Alternating Acquisition Technique for Quantification of in vitro Hyperpolarized [1-13C] Pyruvate Metabolism
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Purpose: To develop a technique for quantifying the 13C-metabolites by performingfrequency-selective hyperpolarized 13C magnetic resonance spectroscopy (MRS)in vitro which combines simple spectrally-selective excitation with spectrallyinterleaved acquisition. Methods: Numerical simulations were performed with varying noise level and Kpvalues to compare the quantification accuracies of the proposed and the conventionalmethods. For in vitro experiments, a spectrally-selective excitation scheme wasenabled by narrow-band radiofrequency (RF) excitation pulse implemented into afree-induction decay chemical shift imaging (FIDCSI) sequence. Experiments with LDH/ NADH enzyme mixture were performed to validate the effectiveness of the proposedacquisition method. Also, a modified two-site exchange model was formulated formetabolism kinetics quantification with the proposed method. Results: From the simulation results, significant increase of the lactate peak signalto noise ratio (PSNR) was observed. Also, the quantified Kp value from the dynamiccurves were more accurate in the case of the proposed acquisition method comparedto the conventional non-selective excitation scheme. In vitro experiment resultswere in good agreement with the simulation results, also displaying increased PSNRfor lactate. Fitting results using the modified two-site exchange model also showedexpected results in agreement with the simulations. Conclusion: A method for accurate quantification of hyperpolarized pyruvate andthe downstream product focused on in vitro experiment was described. By using anarrow-band RF excitation pulse with alternating acquisition, different resonanceswere selectively excited with a different flip angle for increased PSNR while thehyperpolarized magnetization of the substrate can be minimally perturbed with a lowflip angle. Baseline signals from neighboring resonances can be effectively suppressedto accurately quantify the metabolism kinetics.
Abstract
Purpose: To develop a technique for quantifying the 13C-metabolites by performingfrequency-selective hyperpolarized 13C magnetic resonance spectroscopy (MRS)in vitro which combines simple spectrally-selective excitation with spectrallyinterleaved acquisition. Methods: Numerical simulations were performed with varying noise level and Kpvalues to compare the quantification accuracies of the proposed and the conventionalmethods. For in vitro experiments, a spectrally-selective excitation scheme wasenabled by narrow-band radiofrequency (RF) excitation pulse implemented into afree-induction decay chemical shift imaging (FIDCSI) sequence. Experiments with LDH/ NADH enzyme mixture were performed to validate the effectiveness of the proposedacquisition method. Also, a modified two-site exchange model was formulated formetabolism kinetics quantification with the proposed method. Results: From the simulation results, significant increase of the lactate peak signalto noise ratio (PSNR) was observed. Also, the quantified Kp value from the dynamiccurves were more accurate in the case of the proposed acquisition method comparedto the conventional non-selective excitation scheme. In vitro experiment resultswere in good agreement with the simulation results, also displaying increased PSNRfor lactate. Fitting results using the modified two-site exchange model also showedexpected results in agreement with the simulations. Conclusion: A method for accurate quantification of hyperpolarized pyruvate andthe downstream product focused on in vitro experiment was described. By using anarrow-band RF excitation pulse with alternating acquisition, different resonanceswere selectively excited with a different flip angle for increased PSNR while thehyperpolarized magnetization of the substrate can be minimally perturbed with a lowflip angle. Baseline signals from neighboring resonances can be effectively suppressedto accurately quantify the metabolism kinetics.
참고문헌 (29)
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