STUDY ON THE IMPROVEMENT OF IMAGE DEGRADATION FOR ULTRASONIC ECHOGRAPHIC IMAGE BY USING HIGHER ORDER HARMONICS

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This study concentrates on the improvement of image degradation of ultrasonic echographic images by using higher order harmonics which are generated while ultrasound waves propagate through the biological tissues., Since image degradation caused by speckle patterns in the echographic image has been a problem, it is an important task to reduce these patterns to obtain higher quality images. In order to detect the higher harmonic components contained in the echo signals efficiently, a specialized transducer for broadband reception, besides the transmitting transducer is necessary. By constructing a mechanical sector scanner of an ultrasonic diagnosis system using such a PZT-PVDF two-layered ultrasonic probe, an ultra-broadband ultrasonic imaging system capable of a real time imaging was prototyped. Thus, the real time imaging was carried out by obtaining the echo signal from phantoms using a PZT-PVDF two-layered ultrasonic mechanical sector probe, and the effectiveness of its higher harmonic components from the fundamental to the fourth harmonic was confirmed in speckle reduction. Then we prototyped the novel transducer which transmits ultrasonic pulse of dual-frequency and receives multi-frequency echoes from the biological tissues. When the ultrasonic pulse off and 4f_0 are transmitted into the biological tissues, 2f_0, 3f_0, and 5f_0 components are generated as the secondary waves. We have prototyped the PZT disk of 7 mm in diameter coaxially arranged in the PZT ring of 17 mm in outer diameter The ring and circular transducers transmit the pulses of 2 and 8 MHz, respectively. It was confirmed that this transducer formed the ultrasonic beams of 4, 6 and 10 MHz as well as the beams of 2 and 8 MHz in degassed water. Then the experiments of imaging the agar-gel phantom and pork meat were carried out by mechanical scanning. As a result, we also confirmed the improvement of image degradation by reducing the speckle noise.