Generation of Separate Density and Compressibility Images in Tissue

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Abstract
A method is suggested for reconstructing separate images of the variations in density and compressibility in the same tissue sample. The images can be obtained from near-field scattering measurements using only two long, rectangular transducer elements. As in diffraction tomography, 180° access around the region of interest is required. This approach differs from conventional diffraction tomography, however, in that no transducer arrays are required and broadband illumination is used. A flat transducer, assumed long relative to the extent of the object, is used as a source of broadband, plane-wave illumination, and as a receiver of the backscattered sound. A second transducer, oriented at a different angle with respect to the first, is used as a receiver only. The two transducers are rotated together 180° around the object, and the scattered sound is recorded at all angles during the rotation. This arrangement can be shown to sample the plane-wave spectrum of the object directly, and provides sufficient information to reconstruct independent images of the variations in both the density and compressibility of the scattering medium. Image resolution is limited by the bandwidth of the illuminating sound.