This proposal requests funding to establish the feasibility of real-time implementation of a novel 3D coded-excitation pulse-echo ultrasonic imaging system for cardiac imaging. The new approach is based on a discretized linear model of the received sampled data vector that results from the coherent sum of echoes from all scatterers in the region of interest (RO1). The discretization of the model leads to a matrix operator which can be inverted using a regularized pseudoinverse operator. Under simplifying (but realistic) conditions, the pseudoinverse operator is reduced to a transversal filter bank with every filter in the bank determines the number of image lines that cn be acquired simultaneously to meet the real-time requirements of the imaging system. In addition to being well-suited for parallel processing real-time implementation, the transversal filters are capable of decoupling echoes from different directions before performing matched filtering. Thus, our formulation eliminates major drawback of similar coded-excitation systems designed based only on matched filtering. Compared to conventional pulse-echo imaging systems based on delay-and-sum (DAS) beamforming, our approach leads to a system with higher lateral resolution beyond the diffraction limit imposed by DAS beamforming algorithms. The range resolution is achieved by an optimal Wiener filter, i.e., determined by the bandwidth of the imaging system and the system signal-to-noise ratio (SNR). Simulation and experimental verification of the above resolution properties are given in this proposal. A further improvement in the contrast-to-noise ratio (CNR) of the system can be obtained from the use of a single conventional receive beamformer available in all commercial scanners. A conventional DAS beamformer will be used for synthesizing multiple receive beams to serve as spatial masks to allow echoes from R01 at the output of the beamformer while blocking data from other directions. This is a significant improvement over previously proposed coded-excitation systems based on an omnidirectional receiver, which produce artifact-ridden images even in relatively high SNR situations. The combination of a powerful optimal (regularized) reconstruction operator and the use of a single conventional beamformer to control the data flow into the system will result in a robust image reconstruction operator capable of real-time 3D imaging of highly scattering media such as the human tissue.
| Shen, J; Ebbini, E S (1998) Filter-based coded-excitation system for high-speed ultrasonic imaging. IEEE Trans Med Imaging 17:923-34 |
