Prog Med Phys.  2016 Sep;27(3):125-130. 10.14316/pmp.2016.27.3.125.

Optimization of Energy Modulation Filter for Dual Energy CBCT Using Geant4 Monte-Carlo Simulation

• Ju EB
• Ahn SH
• Choi SG
• Lee R

• KMID: 2376542
• DOI: http://doi.org/10.14316/pmp.2016.27.3.125

Abstract

Dual energy computed tomography (DECT) is used to classify two materials and quantify the mass density of each material in the human body. An energy modulation filter based DECT could acquire two images, which are generated by the low- and high-energy photon spectra, in one scan, with one tube and detector. In the case of DECT using the energy modulation filter, the filter should perform the optimization process for the type of materials and thicknesses for generating two photon spectra. In this study, Geant4 Monte-Carlo simulation toolkit was used to execute the optimization process for determining the property of the energy modulation filter. In the process, various materials used for the energy modulation filter are copper (Cu, 8.96 g/cm³), niobium (Nb, 8.57 g/cm³), stannum (Sn, 7.31 g/cm³), gold (Au, 19.32 g/cm³), and lead (Pb, 11.34 g/cm³). The thickness of the modulation filter varied from 0.1 mm to 1.0 mm. To evaluate the overlap region of the low- and high-energy spectrum, Geant4 Monte-Carlo simulation is used. The variation of the photon flux and the mean energy of photon spectrum that passes through the energy modulation filter are evaluated. In the primary photon spectrum of 80 kVp, the optimal modulation filter is a 0.1 mm lead filter that can acquire the same mean energy of 140 kVp photon spectrum. The lead filter of 0.1 mm based dual energy CBCT is required to increase the tube current 4.37 times than the original tube current owing to the 77.1% attenuation in the filter.

Keyword

Dual energy CT; Modulation filter; Monte carlo simulation

MeSH Terms

Copper
Human Body
Niobium
Tin
Copper
Niobium
Tin

Figure

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  Fig. 1 80kVp Photon spectrum. (a) The incident photon spectrum was created by the SpekCalc program and applied to the simulation, (b) the photon spectrum was measured by Geant4.

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  Fig. 2 80 kVp spectrum change by the thickness of energy modulation filter from 0.1 to 1 mm for each material. (a) Copper, (b) Niobium, (c) Stannum, (d) Gold, (e) Lead.

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