title: Comparison between X-rays spectra and their effective energies in small animal CT tomographic imaging and dosimetry.
abstract: Small animal CT imaging and dosimetry usually rely on X-ray radiation produced by X-ray tubes. These X-rays typically cover a large energy range. In this study, we compared poly-energetic X-ray spectra against estimated equivalent (effective) mono-energetic beams with the same number of simulated photons for small animal CT imaging and dosimetry applications. Two poly-energetic X-ray spectra were generated from a tungsten anode at 50 and 120 kVp. The corresponding effective mono-energetic beams were established as 36 keV for the 50 kVp spectrum and 49.5 keV for the 120 kVp spectrum. To assess imaging applications, we investigated the spatial resolution by a tungsten wire, and the contrast-to-noise ratio in a reference phantom and in a realistic mouse phantom. For dosimetry investigation, we calculated the absorbed dose in a segmented digital mouse atlas in the skin, fat, heart and bone tissues. Differences of 2.1 and 2.6% in spatial resolution were respectively obtained between the 50 and 120 kVp poly-energetic spectra and their respective 36 and 49.5 keV mono-energetic beams. The differences in contrast-to-noise ratio between the poly-energetic 50 kVp spectrum and its corresponding mono-energetic 36 keV beam for air, fat, brain and bone were respectively -2.9, -0.2, 11.2 and -4.8%, and similarly between the 120 kVp and its effective energy 49.5 keV: -11.3, -20.2, -4.2 and -13.5%. Concerning the absorbed dose, for the lower X-ray beam energies, 50 kVp against 36 keV, the poly-energetic radiation doses were higher than the mono-energetic doses. Instead, for the higher X-ray beam energies, 120 kVp and 49.5 keV, the absorbed dose to the bones and lungs were higher for the mono-energetic 49.5 keV. The intensity and energy of the X-ray beam spectrum have an impact on both imaging and dosimetry in small animal studies. Simulations with mono-energetic beams should take into account these differences in order to study biological effects or to be compared to experimental data.
authors.affiliation: Department of Electrical Engineering, University of Mostaganem, BP188/227, Mostaganem, 27000, Algeria.
authors.forename: Mahdjoub
authors.initials: M
authors.lastname: Hamdi
authors.affiliation: Department of Electrical Engineering, University of Mostaganem, BP188/227, Mostaganem, 27000, Algeria.
authors.forename: Malika
authors.initials: M
authors.lastname: Mimi
authors.affiliation: Department of Nuclear Medicine and Radiobiology, Université de Sherbrooke, 3001, 12th Avenue North, Sherbrooke, Qc, J1H 5N4, Canada. mhamed.bentourkia@usherbrooke.ca.
authors.forename: M'hamed
authors.identifier: http://orcid.org/0000-0002-7102-5964
authors.initials: M
authors.lastname: Bentourkia
mesh_terms: D000818:Animals; D002138:Calibration; D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D007091:Image Processing, Computer-Assisted; D051379:Mice; D009928:Organ Specificity; D019047:Phantoms, Imaging; D011860:Radiography, Abdominal; D013902:Radiography, Thoracic; D011874:Radiometry; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed; D014867:Water; D014965:X-Rays
chemical_list: D014867:Water
keywords: CT; Dosimetry; Imaging; Small animal; X-ray