Visualization of the distant dipolar field: A numerical study

✍ Scribed by Stefan Kirsch; Peter Bachert

• Book ID: 102103351
• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 274 KB
• Volume: 34A
• Category: Article
• ISSN: 1546-6086
• DOI: 10.1002/cmr.a.20149

✦ Synopsis

Abstract

The magnetization of liquid water in an external field generates an intrinsic magnetic field in the sample called the distant dipolar field (DDF). To visualize the spatial distribution of the DDF a numerical study was performed for the case of liquid–state ^1^H NMR at 7 T. 2D maps of the frequency offset caused by the DDF in pure water were calculated for homogenously magnetized spherical and cylindrical samples as well as for the case of a spatially modulated magnetization distribution occurring e.g., in CRAZED (Cosy Revamped by Asymmetric Z‐Gradient Echo Detection) experiments. The calculation yielded DDF induced frequency offsets in the range of 0.58 Hz to 10.24 Hz inside the homogeneously magnetized cylinders, while DDF‐induced frequency offsets ≤10^−5^ Hz were obtained inside the sphere. The calculated frequency offsets were in good agreement with analytical results available for a sphere and an infinitely long cylinder. In the case of a spatially modulated magnetization distribution, DDF‐induced frequency offsets with maximum values of +0.83 Hz were obtained inside the sphere. The presented 2D maps of the DDF‐induced frequency offset have tutorial character and may help to visualize this phenomenon in a direct manner. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part A 34A:357–364, 2009.