title: 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.
abstract: The purpose of this paper is to compare two methods for quantifying metabolite concentrations using the one-pulse experiment for a sample undergoing chemical exchange and subject to an intervention or other temporal variation. The methods, LATR-C (Long Acquisition TR (interpulse delay); Corrected for partial saturation) and LATR-NC (Long Acquisition TR; Not Corrected), are compared in terms of signal-to-noise ratio, SNR, per unit time and quantitation errors. Parameters relevant to the isolated perfused rat heart are used as a specific application, although the results are general. We assume throughout that spin-lattice relaxation times, T(1), do not change. For a given flip angle, theta, TR's are calculated which result in maximal SNR per unit time under 10%, 5%, and 1% constraints on quantitation errors. Additional simulations were performed to demonstrate explicitly the dependence of the quantitation errors on TR for a fixed theta. We find (i) if the allowed error is large, and when both metabolite concentrations and rate constants vary, LATR-C permits use of shorter TR, and hence yields greater SNR per unit time, than LATR-NC; (ii) for small allowed error, the two methods give similar TR's and SNR per unit time, so that the simpler LATR-NC experiment may be preferred; (iii) large values of theta result in similar constrained TR's and hence SNR per unit time for the two methods; (iv) the ratio of concentrations of metabolites with similar T(1) exhibit similar errors for the two methods.
authors.affiliation: National Institutes of Health, National Institute on Aging, GRC 4D-08, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA.
authors.forename: Craig J
authors.initials: CJ
authors.lastname: Galbán
authors.forename: Richard G S
authors.initials: RG
authors.lastname: Spencer
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D003402:Creatine Kinase / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D009206:Myocardium / Q000378:metabolism*; D051381:Rats
chemical_list: D000255:Adenosine Triphosphate; D003402:Creatine Kinase