Abstract:

Vibro‐acoustography (VA) is an imaging method based on ultrasound radiation force. In this method, a two dimensional image is formed by scanning two co‐focused ultrasound beams with slightly different frequencies over the object (biological tissue) in a C‐scan format and recording resulting sound that is emitted from the focal region at the difference frequency. As in other ultrasound‐based imaging modalities, it is important to study the thermal safety of the technique. This paper addresses tissue heating due to a VA scan using a concentric confocal transducer. The three dimensional ultrasound intensity field calculated by Field II is used with the bio‐heat equation to estimate tissue heating. Results calculated with thermal conduction and with blood perfusion, with conduction and without perfusion, and without conduction and without perfusion are compared. Maximum temperature rise occurs in the transducer near field during VA scans. Heating during one VA scan is below 0.05 °C for soft tissue with attenuation coefficient of 0.3, 0.5, or 0.7 dB∕cm MHz. It is concluded that temperature rise in tissue is not significant. [Work supported by NIH Grants CA 91956, CA 127235, and CA121579. Some of the techniques are patented by Mayo Clinic and the some of the authors (M.F. and J.F.G.).]