《医学超声成像研究技术路线》由会员分享，可在线阅读，更多相关《医学超声成像研究技术路线（2页珍藏版）》请在金锄头文库上搜索。
1、医学超声成像研究技术路线关键字：医学图像；超声成像 ；论文代写网Conventional medical ultrasound systems use single-carrier and short pulses.There are some problems such as poor signal-to-noise ratio （SNR）。 One has to makecompromise between the resolution and penetration of the transmitted signal due tothe low SNR. Recent study of
2、using coded signals can resolve these problems.Conventional code signals used in medical ultrasound imaging have some short-comings and there is less stu勿of code signals currently. It is important to search forcodes with better property and practicability. The study faces several challenges. Firstta
3、sk is to search for the optimal code sequences. Secondly, it is required to fmd thecoded signal to be suitable for the different non-linear environment. Thirdly, it is re-quired that the codes should have both good auto-correlation and cross-correlation.The aim of this dissertation is to investigate
4、 systematically coded signals used inmedical ultrasound imaging and to solve the three difFicult problems mentioned above.Focusing on the third problem, we try to introduce some advanced research resultsfrom the field of telecommunication.As only binary codes and linear frequency modulation signal i
5、s used in medicalultrasound imaging at present, some new ideas of the combination of multiple modu-lations or multiple coded signals are given. Costas signal is introduced into our studyand its adaptation to ultrasound imaging is discussed in detail.As frequency-dependent attenuation effect makes tr
6、ouble for the implementationof coded signals for medical ultrasound imaging, especially about signals withthumbtack ambiguity function, the signals with frequency shift tolerance are investi-gated. Subsequently, staggered code that is a new coding scheme used in ultrasoundimaging is proposed. As the
7、re is not practical construction algorithm, in-depth studyfor that code can not be conducted.A new idea of secondary coding is proposed to meet both good auto-correlationand cross-correlation: auto-correlation and cross-correlation properties of coded sig-nals will be achieved by two mechanisms resp
8、ectively. This idea provides a new wayto the following investigation.According to the idea of secondary coding staggered technique used for reducingcross-talk in medical ultrasound imaging is proposed. This technique is investigateddeeply since it practically increases the frame rate significantly o
9、r improves the im-aging quality. And two schemes are proposed using the staggered idea.First, the increase of frame rate is generally realized by transmitting multiplebeams simultaneously, which leads to increase the cross-talks between different aper-tares. In view of this, a new coding scheme usin
10、g staggered technique is proposed.The theoretical analysis and simulations showed that, the cross-correlation reductionis proportional to the size of repetitions number, and for an arbitrary coded signal agood cross-talk reduction will be achieved if the staggered delay is kept in an appro-priate ra
11、nge. Secondly, a scheme is introduced by using staggered technique to reducecross-talks between different signals caused by increasing pulse repeat frequency.The performance analyse of coded signals should always be integrated with spe-cific application. Therefore at the last of the dissertation a s
12、cheme using Golay codesin time-shift blood velocity estimator is proposed. The scheme is evaluated throughsimulations and implementation. The advantages of Golay codes are maximized andbetter performance is achieved compared with system using single-carrier pulses inthis scheme.From investigations w
13、e come to the following conclusion: good code propertyfor the application of ultrasound imaging is very important. Auto-correlation andcross- correlation properties of coded signals can be achieved by two mechanisms re-spectively. Cross-correlation property can be achieved in various ways, and staggeredtechnique is a feasible one.Keywords: Medical ultrasound imaging; coded signals; ambiguity function; modula-tion; correlation; staggered; time-shifted论文代写网 ,论文 , 毕业论文,代写论文,发表论文,职称论文,论文工场,免费论文,代写医学论文
