Super-resolution ultrasound tomography: A preliminary study with a ring array

Ultrasound tomography attempts to retrieve the structure of an object by exploiting the interaction of acoustic waves with the object. A fundamental limit of ultrasound tomography is that features cannot be resolved if they are spaced less than λ/2 apart, where λ is wavelength of the probing wave, regardless of the degree of accuracy of the measurements. Therefore, since the attenuation of the probing wave with propagation distance increases as λ decreases, resolution has to be traded against imaging depth. Recently, it has been shown that the λ/2 limit is a consequence of the Born approximation (implicit in the imaging algorithms currently employed) which neglects the distortion of the probing wavefield as it travels through the medium to be imaged. On the other hand, such a distortion, which is due to the multiple scattering phenomenon, can encode unlimited resolution in the radiating component of the scattered field. Previously, a resolution better than λ/3 has been reported in these proceedings [F. Simonetti, pp. 126 (2006)] in the case of elastic wave probing. In this paper, we demonstrate experimentally a resolution better than λ/4 for objects immersed in a water bath probed by means of a ring array which excites and detects pressure waves in a full view configuration.