Imaging soft tissue through bone with ultrasound transmission tomography by reconstruction

A phantom consisting of a 2.5-cm-diameter aluminum rod, a balloon filled with castor oil, and a ballon filled with a phenylated silicone fluid was imaged in water with ultrasound transmission tomography by reconstruction (UTTR). This phantom was chosen for investigation of the feasibility of detecting small changes in the ultrasound velocity and ultrasound attenuation coefficient of soft tissues in planes containing bones. Attenuation images of a transverse section of a leg of lamb were obtained as well. Opposed transmitting and receiving transducers were scanned on either side of the imaged object, just as an x-ray tube and detector are scanned in the pencil beam geometry employed with the first x-ray computerized axial tomographic system. More than adequate signal was transmitted through the aluminum rod and the bone to obtain reconstructions; but, in these crude images, there were numerous artifacts which maintain the uncertainty regarding the future utility of this promising technique. Although velocity imaging should not be as sensitive to reflection and refraction as attenuation imaging, a very narrow ultrasound beam must be employed to obtain reasonable resolution in velocity imaging.