Study on Thorax Attenuation Tomography Using Low-frequency Ultrasound Differential Imaging.

Ultrasound is a preferred modality in the field of medical imaging. However, its application in the human thorax faces challenges due to issues such as reflections at the lung-pleural interface and scattering within the lungs. Recent research has shown that low-frequency ultrasound, ranging from 10 kHz to 750 kHz, can effectively penetrate the human thorax. Furthermore, it has been observed that the amplitude of ultrasound signals changes significantly during the subject's respiration, while its traveltime remains relatively constant.In this study, we derive the relationship between the energy attenuation of the first-arrival ultrasound signal as it penetrates the thorax and the attenuation factor of the thorax. Leveraging the principles of differential imaging, we demonstrate that it is possible to reconstruct variations in the thorax's attenuation factor under different ventilation states based on the energy variations and paths of the first-arrival signals that penetrate the thorax. The algorithm is verified with numerical simulation and human subject experiment. Apparent high-attenuation areas in both the left and right sides of the thorax are reconstructed, which substantiates the feasibility of utilizing low-frequency ultrasound for thorax attenuation differential imaging.