Shinichi Ohta

Development and evaluation of a portable amorphous silicon flat-panel x-ray detector

ABSTRACT The design, development and evaluation of a portable x-ray detector are described. The completed detector has a pixelpitch of 100 2m, an active imaging area of 22.5 x 27.5cm 2 (9x11inch), package outer dimensions of 32.5 x 32.5cm 2 (13x13inch 2 ), a thickness of only 20mm, and a weight of around 2.8kg. A number of significant advances in the designand production processes were needed to produce such a compact detector with such a small pixel pitch, while maintainingthe image qualityachieved a current detector (CXDI-22) which has a 160 m pixel pitch. These include the developmentof a low power readout IC, advances in detector packaging design, concentrating on lightweight and strong components,and redesign of the pixel structure to improve the fill-factor.Acomparison is made of the imaging characteristics of this new detector with the CXDI-22 detector, and it is shown thatthe new detector demonstrates improved spatial resolution (CTF), and noise equivalent quanta (NEQ) particularly athigher spatial frequencies. The new detector is also shown to demonstrate superior performance in a contrast-detailphantom evaluation.This newdetector should be particularlyuseful for limb and joint examinations as it offers high spatial resolution,combined with the same freedom in positioning provided byconventional screen-film cassettes.Keywords: x-raydetector, portable detector, digital radiography, amorphous silicon (a-Si:H), thin film transistor (TFT)