Net magnetisation vector

Dr Dan J Bell and Dr Jeremy Jones et al.

The net magnetisation vector in MRI is the summation of all the magnetic moments of the individual hydrogen nuclei.

In the absence of an external magnetic field, the individual magnetic moments are randomly oriented and since they are in opposition, the net magnetisation vector is considered to be zero.

If hydrogen nuclei are placed within a strong external magnetic field, they become aligned within the field in one of two directions parallel to the direction of the field (see: energy difference between spin up and spin down states). 

In MRI, the main magnetic field is termed B0.

  • aligned in the direction of B0 (parallel)
  • aligned in the opposite direction of B0 (antiparallel)

A parallel and antiparallel hydrogen nuclei have equal but opposite magnetic moments and cancel each other out. However, there are always slightly more hydrogen nuclei parallel to B0 and this slight difference is termed the NMV (net magnetisation vector) and given the symbol M.

Physics and Imaging Technology: MRI
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Article information

rID: 6316
Tag: mri
Synonyms or Alternate Spellings:
  • Net magnetization vector (NMV)

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