Efficient array beamformer using spatial filtering for ultrasound B-mode imaging

摘要

We propose an efficient array beamformer using spatial matched filtering. In the proposed method, ultrasound waves are transmitted from an array subaperture with fixed transmit focus as in conventional array imaging. At receive, radio frequency (RF) echo signals from each receive channel are passed through a spatial matched filter that is constructed based on the system transmit-receive spatial impulse response. The filtered echo signals are then summed. The filter remaps and spatially registers the acoustic energy from each element so that the pulse-echo impulse response of the summed output is focused with acceptably low side lobes. Analytical beam pattern analysis and simulation results using a linear array show that the proposed spatial filtering method can provide more improved spatial resolution and contrast-to-noise ratio (CNR) compared with conventional dynamic receive focusing (DRF) method by implementing two-way dynamically focused beam pattern throughout the field. We tested the predictions experimentally using an f/1.5, 8-ring annular array with 10 MHz center frequency focused geometrically at 45 mm. The -6 dB beam width measured with spatial filtering and DRF were measured to be 0.13 mm and 16.64 mm, respectively, at a depth of 25 mm. Spatial filtering was applied to the design of high frequency arrays for small animal imaging where delay and sum beamforming is problematic. Predictions of beam properties at 70 MHz will be presented.