Work Energy Relative Pressure Gradients using 2D Synthetic Aperture Ultrasound

Pressure gradient estimations are used as a biomarker for cardiovascular diseases. Here non-invasive pressure gradients are desired over invasive catheterization. This study estimates non-invasive pressure gradients from synthetic aperture ultrasound using the work-energy method. The method is translated to 2D synthetic aperture ultrasound by assuming rotational symmetric blood vessels and is hypothesised to yield more precise estimation compared to the unsteady Bernoulli method along a streamline. The method uses flow rates, blood velocities and acceleration for estimating the pressure gradient. Data are acquired using a 256 elements, 6.5 MHz GE L3-12-D linear array transducer connected to a Verasonics research scanner with a pulse repetition frequency equal to 5 kHz. A interleaved sequence using 12 virtual sources is used for both flow estimations and B-mode imaging. The interleaved sequence allows correlation frames to be separated by only the pulse repetition time, making it possible to estimate high velocities. The work energy method is compared to a previously validated unsteady Bernoulli method (streamline method) using experimental data from a blood vessel phantom with a 60% stenosis. The result shows that the work-energy method detects a maximum pressure difference of 3.42 Pa and a minimum pressure difference of -53.3 Pa with a precision of 3.04% across eleven pulse cycles. The unsteady Bernoulli method detected pressure differences changing from 5.44 Pa to -68.2 Pa with a precision of 3.23%.