ABSTRACT
Vascular US contrast agents consist of gas-filled microbubbles stabilized by a thin shell (Fig. 1). They are typically less than 8 µm in diameter, which allows them to pass through the pulmonary circulation and the systemic capillary beds (1). When administered intravenously, US contrast agents improve the detection of blood flow and depiction of the vasculature in a variety of structures compared to conventional (i.e., noncontrast) sonography due to the increased signal-to-noise ratio (SNR). These agents significantly enhance the acoustic backscatter from blood in both Doppler and grayscale modes, which results from the large impedance difference between the gasfilled microbubbles and the surrounding blood. In certain contrast-specific imaging modes, the SNR can be further
improved by suppression of tissue signals. The improved SNR can also be exploited in nonvascular structures such as the genitourinary tract, gastrointestinal (GI) tract, fallopian tubes, and lymphatic system.
