title: Electron density measurement with dual-energy x-ray CT using synchrotron radiation.
abstract: Monochromatic x-ray computed tomography (CT) at two different energies provides information about electron density of human tissue without ambiguity due to the beam hardening effect. This information makes the treatment planning for proton and heavy-ion radiotherapy more precise. We have started a feasibility study on dual energy x-ray CT by using synchrotron radiation. A translation-rotation scanning CT system was developed for quantitative measurement in order to clarify what precision in the measurement was achieved. Liquid samples of solutions of K2HPO4 and solid samples of tissue equivalent materials were used to simulate human tissue. The experiments were carried out using monochromatic x-rays with energies of 40, 70 and 80 keV produced by monochromatizing synchrotron radiation. The solid samples were also measured in a complementary method using high-energy carbon beams to evaluate the electron densities. The measured electron densities were compared with the theoretical values or the values measured in the complementary method. It was found that these values were in agreement in 0.9% on average. Effective atomic numbers were obtained as well from dual-energy x-ray CT. The tomographic image based on each of the electron densities and the effective atomic number presents a different feature of the material, and its contrast drastically differs from that in a conventional CT image.
authors.affiliation: National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba-shi 263-8555, Japan.
authors.forename: Masami
authors.initials: M
authors.lastname: Torikoshi
authors.forename: Takanori
authors.initials: T
authors.lastname: Tsunoo
authors.forename: Makoto
authors.initials: M
authors.lastname: Sasaki
authors.forename: Masahiro
authors.initials: M
authors.lastname: Endo
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Noda
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Ohno
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kohno
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Hyodo
authors.forename: Kentaro
authors.initials: K
authors.lastname: Uesugi
authors.forename: Naoto
authors.initials: N
authors.lastname: Yagi
mesh_terms: D003238:Connective Tissue / Q000528:radiation effects; D004583:Electrons; D006801:Humans; D019047:Phantoms, Imaging; D015900:Radiography, Dual-Energy Scanned Projection / Q000295:instrumentation / Q000379:methods; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D011878:Radiotherapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods*; D012680:Sensitivity and Specificity; D017356:Synchrotrons; D014057:Tomography, X-Ray Computed / Q000379:methods*