Experimental observation of super-resolution imaging in highly attenuative materials

Routine applications of ultrasound imaging in medical diagnostics combine array technology and beamforming (BF) algorithms for image formation. Although BF is very robust, it discards a significant proportion of the information encoded in ultrasonic signals. Therefore, BF can reconstruct some of the geometrical features of an object but with resolution limited by the transmitted wavelength according to the Rayleigh criterion. Recent studies have shown that imaging formation techniques based on inverse scattering rather than standard BF can overcome the Rayleigh limit to achieve subwavelength resolution. This allows for high resolution images to be obtained at relatively large wavelengths that can penetrate deep into highly attenuative media such as human tissue. In this paper we present the first experimental demonstration of subwavelength resolution in glycerol whose ultrasonic attenuation is in the order of 1 dB/cm/MHz and which is comparable to the attenuation observed in tissue. Using a commercial clinical scanner and strands of human hairs we show that the inverse scattering approach outperforms current sonography revealing features that are undetected by sonography.