Ultrasound contrast agent detection

In the field of diagnostic imaging we put special emphasis on molecular imaging, i.e. imaging methods that visualize cell properties on a molecular scale by targeted contrast agents. For this application ultrasonic contrast agents based on gas filled microbubbles stabilized by spherical shells play an important role.

When insonifying microbubbles with sound pulses which have centre frequencies in the diagnostic range, the microbubbles are excited to produce highly nonlinear oscillation. This is an important property which can be exploited to improve the detection of the contrast agents. The signal ratio between contrast agent and tissue may be increased by amplification of signal components originating from nonlinear systems and suppression of signal components originating from linear systems. Sound propagation in tissue and scattering, however, may only be considered linear for low amplitudes and small penetration depths. If these conditions are not met, the achievable contrast-to-tissue ratio is degraded. The aim is to employ nonlinear system theory for the development of novel detection methods which exploit the difference in nonlinearity between sound propagation and contrast agent oscillation which enable an improved contrast agent imaging.

Ultrasound image of a contrast agent containing phantom without (left) and with (right) deploying improved nonlinear signal processing.