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

• 作者: Hiraku Iramina Ikuo Kanno Mitsuhiro Nakamura Takashi Mizowaki
• 来源期刊: 医学物理学、临床工程、放射肿瘤学(英文)
• 学科: 医学
• 关键词: X-Ray COMPUTED TOMOGRAPHY ENERGY RESOLVED UNFOLDING Effective Atomic Number
• 年，卷（期）: 2018,（1）
• 页码范围: 61-73
• 页数: 13页
• 分类号: R73

摘要

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.