Conventional MRI (magnetic resonance imaging) equipments are usually bulky,expensive,large noise and difficult to set up,which limits their wide application.Low field mobile MRI devices are expected to solve these disadvantages.In the conventional magnetic resonance imaging,small sample is surrounded by a large magnet and the image is taken in the highly uniform magnetic environment (＜ 5 ppm/40 mm DSV).The hardware design of the conventional magnetic resonance imaging and its corresponding technology are relatively mature and perfect.The open NMR (nuclear magnetic resonance) system is based on extremely inhomogeneous magnetic field conditions (＞ 1000 ppm/mm DSV),and has a wide gap between the traditional hardware design and imaging techniques,and the difficulty is also increased dramatically.This paper reviews the origin,development and key technologies of the low field open magnetic resonance imaging technology,including hardware such as magnet,RF coil,gradient coil and method such as the design of radio frequency pulses,imaging sequence,image post processing.The aim of the review is to provide insights about the research and development of mobile MRI equipment.%传统的磁共振成像设备系统庞大笨重、价格昂贵、检查噪声大、摆位困难等,因此限制其普及应用,而低场可移动式磁共振成像设备可以克服这些缺点.传统核磁共振成像采取大磁体包围小样品的模式,对高度均匀磁场环境(＜5×10-6/40 mm DSV)中的样品进行成像,相应的硬件设计和许可技术相对都比较成熟和完善.开放式核磁共振成像系统基于极度不均匀的磁场条件(＞1 000×10-6/mm DSV),相关的硬件设计、成像技术与传统的核磁共振成像系统差距很大,难度也急剧增加.全面论述低场开放式磁共振成像技术的起源、发展、关键技术,包括磁体、射频线圈、梯度线圈等硬件和射频脉冲设计、成像序列、图像后处理等方法,旨在为可移动式核磁共振成像设备的研发抛砖引玉.
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