Publication

Broadband excitation in magnetic resonance by self-refocusing doubly frequency-modulated pulses

Geoffrey Bodenhausen
1993
Journal Articles

Résumé

It is shown how transverse magnetization can be excited with a single low-power radiofrequency pulse consisting of a superposition of 2 frequency-modulated components. The phase dispersion obtained with this self-refocusing pulse is very small over bandwidths that are far greater than the amplitude of the radiofrequency field. The new pulse shape may be derived from spin-echo sequences employing frequency-modulated chirp pulses by shifting the excitation and refocusing pulses in time so that they are partly or completely superimposed. The duration of chirp spin-echo sequences can be reduced by a factor of 2 by this contraction process, so that the echoes are less sensitive to transverse relaxation. [on SciFinder (R)]

Source officielle

https://infoscience.epfl.ch/entities/publication/21a021b8-dc20-4dcf-9624-8e4a481aaf5b

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Geoffrey Bodenhausen
1993
Journal Articles

Résumé

Source officielle

https://infoscience.epfl.ch/entities/publication/21a021b8-dc20-4dcf-9624-8e4a481aaf5b

À propos de ce résultat

Concepts associés (27)

Spin–spin relaxation

In physics, the spin–spin relaxation is the mechanism by which Mxy, the transverse component of the magnetization vector, exponentially decays towards its equilibrium value in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). It is characterized by the spin–spin relaxation time, known as T2, a time constant characterizing the signal decay. It is named in contrast to T1, the spin–lattice relaxation time.

Spin–lattice relaxation

During nuclear magnetic resonance observations, spin–lattice relaxation is the mechanism by which the longitudinal component of the total nuclear magnetic moment vector (parallel to the constant magnetic field) exponentially relaxes from a higher energy, non-equilibrium state to thermodynamic equilibrium with its surroundings (the "lattice"). It is characterized by the spin–lattice relaxation time, a time constant known as T1.

Spin echo

In magnetic resonance, a spin echo or Hahn echo is the refocusing of spin magnetisation by a pulse of resonant electromagnetic radiation. Modern nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) make use of this effect. The NMR signal observed following an initial excitation pulse decays with time due to both spin relaxation and any inhomogeneous effects which cause spins in the sample to precess at different rates. The first of these, relaxation, leads to an irreversible loss of magnetisation.

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Publications associées (32)

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Broadband excitation in magnetic resonance by self-refocusing doubly frequency-modulated pulses

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