title: Towards optimization in digital chest radiography using Monte Carlo modelling.
abstract: A Monte Carlo based computer model of the x-ray imaging system was used to investigate how various image quality parameters of interest in chest PA radiography and the effective dose E vary with tube voltage (90-150 kV), additional copper filtration (0-0.5 mm), anti-scatter method (grid ratios 8-16 and air gap lengths 20-40 cm) and patient thickness (20-28 cm) in a computed radiography (CR) system. Calculated quantities were normalized to a fixed value of air kerma (5.0 microGy) at the automatic exposure control chambers. Soft-tissue nodules were positioned at different locations in the anatomy and calcifications in the apical region. The signal-to-noise ratio, SNR, of the nodules and the nodule contrast relative to the contrast of bone (C/C(B)) as well as relative to the dynamic range in the image (C(rel)) were used as image quality measures. In all anatomical regions, except in the densest regions in the thickest patients, the air gap technique provides higher SNR and contrast ratios than the grid technique and at a lower effective dose E. Choice of tube voltage depends on whether quantum noise (SNR) or the contrast ratios are most relevant for the diagnostic task. SNR increases with decreasing tube voltage while C/C(B) increases with increasing tube voltage.
authors.affiliation: Department of Radiation Physics, Faculty of Health Sciences, Linköping University, SE-581 85 Linköping, Sweden.
authors.forename: Gustaf
authors.initials: G
authors.lastname: Ullman
authors.forename: Michael
authors.initials: M
authors.lastname: Sandborg
authors.forename: David R
authors.initials: DR
authors.lastname: Dance
authors.forename: Roger A
authors.initials: RA
authors.lastname: Hunt
authors.forename: Gudrun
authors.initials: G
authors.lastname: Alm Carlsson
mesh_terms: D006801:Humans; D009010:Monte Carlo Method; D009369:Neoplasms / Q000000981:diagnostic imaging*; D011785:Quality Assurance, Health Care; D011789:Quantum Theory; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D013902:Radiography, Thoracic / Q000379:methods*; D011874:Radiometry; D014963:X-Ray Intensifying Screens