Perceptual thresholds for differences in CT noise texture

Purpose: The average (f(av)) or peak (f(peak)) noise power spectrum (NPS) frequency is often used as a one-parameter descriptor of the CT noise texture. Our study develops a more complete two-parameter model of the CT NPS and investigates the sensitivity of human observers to changes in it. Approach: A model of CT NPS was created based on its f(peak) and a half-Gaussian fit (sigma) to the downslope. Two-alternative forced-choice staircase studies were used to determine perceptual thresholds for noise texture, defined as parameter differences with a predetermined level of discrimination performance (80% correct). Five imaging scientist observers performed the forced-choice studies for eight directions in the f(peak)/sigma-space, for two reference NPSs (corresponding to body and lung kernels). The experiment was repeated with 32 radiologists, each evaluating a single direction in the f(peak)/sigma-space. NPS differences were quantified by the noise texture contrast (C-texture), the integral of the absolute NPS difference. Results: The two-parameter NPS model was found to be a good representation of various clinical CT reconstructions. Perception thresholds for f(peak) alone are 0.2lp/cm for body and 0.4lp/cm for lung NPSs. For sigma, these values are 0.15 and 2lp/cm, respectively. Thresholds change if the other parameter also changes. Different NPSs with the same f(peak) or f(av) can be discriminated. Nonradiologist observers did not need more C-texture than radiologists. Conclusions: f(peak) or f(av) is insufficient to describe noise texture completely. The discrimination of noise texture changes depending on its frequency content. Radiologists do not discriminate noise texture changes better than nonradiologists. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.