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Glossary • E

Echo → Spin echo.

Echo planar imaging: a technique of planar imaging in which a complete planar im­age is obtained from one selective excitation pulse. The FID is observed while pe­ri­o­di­cal­ly switching a field gradient to generate a train of gradient echoes. The Fourier trans­form of the resulting echo train can be used to produce an image of the excited plane.

Echo train: a sequence of two or more echoes generated by the application of RF pulses or gradients.

Eddy currents: electric currents induced in a conductor by a changing magnetic field or by motion of the conductor through a magnetic field. One of the sources of concern about potential hazard to subjects in very high magnetic fields or rapidly varying gradient or main magnetic fields. Can be a practical problem in the cryostat of superconducting mag­nets, in particular for localized spectroscopy. Can be reduced by the use of shielded gra­di­ents.

Electron spin resonance → Magnetic resonance.

EPI → Echo planar imaging.

ESR → Magnetic resonance.

Even echo rephasing: even echoes in an echo train of spin echoes are compensated for the effects of flow.

Excitation: putting energy into the spin system; if a net transverse magnetization is pro­du­ced, an NMR signal can be observed.

Excitation pulse: pulse used to excite the spin system.

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