title: Optimization of image acquisition techniques for dual-energy imaging of the chest.
abstract: Experimental and theoretical studies were conducted to determine optimal acquisition techniques for a prototype dual-energy (DE) chest imaging system. Technique factors investigated included the selection of added x-ray filtration, kVp pair, and the allocation of dose between low- and high-energy projections, with total dose equal to or less than that of a conventional chest radiograph. Optima were computed to maximize lung nodule detectability as characterized by the signal-difference-to-noise ratio (SDNR) in DE chest images. Optimal beam filtration was determined by cascaded systems analysis of DE image SDNR for filter selections across the periodic table (Z(filter) = 1-92), demonstrating the importance of differential filtration between low- and high-kVp projections and suggesting optimal high-kVp filters in the range Z(filter) = 25-50. For example, added filtration of approximately 2.1 mm Cu, approximately 1.2 mm Zr, approximately 0.7 mm Mo, and approximately 0.6 mm Ag to the high-kVp beam provided optimal (and nearly equivalent) soft-tissue SDNR. Optimal kVp pair and dose allocation were investigated using a chest phantom presenting simulated lung nodules and ribs for thin, average, and thick body habitus. Low- and high-energy techniques ranged from 60-90 kVp and 120-150 kVp, respectively, with peak soft-tissue SDNR achieved at [60/120] kVp for all patient thicknesses and all levels of imaging dose. A strong dependence on the kVp of the low-energy projection was observed. Optimal allocation of dose between low- and high-energy projections was such that approximately 30% of the total dose was delivered by the low-kVp projection, exhibiting a fairly weak dependence on kVp pair and dose. The results have guided the implementation of a prototype DE imaging system for imaging trials in early-stage lung nodule detection and diagnosis.
authors.affiliation: Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada M5G 2M9.
authors.forename: N A
authors.initials: NA
authors.lastname: Shkumat
authors.forename: J H
authors.initials: JH
authors.lastname: Siewerdsen
authors.forename: A C
authors.initials: AC
authors.lastname: Dhanantwari
authors.forename: D B
authors.initials: DB
authors.lastname: Williams
authors.forename: S
authors.initials: S
authors.lastname: Richard
authors.forename: N S
authors.initials: NS
authors.lastname: Paul
authors.forename: J
authors.initials: J
authors.lastname: Yorkston
authors.forename: R
authors.initials: R
authors.lastname: Van Metter
mesh_terms: D003300:Copper / Q000737:chemistry; D004867:Equipment Design; D006801:Humans; D008175:Lung Neoplasms / Q000175:diagnosis / Q000000981:diagnostic imaging*; D008962:Models, Theoretical; D008982:Molybdenum / Q000737:chemistry; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011859:Radiography / Q000379:methods; D013902:Radiography, Thoracic / Q000295:instrumentation* / Q000379:methods*; D011874:Radiometry; D012834:Silver / Q000737:chemistry; D013382:Subtraction Technique; D015040:Zirconium / Q000737:chemistry
chemical_list: D012834:Silver; D003300:Copper; D008982:Molybdenum; D015040:Zirconium