Contrast-based ultrasonic blood flow measurements based on inflow/outflow time intensities

Ultrasonic contrast specific blood flow measurement techniques offer new opportunities to assess blood flow information based on evaluation of time-intensity curves (TICs). Such curves are measured to estimate the concentration of microbubbles in the blood pool. Based on the indicator-dilution theory, hemodynamic parameters such as the volume flow rate can be directly related to the time constant estimated from the TICs. In this paper, the applicability of the indicator-dilution theory is studied with an in vitro experiment setup. Moreover, the linear system assumption of the blood mixing mechanism is also tested. Several flow phantoms are constructed and a self-made, albumin based contrast agent is used. The TIC is measured by using B-mode images obtained from a commercial ultrasound system. It is found that with a bolus injection and a single mixing chamber, the estimated time constants agree with the theory despite the fact that the effective mixing volume may be smaller than the actual mixing chamber volume in some conditions. More importantly, discrepancy also exists with a prolonged injection and/or two mixing chambers with cascade connection. In other words, the linear system assumption is still questionable even under the controlled in vitro experimental conditions. Potential sources of the discrepancy require further investigation in order to develop contrast specific quantitative blood flow measurement techniques.