Blood Speckle Imaging Underestimates Transvalvular Pressure Drops At High Flow Rates
Cameron Dockerill1, Harminder Gill1, Joao F. Fernandes1, Amanda Q. X. Nio1, Ronak Rajani2, Pablo Lamata1.
1King's College London, London, United Kingdom, 2Guy's and ST Thomas' NHS Foundation Trust, London, United Kingdom.
OBJECTIVE: 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 pump was used to circulate blood mimicking fluid at eight different flow rates (100, 150, 200 and 250 mL/s, constant and pulsatile flows; n=2). Eight PendoTech pressure sensors were embedded along the tube wall and wired to input modules of a National Instruments data acquisition USB chassis to record ground-truth pressures (10000Hz). The 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 under 100mL/s conditions, corresponding to peak flow velocity ~1.6m/s (10.4±1.76, 10.3±1.63 vs. 10.7±1.12 mmHg, respectively; p>0.05). Doppler overestimates pressure drop increasingly at higher flow rates, likely due to the error in estimation of momentum from a single velocity value (Bias = 3.54mmHg; Fig.1A). BSI underestimates pressure drop at high flow rates (Bias = -3.68mmHg; Fig.1B), likely due to an inability to track greater flow velocities.
CONCLUSIONS: The results demonstrate that BSI can track flow velocities up to 1.6m/s in controlled phantom conditions. The inaccuracies of Doppler and BSI reinforce the need for novel pressure estimation methods in cardiovascular diseases with elevated flow rates, such as aortic stenosis.
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