Ultrasound computer tomography using single-element directivity measurements

Ultrasound computer tomography (UCT) is a promising medical imaging method for various applications such as the breast and brain. Current UCT image reconstruction methods fall broadly into two categories: time-of-flight (TOF)-based ray-tracing methods and full-waveform inversion (FWI) methods. Ray tracing methods are computationally efficient but often have blurred edges and low spatial resolution, whereas FWI methods demonstrate excellent image quality at high computational cost. To improve the image quality of ray-based methods without greatly increasing their computational cost, we propose bent-ray UCT reconstruction using direction of arrival (DOA) information rather than TOF information.

DOA- and TOF-UCT methods are evaluated in silico using two-dimensional Shepp-Logan and breast tissue phantoms with speeds of sound ranging from 1460 to $1580m/s$ . Both the Shepp-Logan and breast tissue phantoms were imaged with 128-element ring arrays with diameters of 38.5 and 21 cm, operating frequencies of 350 and 600 kHz, and resolutions of 0.71 and 0.41 mm, respectively. Initial measurements were derived from a finite-difference time-difference solution of the viscoelastic wave equation.

We demonstrate that DOA-UCT images have sharper edges and improved structural similarity to ground-truth images than conventional TOF-UCT. DOA-UCT reconstruction is also able to reconstruct images at multiple time points and with various window sizes, reducing the need to find an exact signal onset.

To the best of our knowledge, this is the first demonstration of a bent-ray UCT algorithm that uses only DOA information, without TOF information.