The Application Study On Detection Liver Fibrosis Using Nuclear Resonance Imaging Elastography Technology

With the rapid development of nuclear magnetic resonance (NMR) technology, as one of the most common clinical diagnostic and functional imaging tools, MRI is now an indispensable tool in medical and biology field.The essence of medical imaging technologies is that it can distinguish some physical parameter's differences between normal tissue and diseased tissue by image grey levels or colors for diagnosis.At the present time, physical parameters for use in MRI include macro-parameters such as T1, T2, Proton density, and parameters which reflect function of tissue, such as perfusion modulus, Diffusion modulus, Blood oxygen level dependent modulus, Chemical shift and so on. Yet Magnetic resonance elastic imaging is a new detection means developed in recent years.Tissue elastic is big differential, which ranges from 1 to 108kpa. Magnetic resonance elastography (MRE) has been gradually concerned by clinical doctors because as a huge potential noninvasive manner it can give high resolution image and two-dimensional or three-dimensional elasticity distribution.But it has not been applied to clinical usage. The dissertation has a comprehensive study on the theory and technology of the elastic magnetic resonance imaging technology, offers a platform for MRE research, thought liver fibrosis (hardness) measuring is an objective, and evaluates the experimental result.The dissertation has done the following research work:1,Study of the Magnetic resonance elastography theroyFirstly the dissertation explains the basic principles of MRE, phase image and the theory of phase detection to periodic displacements. And then in the dissertation the basic process and the main content are proposed, key technical issues of MRE are briefly descripted. 2,Development of the shear wave developing stimulatorThe shear wave is the excitation source of MRE research. According to the different research project, shear-wave generator and developing stimulator accepting gated sequence are needed which has adjustable frequency, initial phase and amplitude and can compatible with MRI system. Based on the AVR Microcontroller Mega 16, this dissertation includes design of sinusoidal developing stimulator, shear-wave driven from electromagnetic incentives device after audio amplifier, and realization of propagation of shear-wave and feedback on the examined tissue.3,The design and development of displacement phase imaging sequencePhase detection to Periodic displacement of the particle is one of the key points in the MRE technique. In general, it was achieved by the basic imaging sequence coordinate with motion-sensitive gradient (MSG). However, as we need high speed, noise elimination of background phase for the elastic detection of locomotorium, this dissertation uses basic FLASH combines MSG sequence as elastic imaging sequences. It achieves the elimination of background phase through once a positive and a negative phase of MSG respectively in every two TR cycles. But for the inhibition of liver movement, breath-hold in scanning process is used in this study.4,Tissue biomechanical model analysisAnalysis of tissue biomechanical model in the organisms establishes the foundation for building the model between shear wave's propagation velocity (or wavelength, frequency) and tissue elastic modulus within the organization. For a complex organism, the establishment of such a model within the organization is very difficult. Concerning the Isotropic and small strain, when free from external forces, and ignore the influence of viscosity, this dissertation from the basic elasticity theory gets the relationship of shear wave's propagation wavelength, frequency and tissue elastic modulus, which sets up the foundation for calculating the elasticity.5,Study and achievement on elasto-graphy fit algorithmThe elasticity imaging sequence detects periodic displacement of the particle formed through the transmission of the shear-wave in the tissue to produce the phase image. As the result of biological elasticity mechanics modeling, the dissertation transforms the phase image into the elasto-graphy by use of the relevance fit algorithm. Besides, it shows the principle of local frequency estimation (LFE) algorithm, and finally diplotene wide Gaussian filter was adopted and the algorithm has been fulfilled by Matlab.6,Experiment resultsBased on the foregoing study, the dissertation offers a MRE research platform based on the 1.5T and 3.0T clinical MRI system. After some experiments like as the agarose body pattern, ex-vivo pork liver and the in-vivo volunteer's liver experiment, it gives the analysis and discussion of the experiment results and experiment details which forms a basis for subsequent research on liver fibrosis sufferer clinical trial and liver fibrosis classification.