Ultrasound phase-contrast imaging

Summary: We present a technique to perform ultrasound (US) phase imaging in an arbitrarily thick scattering medium. The technique exploits speckle correlations resulting from the “memory effect” to produce phase contrast in a similar manner as optical differential interference contrast (DIC).

Conventional US imaging is based on pulsed-echo sonography, which is a reflection mode contrast. As such, conventional US imaging can only reveal sharp interfaces or small point-like structures within a sample, and cannot reveal slowly varying structures that impart only weak acoustic phase shifts. Such slowly varying structures can only be revealed in a transmission mode.

We describe a simple technique to perform US transmission-mode imaging in a reflection-mode geometry with a single transducer probe. Instead of imaging acoustic waves that are directly scattered from a focal plane of interest, our technique uses random backscattering from deeper layers within the sample to indirectly trans-insonify the focal plane of interest. We then produce a phase-contrast image by measuring the phase shifts imparted on the random acoustic waves at the focal plane. This is done by performing the acoustic equivalent of optical shearing interferometry, or optical DIC, to reveal transverse phase gradients within the sample. Key to our technique is the use of the “memory effect” to produce the shearing of the backscattered acoustic insonification.

Our differential phase contrast (DPC) technique can be operated in combination with conventional pulse-echo US imaging with no hardware modifications whatsoever. As such, it can be combined with standard B-mode imaging and provide complementary phase contrast essentially for free, enabling weakly varying sample structures to be revealed that would otherwise be invisible.

DPC based on backscattering and the memory effect
(a) Conventional US image. (b) DPC image of same sample based on (b) backscattering, and (c) forward scattering.
  • T. D. Weber, N. Khetan, R. Yang, J. Mertz, “Ultrasound differential phase contrast using backscattering and the memory effect”, Appl. Phys. Lett. 118, 124103 (2021). link
  • N. Khetan, T. Weber, J. Mertz, “Speed-of-sound imaging by differential phase contrast with angular compounding”, arXiv 2007. 03156 (2020) link