Volume Flow
True volume flow becomes very simple and straight forward to measure once 3D/4D color Doppler imaging can be performed. The measurement technique uses Gauss's Theorem, which states that volume flow is equal to the total integrated flux over any surface cutting across a conduit with flow. The theorem is satisfied if a surface can be defined cutting through a blood vessel in cross-section and then imaging the velocity components perpendicular to that surface. The method is independent of Doppler angle, flow profile, vessel geometry, and vessel pulsatility. Hence, it has none of the limitations of the present Doppler volume flow estimation methods. The nearly perfect surface over which to make a volume flow calculation is defined by a standard "C" scan in a 3D/4D color flow acquisition. This technique should make volume flow acquisitions as simple and straightforward as present day routine color Doppler imaging.

Pressure Gradients
3D/4D ultrasound acquisitions in real time can also depict true flow velocities. Using 2D arrays, it should be possible to actually obtain 3D velocity estimates in specific blood vessels. It should then be possible to estimate vascular pressure gradients by locally solving the Navier-Stokes equation. To do this, one needs to know all of the 3D local velocities and their derivatives across a region of flow. This is a computationally extremely difficult problem, but across a finite stenosis, solutions might become tractable. If viable, it may no longer necessary to perform interventional procedures to determine pressure drops across stenoses.