Effective lateral modulations with applications to shear modulus reconstruction using displacement vector measurement

Abstract

High accuracy in measuring target motions can be realized by combined use of our previously developed lateral Gaussian envelope cosine modulation method (LGECMM) and displacement vector measurement methods that enable simultaneous axial and lateral displacement measurements, such as the multidimensional autocorrelation method (MAM). In this paper, LGECMM is improved by using parabolic functions and Hanning windows instead of Gaussian functions in the apodization function, i.e., parabolic apodization and Hanning apodization. The new modulations enable decreases in effective aperture length (i.e., channels) and yield more accurate displacement vector measurements than LGECMM due to increased echo signal-to-noise ratio and lateral spatial resolution. That is, on the basis of a priori knowledge about ultrasound propagation using the focusing scheme and shape of the apodization function, we stopped using Fraunhofer approximation. As practical applications of the modulations, for an agar phantom that is deformed in a lateral direction, stable and accurate 2-D shear modulus reconstructions are performed using our previously developed direct inversion approach together with 2-D strain tensor measurements using MAM.

Ultrasonic agar phantom experiment for comparison of the measurement accuracy of tissue elasticity obtained by displacement vector measurement using lateral modulation with multidimensional autocorrelation and Doppler methods and corresponding one-dimensional methods

“…We have been maximizing beamforming [1][2][3][4][5] by using beam steering and apodization for accurately measuring tissue (eg, breast, liver, and heart) or blood displacement vectors or strain tensors using the multidimensional cross-spectrum phase gradient method (MCSPGM) 6,7 or multidimensional autocorrelation or Doppler methods (MAM and MDM). 1,8,9 For instance, we have reported [1][2][3]9 several lateral modulation (LM) methods in addition to other beamforming methods, ie, the multidirectional synthetic aperture method (MDSAM) and multiple transmitting method (MTM).…”

“…1,8,9 For instance, we have reported [1][2][3]9 several lateral modulation (LM) methods in addition to other beamforming methods, ie, the multidirectional synthetic aperture method (MDSAM) and multiple transmitting method (MTM). Our developed LM is achieved by the coherent superimposition of crossed, steered beams (LM).…”

“…Our developed LM is achieved by the coherent superimposition of crossed, steered beams (LM). [1][2][3]9 The LM has a higher potential for realizing a more accurate measurement of a displacement vector in real-time than the synthesis of the displacement vector using the accurately measured axial displacements obtained by MDSAM or MTM.…”

“…[1][2][3]9 Our developed LM can also be used for B-mode imaging simultaneously. 1,2 If necessary, plural transducers are also used.…”

“…[1][2][3]9 Our developed LM can also be used for B-mode imaging simultaneously. 1,2 If necessary, plural transducers are also used. [1][2][3]9 We also reported another beamforming technique that requires less beam generation and signal processing, ie, ASTA, [3][4][5] which involves the steering of beams through a steering angle.…”