Continuous flow phantom for the calibration of an ultrasonic transit-time flowmeter

INTRODUCTION: Ultrasound Transit-Time flowmeters are based on the fact that the time required for an ultrasound pulse to propagate through a given distance in a moving medium is a function of the vectorial sum of pulse propagation velocity and medium velocity. The most common application of this flowmeter in medicine is in the evaluation of blood flow in arteries and veins during heart vascular surgery. The present article describes the design, construction and evaluation of a flow phantom for transit-time flowmeters calibration. METHODS: Basically, it is a hydraulic circuit containing degassed and distilled water. In such a circuit, a constant differential water level is established between two columns that are interconnected by tubes with defined resistance, which determines a known flow rate. A basic theoretical model to estimate the system Reynolds Number and resistance was developed. RESULTS: A flow range between 4.43 ± 0.18 ml.min-1 and 106.88 ± 0.27 ml.min-1 was found to be compatible with physiological values in small vessels. The pressure range was between 0.20 ± 0.03 cmH2O and 12.53 ± 0.07 cmH2O, and the larger Reynolds Number was 1134.07. Experimental and theoretical resistance values were similar. CONCLUSION: A reproducible phantom was designed and built to be assembled with standard low-cost materials and is capable of generating adjustable and continuous flows that can be used to calibrate TTFM systems.

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