Corrections for off-resonance effects and incomplete saturation in conventional (two-site) saturation-transfer kinetic measurements

• Published in: Magnetic resonance in medicine Vol. 43; no. 6; pp. 810 - 819
• Main Authors: Kingsley, Peter B., Monahan, W. Gordon
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 01.06.2000; Williams & Wilkins
• Subjects: Animals; Biological and medical sciences; Bloch equations; chemical exchange; In Vitro Techniques; Investigative techniques, diagnostic techniques (general aspects); Kinetics; Macromolecular Substances; Magnetic Resonance Imaging - methods; Medical sciences; Miscellaneous. Technology; Models, Theoretical; Radiodiagnosis. Nmr imagery. Nmr spectrometry; saturation transfer; Sensitivity and Specificity; spillover; Incomplete; Chemical exchange; Off effect; Medical imagery; Bloch equation; Saturation transfer; Resonance; Signal analysis; Nuclear magnetic resonance imaging; Relaxation time
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/1522-2594(200006)43:6<810::AID-MRM6>3.0.CO;2-J

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, kDE, in terms of observable signal intensities and relaxation rates. However, kDE can be estimated by measuring the effective spin‐lattice relaxation rate constant of spin D when spin E is saturated, *R1, plus signal intensities with no RF irradiation, M0D and M0E; with irradiation of a control position, M′D and M′E; and with saturation of spin E, *MD and *ME. Several formulas are compared and the best formula for calculating kDE appears to be either kDE = *R1 [(M′D− *MD)/M0D]/[(M′E − *ME)/M0E], or the same formula with M0D and M0E 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.