Development of a non-linear dual-energy technique in chest radiography

Abstract

The dual-energy (DE) technique is useful in chest radiography because it can separate anatomical structures, such as bone and soft tissue. The standard log subtraction, simple smoothing of the high-energy image, anti-correlated noise reduction, and general linear noise reduction algorithms have been used as conventional DE techniques to separate bone and soft tissue. However, conventional DE techniques cannot accurately decompose anatomical structures because these techniques are based on the assumption that X-ray imaging proceeds in a linear relationship. This relationship can cause quantum noise, as well as anatomical loss of normal tissue and difficulty in detecting lesions. In this study, we propose a non-linear DE technique that requires the calculation of the coefficient in advance by using a calibration phantom. The calibration phantom is composed of aluminium and PMMA to calculate non-linear coefficients using the quadratic fitting model for soft tissue and bone. The results demonstrated that the non-linear DE technique exhibited a higher contrast-to-noise ratio, signal-to-noise ratio, and figure of merit at 60/70 kVp and 130 kVp. In addition, it demonstrated better performance and image quality than conventional DE techniques in terms of material decomposition capability. In conclusion, diagnostic accuracy in chest radiography is expected to increase through the non-linear DE technique.