3D ultrasonic mapping of the microvasculature

The central goal of this work is the development and feasibility testing of systems capable of estimating velocity in small vessels at low flow velocities and mapping the vasculature in three dimensions. Specifically, we attempt to measure the velocity profile within vessels with a diameter of 100 microns or less. Estimation of flow within these vessels at the appropriate low velocities is challenging due to the small signal levels, the effect of cardiac and respiratory motion, and the unknown rate of fluctuation of the received signal from the small number of red blood cells contained within the sample volume. Three dimensional flow mapping of a region within the ciliary body of the rabbit eye has now been performed and the methods and results are described in this paper. We find that vessels as small as 40 microns can be mapped in 3D using a 38 MHz transducer. Realignment of the signal from a single line-of-sight is a critical part of this process and our method is presented in detail. Recognition of 3D continuity of a vessel tree is required to eliminate spurious noise.