New stitching algorithm contributes to Sensor Plus digital mammography

Firm seeks low-cost solution for large-format imaging

As full-field digital mammography vendors continue their slow progress toward Food and Drug Administration clearance, a new company has appeared on the horizon with a unique approach to digital mammography. Amherst, NY-based Sensor Plus and its Mosaic Imaging Research Group (MIRG) are developing digital x-ray technology for mammography applications that employs a new method for tiling together digital data into a single full-field image.

Sensor Plus is developing full-field digital detectors based on charge-coupled device (CCD) technology, which is also being used in digital mammography detectors under development by companies like Fischer Imaging of Denver and Trex Medical of Danbury, CT. But Sensor Plus hopes to develop a digital mammography detector that will occupy a lower price point than the more well-known systems approaching the market and thus be more appropriate for markets such as rural hospitals and developing countries.

Sensor Plus is developing two products: a spot imager with a three-by-three array of CCDs and a larger sensor with a six-by-six configuration. CCDs are arrayed along an electronic board with lenses mounted above them and placed close enough together that their imaging areas overlap, eliminating data loss. After running the collected information through lens distortion correction and image reconstruction algorithms, the system employs image processing algorithms to crop the images and tile them together.

One of the key differences between Sensor Plus’ digital x-ray technology and other companies’ overlapping techniques is the method Sensor Plus uses to have its detectors stitch digital data together. The company calls its technique mosaic imaging, according to Dr. Darold Wobschall, company founder and vice president of technology.

“When (other companies) take an overlap, they do the best possible matching with some software technique or another, but they basically keep the average of the two images,” Wobschall said. “We cut the image after we correct it, so we have one or the other image, rather than an averaged image.”

Wobschall is a professor at State University of New York, Buffalo. He established Sensor Plus in 1990. The private company has gained most of its support from government contracts for the development of various sensors, including a digital power transducer and the work-in-progress digital mammography detector. The company’s mammography work is being conducted under contract with the Department of Defense’s Breast Cancer Research Center.

In addition to using CCDs instead of flat-panel detectors, the firm chose to use lenses in its device to control costs, since lenses are less expensive than the fiber-optics usually used with CCDs. The Sensor Plus detectors also employ a CCD manufacturing process based on complementary metal-oxide semiconductors (CMOS), which results in cheaper CCDs.

“We felt there was a need for an intermediate type of technology that will break the image up into segments and individually image them. Then you can use off-the-shelf components; for example, the CCDs,” Wobschall said. “We’re now using CMOS-type CCDs, which are similar to what goes into some digital cameras. Because they’re manufactured in high volume, the cost is quite low.”

Wobschall acknowledges the particular difficulty of using lenses, which are less efficient than fiber-optics in capturing light. The company’s biggest difficulty is refining the sensitivity of the detectors so that the total amount of x-ray exposure will be comparable to film imagers, he said.

Sensor Plus plans to position its full-field digital mammography detectors as low-cost alternatives to more expensive OEM products. The company is negotiating a partnership with InfiMed of Liverpool, NY, for the development of a workstation that could be used for image display and processing. The company would like to sell its detectors to an OEM that would integrate them into complete mammography systems and also handle sales and marketing of the products.

Sensor Plus expects the nine-CCD detector to list at about $10,000 to $14,000, and the 36-CCD imager at approximately $30,000 to $40,000. The company is exploring other uses for the devices as well, such as portable x-ray imaging for trauma applications.