Relaxation dispersion in MRI induced by fictitious magnetic fields

Timo Liimatainen, Silvia Mangia, Wen Ling, Jutta Ellermann, Dennis J. Sorce, Michael Garwood, Shalom Michaeli

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

A new method entitled Relaxation Along a Fictitious Field (RAFF) was recently introduced for investigating relaxations in rotating frames of rank ≥2. RAFF generates a fictitious field (E) by applying frequency-swept pulses with sine and cosine amplitude and frequency modulation operating in a sub-adiabatic regime. In the present work, MRI contrast is created by varying the orientation of E, i.e. the angle between E and the z″ axis of the second rotating frame. When > 45°, the amplitude of the fictitious field E generated during RAFF is significantly larger than the RF field amplitude used for transmitting the sine/cosine pulses. Relaxation during RAFF was investigated using an invariant-trajectory approach and the Bloch-McConnell formalism. Dipole-dipole interactions between identical (like) spins and anisochronous exchange (e.g., exchange between spins with different chemical shifts) in the fast exchange regime were considered. Experimental verifications were performed in vivo in human and mouse brain. Theoretical and experimental results demonstrated that changes in induced a dispersion of the relaxation rate constants. The fastest relaxation was achieved at ≈ 56°, where the averaged contributions from transverse components during the pulse are maximal and the contribution from longitudinal components are minimal. RAFF relaxation dispersion was compared with the relaxation dispersion achieved with off-resonance spin lock T experiments. As compared with the off-resonance spin lock T method, a slower rotating frame relaxation rate was observed with RAFF, which under certain experimental conditions is desirable.

Original languageEnglish (US)
Pages (from-to)269-276
Number of pages8
JournalJournal of Magnetic Resonance
Volume209
Issue number2
DOIs
StatePublished - Apr 1 2011

Fingerprint

Magnetic Fields
Magnetic resonance imaging
Magnetic fields
magnetic fields
Amplitude modulation
Chemical shift
Frequency modulation
Rate constants
Brain
Trajectories
spin resonance
pulses
Experiments
dipoles
sweep frequency
frequency modulation
brain
mice
chemical equilibrium
trajectories

Keywords

  • Human brain
  • Mouse brain
  • Relaxation
  • Relaxation along fictitious field
  • Relaxation dispersion
  • Rotating frame

Cite this

Relaxation dispersion in MRI induced by fictitious magnetic fields. / Liimatainen, Timo; Mangia, Silvia; Ling, Wen; Ellermann, Jutta; Sorce, Dennis J.; Garwood, Michael; Michaeli, Shalom.

In: Journal of Magnetic Resonance, Vol. 209, No. 2, 01.04.2011, p. 269-276.

Research output: Contribution to journalArticle

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