title: Reducing radiation dose by application of optimized low-energy x-ray filters to K-edge imaging with a photon counting detector.
abstract: K-edge imaging with photon counting x-ray detectors (PCXDs) can improve image quality compared with conventional energy integrating detectors. However, low-energy x-ray photons below the K-edge absorption energy of a target material do not contribute to image formation in the K-edge imaging and are likely to be completely absorbed by an object. In this study, we applied x-ray filters to the K-edge imaging with a PCXD based on cadmium zinc telluride for reducing radiation dose induced by low-energy x-ray photons. We used aluminum (Al) filters with different thicknesses as the low-energy x-ray filters and implemented the iodine K-edge imaging with an energy bin of 34-48 keV at the tube voltages of 50, 70 and 90 kVp. The effects of the low-energy x-ray filters on the K-edge imaging were investigated with respect to signal-difference-to-noise ratio (SDNR), entrance surface air kerma (ESAK) and figure of merit (FOM). The highest value of SDNR was observed in the K-edge imaging with a 2 mm Al filter, and the SDNR decreased as a function of the filter thicknesses. Compared to the K-edge imaging with a 2 mm Al filter, the ESAK was reduced by 66%, 48% and 39% in the K-edge imaging with a 12 mm Al filter for 50 kVp, 70 kVp and 90 kVp, respectively. The FOM values, which took into account the ESAK and SDNR, were maximized for 8, 6 to 8 and 4 mm Al filters at 50 kVp, 70 kVp and 90 kVp, respectively. We concluded that the use of an optimal low-energy filter thickness, which was determined by maximizing the FOM, could significantly reduce radiation dose while maintaining image quality in the K-edge imaging with the PCXD.
authors.affiliation: Department of Radiological Science, College of Health Science and Research Institute of Health Science, Yonsei University, Wonju, Gangwon-do 220-710, Korea.
authors.forename: Yu-Na
authors.initials: YN
authors.lastname: Choi
authors.forename: Seungwan
authors.initials: S
authors.lastname: Lee
authors.forename: Hee-Joung
authors.initials: HJ
authors.lastname: Kim
mesh_terms: D019047:Phantoms, Imaging; D017785:Photons; D011829:Radiation Dosage; D059629:Signal-To-Noise Ratio; D013052:Spectrometry, X-Ray Emission / Q000295:instrumentation / Q000379:methods*; D014965:X-Rays