Precision of in vivo pressure gradient estimations using synthetic aperture ultrasound

Non-invasive estimation of pressure differences using 2D synthetic aperture ultrasound imaging offers a precise, low-cost, and risk-free diagnostic tool. Unlike invasive techniques, this preserves natural blood flow and avoids the limitations of devices that occupy lumen space. This paper evaluates a previously published estimator, modified to incorporate Singular Value Decomposition (SVD) echo-cancellation, using data from ten healthy volunteers and one patient. It is hypothesized that the estimator will enable precise pressure differences from the common carotid artery with a coefficient of variation of approximately 10% over a 10-second data acquisition period. Here, precision is essential to demonstrate the method's consistency and its ability to differentiate between healthy and diseased arteries at the earliest possible stage. Data are acquired using a GE-9L-D, 5.2 MHz linear transducer connected to a Vantage 256 research scanner. The estimator was applied to the left common carotid artery of ten healthy volunteers, with precision being evaluated over the recorded heart cycles by using the coefficient of variation. Eight out of ten individuals showed precision below 10%, whereas two individuals showed precision above 20%. The best precision was attained by subject_03 with a coefficient of variation of 4.64% (16.1 Pa) and the worst precision was attained by subject 09 with a coefficient of variation of 23.3% (30.2 Pa). The average range of pressure differences across volunteers (from maximum positive to maximum negative pressure difference) was 297 Pa when measured across a 14 mm streamline. The corresponding average coefficient of variation was found to be 9.95% (24.6 Pa). A comparison of peak systolic velocities between the experimental scanner and the reference scanner demonstrates a strong positive linear correlation (R² = 0.76). The corresponding slope of the linear best fit is 0.95, indicating that the relationship between the two scanners is close to a one-to-one match, with the experimental scanner's measurements being slightly less than those of the reference scanner. Finally, data attained from a single patient example shows pressure differences ranging from -61.81 Pa to 1240.82 Pa with blood velocities as high as 1.73 m/s, which is significantly higher than seen in any of the healthy volunteers, supporting the likelihood of differentiating between stenosis grades in future studies. While this study is limited to 10 healthy volunteers and one patient, a different study design is needed to quantify the severity of stenosis and correlate it with pressure differences.