puyana, a UPMC trauma surgeon, noted that ultrasound already is routinely used by trauma surgeons to rapidly assess patients, determining, for instance, whether a patient has bleeding in the belly. But it takes awhile for any doctor to become proficient in using ultrasound. He suggested that the sonic flashlight, while still a bit crude for clinical use, could shorten the learning curve because of its intuitive design.

Stetten's work on the sonic flashlight thus far has been done with limited, start-up funding he received from Pitt and CMU when he arrived. Further development and clinical testing will require funding from outside sources, he said.

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