Characterization of Blood-Mimicking Fluids for Quantitative Flow Imaging with Ultrasound.

Objective: This study aimed at characterizing blood-mimicking fluids (BMFs), focusing on properties relevant to standardizing quantitative imaging biomarkers in vascular and microvascular ultrasound.

Methods: Three BMF formulations (BMFs 1-3) were prepared following the International Electrotechnical Commission (IEC)-61685 standard, varying in dynamic viscosity and particle buoyancy. A novel figure of merit (FOM) assessed particle buoyancy over time. Density, dynamic viscosity, speed of sound, attenuation, and backscatter coefficient (BSC) were measured for unfiltered and filtered BMFs and compared to IEC-61685 reference values. BMFs were evaluated using power Doppler and contrast-enhanced ultrasound (CEUS) imaging in a calibrated custom-made microflow phantom at 5 and 20 mm/s, using contrast-to-noise ratio (CNR) as a performance metric.

Results: The FOM accurately tracked particle distribution and enabled obtaining neutrally buoyant BMFs. Filtration significantly impacted BSC (p < 0.05) but did not affect other properties. BMF 2 matched all the IEC-61685 reference values (p > 0.05). BMF 1 exhibited the lowest dynamic viscosity, while BMF 3 had the highest BSC. BMF 2 yielded the highest CNR at 5 mm/s in both imaging modes. At 20 mm/s, BMF 3 yielded the highest CNR in power Doppler imaging, while all BMFs performed similarly in CEUS. BMF 2 provided similar CNRs across flow velocities in both imaging modes.

Conclusion: A comprehensive methodology for BMF preparation and characterization was developed, which enabled identifying a formulation that aligned with the IEC-61685 standard. This methodology could establish a foundation for developing reproducible and well-characterized BMFs, facilitating the advance of quantitative flow imaging techniques with ultrasound.