Validation of Intravascular Ultrasound Pressure Gradient Estimation using Micro-tip Catheters

This study validates a newly developed non-invasive ultrasound pressure gradient estimation method against microtip catheters. It is hypothesized that the non-invasive ultrasound method is more precise and accurate compared to micro-tip catheters. The pressure difference is measured in a straight blood vessel phantom with a 70% areal constriction. The design of the mold enables catheters and ultrasound to be used on the same phantom. It contains two insertion channels positioned orthogonal to the blood vessel. Two 3.5F micro-tip catheters were inserted for measuring the pressure difference over the constriction. For the ultrasound measurement a 256 elements, 6.5 MHz GE-12-L3-D linear transducer connected to a Verasonics research scanner was used. It employed an interleaved sequence with 2 x12 virtual sources, which allows the estimation of high velocities. During measurement, the blood vessel phantom was connected to a flow pump, which mimics the pulsatile flow in the carotid artery, with a peak flow rate of 12.9 mL/s. The result of the non-invasive ultrasound method showed pressure differences changing from 7.8 to -81.3 Pa throughout a single flow cycle. This was estimated with a coefficient of variation of 5.9% (4.8 Pa). The result from the catheter measurement showed a pressure difference changing from 0 to -102.5 Pa throughout a single flow cycle. This was estimated with a coefficient of variation of 11.2% (11.4 Pa). This demonstrates that non-invasive pressure differences can be acquired using ultrasound, and, provide better precision compared to micro-tip catheters. The ultrasound procedure is inexpensive, free of risk, quick to perform, and can be acquired in patients not recommended for catheterization.