Yibin Zheng

Closed-form four-channel monopulse two-target resolution

A novel closed-form solution to resolve the directions of arrival (azimuth and elevation) of two sources using a single snapshot (monopulse) of four independent channels is presented. Both phase comparison monopulse and amplitude comparison monopulse are solved. Exceptions where the two targets cannot be resolved are also discussed. Numerical simulation result of a practical phased-array configuration validates the effectiveness of the new solution.

Image reconstruction for small animal SPECT with two opposing half cones

Pinhole imaging is a promising approach for high spatial resolution single gamma emission imaging in situations when the required field of view (FOV) is small, as is the case for small animal imaging. However, all pinhole collimators exhibit steep decrease in sensitivity with increasing angle of incidence from the pinhole axis. This in turn degrades the reconstruction images, and requires higher dose of radiotracer. We developed a novel pinhole SPECT system for small animal imaging which uses two opposing and offset small cone-angle square pinholes, each looking at half of the FOV. This design allows the pinholes to be placed closer to the object and greatly increases detection efficiency and spatial resolution, while not requiring larger size detectors. Iterative image reconstruction algorithms for this system have been developed. Preliminary experimental data have demonstrated marked improvement in contrast and spatial resolution.

Fuzzy two-stage carrier synchronization

This paper presents a novel two-stage carrier synchronization scheme. It provides both faster acquisition and better noise suppression than a conventional digital phase-locked loop (DPLL). The first stage produces the frequency estimate. The second stage is a new phase estimator, a DPLL with fuzzy adaptive bandwidth, to track frequency offset and phase. The simulation results show the improved performance. The main advantage of the proposed scheme over [7] is that it does not need optimization of fuzzy membership functions and a low computational cost of a DPLL is preserved.

Recursive least squares image reconstruction

A recursive least squares algorithm is formulated in the context of image reconstruction, using computed tomography (CT) as an example. Compared to traditional algebraic reconstruction techniques (ART), the new algorithm converges in as little as one iteration and has the ability to incorporate a priori information such as image smoothness. Several approximations of the algorithm are proposed and it is demonstrated that they can be implemented for practical image reconstruction problems and obtain very good results.

Increasing the Depth of Focus in Medical Ultrasound B-Scan

Obtaining hight quality ultrasound images at high frame rates has great medical importance, especially in applications where tissue motion is significant (e.g. the beating heart). Dynamic focusing and dynamic apodization can improve image quality significantly, and they have been implemented on the receive beam in state-of-the-art medical ultrasound systems. However implementing dynamic focusing and dynamic apodization on the transmit beam compromises frame rate. We present a novel transmit apodization scheme where a continuum of focal points can be obtained in one transmission, and uniform sensitivity and uniform point spread function can be achieved over very large range without reducing frame rate. Preliminary simulations demonstrate significant promises of the new technique.

Quadratic equalization: a method for producing extended uniform depth of focus in high frame rate medical ultrasound B-scans

This work describes a new and novel method for achieving the beneficial imaging effects that can be obtained from the coherent superposition of multiple firings with a uniform distribution of transmit foci, with a single transmit firing. It is demonstrated that a sine amplitude modulation of the transmit windowing function with an argument quadratic in the transducer coordinates is essentially equivalent to a synthetic image generated from the coherent superposition of an infinite number of firings with their transmit foci uniformly covering the full range of an extended B-scan. Using these methods, simulation results give range compensated peaks of the range energy impulse response (measure of image brightness) that are flat within /spl sim/ /spl plusmn/0.2 dB over the range scan of the B-mode image at fractional bandwidths commensurate with range resolutions down to /spl sim/ 0.25 mm.

Adaptive fuzzy frequency estimator with applications in fading communication channels

A novel fuzzy frequency estimation algorithm is proposed. Not only linguistic rules from experts but also numerical input/output information is used to improve the convergence rate. By simulation, the proposed algorithm converges faster than another fuzzy frequency estimation algorithm, which cannot use numerical input/output information, in fading communication channels. The proposed algorithm also responds faster to frequency shift which may be caused by the relative motion between the transmitter and receiver (Doppler effect).

Near-field inverse coherent imaging problems: solutions, simulations and applications

This work presents a rigorous mathematical derivation of an effective approximate solution to the near-field 3-D inverse scattering/imaging problem. The model system operates in a synthetic aperture type mode, where the coherent signals are transmitted, and the scattered signals are subsequently received at individual transmitters and receivers. Simulation results show that the point spread function obtained from the algorithmic reconstruction are in close accord with the ground truth point spread function for scatterers located in both the near and far field of the coherent aperture.

Range Super Resolution For Near-field Coherent Imaging

The design of beamformer is a critical component in the development of coherent imaging. Conventional delay-and-sum beamformer is intuitive and easy to implement, however it does not provide good range resolution for narrow-band waveforms. In this paper, we propose a technique that optimizes the reconstruction kernel to approximate an ideal impulse, and has control over mainlobe/sidelobe tradeoff. Preliminary simulation has demonstrated that the new method achieves significantly better range resolution than simple delay-and-sum beamformers for narrow and medium band near-field imaging

Frequency Estimation of 2-D Sinusoids from Very Limited Data

A novel algorithm for estimating the frequencies of nearly maximum number (as bounded by the number of equations vs. unknowns) of 2-D sinusoids is described. The method is parametric model based and therefore it is not Fourier resolution limited. It utilizes redundant data in a least squares manner, therefore is quite robust and approaches asymptotic efficiency relatively fast. Finally, it is computationally affordable and does not require 2-D polynomial rooting. A numerical example of retrieving 12 2-D sinusoids from a 6times5 grid is demonstrated