Development of a microfluidics-based tooth-pulp flow phantom for validation of doppler ultrasound devices

Abstract

I. Introduction Doppler ultrasound is generally used in medical diagnostics for measuring blood flow in a wide range of blood vessels. Recently, Doppler ultrasound has been used for measuring pulpal blood flow (PBF). However, the reliability of this method has not been sufficiently addressed. Flow phantoms have been used to evaluate the velocity estimation using Doppler ultrasound devices. However, most of these phantoms are designed to simulate relatively large blood vessels in milli or centimeter scale, which passes through the matrix material that mimics soft tissue. Therefore, they are not applicable as substitutes for dental hard tissues and pulp. Microfluidics is known as the science of fluid mechanics manipulated at micro or nanometer scales. It has emerged as an important tool in several research fields for microanalytical purposes. There have been a few studies using microfluidics for simulating tissue-vascular network. However, the use of microfluidics for evaluating Doppler ultrasound devices, as well as dental hard tissue and pulp has not been reported. In this study, we present a microfluidics-based flow phantom developed as a blood flow model of dental hard tissue and pulp for use in experiments involving Doppler ultrasound technique. By using the flow phantom, the accuracy of a Doppler ultrasound device in making velocity estimations was evaluated.

II. Materials and methods A computer-controlled microfluidic system was constructed to generate triangular pulsatile flow profiles. Blood-mimicking fluid was pumped through a 200×200 μm-sized channel in the microfluidic chip. A Doppler ultrasound device with a 20 MHz-transducer was used for the measurement of fluid flow. The peak, mean, and minimal flow velocities obtained from the flow phantom and the Doppler ultrasound device were compared using linear regression analysis and Pearson's correlation coefficient. Bland-Altman analyses were performed to evaluate the differences of the velocities between the phantom and the Doppler ultrasound device. III. Results The microfluidic system was able to generate the flow profiles as intended, and the fluid flow could be easily monitored and controlled by the software program. Using the soft lithography technique, we were able to fabricate a micrometer-sized channel. There were excellent linear correlations between the peak, mean, and minimal flow velocities of the phantom and the measured velocities from the Doppler ultrasound device (r = 0.94, 0.98, and 0.996, respectively, p < 0.001). However, it is observed that the Doppler ultrasound device overestimated the flow velocities by 1.69, 2.00, and 2.23 cm/s, with respect to the peak, mean, and minimal velocities.

IV. Conclusions We believe that this phantom provides opportunities for expanding future researches involving Doppler ultrasound, as well as in the field of hemodynamics and physiology of the dental pulp. Although Doppler ultrasound can be an effective diagnostic tool for quantitative measurement of PBF, it is essential to validate and calibrate the system prior to clinical use.