Effective Atomic Number Measurement with Energy-Resolved Computed Tomography Using Two-Dimensional “transXend” Detector

Abstract

Introduction: We have previously developed an effective atomic number (Z eff ) 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 Z eff 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. Z eff 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 Z eff s were systematically underestimated. Median relative error to theoretical Z eff was −6.92% (range: −7.89% -−4.60%). After normalizing measured Z eff s 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: Z eff measurements were performed by energy-resolved CT using 2D transXend detector with numerically-estimated RF data. Normalized Z eff s for How to cite this paper: Iramina, H., Nakamura, M., Mizowaki, T. and Kanno, I.

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