Can sources and receivers be interchanged for imaging?

Abstract

Abstract-The design of ultrasound scanning systems for applications such as breast cancer detection is a challenging task, especially when the number of sources and receivers increases and they become spread over a large surface. In order to determine the number of transducers and above all their position, several approaches could be followed. A simple and straightforward approach is to compute the energy distribution in the region of interest for several configurations, and treat each receiver as if it is a source. Here the underlying assumption is that the number of A-scans, i.e. number of sources times receivers, determines the image quality. This assumption is mainly based on reciprocity; the observation that the response RAB measured by a receiver located at B and a source at A is identical to the response RBA obtained after interchanging the source and receiver locations. This is valid for linear imaging methods. However, the question arises whether this is also the case for nonlinear inversion methods. In this work, we evaluate the SAFT, CG and CSI imaging and inversion methods for different configurations of sources and receivers located uniformly distributed over a circular array, surrounding an heterogeneous medium. The obtained results show that with the linear SAFT and CG methods, the sources and receivers can be interchanged, and the resulting images are the same. However, for the non-linear CSI method, the results show that it is preferred to have more receivers than sources, despite the fact the measured signals are reciprocal.

Ultrasound Imaging of the Brain using Full-Waveform Inversion

“…Less sources (N src = 32) than receivers (N rec = 256) are used to scan the model. It has been shown previously that this will lead to a significant reduction in computational load and inversion time -without hardly any loss in convergence ratewhen FWI is employed [12].…”

Contrast source inversion on experimental data: initial results

“…Note that, for CSI it is advantageous to have more receivers than sources. 22 An example of the raw data for a measurement in water is shown in Figure 3. Note that, the signal is heavily distorted by noise before 2.3 µs and after 8 µs.…”

Design of Ultrasonic Synthetic Aperture Imaging Systems Based on a Non-Grid 2D Sparse Array

“…By the reciprocity principle, it is easy to identify that and introduce equivalent information in the beamformer. By extending this principle, an acquisition strategy that reduces the number of signals by almost half can be used [ 24 , 27 ]. Figure 2 a illustrates this strategy ( ), where each white square corresponds to one acquired signal.…”

“…Compared to sparse matrix arrays, sparse non-grid arrays allow better optimisation of the number of transducers. Regardless, they also show significant levels of redundancy, but, except for the reciprocity principle ( ) [ 24 ], it is not easy to identify other redundancies. Although a reduction in the number of signals has been proposed by random selection of a subset of elements operating as emitters [ 23 ], the study of how redundancy is structured and how it can be used to generate a less-redundant acquisition strategy is the key to design more efficient imaging systems with fewer resources.…”