STRAY FIELD MAGNETIC-RESONANCE-IMAGING

Magnetic resonance imaging (MRI) is well known in a clinical context a s a technique capable of delivering highly detailed anatomical images, particularly of soft tissue. The MRI method is completely non-invasiv e and allows spatial resolution down to a few micrometres in three dim ensions. Image contrast is governed by one of several nuclear magnetic resonance parameters and might reflect water mobility, chemical poten tial, self-diffusion coefficient, coherent flow or temperature, depend ing upon the exact form of the MRI measurement. Less widely realized i s the enormous potential for the use of MRI in materials science. The flexibility that makes MRI such a valuable clinical tool is equally ap plicable in a nonmedical scenario, but the greater technical difficult ies associated with MRI in solid materials have hitherto limited the d evelopment of the technique in this area. This review describes in det ail one approach to MRI in solid materials which is currently benefiti ng from rapidly increasing application: stray field (magnetic resonanc e) imaging (STRAFI). An introduction to the phenomenon of nuclear magn etic resonance and particularly its detection in solids is followed by a description of the steps necessary for its use as an imaging modali ty. The limits of MRI spatial resolution in liquids and solids are bri efly discussed. STRAFI is placed in context throughout this introducti on. The STRAFI technique is then described in detail, in terms of its merits relative to other approaches to solids MRI and the subtleties o f its implementation. The principal areas of current STRAFI applicatio n are reviewed and developments with which STRAFI advancement is close ly linked, are also described. In conclusion, some consideration is gi ven to the promising future of stray field MRI as a widely accepted re search tool in materials science and to the development of the techniq ue itself.