The x-ray sensitivity of amorphous selenium for mammography.
A study of the x-ray sensitivity of amorphous selenium (a-Se) for digital mammography has been performed. A uniform layer of a-Se was deposited on a glass substrate with electrodes on both surfaces. The deposition procedure was identical to that used for a-Se flat-panel detectors. A high voltage was applied to the top surface of the a-Se layer in order to establish an electric field E(Se). Then the sample was exposed to x rays with 27 kVp spectra generated from an x-ray tube with a molybdenum (Mo) target. The mean x-ray energy of the spectrum used was approximately 16.6 keV. The x-ray current generated by the a-Se layer was measured as a function of E(Se). From the current measurement and the estimation of total x-ray energy absorbed in the a-Se, the energy required to create one electron-hole pair (EHP), W, was determined as a function of E(Se). It was found that at the most commonly used E(Se) of 10 V/microm, W was measured as 64 eV. This is considerably higher than the widely accepted typical value of W = 50 eV measured at higher x-ray photon energies (e.g., 50 keV). The dependence of W as a function of E(Se) can be best fitted using the empirical expression of E(Se)-gamma. This relationship is consistent with the results obtained at higher x-ray energies. This article provides an accurate measurement of x-ray sensitivity of a-Se at mammographic energies independent of detector operation, such as the most recently developed flat-panel detectors. The results will be a useful tool for investigation and optimization of a-Se-based x-ray imaging detectors, such as determination of pixel fill-factor and optimal E(Se) during operation.
Stone
Mary F
MF
Department of Physics and Astronomy, State University of New York at Stony Brook, 11794-3800, USA.
Zhao
Wei
W
Jacak
Barbara V
BV
O'Connor
Paul
P
Yu
Bo
B
Rehak
Pavel
P
D004583:Electrons; D005260:Female; D005898:Glass; D006801:Humans; D008327:Mammography / Q000379:methods*; D017785:Photons; D012643:Selenium; D012680:Sensitivity and Specificity; D013997:Time Factors; D014965:X-Rays
D012643:Selenium