Ultrasound phase-contrast transmission imaging of localized thermal variation in a breast tissue model

Abstract

The present numeric study examines an ultrasound phase contrast method for imaging localized temperature rises in tissue, such as heating experienced in thermal ablation treatments. We tested the method’s ability to produce thermal images by simulating the signal from a planar ultrasound source directed through tissue containing skin, fat, and muscle layers. Phase-contrast imaging only requires phase shifts a fraction of a wavelength for detection, thus we tested for the feasibility of imaging at low (submegahertz) frequencies, allowing greater depth penetration and reduced scattering away from the image plane. The tradeoff for lower frequencies was a reduced spatial resolution. It was therefore necessary to determine the lowest possible frequency that could still provide information about the tissue structure and information about the temperature rise in the heated volume. After studying a tomographically reconstructed 4-mm cylindrical heated region in a 100-mm-thick section breast tissue model, thermal effects were detected at frequencies as low as 0.4 MHz, which allowed reconstruction resolution of about 2 mm2 over the image plane. This method may have applications for example in controlling focused ultrasound surgery of breast.