title: Energy weighting improves dose efficiency in clinical practice: implementation on a spectral photon-counting mammography system.
abstract: In x-ray imaging, contrast information content varies with photon energy. It is, therefore, possible to improve image quality by weighting photons according to energy. We have implemented and evaluated so-called energy weighting on a commercially available spectral photon-counting mammography system. The technique was evaluated using computer simulations, phantom experiments, and analysis of screening mammograms. The CNR benefit of energy weighting for a number of relevant target-background combinations measured by the three methods fell in the range of 2.2 to 5.2% when using optimal weight factors. This translates to a potential dose reduction at constant CNR in the range of 4.5 to 11%. We expect the choice of weight factor in practical implementations to be straightforward because (1) the CNR improvement was not very sensitive to weight, (2) the optimal weight was similar for all investigated target-background combinations, (3) aluminum/PMMA phantoms were found to represent clinically relevant tasks well, and (4) the optimal weight could be calculated directly from pixel values in phantom images. Reasonable agreement was found between the simulations and phantom measurements. Manual measurements on microcalcifications and automatic image analysis confirmed that the CNR improvement was detectable in energy-weighted screening mammograms.
authors.affiliation: Philips Healthcare , Smidesvägen 5, 171 41 Solna, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Berglund
authors.affiliation: Philips Healthcare , Smidesvägen 5, 171 41 Solna, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Johansson
authors.affiliation: Philips Healthcare , Smidesvägen 5, 171 41 Solna, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Lundqvist
authors.affiliation: Philips Healthcare , Smidesvägen 5, 171 41 Solna, Sweden.
authors.forename: Björn
authors.initials: B
authors.lastname: Cederström
authors.affiliation: Philips Healthcare , Smidesvägen 5, 171 41 Solna, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Fredenberg
keywords: contrast-to-noise ratio; digital mammography; dose efficiency; energy weighting; photon counting; spectral x-ray imaging