Optimized Pulse Parameters for Reducing Quantitation Errors Due to Saturation Factor Changes in Magnetic Resonance Spectroscopy

Galbán, Craig J.; Spencer, Richard G.

doi:10.1006/jmre.2002.2542

Cited by 6 publications

(5 citation statements)

References 15 publications

(24 reference statements)

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“…We used T 1 , k PCr→γ-ATP , and k Pi→γ-ATP values as above for the control period. During ischaemia, T 1 's were taken to approach end-ischaemia values of T 1 (PCr) = 2.22 s, T 1 (γ−ATP) = 0.50 s, and T 1 (Pi) = 3.6 s [5] in a linear fashion and reaction rates were taken to linearly approach k PCr→γ-ATP = 0.2 s -1 and k Pi→γ-ATP = 0.1 s -1 [6]. A linear recovery to control values was assumed to occur during reflow for T 1 's and k's.…”

Section: Methodsmentioning

confidence: 99%

“…However, It has more recently been recognized that if chemical exchange is present, then this correction scheme may also fail whenever metabolite concentrations or reaction rates change, even if the T 1 's remain constant [4,5]. Although the degree of error will depend upon the specific parameters of the system, it has been shown that the errors can be substantial [5,6]. In general, metabolite concentrations, T 1 's and reaction rates are not constant for intervention experiments; in fact, it is precisely changes in these quantities in response to the intervention which are of interest.…”

Section: Introductionmentioning

confidence: 99%

“…According to the Ernst formulation for saturation effects in the absence of chemical exchange (3), this correction requires only that the T 1 s of the metabolites under consideration remain unchanged. However, more recently it has been recognized that if chemical exchange is present, then this correction scheme may also fail whenever metabolite concentrations or reaction rates change, even if the T 1 s remain constant (4,5). Although the degree of error will depend upon the specific parameters of the system, it has been shown that the errors can be substantial (5,6).…”

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confidence: 99%

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Ongoing dual‐angle measurements for the correction of partial saturation in ³¹P MR spectroscopy

Tyler

Lopez

Cole

et al. 2010

Magnetic Resonance in Med

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Use of a repetition time similar to, or shorter than, metabolite T 1 s is common in NMR spectroscopy of biological samples to improve the signal-to-noise ratio. Conventionally, the partial saturation that results from this is corrected using saturation factors. However, this can lead to erroneous results in the presence of chemical exchange or nonconstant T 1 s. We describe an alternative approach to correction for saturation, based on ongoing dual-angle T 1 measurement. Using 31 P magnetic resonance spectroscopy of the perfused rat heart undergoing ischemia-reperfusion, we demonstrate that signal alternations in the data acquired by the dual-angle approach are eliminated by the ongoing dual-angle T 1 measurement correction scheme, meaning that metabolite concentration and T 1 measurement can be made throughout the course of the ischemia-reperfusion protocol. Simulations, based on parameters pertinent to the perfused rat heart, demonstrate that accurate saturation correction is possible with this method except at times of rapid concentration change. Additionally, compared to the conventional saturation factor correction method, the ongoing dual-angle T 1 measurement correction scheme results in improved accuracy in determining the [phosphocreatine] recovery time constant. Thus, the ongoing dual-angle T 1 measurements procedure permits accurate monitoring of metabolite concentrations even in the setting of chemical exchange and T 1 changes and allows more accurate analysis of bioenergetic status. Magn Reson Med 64:957-966,

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Ongoing dual‐angle measurements for the correction of partial saturation in ³¹P MR spectroscopy

Tyler

Lopez

Cole

et al. 2010

Magnetic Resonance in Med

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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%

“…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).…”

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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

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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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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

Galbán¹,

Spencer²

2003

Journal of Magnetic Resonance

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Optimized Pulse Parameters for Reducing Quantitation Errors Due to Saturation Factor Changes in Magnetic Resonance Spectroscopy

Cited by 6 publications

References 15 publications

Ongoing dual‐angle measurements for the correction of partial saturation in ³¹P MR spectroscopy

Ongoing dual‐angle measurements for the correction of partial saturation in ³¹P MR spectroscopy

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

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

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Optimized Pulse Parameters for Reducing Quantitation Errors Due to Saturation Factor Changes in Magnetic Resonance Spectroscopy

Cited by 6 publications

References 15 publications

Ongoing dual‐angle measurements for the correction of partial saturation in 31P MR spectroscopy

Ongoing dual‐angle measurements for the correction of partial saturation in 31P MR spectroscopy

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

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

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Ongoing dual‐angle measurements for the correction of partial saturation in ³¹P MR spectroscopy

Ongoing dual‐angle measurements for the correction of partial saturation in ³¹P MR spectroscopy