Comparison of patient size‐based methods for estimating quantum noise in CT images of the lung

The authors explored four methods for estimating quantum noise in CT images of the lung, each based on a different definition of patient size (water-equivalent diameter) and the relationship between noise and diameter determined in water phantoms. The accuracies of the four methods were evaluated using an image-subtraction method as a gold standard. Noise estimates based on patient sizes derived from chest area, water-equivalent area, non-lung area, and water-equivalent path length had maximum errors of 229%, 93%, 34%, and 57%, respectively. Considering the magnitude of noise variation across the lung volume (approximately 30%), noise estimate based on non-lung area was reasonably accurate.