IN VIVO LATERAL FLOW ESTIMATION WITH SPATIAL QUADRATURE

The first in vivo lateral blood velocity estimates made using a heterodyned spatial quadrature‐based estimator are presented. Spatial quadrature is a method for quantifying the non-axial components of the blood velocity or tissue motion vector. The motivation of this work is to extend quantitative blood velocity imaging beyond the current display of only the axial component of the flow vector. Digital summed I & Q data for sequences of image frames were captured during scanning of the common carotid artery of an adult male with a 7.5MHz transducer. The ultrasound scanner used was programmed to generate spatial quadrature beams with 2:1 parallel receive processing. The scanner’s B-mode scan line sequence was altered to place an ensemble of 16 lines for flow estimation within the field of view. The frame sequences captured were 2.3 seconds in length, encompassing just over 2 cardiac cycles. These data were processed off-line to produce Mmode style lateral velocity displays and mean velocity profiles. Off-line processing included RF reconstruction and adaptive wall-filtering. It is notable that these measurements were made at Doppler angles greater than 80 degrees, i.e. significantly above the practical Doppler limit of 60 degrees. These results are presented showing pulsatility in the lateral velocity profile coinciding with the pulsation of the vessel walls over the cardiac cycle. The associated measurements of peak systolic velocities in the range of 60‐80 cm/s and of mean velocities on the order of 20‐30 cm/s are also presented, and the clinical implications of these results are discussed.