| The traditional B mode ultrasonic detection uses the amplitude envelope information of ultrasonic backscattered RF signal of biological soft tissue to image,and doesn't utilize the frequency and phase information completely,which is related to the microstructure of soft tissue.The attenuation coefficients,elastic properties,sizes and concentration (the numbers of scatterers per unit volume) of ultrasonic features scatterers of biological soft tissue all will be changed accordingly,when the tissue is disease.The power spectrum of ultrasonic backscattered RF signal is related to the sizes,geometric shapes,concentration and elastic properties of ultrasonic features scatterers,and so on.Using the frequency and phase information of ultrasonic backscattered RF echo signal to study the microstructure characteristics of soft tissue and explore the application of ultrasonic diagnosis technology about physiological and pathology diagnosis in biological soft tissue has become a hot and difficult problem of tissue characterization.In detail,the context includes three parts:(1) Based on the principle of ultrasonic propagation in biological soft tissues,we studied the relationship between the central frequency offset of ultrasonic backscattered RF signals and the scatterer sizes of soft tissues in focal region of focal ultrasonic transducer.We utilized the computer simulation to explore the effect on the central frequency shift by the attenuation coefficient and scatterers concentration of biological soft tissue,the central frequency,bandwidth and focal property of ultrasonic transducer.(2) Based on the theoretical analysis of power spectrum of ultrasonic backscattered RF signals, this paper has made four experimental imitations,which contained different scatterer sizes,and conducted a signal acquisition and processed the data about the experimental imitations,and studied the frequency characteristics.The experimental imitations was composed of gelatin,glass beads,glycerin,distilled water,antiseptic and glutaraldehyde.The average effective scattered radius of glass beads is 36.25μm,47μm,55.25μm and 64.25μm,respectively.(3) We used fresh pig liver to vitro experiments and conducted the statistical analysis of scatterered spectrum of liver's different parts.According to the histological anatomy of liver tissue,Hepatic Lobule is the basic unit of liver.The Hepatic Lobular has important contribution on the ultrasonic scattering in liver tissue.The liver can been divided into three characteristic scattering areas.The first area is the edge and surface layer areas of liver.This area's structural scattering is approximate to the characteristic of rayleigh scattering.The second area is between the below areas of liver surface layer and the center of liver. This area's structural scattering has the characteristic of random scattering; The third area is the central areas of liver.This area's structural scattering has the characteristic of proliferation diffusion,which has stronger reflection.Ultrasonic scattered spectural characteristics and the central frequency offsets of backscattered RF signal are different in different scattered areas.The results of computer simulations reveal that the frequency shifts of ultrasonic backscattered RF signal from biological soft tissues increase approximately linearly with the sizes of scatterers.The frequency offsets are related to the attenuation coefficients of soft tissues and the central frequency and the bandwidth of the launch transducer.The offsets increase with the augmentation of these parameters.While the concentration of scatterers and focal parameters of focal ultrasonic transducer have little influence on the frequency offsets.The research results of imitations experiment show that the central frequency of ultrasonic backscattered RF signals of experimental imitations will trend to low frequency,when the sizes of ultrasonic feature scatterers is increased,and it is closered to the central frequency of launch ultrasonic signal.The results of vitro experiments show that the ultrasonic spectrum of structural scattering has obvious specificity, because of the structure of biological soft tissue is different.The scattering of ultrasonic wave in liver's edge and the surface layer area mainly displays in high frequency.The high frequency components of scattered spectrum will gradually decrease,and the low frequency components will gradually increase with the depth of tissue is increasing.The low frequency components are dominated in central areas of liver.Lots of research results show that there is a certain relationship between the sizes of ultrasonic features scatterers and the central frequency offsets of ultrasonic backscattered RF signal of biological soft tissue in focal region of focal ultrasonic transducer.It is may characterize the characteristics of physiology and pathology of soft tissue through studying the size of ultrasonic features scatterers. In practical application,it should consider the area structural characteristics and the offset of ultrasonic backscattered RF signal of soft tissue to characterize the abnormal tissue.In addition,the focal property of ultrasonic transducer may not be considered while studying the frequency offsets. |
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