TITLE:
Effective Atomic Number Measurement with Energy-Resolved Computed Tomography Using Two-Dimensional “transXend” Detector
AUTHORS:
Hiraku Iramina, Mitsuhiro Nakamura, Takashi Mizowaki, Ikuo Kanno
KEYWORDS:
X-Ray, Computed Tomography, Energy Resolved, Unfolding, Effective Atomic Number
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.7 No.1,
February
13,
2018
ABSTRACT: Introduction: We have previously
developed an effective atomic number (Zeff) measurement
method using linear attenuation coefficients (LACs) obtained by energy-resolved
computed tomography (CT) with one-dimensional (1D) detector. The energy-resolved
CT was performed with a “transXend” detector, which measured X-rays as electric
current and then gave X-ray energy distribution with unfolding analysis using
pre-estimated response function (RF). The purpose of this study is to measure Zeff by the energy-resolved
CT using a flat panel detector (FPD). Methods: To demonstrate a 2D
transXend detector, we developed the stripe absorbers for the FPD. Eleven human
tissue-equivalent material rods which were grouped into four material
categories were measured by X-rays with 120 kVp tube voltage, 2.3 mA tube
current, and 1.0 s exposure time. Zeff is measured by the
ratio of LACs with two different pseudo-monochromatic X-ray energies. RFs of
each rod material were estimated by numerical calculation. First, we employed
the RF estimated for the same rod material (self-RF scenario). Second, we
employed the RF estimated for the different rod materials in the same material
category (cross-RF scenario). The purpose of the cross-RF scenario was to find
representative rod materials in each material category. Results: Upon
the self-RF scenario, measured Zeffs were
systematically underestimated. Median relative error to theoretical Zeff was -6.92% (range: -7.89% - -4.60%). After
normalizing measured Zeffs to the
theoretical one for Breast, median relative error improved to -0.75% (range: -1.79% - +1.73%).
Upon the cross-RF scenario, the representative rod materials were found in two
material categories. Conclusion: Zeff measurements were
performed by energy-resolved CT using 2D transXend detector with numerically-estimated
RF data. Normalized Zeffs for all rod
materials in the self-RF scenario were in good agreement with the theoretical
ones.