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Ultrasound-based blood flow (BF) monitoring is vital in the diagnosis and treatment of a variety of cardiovascular and neurologic conditions. Finite spatial resolution of clinical color flow (CF) systems, however, has hampered measurement of vessel cross Section areas. We propose a resolution enhancement technique that allows reliable determination of BF in small vessels. We leverage sparsity in the spatial distribution of the frequency spectrum of routinely collected CF data to blindly determine the point spread function (PSF) of the imaging system in a robust manner. The CF data are then deconvolved with the PSF, and the volumetric flow is computed using the resulting velocity profiles. Data were collected from phantom blood vessels with diameters between 2 and 6 mm using a clinical ultrasound system at 2 MHz insonation frequency. The proposed method yielded a flow estimation bias of 0 mL/min, standard deviation of error (SDE) of 22 mL/min, and a root-mean-square error (RMSE) of 22 mL/min over a 150 mL/min range of mean flows. Recordings were also obtained in low signal-to-noise ratio (SNR) conditions using a skull mimicking element, resulting in an estimation bias of -13 mL/min, SDE of 23 mL/min, and an RMSE of 26 mL/min. The effect of insonation frequency was also investigated by obtaining recordings at 4.3 MHz, yielding an estimation bias of -16 mL/min, SDE of 16 mL/min, and an RMSE of 22 mL/min. The results indicate that our technique can lead to clinically acceptable flow measurements across a range of vessel diameters in high and low SNR regimes.

We aid in neurocognitive monitoring outside the hospital environment by enabling app-based measurements of visual reaction time (saccade latency) and directional error rate in a cohort of subjects spanning the adult age spectrum. Methods: We developed an iOS app to record subjects with the frontal camera during pro- and anti-saccade tasks. We further developed automated algorithms for measuring saccade latency and directional error rate that take into account the possibility that it might not always be possible to determine the eye movement from app-based recordings. Results: To measure saccade latency on a tablet, we ensured that the absolute timing error between on-screen task presentation and the camera recording is within 5 ms. We collected over 235,000 eye movements in 80 subjects ranging in age from 20 to 92 years, with 96% of recorded eye movements either declared good or directional errors. Our error detection code achieved a sensitivity of 0.97 and a specificity of 0.97. Confirming prior reports, we observed a positive correlation between saccade latency and age while the relationship between directional error rate and age was not significant. Finally, we observed significant intra- and inter-subject variations in saccade latency and directional error rate distributions, which highlights the importance of individualized tracking of these visual digital biomarkers. Conclusion and Significance: Our system and algorithms allow ubiquitous tracking of saccade latency and directional error rate, which opens up the possibility of quantifying patient state on a finer timescale in a broader population than previously possible.

This work details the non-invasive evaluation of a carotid arterial blood pressure (ABP) waveform during the Valsalva maneuver. Unfocused and wide acoustic beams are insonated on the carotid artery to achieve motion-tolerant measurements with a simple two-element ultrasound scanner. Arterial flow and distension waveforms are reliably estimated from spectral Doppler and M-mode ultrasound images whose qualities are consistently maintained in different phases of the maneuver despite possible displacements of the artery. A local pulse wave velocity is estimated using a flow-area method, and it is then combined with the distension waveform to produce the ABP waveform. Human subject validation on seven healthy subjects shows that the bias in pulse pressure estimates across subjects is 0.47 $\pm$ 13.1 mmHg. The average root mean square deviations of the ultrasonically measured waveform across subjects is 10.1 $\pm$ 2.43 mmHg, excluding the strain phase of the Valsalva maneuver, and 17.7 $\pm$ 6.30 mmHg in all phases. The mean correlation coefficient between the ultrasonically measured and reference waveform is calculated to be 0.92 $\pm$ 0.04 across subjects. Detailed morphological features and their changes across different phases are observed as reported. This uninterrupted central ABP waveform monitoring under hemodynamics changes supports the idea of a novel stress test to evaluate the health and dynamics of the cardiovascular system at a spot check in clinical settings.