Experimental Evaluation of a-Se Flat-Panel X-ray Detector for Digital Radiography
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Experimental evaluation of a-Se flat-panel X-ray detector for digital radiography Jang-Yong Choi , Ji-Koon Park, Dong-Gil Lee, Sang-Sik Kang, Sang-Hee Nam* Department of Biomedical Engineering, College of Biomedical Science and Engineering Inje University, Kimhae, Kyungnam, 621-749, Korea Medical Imaging Research Center * Inje University, Kimhae, Kyungnam, 621-749, Korea
ABSTRACT Nowadays, large area, flat panel solid state detectors are being investigated for digital radiography. In this paper, development and evaluation of a selenium-based flat-panel digital xray detector are described. The prototype detector has a pixel pitch of 139 and a total active imaging area of 7″× 8.5″, giving a total of 1.9 million pixel. This detector include a x-ray imaging layer of amorphous selenium as a photoconductor which is evaporated in vacuum state on a TFT flat panel, to make signals in proportion to incident x-ray. The film thickness was about 500. To evaluate the imaging performance of the digital radiography (DR) system developed in our group, sensitivity, linearity of the response of exposure, the modulation transfer function(MTF) and detective quantum efficiency(DQE) of detector was measured. The measured sensitivity was 4.16×106 ehp/pixelmR at the bias field of 10 V/ : The beam condition was 41.9 KeV. Measured MTF at 2.5 lp/mm was 52%, and the DQE at 1.5 lp/mm was 75%. 1. Introduction Film/screen has been used to acquire the conventional radiographic examinations by capturing the pattern of x-rays transmitted through a patient. Recently, however, active matrix flat-panel imagers are beginning to replace the sheets of film.[1,2] These detectors use either the indirect or the direct method to detect x-ray. Indirect detectors convert x-rays to visible light at the scintillating layer. And then this visible light is again converted to electric signal in photodiode. After that, the electrical signal is acquired by the readout component of the imaging system. On the other hand, a direct detector directly converts x-rays to electric charges within a photoconductive layer.[3,4] Amorphous selenium (a-Se) usually has been used for this photoconductive material. The demand for DR systems is increasing because it is expected to solve some problems of analog radiographic systems such as the exhaustion of storage space, film management, and environmental pollution. A direct a-Se based flat panel x-ray detector has been developed for the first time in Korea. The quantitative assessment of image quality of this x-ray detector is an important consideration in any type of imaging system. Several quantitative
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parameters have been devised that correlate with the abilities of imaging devices to perform clinical asks.[5,6] The concepts of modulation transfer function (
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