Some aspects of design of a high-sensitivy ultrasonic imaging system for medical diagnosis



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According to the second and third performance specifications of Sonographic Diagnostic Instrument by National Science Foundation, the ultrasonic transducer of a sonographic diagnostic instrument should supply a pulsed-focused ultrasonic beam which provides less than 0.5 mW/cm[squared] of time-averaged ultrasonic power. The range resolution should be less than 1.5 mm over the total range and the azimuth and elevation resolutions should be less than 1.5 mm at the focal plane of the transducer. None of the existing systems can satisfy all these requirements in imaging deep-lying objects. However, a positively scanning transducer (PST) system has the inherent capability. Such a system can be implemented with an opto-acoustic field pattern transformer. The system can be divided into two parts, that achieves focusing and that achieves scanning. The focusing part is to form a focused sound beam behind the opto-acoustic transducer (OAT) which is activated by an acoustic zone-plate (ZP) pattern; the scanning part provides the motion of the focal spot at the object plane which can be done with a combination of pinhole array and Fourier transform holography.