Development and Validation of a Miniaturized Ultrasonic Measurement System for Acoustic Characterization of Human Urine Samples

Abstract

Urine analysis is a common method of diagnosing conditions in a medical context. Common testing methods, such as a urinalysis dipstick test, use colour-changing pads to detect analytes within the composition of the urine. However, collecting and analyzing a sample using this method introduces contaminants and requires qualitative assessment with introduces human error which may affect the results. Ultrasound (US) wave propagation offers a potential non-invasive method of characterizing urine by measuring acoustic properties like the speed of sound (SoS) and the acoustic attenuation coefficient (AC). These properties vary depending on the physical properties of the medium, including density and composition. Although the SoS and AC of human urine exhibit potential as effective biomarkers for pathological conditions, the SoS and AC of human urine have rarely been investigated in literature. By utilizing the properties of ultrasound wave propagation to characterize the acoustic properties of urine, acoustic information can be collected from individual samples to form a well-defined dataset. A recruited population of 40 volunteer participants, over 18 years of age, provided samples which were analyzed using a custom experimental setup. Transducers transmit pulses in a pitch-catch orientation at variable distances (1 – 10 cm) to obtain both SoS and AC values at two temperatures (37 °C and 23 °C). The measured distance value, along with the time-of-flight of the signal, are used to obtain the SoS. Total signal loss obtained from the amplitude at various distances, is made up from attenuation, diffraction, and system losses. Using characterization and references to isolate and fit the attenuation gives us the AC. The density of the urine was also measured through a simple mass/volume relationship. The 40-volunteer dataset of AC and SoS values were compiled paired with defined typical and non-typical analyte readings. SoS and AC values ranged from 1490 – 1580 m/s and 0.035 – 0.45 dB/cm at 5 MHz across the two measured temperatures. The AC, SoS, and density values for both typical and non-typical samples were statistically compared and analyzed for significance to determine key identifiers within urine such as bilirubin and hemoglobin (p < 0.05). This thesis involves creating and implementing a new instrument design that is used to obtain a reference of urine acoustic properties and demonstrates feasibility of ultrasound-based urine characterization. Lessons learned through the course of the study lead to the refinement of the measurement apparatus, implementing a more accessible form factor while maintaining most functionality. The study findings provide a foundation for investigating AC and SoS as potential biomarkers for pathological conditions and to inform future studies that stem from this work.