Aberration correction in ultrasonic medical imaging with time-reversal techniques
✍ Scribed by Mathias Fink; Christian Dorme
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 444 KB
- Volume
- 8
- Category
- Article
- ISSN
- 0899-9457
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✦ Synopsis
Degradation of image quality is currently observed with assumed to behave as a distribution of scatterers embedded in ultrasonic scanners owing to distortion of the ultrasonic beams a homogeneous medium. When the tissue is illuminated by an through inhomogeneous tissue layers. Adaptive time-delay focusing ultrasonic pulse, each scatterer behaves as a secondary source, techniques allow an efficient correction of these effects when the and it is assumed that the wave emanating from each secondary inhomogeneous layer is close to the transducer array. If the aberrating source is not perturbed by the other scatterers (first-order Born layers are far from the array, these techniques are no longer approapproximation). The purpose of ultrasonic imaging is to reconpriate to correct the propagation effects between the layer and the struct the map of all the scatterers with the best possible accuracy.
transducer array. In this article we show that time-reversal mirrors This reduces to developing a processing technique matched to can solve this problem. In the matched-filter approach that extends each possible scattered wave. Conventional imaging techniques the concept of time reversal mirrors, the Green's function of a dominant scatterer available in the medium is recorded in digital memory make the assumption that each scatterer is a source of a spherical and used to focus on the scatterer in both transmit and receive wave propagating with a constant velocity toward the transducer modes. An extension of this technique is also presented to focus, in array. Then, the processing reduces to the recognition of each of the presence of an aberrating layer, not only on the dominant scatthese spherical waves. This is obtained in conventional beam terer, but also around it to image the surrounding zone. From the forming by using a bank of delay lines adjusted to ensure that knowledge of the Green's function needed to focus on the initial the recorded waveforms in the individual channels are in phase scatterer, new Green's functions matched to the new point of interest before summation. The delay lines are adapted to the curvature are calculated. The algorithm uses the concept of time-reversal propof the divergent wave coming from each scatterer. Such a agation, and theoretical and experimental results obtained with this technique are presented. The calculation of each Green's function matched filter adapted to a spherical wave simulates the action matched to each new desired focal point allows us to realize a Bof a spherical transducer which produces a strong signal when a scan image of the zone surrounding the reflector. ᭧ 1997 John Wiley & scatterer is located at its focus. Steering and dynamic focusing