Abstract
Ultrasonic contrast agents have been used to assist blood flow measurements. Several contrast-specific flow measurement techniques have been proposed during the last few years. Among them, a method based on relative enhancement of the backscattered signal as a function of time is of particular interest. This method is also known as the time-intensity method. The method is based on the indicator-dilution theory, and the time-intensity curve is used to derive blood flow-related parameters such as the flow rate and the blood mixing volume. Previous in vitro studies done by other research groups were mainly based on a perfusion model or an artery model. Results showed that several parameters derived from the time-intensity curve had a good correlation with the flow rate under certain conditions. However, the studies did not focus on factors such as mixing volume, mixing chamber configuration and different types of mixing chamber. In this paper, dependence of the time-intensity curve is further studied. Specifically, two types of blood-mixing chambers were constructed. One was a spherical compartment phantom with two different sizes (260 and 580 mL) and different inflow/outflow configurations. The other was a perfusion phantom consisting of dialysis cartridges with the volume ranging from 114 to 351 mL. The time intensities were also measured at both the input and the output of the mixing chamber. A commercial agent (Levovist®) and a self-made, albumin-based agent were used and the wash-out time constant and the mean transit time were derived for flow rates ranging from 500 to 1300 mL/min. For the perfusion phantom, results showed that the parameters had a good correlation with both the flow rate and the mixing volume. Results from the compartment phantom, on the other hand, indicated that the inflow/outflow configuration and the mixing size significantly affected the derived time constants. Potential applications of new volumetric flow estimation techniques based on both input and output intensities were also discussed. (E-mail: paichi@cc.ee.ntu.edu.tw)
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