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Abstract
Non-uniform sampling (NUS) allows the accelerated acquisition of multidimensional NMR spectra. The aim of this contribution was the systematic evaluation of the impact of various quantitative NUS parameters on the accuracy and precision of 2D NMR measurements of urinary metabolites. Urine aliquots spiked with varying concentrations (15.6–500.0 µM) of tryptophan, tyrosine, glutamine, glutamic acid, lactic acid, and threonine, which can only be resolved fully by 2D NMR, were used to assess the influence of the sampling scheme, reconstruction algorithm, amount of omitted data points, and seed value on the quantitative performance of NUS in 1H,1H-TOCSY and 1H,1H-COSY45 NMR spectroscopy. Sinusoidal Poisson-gap sampling and a compressed sensing approach employing the iterative re-weighted least squares method for spectral reconstruction allowed a 50% reduction in measurement time while maintaining sufficient quantitative accuracy and precision for both types of homonuclear 2D NMR spectroscopy. Together with other advances in instrument design, such as state-of-the-art cryogenic probes, use of 2D NMR spectroscopy in large biomedical cohort studies seems feasible.
Highlights
The experimental time needed for 2D NMR experiments to obtain sufficient digital resolution in the indirect dimension is dependent on the number of t1 increments collected[9]
We started with 1H,1H-TOCSY spectra to investigate the choice of either of the two different reconstruction algorithms implemented in TopSpin3.1 on the recovery of the six spiked-in urinary metabolites, as this type of spectra yields a larger number of signals than 1H,1H-COSY45 spectra, rendering reconstruction of Non-uniform sampling (NUS) spectra more challenging
With regard to the initiatory evaluation of NUS on the spike-in dataset, we find that, especially for the reconstruction of weak signals, compressed sensing (CS)-iterative re-weighted least squares (IRLS) is clearly superior to both recursive multidimensional decomposition (R-MDD) and maximum entropy (MaxEnt), whereas it performed slightly better than CS-iterative soft thresholding (IST)
Summary
The experimental time needed for 2D NMR experiments to obtain sufficient digital resolution in the indirect dimension is dependent on the number of t1 increments collected[9]. Non-uniform sampling (NUS) acquires only a fraction of the indirect data points and reconstructs the spectra by non-Fourier methods, accelerating the acquisition of multidimensional NMR spectra[10,11]. NUS has been primarily tested on standard mixtures of selected metabolites in often non-physiological concentration ranges[8,9,10]. We used urine as a background matrix spiked with varying concentrations (15.6–500.0 μM) of tryptophan, tyrosine, glutamine, glutamic acid, lactic acid, and threonine to determine the impact of different sampling schemes, reconstruction algorithms and seed values on the fraction of indirect points that might be omitted without affecting the quantitative performance of both 1H,1H-TOCSY and www.nature.com/scientificreports/. The best combination of acquisition parameters was applied to the determination of differences in urinary metabolite levels between apparently healthy subjects and patients suffering from chronic kidney disease (CKD)
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