A Feasibility Study of Low-frequency Ultrasound Tomography for Human Thorax

Ultrasound is widely used in biomedical imaging. High-frequency ultrasound at MHz is usually used for good resolution. However, ultrasound at this band cannot permeate human thorax, for it is strongly scattered and reflected by air inclusions in the thorax. We attempt to detect thorax using low-frequency ultrasound transmitting through thorax with travel-time tomography. The ultrasound we use is at a few tens of kHz, which mitigates the influence of scattering and reflection. Transducers are fixed around the thorax via a manual elastic belt. Each of them serves as transmitter in turn and the rest serve as receivers. The traveltime of signals is picked and the acoustic velocity distribution of thorax is computed, from which we can compute the acoustic velocity distribution of the subject's thorax. In the inversion result, the outline of lungs can be seen and the distribution differs when the subject breathes in and out. This result verifies that it is possible to imaging human thorax using low-frequency ultrasound.