title: Comparison of signal to noise ratios from spatial and frequency domain formulations of nonprewhitening model observers in digital mammography.
abstract: OBJECTIVE
  Image quality indices based upon model observers are promising alternatives to laborious human readings of contrast-detail images. This is especially appealing in digital mammography as limiting values for contrast thresholds determine, according to some international protocols, the acceptability of these systems in the radiological practice. The objective of the present study was to compare the signal to noise ratios (SNR) obtained with two nonprewhitening matched filter model observer approaches, one in the spatial domain and the other in the frequency domain, and with both of them worked out for disks as present in the CDMAM phantom.
  
  
  METHODS
  The analysis was performed using images acquired with the Siemens Novation and Inspiration digital mammography systems. The spatial domain formulation uses a series of high dose CDMAM images as the signal and a routine exposure of two flood images to calculate the covariance matrix. The frequency domain approach uses the mathematical description of a disk and modulation transfer function (MTF) and noise power spectrum (NPS) calculated from images.
  
  
  RESULTS
  For both systems most of the SNR values calculated in the frequency domain were in very good agreement with the SNR values calculated in the spatial domain. Both the formulations in the frequency domain and in the spatial domain show a linear relationship between SNR and the diameter of the CDMAM discs.
  
  
  CONCLUSIONS
  The results suggest that both formulations of the model observer lead to very similar figures of merit. This is a step forward in the adoption of figures of merit based on NPS and MTF for the acceptance testing of mammography systems.
authors.affiliation: Dipartimento di Fisica dell' , Università di Ferrara, Ferrara, Italy. francesco.sisini@unife.it
authors.forename: Francesco
authors.initials: F
authors.lastname: Sisini
authors.forename: Federica
authors.initials: F
authors.lastname: Zanca
authors.forename: Nicholas W
authors.initials: NW
authors.lastname: Marshall
authors.forename: Angelo
authors.initials: A
authors.lastname: Taibi
authors.forename: Paolo
authors.initials: P
authors.lastname: Cardarelli
authors.forename: Hilde
authors.initials: H
authors.lastname: Bosmans
mesh_terms: D008327:Mammography / Q000379:methods*; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement / Q000379:methods*; D059629:Signal-To-Noise Ratio; D035501:Uncertainty