Overdetermined Least-Squares Aberration Estimates Using Common-Midpoint Signals

Abstract

As medical ultrasound imaging moves to larger apertures and higher frequencies, tissue sound-speed variations continue to limit resolution. In geophysical imaging, a standard approach for estimating near-surface aberrating delays is to analyze the time shifts between common-midpoint signals. This requires complete data-echoes from every source/receiver pair in the array. Unfocused common-midpoint signals remain highly correlated in the presence of delay aberrations; there is also tremendous redundancy in the data. In medical ultrasound, this technique has been impaired by the wide-angle, random-scattering nature of tissue. This has made it difficult to estimate azimuth-dependent aberration profiles or to harness the full redundancy in the complete data. Prefiltering the data with two-dimensional fan filters mitigates these problems, permitting highly overdetermined, least-squares solutions for the aberration profiles at many steering angles. In experiments with a tissue-mimicking phantom target and silicone rubber aberrators at nonzero stand-off distances from a one-dimensional phased array, this overdetermined, fan-filtering algorithm significantly outperformed other phase-screen algorithms based on nearest-neighbor cross-correlation, speckle brightness maximization, and common-midpoint signal analysis. Our results imply that there is still progress to be made in imaging with single-valued focusing operators. It also appears that the signal-to-noise penalty for using complete data sets is partially compensated by the overdetermined nature of the problem.

Forward model for quantitative pulse-echo speed-of-sound imaging

“…This concept is closely related to approaches that have been developed for aberration correction of superficial SoS variations that act like a phase-distorting screen directly in front of the transducer array. They are based on analysing the differential echo phase as function of transducer element position in the channel data [32][33][34][35][36][37]. CUTE goes beyond these approaches: By determining the phase shift in the beamformed images as opposed to the channel data, lateral resolution of phase shift data is achieved also away from the aperture.…”

“…Even if the Rx aperture is constant while changing the Tx angle, the echo phase shift contains the influence of a virtually changing Rx angle. To avoid ambiguities, we propose to switch from a pure Tx-steering approach to simultaneously steering both, the Tx-and the Rx-angles, around a variety of common mid-angles, in an approach similar to the common mid-point gather that has been used in seismic imaging [41] as well as in US [35][36][37].…”

Improving Image Quality by Deconvolution Recovery Filter in Ultrasound Imaging

“…Furthermore, the channel signals of the two datasets were band-pass filtered in time and dip filtered in space-time first. 27 The dip filter is a finite impulse response filter based on the Hamming window function to compensate for phase aberrations. 3 In order to reduce the complexity, a single PSF is used for all depths.…”

“…26 A Panametrics 5800 PR ultrasound device (GE Panametrics, Waltham, MA) is used in the ATS#539 tissue-mimicking phantom to acquire these experimental datasets. 27 A GPIB-controlled radio frequency multiplexer (Matrix Systems, Calabasas, CA) can select array elements for receiving or transmitting. And a digital oscilloscope (LeCroy, Chestnut Ridge, NY) with a 12-bit resolution is used for digitization.…”

Sidelobe suppression in ultrasound imaging using dual apodization with cross-correlation

“…Borrowing concepts from common midpoint apertures [9, 10], spatial compounding [11–13] and the translating apertures algorithm [14], the next pair of apodization functions to be investigated is two uniformly weighted apertures that have a fractional translation of the active subaperture. The speckle patterns obtained from the two apertures with a large number of common elements are still well correlated.…”