Blood speckle imaging compared with conventional Doppler ultrasound for transvalvular pressure drop estimation in an aortic flow phantom

Abstract

Background Transvalvular pressure drops are assessed using Doppler echocardiography for the diagnosis of heart valve disease. However, this method is highly user-dependent and may overestimate transvalvular pressure drops by up to 54%. This work aimed to assess transvalvular pressure drops using velocity fields derived from blood speckle imaging (BSI), as a potential alternative to Doppler. Methods A silicone 3D-printed aortic valve model, segmented from a healthy CT scan, was placed within a silicone tube. A CardioFlow 5000MR flow pump was used to circulate blood mimicking fluid to create eight different stenotic conditions. Eight PendoTech pressure sensors were embedded along the tube wall to record ground-truth pressures (10 kHz). The simplified Bernoulli equation with measured probe angle correction was used to estimate pressure drop from maximum velocity values acquired across the valve using Doppler and BSI with a GE Vivid E95 ultrasound machine and 6S-D cardiac phased array transducer. Results There were no significant differences between pressure drops estimated by Doppler, BSI and ground-truth at the lowest stenotic condition (10.4 ± 1.76, 10.3 ± 1.63 vs. 10.5 ± 1.00 mmHg, respectively; p > 0.05). Significant differences were observed between the pressure drops estimated by the three methods at the greatest stenotic condition (26.4 ± 1.52, 14.5 ± 2.14 vs. 20.9 ± 1.92 mmHg for Doppler, BSI and ground-truth, respectively; p < 0.05). Across all conditions, Doppler overestimated pressure drop (Bias = 3.92 mmHg), while BSI underestimated pressure drop (Bias = -3.31 mmHg). Conclusions BSI accurately estimated pressure drops only up to 10.5 mmHg in controlled phantom conditions of low stenotic burden. Doppler overestimated pressure drops of 20.9 mmHg. Although BSI offers a number of theoretical advantages to conventional Doppler echocardiography, further refinements and clinical studies are required with BSI before it can be used to improve transvalvular pressure drop estimation in the clinical evaluation of aortic stenosis.

Multi-modal Phantom Experiments, mimicking Flow through the Mitral Heart Valve

“…A higher velocity through the valve is observed for increased CO and valve stiffness, an effect also seen for the mean and maximum pressure differences, consistent with the Bernoulli equation. However, a comparison of catheter pressure measurements and Doppler measurements shows Doppler tends to overestimate the maximum pressure difference across the valve, consistent with literature [33]– [35]. Despite this, Echo measurements are commonly used in the clinical setting, since it is a non-invasive and easily accessible method [36], which further highlights the importance of the conducted measurements in our study as they provide additional insights into Echo measurements.…”

Aortic Stenosis: Haemodynamic Benchmark and Metric Reliability Study

“…Transverse images were obtained by insonation of the valve at an oblique, shallow angle (refer to Fig. 3 Dockerill et al [ 16 ].). Longitudinal images were obtained placed with the probe parallel to the direction of fluid flow.…”

“…The net pressure drop was measured as the difference between channels 1 and 7 at the time of the peak pressure drop. Details of the pressure analysis have been reported by our group[ 16 ]. The peak-to-peak pressure was identified as the absolute difference between the peak pressure measured in channel 1 and the peak pressure measured in channel 7.…”

“…In this report, we document a fabrication technique which yields functional and imaging-compatible aortic valves, created rapidly and at a low cost (see supplementary materials for an in-depth discussion of material choices and consideration). The phantom has already allowed the study of the USbased blood speckle imaging alternative for a more accurate estimation of the peak pressure drop [16] and the validation of an MRI-based method to estimate the pressure recovery distance (JCMR-D-22-00247 accepted for publication). The silicone elastomer presented was a very cost-effective choice to generate a varying range of aortic valve flow conditions, and this has been reported previously [17].…”

Invasive assessment of aortic stenosis in contemporary practice

“…It relies on two assumptions: (1) the pressure drop is entirely due to spatial acceleration of blood flow, neglecting the impact of unsteady and viscous components, and (2) the blood flow is considered a single streamline, which neglects the velocity distribution across the aortic valve plane ( 3 ). While it is known that the first assumption is indeed accurate as the spatial acceleration of blood is the dominant pressure component, there is evidence that the use of a single peak velocity value to the detriment of a complete velocity profile results in consistent overestimation of transvalvular pressure drop and is a source of uncontrolled variability ( 3 , 23 ).…”