Ultrasonic Imaging Based on Pulsed Airy Beams.

In ultrasonic imaging, high impedance obstacles in tissues may lead to artifacts behind them, making the examination of the target area difficult. Acoustical Airy beams possess the characteristics of self-bending and self-healing within a specific range. They are limited-diffracting when generated from finite aperture sources and are expected to have great potential in medical imaging and therapy. In this article, pulsed Airy (pAiry) beams are employed for ultrasonic imaging at megahertz frequency, and the protocol is demonstrated via both simulations and experiments. First, the generation of pAiry beams using a linear array is simulated, and the pulsed beams inherit some characteristics of continuous wave Airy beams, such as propagating along curved paths and self-healing. In experiments where obstacles are present at the beam paths, the image quality in pAiry-based imaging is superior to that in classical iso-depth imaging. The results demonstrate the feasibility and benefits of ultrasonic imaging based on pAiry beams and provide an important basis for developing imaging techniques employing nondiffracting acoustic beams.

In Vivo Multithread Ultrasound Thermal Strain Imaging.

While thermal therapy is increasingly applied in clinics, real-time temperature monitoring in the target tissue can facilitate improvements in the planning, controlling, and evaluating of therapeutic procedures. Thermal strain imaging (TSI), based on tracking the echo shifts in ultrasound images, has great potential for temperature estimation as is demonstrated in vitro. However, due to physiological motion-induced artifacts and estimation errors, employing TSI for in vivo thermometry is still challenging. Building on our earlier development of respiration-separated TSI (RS-TSI), a multithread TSI (MT-TSI) approach is proposed as the first part of a bigger plan. A flag image frame is first identified by analyzing the correlation between ultrasound images. Then, the quasi-periodic phase profile of respiration is determined and split into multiple parallelly distributed periodical subranges. Multiple threads of independent TSI calculations are thus established, with image matching, motion compensation, and thermal strain estimation performed in each thread. Finally, after applying temporal extrapolation, spatial alignment, and interthread noise suppression, the TSI results obtained in different threads are averaged to obtain the merged output. In microwave (MW) heating experiments targeting porcine perirenal fat, the thermometry accuracy of MT-TSI is comparable to that of RS-TSI, while the former exhibits lower noise and higher temporal density.