Selecting the number and location of sources and receivers for non-linear time-domain inversion

The design of ultrasound scanning systems for breast cancer detection is a challenging task. To decide on the number of transducers and where to place them, several approaches could be followed. A simple and straightforward approach is to compute for several configurations the energy distribution in the region of interest, and treat each receiver as if it is a transmitter. In that case, the assumption is made that the effect a source or a receiver has on the resulting image is on an equal level. This assumption is mainly based on reciprocity; the observation that the response RAB measured by a receiver at the location B and for a transmitter at location A is identical to the response RBA obtained after interchanging the source and receiver. This is true for linear imaging methods, where a source can be interchanged with a receiver without affecting the resulting image. However, for the non-linear imaging method named Contrast Source Inversion (CSI), it does matter. In the past we showed that interchanging sources with receivers does affect the image. In this work, we evaluate the reciprocity property for the non-linear time-domain inversion (TDI). We show that the reciprocity principle is satisfied when using TDI for imaging, by using a synthetic experiment design.