Ultrasound imaging of extended targets using a windowed time-reversal MUSIC method

Time-reversal with Multiple Signal Classification (TR-MUSIC) is an ultrasound imaging algorithm for detecting small targets embedded in a medium. This technique can produce images with subwavelength resolution when the targets are pointlike, and when the number of targets is fewer than the number of transducer elements used to image the medium. In this experimental study, we evaluate the performance of the TR-MUSIC algorithm when the interrogated medium contains extended targets that cannot be considered as point scatterers. We construct tissue-mimicking phantoms embedded with distributed glass spheres. We show that the quality of the phantom images obtained using the TR-MUSIC algorithm decreases with increasing sphere size. However, significant improvement is achieved when the image plane is divided into sub-regions, where each sub-region is imaged separately. The windowed TR-MUSIC algorithm accurately locates the spheres (extended targets), but the images do not provide quantitative information about the shape and reflectivity of the spheres.