The axial resolution which is a figure of merit in the medical ultrasonic imaging is determined by the temporal duration of the impulse response of an ultrasonic peizoelectric transducer to a single point target. In general, we have much difficulty in improving the axial resolution because an improved axial resolution usually results in a deteriorated transducer sensitivity to low-reflectivity targets. Therefore, we propose a new scheme referred to as the reverse excitation method for improving the axial resolution by a factor of two or so.
In order to verify the proposed reverse excitation method, the piezoelectric material, transducer, and pulser are exactly modeled and simulated on a VAX-11/750 computer. The reverse excitation method is experimentally applied to a prototype ultrasonic disk-shaped transducer as well as a commercially available linear transducer array. The experimental results agree well with those obtained with the computer simulation studies, thereby corroborating the proposed reverse excitation method and making it possible to apply the method in diagnositc ultrasound B-scanners for obtaining well-resolved images.
