A nonlinear imaging technique that demodulated the second harmonic component of the response of the Ultrasound Contrast Agent （UCA） was proposed. The UCA perfusion imaging method has been investigated from three aspects, mathematics principle, simulation and ultrasound experiment, respectively. Frequency-Modulated （FM） signal excitation has been introduced to increase Signal-to-Noise Ratio （SNR） in medical ultrasound imaging firstly. A theoretical simulation and an ultrasound experiment were performed to investigate if a cosine- enveloped frequency-modulated signal excitation could be applied in UCA imaging to increase SNR and Contrast-to-Tissue Ratio （CTR）. To obtain a good imaging, suitable parameters and a right envelope on the transmitted signal were needed, and a gap was also needed between the transmitted signal bandwidth and the decoded match filter bandwidth. A harmonic image was obtained with using of coded excitation and the decoded filter. The results suggested that using this harmonic imaging method, image could be got with good SNR and CTR. At the same time, the acoustical results were agreed with the theoretical results well.
GU Jinhong WAN Mingxi WANG Supin ZONG Yujin CHEN Ping
The present study was to investigate the differential imaging method for detecting HIFU （High Intensity Focused Ultrasound）-induced lesions and the estimation of variation of attenuation for lesion evaluation with log spectral difference algorithm. Experiment results of bovine muscle and liver in vitro were acquired. Several algorithms for lesion detection - Absolute Difference （AD）, Sum Absolute Differences （SAD） and Sum Squared Differences （SSD） - were analyzed with several window sizes and threshold values. Then three attenuation parameters were compared to evaluate the degree of tissue damage. It was found that variation of the mean attenuation △a^- was an effective parameter to evaluate lesions.
