Coded EXcitation with Spectrum Inversion (CEXSI) to improve SNR in sparse array imaging

We have proposed a forward-viewing ring-annular array for intravascular ultrasound imaging. Our proposed beamformer involves a total of 210 transceiver firings per frame. To maintain adequate signal to noise ratio (SNR) in such sparseness, an additional 10 dB SNR improvement is required. Conventional correlation-based coded excitation leads to substantial side-lobes due to small time bandwidth product. A scheme called Coded EXcitation with Spectrum Inversion (CEXSI) is presented. An established optimal binary code whose spectrum has no s and possesses the least variation is used for transmission. Decoding is a simple matter of spectrum inversion. Code transmission can be closely coupled to the transducer pass-band. For a 2.6 μs code, an array element with a center frequency of 10 MHz and fractional bandwidth of 38%, range side-lobes of about 40 dB have been achieved experimentally with little compromise in range resolution. SNR improvement also has been characterized at 14.5 dB. CEXSI can be extended to improve SNR in general sparse array imaging.