SURF imaging for ultrasound contrast agents

Objectives: Ultrasound contrast bubbles are true blood pool agents that can be used for improved diagnosis in many clinical situations. However, current contrast agent detection methods have some fundamental limitations reducing the applicability of contrast-enhanced ultrasound. Available methods rely on driving the contrast bubbles into strong nonlinear oscillations by the imaging pulse limiting the imaging frequency and hence spatial image resolution. Current methods utilize only a fraction of the scattered contrast agent signal where the received linear part is suppressed to suppress tissue hence limiting the sensitivity. Also, nonlinear signal components from tissue which are accumulated in the forward propagating transmit pulse are not suppressed resulting in reduced specificity. In Trondheim we have developed improved nonlinear methods that are given the name Second order UltRasound Field imaging, with the acronym SURF imaging.

Methods: The SURF contrast imaging method is achieved by processing of the received echoes from transmitted dual frequency band pulse complexes with overlapping high and low frequency pulses. The transmitted high frequency pulses are used for image reconstruction whereas the transmitted low frequency pulses are used to manipulate the scattering from the contrast agents.

Results: Using SURF pulse complexes the imaging pulse can be decoupled from the resonant properties of the contrast bubbles allowing contrast detection at any frequency. Also, improved specificity and sensitivity can be obtained. Examples from in vitro and in vivo SURF contrast imaging will be shown.

Conclusions: SURF contrast imaging has the potential of improving the significance of contrast-enhanced ultrasound.