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.

Siehe auch:

• MR spectroscopy
• T2*

und weiter:

• t2* relaxation