A convex lens using room temperature vulcanization (RTV) silicone rubber, whose acoustic impedance matches well with that of water, is a typical acoustic lens. However, some considerations are required to reduce the thickness of the lens because attenuation is very large in the RTV silicone rubber. Therefore, we have proposed a phase continuous Fresnel lens, which has some devices to keep the phase continuous in the entire lens aperture without an unequal phase on the exit side. This lens is fabricated by removing its thickness in a staircase shape in which the difference between each step is an integer multiple of wavelength. In this study, the sound fields focused by the phase continuous Fresnel lens are analyzed using a finite difference time domain (FDTD) method. Using a two-dimensional (2-D) FDTD method, we surveyed the sound pressure field of the focal region by changing the burst pulse length, angle of incidence, and frequency. Results show that the lens gain of the phase continuous Fresnel lens is greater than that of the convex lens, that focusing characteristics depend on the burst pulse length of sound source signal, and also that focal points strongly depend on frequency. In another analysis using a three-dimensional FDTD method, we found that the main lobe is the same as that indicated by 2-D analysis results and that the level outer of the main lobe is lower than that in the 2-D analysis results.

The effects of pulsed ultrasound (US) on early mouse embryos were investigated. Two-cell embryos contained in oviducts were irradiated to US (1.875 MHz with an I SPTA of 2.96 W/cm2) in an experimental unit for either 1 or 5 min (exposure groups). The embryos were cultured to examine the rate of developing to blastocysts, and the uptake of 2-deoxyglucose (2-DG) into blastocysts was measured to evaluate their viability. The rates in the exposure groups were essentially the same, with those of the embryos treated similarly in the unit unless being exposed to US (nonexposure groups). However, they were lower than that of embryos not treated in the experimental unit (a control group). There were no significant differences of 2-DG uptake among the 1-min exposure, 1-min nonexposure, and control groups. The uptake in the 5-min exposure group did not differ from that in the 5-min nonexposure group; however, uptake in both groups was lower than that in the control group. Pulsed US for 1 min did not affect viability of preimplantation mouse embryos.

Knowledge of interaction mechanisms between ultrasound (US) and contrast agents (CA) suspended in blood is important for a correct interpretation of clinical investigation results. Experiments performed in different laboratories have shown that, as a consequence of primary radiation force, CA tend to move away from the US transducer. Accordingly, Doppler spectra produced by particles suspended in moving water turn out to be significantly altered from what is theoretically expected. The purpose of this paper is twofold. First, an original model describing the bubble dynamics as the outcome of the balance between US radiation force and fluid drag force is validated for the case in which bubbles are suspended in blood. The high fluid viscosity is shown to prevent significant bubble deviations from the unperturbed fluid streamlines so that, in large vessels, a residual spectral distortion may exist only at the highest intensity levels permitted by current regulations. Finally, the relative importance and differences between the effect of primary radiation force and streaming mechanisms that, in principle, could lead to similar effects, are discussed.