Second harmonic ultrasonic blood perfusion measurement.

In vitro and in vivo testing of a recently introduced method of evaluating blood perfusion is presented, where the Doppler shift of the second harmonic component of the backscattered echo is measured. Central to this measurement is the administration of a galactose-based contrast agent (Schering AG, Berlin, Germany, SHU-508 or derivative) which has been shown in vitro to exhibit extraordinary nonlinear backscattering properties. Two types of experiments are described: in vitro studies on excised sheep kidneys and in vivo studies on living rabbits. In the animal model, blood perfusion was manipulated by various mechanisms to obtain some indication of the quantitative ability of the measurement. Comparisons between measurements made at the fundamental component of the backscattered echo and at the second harmonic show that use of the second harmonic measurement results in a much improved ratio of blood echo intensity to tissue echo intensity (signal-to-clutter ratio), allowing detection of blood flowing in smaller vessels and opening up the potential for real-time determination of blood volume fluctuations in tissue.