Implications of X-ray beam hardening in the optimization of chest radiography techniques

Abstract

This study aimed to evaluate X-ray beam modulation through an increase in tube voltage (kV) and a reduction in tube current-time product (mAs) according to the 15% rule, assessing its effects on radiation dose and image quality (IQ) in chest radiography. The methodology employed a semi-anthropomorphic phantom and four progressive exposure techniques, including the evaluation of IQ descriptors using quantitative metrics such as Signal-to-Noise Ratio (SNR), Contrast-to-Noise Ratio (CNR), and Contrast Ratio (CR), obtained through histogram analysis and Regions of Interest (ROIs). The results demonstrated a substantial reduction in Entrance Skin Air Kerma (ESAK), with values of 0.284 mGy (Technique 3) and 0.147 mGy (Technique 4), both below the diagnostic reference level of 0.4 mGy established by Brazilian Normative Instruction No. 90/2021. The transmission factor increased to 5.70% and 6.69%, respectively, confirming beam hardening and enhanced X-ray penetrability. In the discussion, Techniques 3 and 4 yielded effective doses (0.076 and 0.048 mSv, respectively) lower than the average values reported in the literature, with Technique 4 demonstrating the highest efficiency due to its superior Figure of Merit. It was concluded that X-ray beam modulation exerts a more pronounced effect on reducing ESAK than on image quality descriptors, which were less significantly affected. Nevertheless, the increased beam transmission resulted in a greater amount of diagnostic information reaching the image receptor.