Universal Synthetic Aperture Sequence for Anatomic, Functional, and Super Resolution Imaging.

Synthetic aperture (SA) can be used for both anatomic and functional imaging, where tissue motion and blood velocity are revealed. Often, sequences optimized for anatomic B-mode imaging are different from functional sequences, as the best distribution and number of emissions are different. B-mode sequences demand many emissions for a high contrast, whereas flow sequences demand short sequences for high correlations yielding accurate velocity estimates. This article hypothesizes that a single, universal sequence can be developed for linear array SA imaging. This sequence yields high-quality linear and nonlinear B-mode images as well as accurate motion and flow estimates for high and low blood velocities and super-resolution images. Interleaved sequences with positive and negative pulse emissions for the same spherical virtual source were used to enable flow estimation for high velocities and make continuous long acquisitions for low-velocity estimation. An optimized pulse inversion (PI) sequence with 2 ×12 virtual sources was implemented for four different linear array probes connected to either a Verasonics Vantage 256 scanner or the SARUS experimental scanner. The virtual sources were evenly distributed over the whole aperture and permuted in emission order for making flow estimation possible using 4, 8, or 12 virtual sources. The frame rate was 208 Hz for fully independent images for a pulse repetition frequency of 5 kHz, and recursive imaging yielded 5000 images per second. Data were acquired from a phantom mimicking the carotid artery with pulsating flow and the kidney of a Sprague-Dawley rat. Examples include anatomic high contrast B-mode, non-linear B-mode, tissue motion, power Doppler, color flow mapping (CFM), vector velocity imaging, and super-resolution imaging (SRI) derived from the same dataset and demonstrate that all imaging modes can be shown retrospectively and quantitative data derived from it.

Anatomic and Functional Imaging Using Row-Column Arrays.

Row-column (RC) arrays have the potential to yield full 3-D ultrasound imaging with a greatly reduced number of elements compared to fully populated arrays. They, however, have several challenges due to their special geometry. This review article summarizes the current literature for RC imaging and demonstrates that full anatomic and functional imaging can attain a high quality using synthetic aperture (SA) sequences and modified delay-and-sum beamforming. Resolution can approach the diffraction limit with an isotropic resolution of half a wavelength with low sidelobe levels, and the field of view can be expanded by using convex or lensed RC probes. GPU beamforming allows for three orthogonal planes to be beamformed at 30 Hz, providing near real-time imaging ideal for positioning the probe and improving the operator's workflow. Functional imaging is also attainable using transverse oscillation and dedicated SA sequence for tensor velocity imaging for revealing the full 3-D velocity vector as a function of spatial position and time for both blood velocity and tissue motion estimation. Using RC arrays with commercial contrast agents can reveal super-resolution imaging (SRI) with isotropic resolution below [Formula: see text]. RC arrays can, thus, yield full 3-D imaging at high resolution, contrast, and volumetric rates for both anatomic and functional imaging with the same number of receive channels as current commercial 1-D arrays.