  A novel method to estimate the pixels simultaneous detection probability and
the spatial resolution of pixelized detectors is proposed, which is based on
the determination of the statistical correlations between detector neighbor
pixels. The correlations are determined by means of noise variance measurement
for a isolated pixels and the difference between neighbor pixels. The method is
validated using images from the two different GE Senographe 2000D mammographic
units. The pixelized detector has been irradiated using x-rays along its entire
surface. It is shown that the pixel simultaneous detection probabilities can be
estimated within accuracy 0.001 - 0.003, where the systematic error is
estimated to be smaller than 0.005. The presampled two-dimensional point-spread
function (PSF0) is determined using a single Gaussian and a sum of two Gaussian
approximations. The obtained results for the presampled PSF0 show that the
single Gaussian approximation is not appropriate, and the sum of two Gaussian
approximations providing the best fit predicts the existence of a large (~50%)
narrow component. Another proof of this fact is the latest simulation study of
columnar indirect digital detectors by A. Badano et al. The sampled
two-dimensional PSF is determined using Monte Carlo simulation for the L-shape
uniform distributed acceptance function for different values of fill factors.
The detector spatial resolution is estimated using sampled PSF and has values
54 and 58 mkm for two different units. The calculation of the presampled
modulation transfer function based on the PSF0 estimation shows that the
existing data can only be reproduced using a single Gaussian approximation and
the usage of the sum of two Gaussian show significantly larger values in the
higher frequency region for both units.
