A linear ultrasound array system usually has a larger pitch and is less costly than a phased array system, but loses the ability to fully steer the ultrasound beam. In this paper, we propose a system whose hardware is similar to a large-pitch linear array system, but whose ability to steer the beam is similar to a phased array system. The motivation is to reduce the total number of measurement channels <i>M</i> (the product of the number of transmissions, <i>n<sub>T</sub></i>, and the number of the receive channels in each transmission, <i>n<sub>R</sub></i>), while maintaining reasonable image quality. We combined adjacent elements (with proper delays introduced) into groups that would be used in both the transmit and receive processes of synthetic transmit aperture imaging. After the <i>M</i> channels of RF data were acquired, a pseudo-inversion was applied to estimate the equivalent signal in traditional STA to reconstruct a STA image. Even with the similar <i>M</i>, different choices of <i>n<sub>T</sub></i> and <i>n<sub>R</sub></i> will produce different image quality. The images produced with <i>M</i>=<i>N<sup>2</sup></i>/15 in the selected regions of interest (ROI) were demonstrated to be comparable with a full phased array, where <i>N</i> is the number of the array elements. The disadvantage of the proposed system is that its field of view in one delay-configuration is smaller than a standard full phased array. However, by adjusting the delay for each element within each group, the beam can be steered to cover the same field of view as the standard fully-filled phased array. The LPSSTA system might be useful for 3D ultrasound imaging.
The electric field induced optical changes (EIOC) measured by the optical coherence tomography (OCT) reflect the local electro-kinetic properties of the tissue. In this study we developed a method to use the phase of the complex OCT images to map EIOC in tissue samples. Switching the polarity of the electric field induced significant reversible changes in the phase of the complex OCT images. Since the resulting phase was degraded by the noise an advanced signal processing algorithm was developed to obtain the EIOC images. The developed algorithm made it possible to get structural phase images from a standard commercial OCT system, potentially yielding important insights into the local electro-kinetic properties of the tissue. We use a simple theoretical model to simulate main features of amplitude and phase EIOC observed using frequency-domain OCT.
We have measured changes in optical coherence signals during the application of an external electric field to tissue samples. We employed the swept-source OCT engine with a broadband light source of 140-nm spectral bandwidth centered at 1300 nm. Switching the polarity of the electric field induced significant reversible changes in the phase of the OCT signal. Since the phase signal was corrupted by phase noise, it required a formidable signal processing to obtain the images of electrically induced phase changes.