Synthetic aperture imaging with a virtual source element

Currently ultrasonic imaging is performed in one of two modes: conventional B-scan imaging with a focused transducer or array imaging using beamforming processing to achieve the focus. Conventional B-mode imaging suffers from a limited depth of focus while synthetic aperture imaging is limited by a low signal to noise ratio (SNR). A new technique has been proposed that combines these two techniques to overcome the limited depth of focus. The new technique involves focusing the region beyond the focus of the transducer by considering the focus a virtual element. In this paper, the use of the focus as a virtual element is examined, considering the model for the focus as an element, the use of apodization weights to lower sidelobes, and the SNR of the processed image. Using data collected with tungsten wires in a waterbath, it was found that resolution comparable to the resolution at the focus could be achieved while obtaining an acceptable SNR. Apodization was found to lower the sidelobes, but only at the expense of lateral resolution. With these experiments, the virtual source has been shown to exhibit the same behavior as an actual transducer element in response to synthetic aperture processing techniques.