Long repetition time experiments for measurement of concentrations in systems with chemical exchange and undergoing temporal variation–comparison of methods with and without correction for saturation

Galbán, Craig J.; Spencer, Richard G.

doi:10.1016/s1090-7807(02)00104-0

Cited by 1 publication

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References 8 publications

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“…Recent work (12)(13)(14)(15)(16)(17)(18)(19) has explored the theoretical and experimental consequences of the dependence of SFs on chemical parameters in exchanging systems. In this study, we exploited this dependence to derive these parameters.…”

Section: Discussionmentioning

confidence: 99%

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Measurement of spin‐lattice relaxation times and chemical exchange rates in multiple‐site systems using progressive saturation

Galbán

Spencer

2007

Magnetic Resonance in Med

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A new method for measuring spin-lattice relaxation times and chemical exchange (CE) rate constants in multiple-site exchanging systems is described. The method, chemical exchange and T 1 measurement using progressive saturation (CUPS), was applied to determine T 1 s and analyze phosphorus exchange among phosphocreatine (PCr), ATP, and inorganic phosphate (Pi), mediated by creatine kinase (CK) and ATP synthase, using 31 P-MRS. Two-site exchange was analyzed in vitro and in the rat leg, and three-site exchange was analyzed in the rat heart. Data were fitted to a model of progressive saturation incorporating T 1 relaxation and CE. For the in vitro system at 8.45T, we found T 1 (PCr) ‫؍‬ 2.86 s and T 1 (␥-ATP) ‫؍‬ 1.72 s. For the rat gastrocnemius at 1.9T, we found T 1 (PCr) ‫؍‬ 6.60 s and T 1 (␥-ATP) ‫؍‬ 2.06 s. For the rat heart at 9.4T, we found T 1 (PCr) ‫؍‬ A number of NMR techniques are available for determining spin-lattice relaxation times (T 1 s) and kinetic rate constants in exchanging systems. Selective inversion and transient saturation transfer (TST) experiments (1-3) are widely used, but they require selective RF irradiation. This is problematic for a number of reasons, including RF spillover, off-resonance effects, and incomplete saturation (4 -6). Nonselective inversion and saturation experiments may also be used, but achieving proper initial conditions is difficult, and modeling is typically more complicated than for experiments involving selective saturation. These problems are particularly acute in clinical applications of NMR spectroscopy, in which full control over pulse characteristics may not be available. Additional methods for obtaining T 1 s and rate constants include 2D NMR (7-9) and a 1D nonselective method based on the 2D-exchange pulse sequence (10). These approaches also have limitations, including lengthy experimental times. The selection of a particular method for evaluating T 1 s and chemical exchange (CE) rates, then, is largely dependent on the particular requirements of the experiment in terms of time resolution and accuracy, and the available equipment.Progressive saturation (11) is another widely used method for T 1 measurement; however, the observed resonance intensities are affected by . Although the standard analysis of progressive saturation data yields erroneous T 1 values in the presence of CE, this dependence indicates that it should be possible to extract T 1 s and exchange rates from progressive saturation data under certain circumstances. Here we introduce a method to achieve this, which we refer to as CUPS, for chemical exchange and T 1 measurement using progressive saturation. The data collection itself uses the simplest possible NMR pulse sequence, i.e., a one-pulse sequence performed at several repetition times (TRs) using a broadband pulse. This avoids the use of selective irradiation and complex pulse timings or shapes. Due to the simplicity of the pulse sequence and the lack of RF-related artifacts, the data obtained are of high quality. The tradeoff for experi...

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Section: Discussionmentioning

confidence: 99%

“…The analysis is based on a model that describes the observed magnetization of a chemically exchanging resonance subjected to the one-pulse sequence (13). This model has been extensively examined both theoretically and experimentally (12)(13)(14)(15)(16)(17)(18)(19).…”

mentioning

confidence: 99%

Measurement of spin‐lattice relaxation times and chemical exchange rates in multiple‐site systems using progressive saturation

Galbán

Spencer

2007

Magnetic Resonance in Med

View full text Add to dashboard Cite

show abstract

Long repetition time experiments for measurement of concentrations in systems with chemical exchange and undergoing temporal variation–comparison of methods with and without correction for saturation

Cited by 1 publication

References 8 publications

Measurement of spin‐lattice relaxation times and chemical exchange rates in multiple‐site systems using progressive saturation

Measurement of spin‐lattice relaxation times and chemical exchange rates in multiple‐site systems using progressive saturation

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