Research On High-frequency Ultrasonic Tissue Harmonic Information Extraction Based On Phase Inversion Technique

Ultrasound tissue harmonic imaging (THI) is not only one of new technologies in the field of medical ultrasonic imaging, but also one of highlights and difficulties during the last several years. Better resolution and contrast can be obtained by employing THI technique in ultrasonic imaging. It has shown us remarkable advantages in clinic application. Now, it has just been used successfully in low-frequency (below 10MHz, large apparatus like abdomen) diagnostic ultrasound. Due to the characters of the HF ultrasound, there are more requirements on methods and the system to extract the harmonic frequency component. Still was the blank in the application of THI in high frequency (dozens of MHz, small apparatus like eye) ultrasonic diagnostic.This paper designs a pulse-coded transmitting and wide-band receiving system. By using coding transmitting, it can adjust the spectrum of the transmitting pulse, make the transmitting signals match with transducers effectively, so it can improve the spectrum of the echoes and reduce the overlap of frequency bands. Using the wide-band transducers, abundant information of the tissues can be obtained. Thus, with this system, it can have a better harmonic exaction by using phase inversion technique. The data of the echoes in the experiment are processed with Matlab.The experiment result indicates: with the high-frequency ultrasonic digital coded transmitting and the wide-band amplifier designed in this paper, in HF phase inversion harmonic extraction, it can reduce the influence of the fundamental frequency, and simultaneity can increase in the magnitude of the HF harmonic component by about six dB. It has an obvious advantage over the conventional RF filter method in the aspect of harmonic separation.This study provides a method for the application of medical ultrasonic harmonic imaging to the high frequency band. It has laid the foundations for the generalization of ultrasonic harmonic imaging system from low frequency (several MHz) to high frequency (dozens of MHz ), for small apparatus(ophthalmology), and even for UBM.