February 2, 1998

4 Min Read
Body scanners give prostheses perfect fit

Boca Raton, FL--Greg Pratt was working for several years to bring CAD solutions to the prosthetics and orthotics industry without finding an acceptable way for practitioners to use digital technology. For starters, the basic plaster-molding methods they use hadn't changed in decades. A labor and time intensive, as well as somewhat messy process, it involves making a plaster wrap of a patient's residual limb. A positive is then made, which is hand-carved by a prosthetist to ensure proper fit, which is necessary to distribute weight-bearing loads and relieve sensitive areas from pressure. From this model the final device is manufactured.

While this effort takes only a few hours, it is spread over several days. Given the long cycle time, a patient may not be readily available for the critical hand-shaping stage. The advent of CAD helped somewhat since a limb shape could be digitized via a mechanical arm, but the plaster wrap was still necessary. A cast was also required for scanning into optical-based systems. And few medical practitioners had the computer skills to fully exploit the technology.

Pratt founded Tracer Corporation in 1995 to develop an easy-to-use system that would eliminate the physical and time constraints, and be portable, hand-held, and plaster free. He considered various optical and electromagnetic technologies for an accurate shape-capture system to determine surface-point positions and angles in what would become TracerCAD(TM). "Optical systems quickly fell out of the running," says Pratt, "because prosthetists need to move around the patient. At some point, any lens would be blocked. And multiple cameras would require precise camera positioning, and the idea is to reduce effort and set up time." He chose the FASTRAK(reg) electromagnetic position/orientation technology from Polhemus (Colchester, VT) as giving the greatest accuracy.

With TracerCAD, the prosthetist uses a 3 1/2-inch long "pen" that contains the FASTRAK receiver. With the intuitive hand skills learned over years of practice in shaping plaster models, he or she measures the patient's residual limb directly, obviating the need for a plaster cast. But next comes an added benefit: the practitioner can perform hands-on limb compressions and observe the effects in a real-time, 3-D computer image with the patient available for input. "Not only is the anatomy in hand," adds Pratt, "but the patient knows the limb best and can tell the prosthetist when discomfort may occur during compression, etc." Jeff Peterman, of Lubbock Orthotics and Prosthetics (Lubbock, TX) says, "TracerCAD allows me to continue using my existing hand skills when working with the patient. I don't have to learn new skills in order to take full advantage of a CAD system."

The compact system, including transmitter, pen, and laptop computer, fits inside "a little black bag" for set up within a couple of minutes. The measuring process usually takes under 10 minutes, and the prosthesis model data can be relayed via the Internet directly to a fabricator.

Learning ease is another key. Pratt notes, "Prosthetists are tactile, used to working with their hands to shape plaster to the intimate contours of a patient. Rather than needing to learn CAD, prosthetists teach the computer by using the pen in 3-D space and their hands. They forget the computer is attached." This is done with a single-button on the pen that walks the computer through a procedure macro. The practitioner selects a desired sequence from a set previously entered into the computer using the pen while going through sample procedures. "Our philosophy is to continually improve the system," concludes Pratt, "so software updates are available on our website."

Seeing the light. While electromagnetic contour measuring may be ideal for prosthesis fabrication, whole-body imaging of a person within a special enclosure can be done optically. One system using laser scanning by Cyberware (Monterey, CA) was developed for the US Air Force Computerized Anthropometric Research and Design Lab at Armstrong Laboratories (Wright-Patterson AFB, OH). Within 17 seconds, a laser projects a stripe of light across a subject which is viewed by cameras for a 3-D digitized image.

The Air Force is using whole-body scanner data to improve the fit of anti-G suits, uniforms, and other equipment such as oxygen masks. Studies of range-of-human-motion with the device will revise the switch and controls layout of cockpits and crew stations. And human body models used in various aspects of aircraft design will be "fleshed out." The scanner also provides a non-contact way of monitoring wound healing and improving the fit of masks for burn victims. The masks help to support the tissue and prevent scarring.

Civilian uses of the laser scanner include animation studies and the garment industry, where customer body profiles might be scanned and used to mass produce custom-tailored clothes. However, with a current price tag of $410,000 don't expect to walk into Frugal Fannie's next week for a fitting. Instead, an LED-based scanner under development in Japan may pioneer low-cost made-to-order clothing. Such scanners would give a unique body-profile data set, enabling customers to mail order correct-size clothing the first time. Mail-order returns are a major inconvenience, occuring in about one third of such sales.

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