Supplementary Golay pair for range side lobe suppression in dual-frequency tissue harmonic imaging

Abstract

BackgroundIn dual-frequency (DF) harmonic imaging, the second harmonic signal at second harmonic (2f0) frequency and the inter-modulation harmonic signal at fundamental (f0) frequency are simultaneously imaged for spectral compounding. When the phase-encoded Golay pair is utilized to improve the harmonic signal-to-noise ratio (SNR), however, the DF imaging suffers from range side lobe artifacts due to spectral cross-talk with other harmonic components at DC and third harmonic (3f0) frequency. MethodsIn this study, a supplementary Golay pair is developed to suppress the range side lobes in combination with the original Golay pair. Since the phase code of the DC interference cannot be manipulated, the supplementary Golay is designed to reverse the polarity of the 3f0 interference and the f0 signal while keeping the 2f0 signal unchanged. For 2f0 imaging, the echo summation of the supplementary and the original Golay can cancel the 3f0 interference. On the contrary, the echo difference between the two Golay pairs can eliminate the DC interference for f0 imaging. ResultsHydrophone measurements indicate that the range side lobe level (RSLL) increases with the signal bandwidth of DF harmonic imaging. By using the combination of the two Golay pairs, the achievable suppression of RSLL can be 3 and 14dB, respectively for the f0 and 2f0 harmonic signal. B-mode phantom imaging also verifies the presence of range side lobe artifacts when only the original Golay pair is utilized. In combination with the supplementary Golay pair, the artifacts are effectively suppressed. The corresponding range side lobe magnitude reduces by about 8dB in 2f0 imaging but remains unchanged in f0 imaging. Meanwhile, the harmonic SNR improves by 8–10dB and the contrast-to-noise ratio of harmonic image increases from about 1 to 1.2 by spectral compounding. ConclusionFor DF tissue harmonic imaging, the spectral cross-talk in Golay excitation results in severe range side lobe artifacts. To restore the image quality, two particular phase-encoded Golay pairs are required to perform either echo summation or difference for elimination of unwanted harmonic components.