Performance of a 41×41‐cm amorphous silicon flat panel x‐ray detector for radiographic imaging applications

Abstract

We report the performance of a 41 X 41-cm2 amorphous silicon-based flat panel detector designed for radiographic imaging applications. The detector consists of an array of photodiodes and thin film transistor switches on a 0.2-mm pitch with an overlying thallium-doped cesium iodide scintillator. The performance of the detector was evaluated through measurement of the frequency-dependent detective quantum efficiency [DQE(f)]. Measurements of the characteristic curve and modulation transfer function (MTF) are also reported. All measurements were made in a radiographic imaging mode with a readout time of 125 ms. We evaluated a total of 15 detectors. One detector was characterized at a range of exposures and at three different electronic gain settings. Measurements of DQE(f) and MTF were also performed as a function of position on one detector. The measured DQE at an exposure of about 1 mR was 0.66 at zero spatial frequency and fell smoothly with frequency to a value of 0.24 at the Nyquist frequency, 2.5 cycles/mm. The DQE is independent of exposure for exposures in the upper 80% of each gain range, but is reduced somewhat at lower exposures because of the influence of additive system noise. The reduction can be controlled by adjusting the electronic gain. For a gain that allows a maximum exposure of 5 mR, the DQE at 0.056 mR was 0.64 at zero frequency and 0.19 at 2.5 cycles/mm. The standard deviation in DQE among measurements on different detectors was less than 0.02 at any frequency. The presampling MTF was 0.26 at 2.5 cycles/mm. The standard deviation in MTF among measurements on different detectors was less than 0.01 at any frequency. Both MTF and DQE were substantially independent of position on the detector.

An evaluation of the stability of image quality parameters of Elekta X‐ray volume imager and iViewGT imaging systems

“…This arm allows the detector to be positioned at source to electronic portal imaging device (EPID) distance of 160 cm with an active imaging area of 41 × 41 cm 9. The image matrix is created from an array of 1024 × 1024 photodiodes with a pitch of 400 μm 10. While the EPID can be operated in various acquisition modes, a single exposure, 6 MV planar radiographic mode was used in this study.…”

Estimation of the two‐dimensional presampled modulation transfer function of digital radiography devices using one‐dimensional test objects

“…Other detector properties have been described extensively in the literature. 6,16 A standard MX 100 x-ray tube insert and housing (GE Healthcare, Waukesha, WI) were used with an ULTRANET SA beam collimator (Medys, Monza, Italy). The system source to image distance (SID) was 186 cm.…”

“…4,5 Examples from digital radiography have also shown that 2D undersampling and aliasing effects are important to consider, especially in calculations of noise equivalent quanta (NEQ) and detective quantum efficiency (DQE). [6][7][8] Complete assessments of the 2D NEQ and DQE are valuable in assessments of observer task performance since image interpretation is an inherently 2D task. 5 And although the 2D noise power spectrum (NPS) is easily measured, regular evaluations of the full 2D NEQ and DQE have been difficult due to various challenges in obtaining accurate estimates of the 2D MTF.…”

Dual-Energy Digital Mammography with a Full-Field aSi/CsI Flat-Panel Imager

“…Studies [15][16][17][18][19][20][21][22][23][24] have shown that FP detectors developed for use in general radiography have a significantly higher detective quantum efficiency (DQE) than both SF and CR systems. This higher DQE may lead to a better low contrast performance that should be evaluated and investigated with reception studies.…”