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Purpose: The objective of this project is to demonstrate the principle and operation for a simple, inexpensive, and highly portable Doppler ultrasound quality assurance (QA) phantom intended for routine QA testing. A prototype phantom has been designed, fabricated, and evaluated. The phantom described here is powered by gravity alone, requires no external equipment for operation, and produces a stable fluid velocity useful for quality assurance. Many commercially available Doppler ultrasound testing systems can suffer from issues such as a lengthy setup, prohibitive cost, nonportable size, or difficulty in use. This new phantom design aims to address some of these problems and create a phantom appropriate for assessing Doppler ultrasound stability. Methods: The phantom was fabricated using a 3D printer. The basic design of the phantom is to provide gravity-powered flow of a Doppler fluid between two reservoirs. The printed components were connected with latex tubing and then seated in a tissue mimicking gel. Spectral Doppler waveforms were sampled to evaluate variations in the data, and the phantom was evaluated using high frame rate video to find an alternate measure of mean fluid velocity flowing in the phantom. Results: The current system design maintains stable flow from one reservoir to the other for approximately 7 s. Color Doppler imaging of the phantom was found to be qualitatively consistent with laminar flow. Using pulsed spectral Doppler, the average fluid velocity from a sample volume approximately centered in the synthetic vessel was measured to be 56 cm/s with a standard deviation of 3.2 cm/s across 118 measurements. An independent measure of the average fluid velocity was measured to be 51.9 cm/s with a standard deviation of 0.7 cm/s over 4 measurements. Conclusions: The developed phantom provides stable fluid flow useful for frequent clinical Doppler ultrasound testing and attempts to address several obstacles facing Doppler phantom testing. Such an ultrasound phantom can make routine testing more approachable for institutions that wish to initiate a Doppler QA program or complement a previously existing QA program. [ABSTRACT FROM AUTHOR]

Purpose: Doppler optical coherence tomography (OCT) is widely used for measuring retinal blood flow. Existing Doppler OCT methods require the eyeball axial length, in which empirical values are usually used. However, variations in the axial length can create a bias unaccounted for in the retinal blood flow measurement. The authors plan to develop a Doppler OCT method that can measure the total retinal blood flow rate without requiring the eyeball axial length. Methods: The authors measured the retinal blood flow rate using a dual-ring scanning protocol. The small and large scanning rings entered the eye at different incident angles (small ring: 4; large ring: 6), focused on different locations on the retina, and detected the projected velocities/phase shifts along the probing beams. The authors calculated the ratio of the projected velocities between the two rings, and then used this ratio to estimate absolute flow velocity. The authors tested this method in both Intralipid phantoms and in vivo rats. Results: In the Intralipid flow phantom experiments, the preset and measured flow rates were consistent with the coefficient of determination as 0.97. Linear fitting between preset and measured flow rates determined the fitting slope as 1.07 and the intercept as -0.28. In in vivo rat experiments, the measured average total retinal blood flow was 7.02±0.31μl/min among four wild-type rats. The authors' measured flow rates were consistent with results in the literature. Conclusions: By using a dual-ring scanning protocol with carefully controlled incident angle difference between the two scanning rings in Doppler OCT, the authors demonstrated that it is feasible to measure the absolute retinal blood flow without knowing the eyeball axial length. [ABSTRACT FROM AUTHOR]

Purpose: There is a lot of speculation about the role of nitric-oxide (NO) in the improvement usually noticed in microcirculatory function, following exercise. The knowledge of the underlying mechanisms leading to such an improvement is important as it may help in targeting and implementing therapies for microcirculatory diseases. Through a laser Doppler flowmetry (LDF) signal processing study, the authors' goal is to compare multifractal spectra of LDF data recorded in both lower leg and forearm, during different exercise conditions, in an older, untrained but healthy population. Methods: Using the method suggested by Halsey et al. [Phys. Rev. A 33, 1141-1151 (1986)], multifractal spectra of LDF signals recorded on lower leg and forearm before and after exercise (arm-cranking), before and after acetylcholine (ACh) iontophoresis, were determined on scales in relation with the NO-dependent endothelial activity. The width of each multifractal spectrum was then computed through the maximum and minimum Hölder exponent values for which the multifractal spectrum reaches its minimal values. The results were then compared. Results: Following exercise and on the scales studied, the average width of the multifractal spectra in both lower leg and forearm does not vary significantly before and after ACh iontophoresis. Similarly, following ACh iontophoresis and exercise, the average width of multifractal spectra remains statistically unchanged, when compared to that measured prior to exercise, in both upper and lower body, although negative trends can be observed. Conclusions: For the authors' population and for the type of exercise that the authors have chosen, the authors showed that the width of the multifractal spectra of LDF signals does not change significantly on scales in relation with the NO-dependent endothelial activity. Future studies may involve comparisons with signals obtained in patient populations. [ABSTRACT FROM AUTHOR]