Accurate effective atomic number determination with polychromatic grating-based phase-contrast computed tomography

Abstract

The demand for quantitative medical imaging is increasing in the ongoing digitalization. Conventional computed tomography (CT) is energy-dependent and therefore of limited comparability. In contrast, dual-energy CT (DECT) allows for the determination of absolute image contrast quantities, namely the electron density and the effective atomic number, and is already established in clinical radiology and radiation therapy. Grating-based phase-contrast computed tomography (GBPC-CT) is an experimental X-ray technique that also allows for the measurement of the electron density and the effective atomic number. However, the determination of both quantities is challenging when dealing with polychromatic GBPC-CT setups. In this paper, we present how to calculate the effective atomic numbers with a polychromatic, laboratory GBPC-CT setup operating between 35 and 50\,kVp. First, we investigated the accuracy of the measurement of the attenuation coefficients and electron densities. For this, we performed a calibration using the concept of effective energy. With the reliable experimental quantitative values, we were able to evaluate the effective atomic numbers of the investigated materials using a method previously shown with monochromatic X-ray radiation. In detail, we first calculated the ratio of the electron density and attenuation coefficient, which were experimentally determined with our polychromatic GBPC-CT setup. Second, we compared this ratio with tabulated total attenuation cross sections from literature values to determine the effective atomic numbers. Thus, we were able to calculate two physical absolute quantities -- the electron density and effective atomic number -- that are in general independent of the specific experimental conditions like the X-ray beam spectrum or the setup design.

Scattering of therapeutic radiation in the presence of craniofacial bone reconstruction materials

“…The physical density of pure titanium is 4.50 g/cm 3 , PEEK 1.32 g/cm 3 , FRC 1.20 g/cm 3 , bioactive glass 2.6 g/cm 3 and bone 1.85 g/cm 3 while the density for soft tissue is 1.00 g/cm 3 . The Z for PEEK is lower than the other tested composites but the attenuation and back scatter results with tested radiation energies were similar . The high density of titanium in comparison with the other tested materials accounts for the higher backscattering dose.…”

Quantitative evaluation on 3D fetus morphology via X‐ray grating based imaging technique

“…It is difficult to reveal weakly absorbing structures of soft tissues consisting of low‐Z elements (such as C, H, O, N, and so on) due to poor image contrast arisen from soft tissues almost transparent to hard X‐rays. Compared with traditional micro‐CT based on the attenuation effect, the phase sensitive imaging technique generally provides much higher image contrast and lower radiation dose for low‐Z elemental samples . Therefore, X‐ray phase‐contrast imaging (XPCI) enables us to observe inner weakly absorbing structures with high phase sensitivity, particularly suitable for visualizing and quantifying fine electron density differences of biomedical structural information with sufficient image contrast.…”

“…image contrast and lower radiation dose for low-Z elemental samples. [4][5][6] Therefore, X-ray phase-contrast imaging (XPCI) enables us to observe inner weakly absorbing structures with high phase sensitivity, particularly suitable for visualizing and quantifying fine electron density differences of biomedical structural information with sufficient image contrast. In recent years, many XPCI techniques, including crystal interferometry, analyzer-based imaging, grating-based imaging, and propagation-based imaging, have been proposed and developed to improve hard X-ray image contrast through translating the phase shift into the accessibly recorded intensity variations.…”

Investigation of YAG:Ce-Based Optical Fibre Sensor for Use in Ultra-Fast External Beam Radiotherapy Dosimetry

“…Eu, La also exhibit a significant energy effect as it has a relatively high effective atomic number (Zeff), which means that the scintillating material-based sensor as a radiation dosimeter requires energy correction of the calibration to reference dosimeters. The effective atomic number of the scintillator GOS is 66.1 [15,16], whilst the Zeff of water, muscle, skin, fat and bone is 7.42, 7.42, 7.31, 5.92 and 13.8, respectively [17,18]. The radiation effect has a very strong dependence on the effective atomic number of the absorbed materials.…”

“…As an alternative, the commercial plastic scintillating fibre BCF-12, with a low Zeff ~ 6.56 [17], manufactured by Saint Gobain Crystal [19] has been widely investigated due to its relatively short decay time (3.2 ns). However, the light yield is extremely low (~ 8000 / MeV) limiting its use for low dose and dose rate applications.…”