Efficient detrending of uniform images for accurate determination of the noise power spectrum at low frequencies.

Efficient detrending of uniform images for accurate determination of the noise power spectrum at low frequencies.
Phys Med Biol. 2019 Apr 17;:
Authors: Gonzalez-Lopez A, Campos-Morcillo PA
Abstract
The noise power spectrum (NPS) of a digital x-ray imaging device is usually estimated from the average of periodograms of ROIs in images obtained with uniform radiation fields. In order to mitigate low frequency trends, present in the images and not arising from stochastic processes, detrending methods are applied to the images before being Fourier transformed. The most common of these methods subtracts a second-order polynomial fit from the image.
 
 In this work, it is shown that the characteristics of low frequency trends can deviate from the quadratic dependence on spatial coordinates. This results in large residual trends that give rise to important correlations in the detrended images and produce an inaccurate rise of the NPS calculations at low frequencies.
 
 A new detrending method of uniform images is presented. The method operates in the subbands of a wavelet transform, removing the low frequency contents of the uniform image. To do this, the approximation subband of the highest level of the wavelet transform is cancelled.
 
 The effect on the NPS calculations for three digital detectors is shown and the importance of the parameters of the wavelet transform is discussed. The main r...

Source: Physics in Medicine and Biology - April 16, 2019 Category: Physics Authors: Gonzalez-Lopez A, Campos-Morcillo PA Tags: Phys Med Biol Source Type: research