AbstractID: 7741 Title: Noise Simulation for studying the effects of scanning geometries and equalization
schemes in scan exposure-equalization digital radiography (SEDR)
Purpose: In order to investigate the scatter and noise properties in scan exposure-equalization digital radiography (SEDR), spot
collimated, full field images will be used to create images simulating various scanning geomotries and equalization schemes. To
reduce the total number of images needed, we will take images at a high exposure level and use them to simulate images
corresponding to lower exposures, as called for by various equalization schemes.
Methods: Flat field images were acquired with an aSi:H/CsI(Tl) flat panel based digital chest unit at 70 and 120 kVp. Total noise was
estimated from these images and random noise was estimated by subtracting two identically acquired images, giving total and random
noise as a function of signal. Simulation was accomplished by using the random noise function to estimate the amount of noise to be
added to a high exposure image when simulating lower exposures.
Results: It was found that, for 120 kVp, the noise versus signal relationship remained largely the same whether the signal change was
due to variation of the exposure setting or attenuator thickness. Thus, the noise in a given pixel can be estimated directly from the
pixel’s value. The total noise was found to consist of a structured component linear with signal and a random component, which,
beyond the lower 10% of the detector’s range increases slowly with signal. By using the random noise function to estimate the amount
of noise to inject, we have demonstrated an excellent agreement between noise levels in simulated and acquired images.