EFFECTS OF DIFFRACTION ON ULTRASONIC COMPUTER-ASSISTED TOMOGRAPHY.

Ultrasonic computer-assisted tomography has been developed as a analog to the x-ray computer-assisted tomography techniques1 and has been used for measuring acoustic speed and attenuation in tissues2,3,4,5. The advantages of computer-assisted tomography are that quantitative images representing parameters such as attenuation or acoustic speed, can be obtained relating values represented by an image to fundamental properties of the tissue. The disadvantage of computer-assisted tomography is that a large pleurality of angles of view are required to obtain the necessary data6. This results in the technique being applied primarily to imaging accessible organs such as the breast around which 360° of views can be obtained using specially designed ultrasound scanners7. The most commonly used form of ultrasonic transmission tomography algorithm is that in which the ultrasonic energy is assumed to travel in a straight line8, although more advanced techniques have been proposed by ourselves and others such as Mueller, et al.9,Stenger and Johnson10 and Dines and Kaki11 and Schomberg12.

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