Mammography add-on captures 'lost' x-ray data

Experimental device records scatter data

Specialty x-ray source manufacturer X-Tek is working with researchers from University College London in the U.K. to boost the quantity and quality of diagnostic data obtained from breast imaging exams. The collaboration has focused on the development of a system that not only records radiation passing straight through the breast, as with conventional mammography, but also captures scattered x-rays. This additional information could make it easier to detect tumors, which scatter x-rays in certain characteristic ways.

"The diffracted signal is there all the time in the conventional mammographic system, but you can't record it," said project leader Robert Speller, Ph.D., a professor of medical physics at University College London. "We're trying to design a system that allows you to record both, so there will be no additional dose to the patient. You would simply superimpose the diffraction image on top of the transmission image."

The approach, known as Diffraction Enhanced Breast Imaging (DEBI), uses a setup similar to conventional mammography but adds two x-ray detectors positioned at 9 degrees from the line of the main x-ray beam. Tumor cells, unlike healthy tissue, scatter the x-rays at this particular angle, according to Speller.

A CCD camera records high-spatial-resolution information from the scattered x-rays, while a silicon pad array designed in-house captures high-sensitivity, low-resolution data. Radiation passing straight through the breast tissue is magnified by a factor of four, to maintain high spatial resolution, and is then recorded on a flat-panel digital detector.

Dr. Daniel Kopans, director of breast imaging at Massachusetts General Hospital, agrees that approaches using scattered radiation have significant potential for improving breast cancer detection. Kopans has experimented with the method, but he contends that constructing a viable system suitable for patient exams could be difficult.

Key to the DEBI system is an especially intense x-ray source, generating high power from a tightly focused point. This ensures that data from both components of the dual imaging system are diagnostically useful, but without lengthening exam time.

"Most x-ray tubes are sealed vacuum tubes, and because they can't be opened or repaired, they are very conservatively designed. That limits the maximum power and maximum source brightness," said Ian Haig, X-Tek's technical director. "It also means that you can't magnetically focus the electron beam very easily."

The source supplied by X-Tek, however, has its own vacuum pump attached, providing easy access to the internal components. This allows inclusion of a magnetic lens to tightly focus the electron beam onto its molybdenum target. The resulting x-ray stream is sufficiently intense to provide diagnostic information from both transmission through and scattering by breast tissue.

The UCL team has tested the device on biopsied tissue samples implanted into full-sized breast phantoms. Initial results suggest the technique would pick up tumors with diameters as small as 4 mm, improving the likelihood of detecting and, ultimately, excising a cancer before it produced secondary tumors.

Speller is hopeful that a small and innovative mammography company might now recognize the system's potential and help take the technology forward into clinical trials. Such trials would be aimed at proving that detecting tumors as small as 4 mm in diameter provides an improved clinical outcome for the patient, particularly considering the added difficulty in building such devices for mainstream use. Kopans noted that half or more of the cancers now found with conventional x-ray mammography are less than 10 mm in diameter.