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Molecular theory of field-dependent proton spin-lattice relaxation in tissue

Halle, Bertil LU (2006) In Magnetic Resonance in Medicine 56(1). p.60-72
Abstract
A molecular theory is presented for the field-dependent spin-lattice relaxation time of water in tissue. The theory attributes the large relaxation enhancement observed at low frequencies to intermediary protons in labile groups or internal water molecules that act as relaxation sinks for the bulk water protons. Exchange of intermediary protons not only transfers magnetization to bulk water protons, it also drives relaxation by a mechanism of exchange-mediated orientational randomization (EMOR). An analytical expression for T, is derived that remains valid outside the motional-narrowing regime. Cross-relaxation between intermediary protons and polymer protons plays an important role, whereas spin diffusion among polymer protons can be... (More)
A molecular theory is presented for the field-dependent spin-lattice relaxation time of water in tissue. The theory attributes the large relaxation enhancement observed at low frequencies to intermediary protons in labile groups or internal water molecules that act as relaxation sinks for the bulk water protons. Exchange of intermediary protons not only transfers magnetization to bulk water protons, it also drives relaxation by a mechanism of exchange-mediated orientational randomization (EMOR). An analytical expression for T, is derived that remains valid outside the motional-narrowing regime. Cross-relaxation between intermediary protons and polymer protons plays an important role, whereas spin diffusion among polymer protons can be neglected. For sufficiently slow exchange, the dispersion midpoint is determined by the local dipolar field rather than by molecular motions, which makes the dispersion frequency insensitive to temperature and system composition. The EMOR model differs fundamentally from previous models that identify collective polymer vibrations or hydration water dynamics as the molecular motion responsible for spin relaxation. Unlike previous models, the EMOR model accounts quantitatively for H-1 magnetic relaxation dispersion (MRD) profiles from tissue model systems without invoking unrealistic parameter values. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
internal water, proton exchange, magnetic relaxation dispersion, spin, cross-relaxation, diffusion
in
Magnetic Resonance in Medicine
volume
56
issue
1
pages
60 - 72
publisher
Wiley Online Library
external identifiers
  • wos:000238823600008
  • pmid:16732594
  • scopus:33745699931
ISSN
1522-2594
DOI
10.1002/mrm.20919
language
English
LU publication?
yes
id
5c8729ee-1f80-4f1b-b325-88afc7c3d4da (old id 403942)
date added to LUP
2016-04-01 12:36:57
date last changed
2020-01-15 02:49:16
@article{5c8729ee-1f80-4f1b-b325-88afc7c3d4da,
  abstract     = {A molecular theory is presented for the field-dependent spin-lattice relaxation time of water in tissue. The theory attributes the large relaxation enhancement observed at low frequencies to intermediary protons in labile groups or internal water molecules that act as relaxation sinks for the bulk water protons. Exchange of intermediary protons not only transfers magnetization to bulk water protons, it also drives relaxation by a mechanism of exchange-mediated orientational randomization (EMOR). An analytical expression for T, is derived that remains valid outside the motional-narrowing regime. Cross-relaxation between intermediary protons and polymer protons plays an important role, whereas spin diffusion among polymer protons can be neglected. For sufficiently slow exchange, the dispersion midpoint is determined by the local dipolar field rather than by molecular motions, which makes the dispersion frequency insensitive to temperature and system composition. The EMOR model differs fundamentally from previous models that identify collective polymer vibrations or hydration water dynamics as the molecular motion responsible for spin relaxation. Unlike previous models, the EMOR model accounts quantitatively for H-1 magnetic relaxation dispersion (MRD) profiles from tissue model systems without invoking unrealistic parameter values.},
  author       = {Halle, Bertil},
  issn         = {1522-2594},
  language     = {eng},
  number       = {1},
  pages        = {60--72},
  publisher    = {Wiley Online Library},
  series       = {Magnetic Resonance in Medicine},
  title        = {Molecular theory of field-dependent proton spin-lattice relaxation in tissue},
  url          = {http://dx.doi.org/10.1002/mrm.20919},
  doi          = {10.1002/mrm.20919},
  volume       = {56},
  year         = {2006},
}