Synthetic sinc wave employs pulsed plane waves as a transmit beam with linear time delay curve. The received echoes in different transmit directions at different transmit times are superposed at imaging points with proper time delay compensation using synthetic focusing scheme. This scheme, which uses full aperture on transmit, obtains a high SNR image, and also features high lateral resolution by using two-way dynamic focusing at all imaging depths. In this paper, we consider the realization problem of the synthetic sinc wave. It is experimentally explored by obtaining phantom and in vivo data with a linear array of 5 MHz. The phantom experiments indicate that the synthetic sinc wave maintains a high resolution over a more extended imaging depth than conventional fixed point transmit and dynamic receive focusing schemes. In vivo images show that the resolution of the synthetic sinc wave does not exceed the conventional focusing systems because of tissue motion, phase aberration, or both, but that the frame rate can be increased by a factor of more than five compared to the conventional focusing schemes, while maintaining competitive resolution at all imaging depths.
This paper proposes a method of imaging the stiffness of soft tissue to help diagnose cancers or tumors which have been difficult to detect with ultrasound B-mode imaging modality. To measure the soft tissue stiffness, sinusoidal vibrations are applied to it, and the magnitude of its mechanical vibration is determined by estimating the temporal variation of speckle pattern brightness in ultrasound B-mode images. It is verified by simulation and experiment that the proposed method can estimate the relative tissue stiffness from B-mode images with a modest amount of computation.
Waveform synthesis for pulse-echo medical ultrasonic imaging, in conjunction with post-beamforming filtering, will undoubtedly play an important role in defining the ultimate quality of the next generation of medical ultrasonic imaging. Two important applications that will rely heavily on appropriate waveform synthesis are contrast- assisted imaging and multi-modal high-speed imaging with parallel processing of multiple image lines using coded excitation and filterbank reconstruction. In this paper, we address the issue of beam-space waveform synthesis using ultrasound phased arrays typically used in medical pulse- echo imaging applications. Simulation and experimental results will be presented to illustrate the role of the transducer aperture and bandwidth characteristics in the waveform synthesis. Furthermore, we generalize the concept of point-spread function (PSF) to allow for the post- beamforming filter-based image reconstruction. We show experimentally that these PSFs serve as a reliable predictor of the image quality for multi-modal pulse-echo imaging systems employing post-beamforming filter-based reconstruction. Combined with a computationally efficient Fourier-based method for their derivation, these PSFs thus serve as a powerful tool in the design and optimization of coded waveforms for pulse-echo imaging applications. A description of the waveform synthesis algorithm will be given along with illustrative examples using computer simulations and experimental results from tissue-mimicking phantoms.