Suppression of propagating second harmonic in ultrasound contrast imaging

Abstract

Contrast agents, such as bubbles, are used in ultrasound to enhance backscatter from blood. To increase contrast between these agents and tissue, nonlinear methods such as harmonic imaging can be used. Contrast is limited, however, by tissue second harmonic signals. We show that a major source of this signal is nonlinear propagation through tissue. In addition, we present methods to suppress this second harmonic generation. One simple approach is to decrease the f/number of the imaging system. Simulations show that doubling the size of the array, while keeping total power output constant, decreases propagating second harmonic generation. A second approach uses active noise cancellation to suppress second harmonic generation. A specific method, the harmonic cancellation system (HCS), is developed and presented as an example. In simulations, HCS decreased second harmonic generation by over 30 dB. Using such methods, contrast can be improved between tissue and bubbles in harmonic imaging.

Broadband Reduction of the Second Harmonic Distortion During Nonlinear Ultrasound Wave Propagation

“…The second criterion to quantify the harmonic suppression method is to consider the percentage of the second harmonic band that is being reduced. It was applied in the work of Krishnan et al (1998) and in a more recent work of Couture et al (2008) without any quantification.…”

“…By changing P*, the transmitted energy of the multiple component SHRS (E SHRS ) is influenced. In the case when m 5 0, single component SHRS is transmitted as proposed by previous authors (Krishnan et al 1997;Krishnan et al 1998;Christopher 1999).…”

“…A similar approach was used by Krishnan et al (1998), when the second harmonic signal in focus was filtered out and linearly back-propagated to the surface of the transducer.…”

“…The main difference between these methods lies in how the source prebiasing signal is computed. Krishnan et al (1997Krishnan et al ( , 1998) used a nonlinear scheme to predict the waveform in the focus, filtered out the second harmonic and linearly propagated it back to the surface of the transducer. The obtained signal was further inverted and mixed with the imaging pulse to define the source prebiasing signal.…”

A Wideband High-Voltage Power Amplifier Post-Linearizer for Medical Ultrasound Transducers

“…However, this method is not efficient because it is difficult to generate the appropriate leakage signal amplitude. (3) Nonlinear schemes have been reported to filter out the second harmonic signal before feeding to the transducer [25]. The disadvantage of this scheme is that pre-definition of the inverted and mixed signals before obtaining the echo signal in the system level is necessary.…”