AbstractID: 7722 Title: Model of Compton Scatter on Signal and Noise Transfer in
Medical Imaging Systems
X-ray images are generated when an x-ray beam deposits energy into a recording medium through any of
several x-ray interactions. Compton interactions deposit photon energies along the paths of recoil
electrons. Light from each interacting x-ray is not isotropic about the primary interaction site. Models
describing the “Compton” modulation transfer function (MTF) and the transfer of noise power spectrum
(NPS) are required to predict the “Compton” detective quantum efficiency (DQE). In this presentation,
Compton scatter is considered as a random process and is modeled as an “input-labeled” model to
describe the transfer relationship of signal and noise. The input to the model is a random point process
representing a spatial distribution of Compton events. The output represents a spatial distribution of
secondary quanta generated by the recoil electrons. The random recoil-electron angles are required to
describe the recoil electron path and the Klein-Nishina cross section is used to derive the probability
density function of the polar angle. We determine the spatial dependence and statistical correlation of
secondaries from the initial energy of a recoil electron and its range, resulting in the “Compton” MTF
and NPS. Results are presented as functions of x-ray energy and compared with Monte Carlo
calculations for an active-matrix flat-panel detector for portal imaging at 6 MV where non-Compton
interactions can be ignored. This representation of Compton scatter is a step towards a comprehensive
framework of theoretical methods for optimizing detector design and exposure techniques on the MTF
and DQE of radiographic imaging systems over a wide range of energies.