DQE(f) of an amorphous-silicon flat-panel x-ray detector: detector parameter influences and measurement methodology

We discuss how the frequency dependent detective quantum efficiency [DQE(f)] in a well-designed amorphous silicon flat panel detector is affected by several phenomena that reduce the DQE in other types of medical imaging detectors. The detector examined employs a CsI(Tl) scintillator and is designed for general diagnostic x-ray imaging applications. We consider DQE degradation due to incomplete x-ray absorption, secondary quantum noise, Swank factor, Lubberts effect, spatial variation in gain, noise aliasing, and additive system noise. The influences of detector design parameters on the frequency- and exposure-dependent DQE are also examined. We find that the DQE does not depend directly on MTF and that DQE is independent of exposure within the detector's operating range, except at the lowest exposures. Likewise the signal per absorbed x-ray, which contains the fill factor as one of several multiplicative components, does not affect DQE except at the lowest exposures. A methodology for determining DQE(f) from measurements of MTF(f), noise power spectrum (NPS), average signal, and x-ray exposure is presented. We find that it is important to incorporate several corrections in the NPS measurement procedure in order to obtain accurate results. These include corrections for lag, non-linearity, response variation from pixel to pixel, and use of a finite number of flat-field images. MTF, NPS, and DQE results are presented for a 41 X 41-cm2 flat panel detector designed for radiographic applications.

[1]  W. Hillen,et al.  Imaging performance of a digital storage phosphor system. , 1987, Medical physics.

[2]  R. K. Swank.  Absorption and noise in x‐ray phosphors , 1973 .

[3]  G. Lubberts,et al.  Random Noise Produced by X-Ray Fluorescent Screens* , 1968 .

[4]  M J Yaffe,et al.  Effect of various noise sources on the detective quantum efficiency of phosphor screens. , 1990, Medical physics.

[5]  J A Rowlands,et al.  Digital radiology using active matrix readout of amorphous selenium: theoretical analysis of detective quantum efficiency. , 1997, Medical physics.

[6]  H. Blume,et al.  DQE(f) of four generations of computed radiography acquisition devices. , 1995, Medical physics.

[7]  Tao-Yi. Fu.  INFORMATION TRANSFER EFFICIENCY OF X-RAY IMAGE INTENSIFIER-BASED IMAGING SYSTEMS. , 1984 .

[8]  Thierry Ducourant,et al.  New CsI/a-Si 17" x 17" x-ray flat-panel detector provides superior detectivity and immediate direct digital output for general radiography systems , 1998, Medical Imaging.

[9]  E. Samei,et al.  A method for measuring the presampled MTF of digital radiographic systems using an edge test device. , 1998, Medical physics.

[10]  K Stierstorfer,et al.  Self-normalizing method to measure the detective quantum efficiency of a wide range of x-ray detectors. , 1999, Medical physics.

[11]  R Van Metter,et al.  Objective performance characteristics of a new asymmetric screen-film system. , 1994, Medical physics.

[12]  Paul R. Granfors.  Performance characteristics of an amorphous silicon flat-panel x-ray imaging detector , 1999, Medical Imaging.

[13]  A Fenster,et al.  A spatial-frequency dependent quantum accounting diagram and detective quantum efficiency model of signal and noise propagation in cascaded imaging systems. , 1994, Medical physics.

[14]  J A Rowlands,et al.  Measurement of the spatial Wiener spectrum of nonstorage imaging devices. , 1988, Medical physics.

[15]  Brian G. Rodricks,et al.  Improved imaging performance of a 14"x17" direct radiography system using a Se/TFT detector , 1998, Medical Imaging.

[16]  J Yorkston,et al.  Signal, noise power spectrum, and detective quantum efficiency of indirect-detection flat-panel imagers for diagnostic radiology. , 1998, Medical physics.

[17]  P. Granfors,et al.  Performance of a 41X41-cm2 amorphous silicon flat panel x-ray detector for radiographic imaging applications. , 2000, Medical physics.

[18]  Arnold R. Cowen,et al.  A physical image quality evaluation of a digital spot fluorography system , 1992 .

[19]  M J Yaffe,et al.  Effect of finite phosphor thickness on detective quantum efficiency. , 1989, Medical physics.

[20]  Ian A. Cunningham.  Degradation of the detective quantum efficiency due to a nonunity detector fill factor , 1997, Medical Imaging.

[21]  R. F. Wagner,et al.  Absolute measures of physical image quality: measurement and application to radiographic magnification. , 1982, Medical physics.