Title :
Band-pass filtering for optimal displacement estimation in the presence of grating lobes at large beam steering angles
Author :
Hansen, Hendrik H. G. ; Idzenga, Tim ; de Korte, Chris L.
Author_Institution :
Dept. of Radiol., Radboud Univ. Nijmegen Med. Centre, Nijmegen, Netherlands
Abstract :
Multi-dimensional ultrasound displacement estimation accuracy can be improved by projecting high resolution radio frequency (RF) based axial (along the beam) displacements estimated at multiple beam steering angles. When the beam steering angle increases or when the ratio between ultrasound frequency and element pitch becomes larger, grating lobe artifacts increase, which distorts the displacement estimation. This study investigates the effect of low-pass filtering with various cut-off frequencies on the displacement estimation accuracy. The goal is to determine if there is a frequency cut-off point below which the grating lobe distortion ceases to dominate the increase in displacement estimation accuracy due to the addition of main lobe signal. Ultrasound RF data were obtained of a homogeneous block phantom (10×10×4 cm3) before and after 400 μm vertical displacement applied using a micromanipulator. An L11-3 (Sonos 7500, Philips) and an L5-13 (Accuvix V10, Samsung) linear array transducer were used to acquire RF data at beam-steering angles of 0°, 10°, 20° and 30°. Both transducers had -20 dB bandwidths of 3-13 MHz. The measurements were repeated more than fifteen times. Pre- and post-displacement datasets were created after band-pass filtering with upper frequency cut-off points varying between 3.5 and 13.5 MHz in steps of 1 MHz. The lower frequency cut-off was kept fixed at 2.5 MHz. Axial displacements for each dataset were determined using a coarse-to-fine 2D cross-correlation based algorithm. The angular axial displacement fields were projected vertically and the root mean squared errors of the displacements were calculated. It was found that for optimal displacement estimation accuracy it was beneficial not to fully remove the grating lobe signal by low-pass filtering, but to set the upper frequency cut-off slightly higher. In that way, an essential part of the main lobe signal was maintained - nd the major part of the grating lobe artifacts was removed.
Keywords :
acoustic correlation; acoustic field; acoustic variables measurement; band-pass filters; beam steering; low-pass filters; mean square error methods; phantoms; ultrasonic transducer arrays; Accuvix V10 linear array transducer; L11-3 sonos linear array transducer; L5-13 linear array transducer; angular axial displacement fields; band-pass filtering; beam steering angle; coarse-fine 2D cross-correlation based algorithm; displacement estimation accuracy; distance 400 mum; element pitch; frequency 2.5 MHz to 13.5 MHz; frequency cut-off point; grating lobe artifacts; grating lobe distortion; high resolution radio frequency based axial displacements; homogeneous block phantom; lobe signal grating; low-pass filtering; micromanipulator; multidimensional ultrasound displacement estimation accuracy; multiple beam steering angles; optimal displacement estimation; optimal displacement estimation accuracy; postdisplacement datasets; root mean squared errors; ultrasound RF data; ultrasound frequency; vertical displacement; Accuracy; Beam steering; Cutoff frequency; Estimation; Gratings; Transducers; Ultrasonic imaging; beam steering; compounding; grating lobes; strain imaging; ultrasound;
Conference_Titel :
Ultrasonics Symposium (IUS), 2012 IEEE International
Conference_Location :
Dresden
Print_ISBN :
978-1-4673-4561-3
DOI :
10.1109/ULTSYM.2012.0641