Based On Coded Excitation And Pulse Compression Deep Media Signal-to-noise Ratio And Resolution Of Ultrasound Elastography Improved

The distribution characteristics of elastic parameters of the biological soft tissue can be detected by the elastography technique. Compared to the conventional ultrasonic imaging method, elastography has the capability of detecting distribution characteristics of elastic parameters in the tissue, thus has a bright prospect in medical ultrasonic imaging. However for deep tissue detection, it has drawbacks like low SNR (Signal to Noise Ratio) and low SR (Spatial Resolution) due to serious noise influence, which limits its applications.In conventional elastography method, Quasi-static Ultrasonic Cross-correlation Estimation approach is used to compare the two signals echoed and received from tissue before and after applying an external compression. Thus inner strain of the tissue and the inversed hardness distribution can be obtained. Generally, in this approach, the signal transmitted through transducer is a short-time pulse whose amplitude is limited due to the threshold of ultrasonic damaging on human body, thus is vulnerable to noise, while the signal attenuates by being absorbed and scattered in the tissue. When in greater detection depth, the elastographic result has a low SNR and a relatively poor SR.To increase the SNR of echoed signals, we could increase the pulse transmission power and increase the pulse length. However increased transmission power may have chance to damage human body, thus this lays a contradiction ensuring the SR and increasing the SNR. In radar systems, CE (Coded Excitation) and PC (Pulse Compression) is commonly used to improve the average transmission power. Under the same average transmission power, both better SR and higher SNR can be achieved using the approach introduced above.In this paper CE/PC and elastography was combined to achieve elastographic imaging using CE/PC method. In this paper following work has been done.(1) SNR and SR of elastographic imaging results under range of noise conditions and two CE/PC approach and also the acceptable noise level ensuring the strain imaging accuracy was analyzed.(2) Based on Mathematical model of absorption, scattering and noise of biological tissue, a biological tissue model for elastographic imaging was established, which contains a simulated region with different hardness implanted into normal tissue. A transducer with specific parameter was simulated and an ultrasonic strain imaging simulation was achieved.(3) Tissue strain imaging results which applied CE/PC approach was obtained, which was also compared to ones by conventional ultrasonic imaging method.After the study on ultrasonic strain imaging results mentioned above, we now have the conclusion that:(1) Imaging result obtained using conventional method has blurred edges within that indicate relatively low SNR and poor SR.(2) Imaging results obtained using CE/PC methods have higher SNR and enhanced SR compared to that of conventional method.(3) Sidelobe disturbance occurs in the imaging result of Matched-filtering method that affects accuracy of imaging results.(4) Sidelobe disturbance does not occur in the imaging result of Mismatched-filtering method thus is more accurate while guarantees almost same SNR and SR.