Coded excitation for synthetic aperture ultrasound imaging
Peak acoustic power limits the signal-to-noise ratio (SNR) of real-time ultrasound images. For most conventional scan formats, however, the average power is well below heating limits. This means the SNR can be significantly increased using coded excitation. A coded system transmits a broadband, temporally elongated excitation pulse with a finite time-bandwidth product. The received signal must be decoded to produce an imaging pulse with improved SNR resulting from the higher average power in the elongated excitation. Decoding can produce significant range side lobes, however, greatly reducing image quality. All practical coding designs, therefore, represent a trade-off between SNR gain and range side lobes. A specific coding scheme appropriate for synthetic aperture imaging is presented. A 14.5 dB SNR improvement with acceptable range side lobes is demonstrated on a forward-looking imaging system appropriate for intravascular applications.