Ultrasonic thermal imaging of microwave absorption

We propose a new ultrasonic imaging method for tissue differentiation based on thermal and dielectric properties of tissue. Electromagnetic radiation, when applied to tissue over a short period, causes a small temperature rise depending on tissue dielectric constant. Ultrasound speckle displacements related to this temperature change can be determined from local changes in the sound speed using speckle tracking. A more detailed analysis revealed that microwave absorption contrast and speed contrast (specifically, temperature derivative of the sound speed) are the primary contributing factors to final image contrast. In this paper, we present the theoretical background and initial experimental evaluation of this imaging modality, which suggests that it may supplement existing intravascular ultrasound (IVUS) imaging systems to identify vulnerable arterial plaque due to the strong contrast between water-bearing and lipid-bearing tissue.