关键词: 单边MRI, 非均匀场MRI, NMR表面检测仪, 便携式MRI, U形磁体

Abstract: For the inhomogeneous magnetic field MR imager, the polarization field is virtually uniform within horizontal degrees of freedom and decreases monotonically in a direction away from the surface. The authors describe the imaging principle, and present requirements and constraints by terms of key points of physical design such as 90° excitation pulse,180° refocused pulse, encoding manner and pulse sequences. In addition, it reveals that the echo time is restricted by the diffusion effect on signal amplitude due to the huge static field gradient. The data evaluated from diffusion not only restrict the usable TE, but also determine the strength of encoding gradient G_x, G_z and RF excitation field B₁ and virtually usable RF pulse. The time spent for scanning one slice of human brain and inability of covering whole brain prohibit such MR imager from surgical intervention. It indicates that the advantage of the unilateral MR imager is portable. It can be used for arbitrary large sample to render MRI analysis of surface-layer in a non-invasive manner.

Key words: unilateral MRI, inhomogeneous field MRI, NMR MOUSE, portable MRI, U-shaped magnet