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Technical note: further development of a resolution modification routine for the simulation of the modulation
Anastasios C Konstantinidis1, Alessandro Olivo, Robert D Speller
1Department of Medical Physics and Bioengineering, University College London, London, UK.
Purpose:
This paper proposes the further development of a resolution modification routine which is used to simulate the presampling modulation transfer function (pMTF) of digital x-ray detectors.
Methods:
It suggests a method to reconstruct anisotropic two dimensional (2D) pMTF matrices from the experimentally measured horizontal and vertical 1D pMTFs. In this study, the horizontal dimension of the detector is 17.3 cm, while the vertical one is 24 cm. This matrix is multiplied with the 2D Fourier transform of the super-sampled ideal input image to simulate blurring. Then, the restored image is sampled to form the pixels of the digital image. The authors suggest convolution with the comb function instead of the rectangular function to avoid the correction with the sinc function required by the latter. It is demonstrated that this correction is avoided when the comb function is used. Moreover, this study suggests a way to effectively sample the images in the case when the ratio between the "analog" pitch of the super-sampled input image and the pixel pitch of the digital x-ray detector is a semi-integer.
Results:
The validation of the simulation algorithm demonstrated that when the comb function was used the average absolute difference between the pMTF measured from the output images and the input ones was less than 1%, while this was of 13% when the rectangular function was used. When a sinc correction was applied in the latter case the difference decreased again to less than 1%.
Conclusions:
The developed modification routine provides the means to simulate the spatial resolution of digital x-ray detectors under a wider range of conditions.
