Abstract
The newer diagnostic ultrasound equipments such as a color Doppler equipment and/or a harmonic imaging equipment require higher pressure ultrasound than the conventional B-mode imaging systems. We investigated the temperature rise in soft tissue caused by ultrasound irradiation using a simulation program for a single disk transducer and a phased array focused transducer . The simulation program consisted of two codes capable of estimating the temperature distribution in various media. First, the sound pressure distribution in media was calculated by the finite-difference time-domain (FDTD) method. There are two types of FDTD codes, i.e., for a fluid model and an elastic model, to calculate the pressure in soft tissue and the stress in bone. The common heat conduction equation (HCE) method was used to calculate the thermal conduction profile generated by absorption of ultrasound. It is very important to show that this simulation program would be able to confirm the exact temperature distribution in the media. This paper describes a comparison between two-dimensional FDTD-HCE simulation and measurement of the temperature rise in soft tissue phantom with mimic bone to show the validity of this method. Agar and acrylic plates were used for the sham soft tissue and human bone. The main focus of the study was the reflection effect from the mimic bone when the absorption coefficient of the agar phantom was about 0.5dB/cm/MHz, which is the typical absorption value of soft tissue. The measuring results without mimic bone agreed well with the simulation results. The measuring results with bone, however, did not agree with the simulation near the bone surface. It was clearly seen that the reflected waves increased the temperature in front of the bone.
