Cambridge, MA-- Getting useful sound amplification from a hearing aid depends on a tight fit between hearing aid and ear canal, but the current method of modeling patients’ ears is messy and not always accurate, potentially leading to a device that fits poorly and offers little benefit.
“A lot of people with hearing aids are likely walking around with hearing aids that don’t fit, because they don’t know what they’re supposed to feel like,” says Douglas Hart, MIT professor of mechanical engineering.
Hart has patented a new way of scanning the ear canal with 3D imaging technology — a process that is much faster, easier, and more accurate than the plaster-mold technique. He plans to market the technology to hearing-aid manufacturers first, but believes it could also be useful to build fitted earphones for MP3 music players, or custom-fit earplugs for military personnel and other people who work in noisy environments.
The new technology is similar to a recently commercialized 3D scanning system that Hart developed for dentistry, designed to replace the silicone molds traditionally used to make impressions for dental crowns and bridges. While Hart was working on that imaging system, hearing-aid manufacturers approached him to see what he could do to improve their fitting process.
With the new MIT system, a very stretchy, balloon-like membrane is inserted into the ear canal and inflated to take the shape of the canal. The membrane is filled with a fluorescent dye that can be imaged with a tiny fiber-optic camera inside the balloon. Scanning the canal takes only a few seconds, and the entire fitting process takes only a minute or two.
Because the camera captures 3D images so quickly, it can measure how much the surface of the ear canal deforms when the pressure changes, or how the canal shape changes when the wearer chews or talks. That could help hearing-aid manufacturers design devices that keep their tight seal in those situations.
The higher accuracy of digital scans could also eliminate the need for repeated impressions.
The Deshpande Center for Technological Innovation funded the development of the new technology, which Hart described in a 2004 article in the journal Applied Optics. He patented the system in January and has founded a company in the hope of bringing the innovation to market.
The researchers have built a prototype scanner to demonstrate the proof of concept, and are now working on a handheld version of the device. Once it’s ready, they plan to do a study comparing the fit of hearing aids built with the new scanner to that of traditional hearing aids.