Synthetic transmit aperture imaging using orthogonal Golay coded excitation

The frame rate in medical ultrasound imaging may be increased significantly by reducing the number of transmits per image frame. Cooley et al. (1994) and Lockwood et al. (1995) have described synthetic transmit aperture (STA) systems where each frame is imaged using data obtained from a small number of point sources fired in succession. These systems have potential for very high frame rates, but they also suffer from low SNR. In this paper we present a computationally efficient method to increase the SNR of STA systems by using spatio-temporal encoding which increases SNR by 101og(ML) dB, where M is the number of active phase centers or transmits and L is the temporal code length. By using an orthogonal Golay set for the spatio-temporal encoding, the received data can be sorted by each transmit phase center and pulse-compressed for subsequent synthetic aperture beamforming. Computer simulations are used to demonstrate the method.