Microvascular imaging — results from a phase I study of the novel polymeric ultrasound contrast agent SHU 563A

Abstract

Ultrasound diagnosis uses B-mode images to provide anatomical information and Doppler analysis to measure the velocity of blood flow. In the capillaries, however, the velocity of blood flow (0.03–0.3 cm/s) is comparable to the speed of motion of the surrounding tissue, so capillary flow cannot be imaged by conventional Doppler techniques. Another limiting factor is the extreme spatial complexity of the capillary network. A new ultrasound contrast enhancer, SHU 563A, with non-linear acoustic properties, could overcome these limitations [1]. When the new agent is exposed to high power ultrasound it produces a characteristic sound which, on a color Doppler display, appears as pseudo-Doppler shifts. Color Doppler flow mapping depends upon the correlation between successive pulses which is infringed by the non-linear response of SHU 563A. The image based on pseudo-Doppler shifts shows the location of the contrast enhancer and gives a map of microparticle distribution. This new procedure may be described as ‘LOC’ imaging (loss of correlation representing contrast agent localization). The image provided by a conventional color Doppler ultrasound scanner after injection of SHU 563A contains no information on fluid flow velocities. Instead it provides a color map of the distribution of the contrast agent. It gives a direct image of the microvascular compartment that contains anatomical and functional information on microvascular perfusion.