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A novel method, based on X-ray Light Valve (XLV) technology, is proposed for making good image quality yet
inexpensive flat panel detectors for digital mammography. The digital mammography markets, particularly in the
developing countries, demand quality machines at substantially lower prices than the ones available today. Continuous
pressure is applied on x-ray detectors' manufacturers to reduce the flat panel detectors’ prices. XLV presents a unique
opportunity to achieve the needed price - performance characteristics for direct conversion, x-ray detectors. The XLV
based detectors combine the proven, superior, spatial resolution of a-Se with the simplicity and low cost of liquid
crystals and optical scanning. The x-ray quanta absorbed by a 200 μm a-Se produce electron - hole pairs that move
under an electric field to the top and bottom of a-Se layer. This 2D charge distribution creates at the interface with the
liquid crystals a continuous (analog) charge image corresponding to the impinging radiation's information. Under the
influence of local electrical charges next to them, the liquid crystals twist proportionally to the charges and vary their
light reflectivity. A scanning light source illuminates the liquid crystals while an associated, pixilated photo-detector,
having a 42 μm pixel size, captures the light reflected by the liquid crystals and converts it in16 bit words that are
transmitted to the machine for image processing and display.
The paper will describe a novel XLV, 25 cm x 30 cm, flat panel detector structure and its underlying physics as well as
its preliminary performance measured on several engineering prototypes. In particular, the paper will present the results
of measuring XLV detectors' DQE, MTF, dynamic range, low contrast resolution and dynamic behavior. Finally, the
paper will introduce the new, low cost, XLV detector based, digital mammography machine under development at XLV
Diagnostics Inc.
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