Basic study on velocity‐flow urodynamics using Doppler sonography: Simultaneous detection of cavitation and Doppler signals in an artificial urethral model

Abstract

Background: We have developed velocity-flow urodynamics using Doppler sonography based on the hypothesis that microbubbles formed in the urethra are responsible for Doppler signals. In order to confirm this hypothesis derived from Bernoulli's principle, we investigated the simultaneous detection of cavitation noise and Doppler signals in an experimental system. Methods: An experimental circuit was built in which a stenosis was created using a glass or silicon tube with tap water used as the sample fluid. Doppler signals, pressure before and after the stenosis, flow rate, flow velocity and cavitation noise were measured. Direct detection of cavitation with a high-speed charged-coupled device (CCD) camera was conducted in the glass tube. The relationship between cross-sectional area and flow velocity in terms of the detection of Doppler signals was analyzed in the silicon tube study. Results:In the glass tube study, a high-speed CCD camera clearly detected masses of microbubbles associated with cavitation. The range of flow rates creating cavitation completely corresponded with those producing Doppler signals detected by ultrasonography. A similar correlation was observed in the silicon tube study, which showed that a low flow velocity of 41.5 cm/sec through a stenosis with a cross-sectional area of 20 mm 2 created Doppler signals at a flow rate of 8.3 mL/sec. Conclusion:The results of the present study confirmed that microbubbles created in flowing urine are responsible for Doppler signals. Measurement of velocity-flow urodynamics has great potential to become a non-invasive and reliable alternative to conventional pressure-flow urodynamic studies.

The future of urodynamics: Non‐invasive ultrasound videourodynamics

“…Urine normally contains no blood cells so urinary flow was presumed not to create the backscattered signals that are essential for Doppler flow imaging 25 . We demonstrated that normal urine contains enough echodense microbubbles to allow clear visualization through Doppler ultrasonography 3,27 . The contrast material is not necessary.…”

“…How can Doppler signals be obtained from urine without particles? We hypothesize that microbubbles formed in liquid and/or tiny particles in the urine during flow are responsible for creating the Doppler effects based on Bernoulli's principle 27 . Bernoulli's principle states that where the velocity of a fluid is high, the pressure of the flow becomes low, and where the velocity is low, the pressure becomes high 28 .…”

Sonography of the distal urethra in lambs

“…Both techniques are used to create contrast through the introduction of microbubbles present in the catheter or the NaCl solution [11]. In this study, these techniques were not used because of the different anatomy of small ruminants’ urethra; in small ruminants, the narrow lumen of the processus urethralis at the tip of the penis makes the insertion of a urinary catheter difficult.…”

Use of Doppler ultrasound for non-invasive urodynamic diagnosis

“…A high Reynolds number (R > 2100) indicates turbulent flow, while a low Reynolds number (R<2000) indicates laminar flow. [10] Blood flow is usually laminar, mainly due to low viscosity, urine is likely to show turbulent flow in the urethra, which increases fluctuation of the regional flow velocity and flow pressure. Interactions between such factors inside a collapsible tube may explain why a smaller pressure decrease was required to create Doppler signals in the urethra.…”

“…Interactions between such factors inside a collapsible tube may explain why a smaller pressure decrease was required to create Doppler signals in the urethra. [10]…”