IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 53, NO. 6, DECEMBER 2004 1479 Detective Quantum Efficiency [DQE(0)] of CZT Semiconductor Detectors for Digital Radiography G. C. Giakos, S. Suryanarayanan, R. Guntupalli, J. Odogba, N. Shah, S. Vedantham, S. Chowdhury, K. Mehta, S. Sumrain, N. Patnekar, A. Moholkar, V. Kumar, and R. E. Endorf Abstract—In this paper, the detective quantum efficiency (DQE) of cadmium zinc telluride (CZT) detector samples for digital radi- ography has been measured. Specifically, this study is aimed at in- vestigating the zero-frequency DQE(0) under different X-ray tube and detector parameters. The experimental results of this study in- dicate that the DQE(0) of the CZT samples is strongly dependent upon the irradiation geometry. This is attributed to the incomplete charge collection process, which can be further improved by con- trolling the purity of the samples and the contact type. Index Terms—Detective quantum efficiency, digital radiog- raphy, semiconductor detectors. I. INTRODUCTION F LAT-PANELimage sensor arrays are being developed for medical imaging applications [1]–[5], [7]–[12], [17]–[32]. These systems are comprised of large-area pixel arrays that use matrix addressing to read out charges resulting from X-ray ab- sorption in the detector medium. There are two methods for making flat panel image sensors. In the indirect method [1], [9], [10], a phosphor converter absorbs the incident X-rays and emits visible light, which is converted by an a-Si:H p-i-n photodiode into an electronic image. This process is inefficient and can lead to increased image noise, particularly when signals are low. The direct method [2], [17]–[32] uses a photoconductive layer to absorb X-rays and collect the ionization charge which is sub- sequently read out by an active matrix array. The direct method has a higher intrinsic resolution compared to the indirect method because it avoids the X-ray to light conversion stage. The primary advantages of photoconductors for good quality imaging include efficient radiation absorption, large band gap energy which limits the thermal generation of charge carriers in the bulk, good linearity, good charge transport properties, high stability, high sensitivity, and wide dynamic range. Lead Manuscript received June 15, 2003; revised June 15, 2004. G. C. Giakos and S. Sumrain, are with the Imaging Systems, Detectors and Sensors Laboratory, Department of Electrical and Computer Engi- neering, The University of Akron, Akron, OH 44325-3904 USA (e-mail: giakos@uakron.edu). S. Suryanarayanan, R. Guntupalli, J. Odogba, N. Shah, S. Vedantham, S. Chowdhury, K. Mehta, N. Patnekar, and A. Moholkar are with the De- partment of Biomedical Engineering, The University of Akron, Akron, OH 44325-0302 USA. V. Kumar is with the Imaging Systems, Detectors and Sensors Laboratory, Department of Electrical and Computer Engineering, Department of Electrical and Computer Engineering, The University of Akron, and the Division of Engi- neering and Applied Mathematics, The University of Akron, Akron, OH 44325- 0302 USA. R. E. Endorf is with the Department of Physics, University of Cincinnati, Cincinnati, OH 45221 USA. Digital Object Identifier 10.1109/TIM.2004.834590 Fig. 1. Quantum efficiency of CZT detectors at different detector thicknesses. Fig. 2. Experimental X-ray irradiation geometries. iodide PbI , cadmium zinc telluride (CZT), and amorphous selenium (a-Se) are good candidates. Significant progress has been achieved in the growth of high-quality CZT semi- conductor crystals using the high-pressure Bridgman (HPB). Specifically, by alloying CdTe with Zn, the bulk resistivity of the resulting semiconductor becomes approximately -cm [13] and[14]. 0018-9456/04$20.00 © 2004 IEEE