title: Spectral analysis of fundamental signal and noise performances in photoconductors for mammography.
abstract: OBJECTIVE
  This study investigates the fundamental signal and noise performance limitations imposed by the stochastic nature of x-ray interactions in selected photoconductor materials, such as Si, a-Se, CdZnTe, HgI(2), PbI(2), PbO, and TlBr, for x-ray spectra typically used in mammography.
  
  
  METHODS
  It is shown how Monte Carlo simulations can be combined with a cascaded model to determine the absorbed energy distribution for each combination of photoconductor and x-ray spectrum. The model is used to determine the quantum efficiency, mean energy absorption per interaction, Swank noise factor, secondary quantum noise, and zero-frequency detective quantum efficiency (DQE).
  
  
  RESULTS
  The quantum efficiency of materials with higher atomic number and density demonstrates a larger dependence on convertor thickness than those with lower atomic number and density with the exception of a-Se. The mean deposited energy increases with increasing average energy of the incident x-ray spectrum. HgI(2), PbI(2), and CdZnTe demonstrate the largest increase in deposited energy with increasing mass loading and a-Se and Si the smallest. The best DQE performances are achieved with PbO and TlBr. For mass loading greater than 100 mg cm(-2), a-Se, HgI(2), and PbI(2) provide similar DQE values to PbO and TlBr.
  
  
  CONCLUSIONS
  The quantum absorption efficiency, average deposited energy per interacting x-ray, Swank noise factor, and detective quantum efficiency are tabulated by means of graphs which may help with the design and selection of materials for photoconductor-based mammography detectors. Neglecting the electrical characteristics of photoconductor materials and taking into account only x-ray interactions, it is concluded that PbO shows the strongest signal-to-noise ratio performance of the materials investigated in this study.
authors.affiliation: School of Mechanical Engineering, Pusan National University, Jangjeon-dong, Geumjeong-gu, Busan, Republic of Korea. hokyung@pusan.ac.kr
authors.forename: Ho Kyung
authors.initials: HK
authors.lastname: Kim
authors.forename: Chang Hwy
authors.initials: CH
authors.lastname: Lim
authors.forename: Jesse
authors.initials: J
authors.lastname: Tanguay
authors.forename: Seungman
authors.initials: S
authors.lastname: Yun
authors.forename: Ian A
authors.initials: IA
authors.lastname: Cunningham
mesh_terms: D000042:Absorption; D008027:Light; D008327:Mammography / Q000379:methods*; D009010:Monte Carlo Method; D013057:Spectrum Analysis