Imaging and spectrum analysis of contrast agents in the in vivo rabbit eye using very-high-frequency ultrasound.

We have conducted initial studies that demonstrated the feasibility of employing ultrasonic contrast agents with very-high-frequency ultrasound (VHFU), using wideband transducers with center frequencies near 40 MHz. These studies were undertaken with an ultimate objective of quantifying perfusion in vessels in the eye and other organs. We expanded the model developed by Lizzi et al. (1983) to incorporate the scattering characteristics from encapsulated bubbles, such as contrast agents. Our analysis shows how the spectral slopes and intercepts measured from contrast agents are related to factors that include the radii and concentration of contrast-agent particles. We conducted in vitro experiments to validate the theoretical predictions and obtained excellent agreement. We obtained in vivo VHFU data from the eyes of anesthetized rabbits before and after injection of Albunex and Aerosomes. Digitally computed B-mode images demonstrated echo enhancement within the ciliary body and its processes. The magnitudes of these enhancements were quantified using calibrated spectrum-analysis techniques.