LUFT: A low-frequency ultrasound tomography system designed for lung imaging

Pulmonary imaging with ultrasound in the conventional MHz range suffers from significant artifacts, as the high frequency acoustic waves primarily reflect off of the lung pleura with little to no penetration through the lung tissue. Furthermore, B-mode ultrasound images are difficult to interpret and require a skilled technician to obtain. Motivated by the finding that acoustic frequencies in the kHz penetrate lung tissue, a low-frequency tomographic ultrasound system is presented. A Verasonics Vantage 64 low-frequency ultrasound system is programmed to work with a novel low-frequency Tonpilz transducers set arranged in a circular array on a belt. After signal processing, a time-of-flight (TOF) tomographic reconstruction algorithm with refraction correction is applied to estimate the sound speed in the plane of the transducer array. Data were collected on experimental phantoms made of ballistic gel containing targets of varying sound speeds, and reconstructions TOF were computed. Results demonstrate that the low-frequency ultrasound tomography system effectively detects targets in an experimental phantom with the ability to resolve multiple targets and distinguish between targets of high and low sound speed compared to the background medium.