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Corrections for off‐resonance effects and incomplete saturation in conventional (two‐site) saturation‐transfer kinetic measurements
Author(s) -
Kingsley Peter B.,
Monahan W. Gordon
Publication year - 2000
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/1522-2594(200006)43:6<810::aid-mrm6>3.0.co;2-j
Subject(s) - saturation (graph theory) , chemistry , resonance (particle physics) , nuclear magnetic resonance , kinetic energy , relaxation (psychology) , spin–lattice relaxation , irradiation , observable , atomic physics , physics , nuclear physics , mathematics , quantum mechanics , nuclear quadrupole resonance , psychology , social psychology , combinatorics
The effects of off‐resonance irradiation and incomplete saturation on saturation‐transfer measurements of chemical‐exchange rates are discussed. With off‐resonance effects there is no exact formula for the exchange rate constant from spin D to spin E , k DE , in terms of observable signal intensities and relaxation rates. However, k DE can be estimated by measuring the effective spin‐lattice relaxation rate constant of spin D when spin E is saturated, * R 1 , plus signal intensities with no RF irradiation, M 0 D and M 0 E ; with irradiation of a control position, M′ D and M′ E ; and with saturation of spin E , * M D and * M E . Several formulas are compared and the best formula for calculating k DE appears to be either k DE = * R 1 [( M′ D − * M D )/ M 0 D ]/[( M′ E − * M E )/ M 0 E ], or the same formula with M 0 D and M 0 E replaced by M′ D and M′ E . These formulas are exact with incomplete saturation and no off‐resonance effects, and are better than previously published formulas when off‐resonance effects are present. More accurate formulas are available if signal intensities and relaxation rates can be measured while the exchange process is stopped. Magn Reson Med 43:810–819, 2000. © 2000 Wiley‐Liss, Inc.