【作者】 李志宾；

【导师】 汪洋；

【作者基本信息】 哈尔滨工业大学 ， 信息与通信工程， 2010， 硕士

【摘要】 磁共振成像是现代医学影像的重要组成。随着磁共振成像技术的快速发展,它对磁共振谱仪有着新的要求。现有的商用磁共振谱仪由于其昂贵的价格使得磁共振成像系统难以普及。因此,研究低成本的磁共振成像系统对于我国磁共振成像的普及和推广有着重要的意义。磁共振接收机是磁共振系统的重要组成部分,接收机性能的好坏对磁共振成像质量有着很大的影响。虽然接收机广泛应用于通信以及雷达等各个领域,但由于磁共振成像的特殊性,磁共振成像系统对磁共振接收机在动态范围、噪声以及线性等各项指标有着较高的要求。现有的磁共振接收机为满足磁共振成像的要求,采用了大量高性能但是价格昂贵的器件,使得磁共振接收机成本较高。直接射频接收机广泛应用于软件无线电当中。通过对信号的直接射频采样,一方面使得模拟电路能得到最大限度的简化,降低接收机成本;另一方面,信号处理的大部分过程将在数字域完成,随着DSP以及FPGA技术的不断成熟,诸如滤波、混频及解调等功能都能在数字域方便地完成,而且其性能也远远优于传统的模拟接收机。基于以上分析,将直接射频接收机应用于磁共振成像,将有利于于接收机构造的简化及成本的降低。本文将对直接射频采样接收机进行研究与设计,首先分析了时钟稳定度对于接收机性能的影响,在此基础上提出了一种测量相位噪声的方法。对几种模数转换器的实际性能进行测试,并结合具体电路对信号动态范围的改善进行分析。最后提出一种将导频信号与可控增益放大器相结合应用于直接射频磁共振接收机的方法,以此改善接收机动态范围,满足磁共振成像的要求。更多还原

【Abstract】 Magnetic Resonance Imaging is an important part of modern medical imaging. With the development of MRI technology, there’re new requirements for MR spectrometer. The commercial MR spectrometer has high performance and powerful functionality. However, the price is an important factor that limits the universalization of the MRI system. Therefore, the research of low cost MRI system means a lot to the healthcare business in our country.MRI receiver plays an important role in MRI system. The performance of receiver may be decisive in the imaging quality. Different from receiver application in other fields, MRI system requires that MRI receiver has very high dynamic range, low noise and good linearity. To achieve the specification of MRI receiver, many devices with high performance but also high price are applied, which pushes up the cost of MRI receiver.Direct radio frequency sampling receiver is applied in software define radio. There’re benefits with application of direct radio frequency sampling receiver in MRI system. First, the part of analog circuit can be simplified which helps cost down. Second, with the development of DSP and FPGA technologies, the signal processing such as filtering and frequency mixing can be done in digital field. The digital way of signal processing is more flexible and its performance is much better than the analog way. In conclusion, the application of direct RF sampling receiver in MRI system will simplify the structure of system and reduce the cost.The direct RF sampling receiver is researched in this article. The influence of clock stability to the performance of receiver is analyzed. An improved method of phase noise measurement is introduced. Several ADCs are analyzed and tested. The issue of dynamic range in MRI system is discussed. A method that combines automatic gain control technology with pilot signal in MRI receiver is introduced to improving the dynamic range of MRI receiver.更多还原