Dental x-rays go digital

January 20, 1994

By Diane LaMacchia,

After a search through the file room, the dental technician appears with last year's x rays in hand. The dentist says it's time for more x rays. "Open wider," says the technician. "Now bite down." Fingers out of your mouth just in time, the dental technician points an x-ray tube at your jaw, stands behind a lead wall, and turns on the machine. A trip down the hall to the developing tank, a few minutes of processing, and the new x rays are ready for scrutiny.

This familiar scenario will soon be a memory, thanks to the emergence of digital radiography and the electronic readout device. Patients will still have to "open wide" and "bite down," but in place of dental film they will be closing their mouths around electronic sensors.

To develop the new technology, LBL has recently signed a Cooperative Research and Development Agreement (CRADA) with a Hicksville, NY, company called Air Techniques Inc.--the nation's largest supplier of automatic dental film processors.

With the new technology, instead of the trip to the developing tank, dentist and patient will watch images come up on a computer screen seconds after the device is inserted into the patient's mouth. The images will be higher resolution than film images and will be stored in computer memory, from which they can be easily retrieved, combined, and manipulated to supply more information. The chemical waste associated with film processing will be eliminated. Most significantly, patients will be exposed to one tenth the x-ray dosage typically delivered today.

The conventional way to x-ray teeth is with a piece of thick film that is moderately sensitive to x rays. To increase its efficiency and lower the required dosage of x-rays, the film can be sandwiched between sheets of plastic called intensifying screens. The disadvantage of using the screens is that they scatter radiation, resulting in decreased spatial resolution and accuracy.

Soon to be manufactured by Air Techniques, the alternative electronic technology developed at LBL by physicists Victor Perez-Mendez, John Drewery, and graduate student Tao Jing involves a light-emitting material, or scintillator. It differs from other dental digital radiographic devices that have recently come on the market in that it provides a better spatial resolution for a given sensitivity to x rays.

To make the x-ray-sensitive material, the LBL researchers use vacuum evaporation, a technique in which the scintillator cesium iodide is deposited on raised disks, or pucks, dotting the surface of a piece of high-temperature plastic. In the process of evaporation, the cesium iodide forms columns on the plastic pucks. When x-rays hit these columns, the material emits light (scintillation) which is partially lined up (collimated); sideways spreading is minimized for better resolution and accuracy.

"The net result is that our x-ray-detecting devices are more efficient and more accurate than the commercial Kodak film combination," says Perez-Mendez.

LBL and Air Techniques have signed a one-year, $100,000 CRADA to develop the scintillator for the electronic dental readout device. Air Techniques researchers Claude Goodman and Daniel Wildermuth are currently working at LBL to refine the scintillator manufacturing process. A prototype device is
expected to be ready within the year.

Perez-Mendez, who is also a professor of radiology at UC San Francisco, says the next step in the development of the technology will be to make larger digital devices for mammography or heart imaging.

"The ultimate aim," he says, "is to avoid the use of film for medical x-ray imaging. We're starting small, making devices like this for dental radiography, because the electronics are easier to make."

Eventually, he says, standard 11x14-inch radiology film and developing tanks will be replaced by electronic detectors, high definition display screens, and computer-stored data. These technologies will simplify procedures in a hospital's radiology department, and patients will be exposed to much lower doses of radiation.