Tradeoffs in Noise, Resolution, and Dose with Reconstruction Filter in Lung Nodule Detection in CT

摘要

Low contrast detection tasks, such as the detection of subtle ground glass nodules, are low signal to noise (SNR)situations that can be greatly influenced by choice of reconstruction filter. The goal of this work is to examine tradeoffsin noise, resolution, and dose on the SNR of low contrast test objects, resembling spherical lung nodules, to potentiallyimprove reconstruction filter selection for a given nodule detection task. To perform these experiments, the ModulationTransfer Function (MTF) was calculated for each reconstruction filter available. Next, simulated signal images werecreated using 2mm section thicknesses of 1 cm diameter spheres of varying contrast levels. The Noise Power Spectra(NPS) were then calculated for each reconstruction filter to be examined. The signal to noise metric used is the idealBayesian observer SNR metric, which takes into account the spatial correlations in noise introduced by the filter (anddescribed by the NPS). The IBO SNR was calculated under a variety of reconstruction conditions: (a) varying mAs sothat each reconstruction filter results in the same standard deviation; (b) constant mAs and varying reconstruction filter;(c) one reconstruction filter using varying mAs. These measurements provide an opportunity to examine the importanttradeoffs in SNR with noise, resolution, and dose that occur with selection of a reconstruction filter and can potentiallylead to a quantitative basis for filter selection, improving lesion detectability.