VOLUMETRIC ARTERIAL FLOW QUANTIFICATION USING ECHO CONTRAST - AN IN-VITRO COMPARISON OF 3 ULTRASONIC INTENSITY METHODS - RADIO-FREQUENCY, VIDEO AND DOPPLER

The two hypotheses presented in this paper are: (1) absolute and relative volumetric flow rates in vessels can be measured by echo contrast time-intensity curves; and (2) echo contrast time-intensity curves generated by different ultrasound backscatter intensity techniques have equivalent capability for flow measurements. A nonpulsatile flow system was built for quantitative ultrasound backscatter measurements from bolus echo contrast injections using two different volumes of mixing. A total of 49 echo contrast bolus injections were made at various flow rates (0.44-2.59 L/min). Ultrasound backscatter time-intensity curves were generated by ultrasound radio frequency, video and Doppler techniques. The rate of backscattered ultrasound intensity washout for each technique (WASHOUT RATE), and relative change in WASHOUT RATE (partial derivative WASHOUT RATE) were compared to the volumetric flow rate (FLOW) and changes in flow rate (partial derivative FLOW), respectively. The relationship between WASHOUT RATE, FLOW and the volume of contrast mixing was studied. A linear relationship was demonstrated between WASHOUT RATE and partial derivative WASHOUT RATE and the corresponding FLOW and partial derivative FLOW by all three methods (r > 0.90 for all comparisons). The WASHOUT RATE was found to depend on the FLOW and the volume of contrast mixing, but the partial derivative WASHOUT RATE was equal to the partial derivative FLOW and independent of the volume of mixing. Time-intensity curves can be generated from different ultrasound backscatter intensity techniques and the WASHOUT RATE correlates well with FLOW. Partial derivative FLOW can be determined directly from the corresponding partial derivative WASHOUT RATE. Doppler ultrasound, because of its natural association with the assessment of flow in chambers and vessels, is uniquely suited to assessment of arterial volumetric blood flow in vivo.