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

Abstract

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 cmH 2 O and 12.53 ± 0.07 cmH 2 O, 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.

Design, confection and calibration of a flow phantom with ultrasound applications

“…The theoretical and experimental resistance values are compatible with literature [7]. As the theoretical resistance values of a R are smaller when compared to c R , it can be assumed the influence of the accessories on flow resistance is minimum, so the flow tends to be laminar in the phantom.…”

“…The dimension and flow rate values on phantom are compatible with brachial artery [2][3]. The pressure values on the phantom were compatible with similar models of literature [6][7]. This work aims to improve the experimental models for studying the heating pattern in biological tissues, especially therapeutic ultrasound safety tests.…”

“…Flow phantoms are hydraulic circuits capable of generating known and adjustable flow pattern pproviding a controllable experimental system against which hypotheses can be tested or measurements validated [7]. A flow phantom will typically consist of a vessel (generally confectioned in a rubber based material) suspended in a tissue mimic material and a fluid, which is pumped through the phantom.…”

“…The use of the reservoirs (B1 and B2) dampens oscillations from the peristaltic pump flow, and minimizes variation of the water level in the column during the pump cycle, which makes the flow laminar and continuous. The continuous flow system was chosen because it facilitates obtaining a laminar flow that is more common in small arteries [6][7].…”