Speaker
Description
Chest radiography is a widely used imaging modality for diagnosing and monitoring thoracic diseases due to its accessibility, cost-effectiveness, and relatively low radiation dose. However, conventional chest radiographs often struggle to differentiate overlapping anatomical structures, such as bones and soft tissues, which can obscure important pathological findings. To address these limitations, dual energy imaging (DEI) has emerged as a key advancement in chest radiography [1]. DEI utilizes two distinct X-ray energy levels to acquire separate image sets, enabling material decomposition based on their unique attenuation characteristics. By selectively reducing the contrast of non-relevant regions and background structures, DEI enhances the visibility of the material contrast of interest [2].
The performance of DEI can be influenced by various factors, such as imaging techniques (e.g., low and high kVp settings and dose allocation between them) and detector designs (e.g., materials like CsI or a-Se, thickness, and pixel pitch). Recently, the International Electrotechnical Commission (IEC) introduced the concept of DE subtraction efficiency (DSE) to characterize DEI systems [3]. DSE represents the contrast-to-noise ratio (DE contrast or DEC, as defined by the IEC) at the exposure level K_a used for imaging. The IEC also provides a standard phantom design made of aluminum (Al, representing hard tissue) and acrylic (Ac, representing soft tissue) with various thicknesses, as shown in Fig. 1(a), for the objective evaluation of DSE.
In this study, we evaluate the DSE performance of various detector designs by incorporating the IEC phantom into a Monte Carlo (MC) simulation framework. We use the commercial MCNP code (Version 5, RSICC, Oak Ridge, TN) and conduct the simulations using the pTrac function. An example MC image from a 0.5-mm-thick CsI detector for the IEC phantom is shown in Fig. 1(b). Fig. 2 illustrates the DSE performance of soft-tissue-subtracted images obtained from the CsI detector, where DE reconstruction was performed using weighted log-subtraction for a 6-mm-thick Ac feature, as suggested by the IEC. Different plots correspond to low-energy settings of 60, 70, and 80 kVp, with a fixed high-energy setting of 120 kVp.
The MC simulation results are being analyzed to determine the DSE as a function of detector materials (CsI, a-Se, CdTe), thicknesses, and pixel pitches. The simulation framework will be validated through experimental measurements of two different designs of CsI-coupled flat-panel detectors.
Reference
[1] J. E. Kuhlman, J. Collins, G. N. Brooks, D. R. Yandow, and L. S. Broderick, “Dual-energy subtraction chest radiography: what to look for beyond calcified nodules”, Radiographics, Vol. 26, No. 1, pp. 79-92, 2006.
[2] H. Shin, S. Yoo, S. Oh, J. Lee, and H. K. Kim, “Detective quantum efficiency of a double-layered detector for dual-energy x-ray imaging”, Journal of Instrumentation, Vol. 18, No. 11, pp. C11005, 2023.
[3] IEC, “Medical electrical equipment – Characteristics of digital X-ray imaging devices – Part 2-1: Determination of dual-energy subtraction efficiency – Detectors used for dual-energy radiographic imaging; IEC 62220-2-1”, International Electrotechnical Commission, 2023.
Acknowledgement
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2024-00340520). J. Lee was supported by the 'Human Resources Program in Energy Technology' of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), which was funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea) (No. RS-2024-00398425).
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