A Novel Nonlinear Frequency Compounding Method for B-mode Imaging

A very low frequency signal centered at DC (0 Hz) is generated together with the 2^nd harmonic signal as the acoustic waves propagate in nonlinear tissue. This DC harmonic (DCH) signal is usually regarded as “noise” and is eliminated. However, this signal contains information that can potentially improve image penetration given that it occupies the low frequency band. Currently, with wide-band probes to cover the DCH signal and advanced processing schemes to separate signals that occupying different spectral bands, the DCH signal can be “extracted” and exploited to help improve image quality, such as penetration. Furthermore, the pulse inversion (PI) transmit scheme is usually employed in the harmonic imaging as it provides better suppression of fundamental leakage. The summation of the received signals from the positive and negative pulses in PI yields the DCH and even-order harmonics, while the subtraction yields the fundamental and odd-order harmonics. Therefore, with a regular PI transmission, we can generate the DCH, the fundamental and the 2^nd harmonic signals simultaneously (assuming higher-order harmonics are out of transducer band). 3 distinct images can be created from signals of these 3 distinct spectral bands. And these images are selectively compounded to achieve optimal image quality throughout depths. Moreover, the frame rate is equivalent to regular THI with the PI transmit scheme.