Xerox PARC spins off new companyto market x-ray digitization sensors

DpiX arrays can be used for display and acquisition

Add another entrant to the race to digitize conventional x-rayexams. Technology R&D lab Xerox PARC (Palo Alto Research Center)announced March 11 that it has spun off a new company, dpiX, tocommercialize a thin-film transistor (TFT) array technology thatcan be used both for digitizing x-ray studies and for viewingimages.

X-ray digitization gained increased attention at last year'sRadiological Society of North America meeting. Du Pont debutedits direct radiography method for digitizing x-ray exams, whileSwissray chimed in with Add-On Bucky, and Trex Medical said itwould adapt its full-breast digital technology to basic x-ray(SCAN 12/13/95). These firms and others are angling for a shareof the 200,000 conventional x-ray systems around the world thatmust receive digital retrofits in order to be included in digitalimage management networks.

In forming dpiX, Xerox PARC plans to take a slightly differentapproach from the other vendors. Rather than market an x-ray digitizationdevice directly to end users, dpiX hopes to provide its digitizationsensors to medical imaging vendors for inclusion in their x-raysystems, according to Jean-Pierre Georges, a former Fischer Imagingand GE Medical Systems executive hired Jan. 1 as general managerof dpiX's image sensor products group.

Xerox PARC's technology uses thin-film transistors to createactive-matrix liquid crystal display (AMLCD) arrays. Xerox PARCbegan work on the technology 15 years ago and has received severalcontracts from the U.S. government's Advanced Research ProjectsAgency to fund development.

Military avionics and medical imaging are the two initial marketsdpiX has identified for its technology, due to their requirementsfor high-resolution image quality. Last year, Xerox PARC begandistributing toolkits that included the arrays to medical imagingvendors to allow them to evaluate the technology (SCAN 8/2/95).

At its most basic level, a dpiX array consists of a glass substrateon which is deposited a layer of amorphous silicon, a semiconductormaterial that acts as a thin-film transistor switching element.From there, the arrays are customized for either image displayor image sensor applications. Image sensor arrays contain a phosphor-basedx-ray conversion layer that converts x-rays into light. The lightis then converted into electrons by millions of photodiodes implantedin the array, and these electrons are transformed into digitaldata by analog-to-digital converters. The array is self-scanningand does not need to be taken to a readout device, Georges said.

For image display panels, the photodiodes are replaced by electrodes,with an electrode for each pixel. Data input into the array isconverted into images, using liquid crystal display technology,with each array including a backlight, polarizers, and filtersto display the images.

The image sensors for medical imaging applications are closestto commercialization. DpiX believes that the sensors could beused to replace bulky image intensifiers and film cassettes onx-ray systems.

"The industry has used image intensifiers and video camerasto go into digital imaging, but that has never replaced film totallybecause the image quality is still lower than film," Georgessaid. "With these kinds of panels you will have the videorate capability as well as image quality that you can expect bytaking a single shot or record as a film."

The sensors have a pixel size of 127 microns, or about 4 linepairs/mm, which is within the acceptable range for conventionalradiography. DpiX will have to improve that resolution to the50 to 80-micron range for high-resolution applications such asfull-view digital mammography, he said.

DpiX is shipping sensors to potential OEM partners for inclusionin their devices. The company expects to see prototype x-ray systemsusing the sensors by 1997. The sensors are also appropriate asa retrofit for existing systems in the field, Georges said.

Seven-million-pixel displays. Equally intriguing but furtherfrom market for medical imaging applications are dpiX's flat-paneldisplays. The displays, which would replace conventional cathode-raytube (CRT) monitors, are capable of displaying nearly 7 millionpixels of information in a 3072 x 2240 matrix, according to KathyMiddo, general manager for the display products group.

DpiX believes that it may need to improve the gray-scale depthof the displays before they can be used clinically, however. Itshigh-resolution displays under development have 3 to 4 bits ofgray scale, compared to 8 bits for CRT-based monitors. The highresolution of the displays may offset this disadvantage, however.DpiX will launch its first displays for the military avionicsmarket later this year.

The formation of dpiX is part of Xerox's new enterprise familyof companies, an initiative started last year to create start-upbusinesses to commercialize Xerox technologies. Xerox PARC hasa reputation for developing cutting-edge technologies, such asthe first graphical user interface for personal computers, andlaser printer technology. On several occasions, however, its inventionshave been perfected and commercialized by other companies.

DpiX will be wholly owned by Xerox and will be based next toXerox PARC's headquarters in Palo Alto, CA. Xerox PARC chief technologistMalcolm Thompson has been named CEO of dpiX, which has about 100employees.

The philosophy behind dpiX's formation is to create an entrepreneurialfirm that has the backing of a $16 billion industrial giant, accordingto Middo.

"Xerox has put us in an environment where we can be faston our feet and respond rapidly to market changes and customerdemands," Middo said. "It's the best of both worlds."