Real-time implementation of lateral flow estimation using spatial quadrature

The first real-time implementation of lateral flow estimation using spatial quadrature is described and results of its application in flow-phantom experiments presented. Spatial quadrature (SQ) is a recently-introduced technique for two- or three-dimensional flow velocity estimation. In its most basic form, this technique interrogates the region of interest with a pair of point spread functions which have weightings in the lateral dimension with a quadrature relationship. These weightings produce a modulation in the echoes from scatterers moving laterally through a resolution volume. This modulation can be decoded to quantify the lateral velocity component. In this SQ implementation, summed radio-frequency echo data was captured in an M-mode scan geometry using 2:1 parallel processing in spatial quadrature with a 7.5 MHz linear array and a conventional ultrasound scanner. The target for these experiments was a phantom vessel composed of an 8 mm latex tube in a water tank. Using a computer-controlled calibrated flow pump, blood-mimicking fluid was circulated through this vessel at constant volume flow rates of 5-25 ml/s, corresponding to peak flow velocities in the range of 10-45 cm/s. Laminar flow was established in the vessel through the use of a long, straight in-flow tube leading into the vessel. Lateral velocity estimates were subsequently processed off-line to produce velocity profiles over range. These velocity profiles show the parabolic shape characteristic of laminar flow. Volume flow rates were estimated from these profiles using a parabolic curve fit. At optimum pulse repetition frequencies, these SQ-based estimates agreed with the known volume flow to ⩽5.1% for all flow rates tested