Free induction decay

Free induction decay (FID) refers to a short-lived sinusoidal electromagnetic signal which appears immediately following the 90° pulse. It is induced in the receiver coil by the rotating component of the magnetization vector in the x-y plane which crosses the coil loops perpendicularly. It does not contribute to MR image but is used for single voxel MR spectroscopy.This sinusoidal signal decays exponentially with a time constant of T2*

A spin echo produced by a 180° pulse following a 90° pulse appears as a back-to-back FID where the signal increases exponentially to the middle of the signal then decreases exponentially like the FID.

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Article information

rID: 16493
Section: Physics
Tag: stub, refs
Synonyms or Alternate Spellings:
  • Free induction decay (FID)
  • FID

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  • Diagram - free induction decay
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