NMR signal-to-noise

With other things equal, the NMR signal-to-noise ratio increases with increasing nuclear moment. 

The biochemical composition of mine varies considerably from species to species and also with the age of the animal as almost all species have age-related changes in renal function. Rats and other rodents have much higher levels of taurine, citrate, succinate, 2-oxoglutarate and allantoin than humans and this is clearly apparent in the H NMR spectra. Rat urine (and that of other rodents) is generally much more concentrated than human urine, and so NMR signal-to-noise ratios may be better for many metabolites. All animals have physiological processes which are modulated by biological rhythms. This includes excretory processes and the urinary composition of an... 

The NMR signal-to-noise ratio is directly proportional to the square root of the number of transitions and the total experimental time is mainly determined by the repetition time between two successive transitions, that is about five times of the spin longimdinal relaxation time Tj. Therefore, NMR sensitivity enhancement can be achieved by shortening the spin longitudinal relaxation time T. Ishii and colleagues have demonstrated that H Tj values of the two model proteins. 

NMR signal-to-noise ratio ca. 10-fold better than with corresponding DEPMPO species." ... 

Finally a brief account is given of Behrendt s interesting suggestions for increasing the sensitivity of % NMR spectroscopy. At a temperature T near to absolute zero, the NMR signal-to-noise will improve very markedly as Samples at that... 

However unlike H which is the most abundant of the hydrogen isotopes (99 985%) only 1 1% of the carbon atoms m a sample are Moreover the intensity of the signal produced by nuclei is far weaker than the signal produced by the same number of H nuclei In order for NMR to be a useful technique in structure deter mination a vast increase in the signal to noise ratio is required Pulsed FT NMR pro vides for this and its development was the critical breakthrough that led to NMR becoming the routine tool that it is today... 

Consequently by collecting the FID signal as a function of time and carrying out a Fourier transformation, the conventional NMR spectmm is obtained. This procedure possesses great advantages, one of which is the ability to time-average successive FIDs so as to improve the signal-to-noise ratio. 

A poor digital resolution will result in loss of some of the fine structure of an NMR signal. To increase the digital resolution, we need either to maintain the same number of data points but reduce the spectral width or, alternatively, to maintain the spectral width but increase the number of data points. Which method would you prefer for achieving a better signal-to-noise ratio ... 

Apodization (exponential multiplication) is used to improve the signal-to-noise ratio, and it does not affect the chemical shifts of the NMR signals. 

The simplest definition of sensitivity is the signal-to-noise ratio. One criterion for judging the sensitivity of an NMR spectrometer or an NMR experiment is to measure the height of a peak under standard conditions and to compare it with the noise level in the same spectrum. Resolution is the extent to which the line shape deviates from an ideal Lorentzian line. Resolution is generally determined by measuring the width of a signal at half-height, in hertz. 

The sine-bell, sine-bell squared, phase-shifted sine-bell, and phase-shifted sine-bell squared window functions are generally used in 2D NMR spectroscopy. Each of these has a different effect on the appearance of the peak shape. For all these functions, a certain price may have to be paid in terms of the signal-to-noise ratio, since they remove the dispersive components of the magnitude spectrum. This is illustrated in the following COSY spectra ... 

As described in Section II.B, NMR is a powerful method for providing dynamic information. When signals of interest can be measured with a sufficient signal-to-noise ratio at different frequencies, the two relaxation times, the longitudinal relaxation time. 

Multiple receive systems with multi-coil arrays have become widely distributed in medical MRI. The benefit is the enhancement of the signal-to-noise ratio per time or a reduction of the acquisition time. This technique is not used in NMR microscopy for objects of intermediate size in standard bore (52-mm id) and wide bore (89-mm id) magnets, which are the most widely distributed magnet types for NMR microscopy. The main reason is the restricted space in such magnets for the shim... 

The most fundamental aspect of a sensitivity discussion of remote detection is the fact that it is inherently a point-by-point technique. Each spectrum recorded by the detector does not contain any information other than its amplitude. Conceptually, a remote NMR experiment is very similar to a 2D NMR experiment with a z filter between encoding and detection, which causes all transverse magnetization to dephase. For 2D NMR experiments, it has been shown that the signal-to-noise ratio (SNR) per square root time, which will be denominated as sensitivity in the following, is the same as in the ID case when neglecting T2 relaxation [20, 21]. To compare the sensitivity of a remotely detected spectrum [Figure 2.6.4(b)] with an equivalent experiment with direct detection [Figure 2.6.4(a)], we can use an expression similar to the discussion in Ref. [20] ... 

In order to use Eqs. (2.6.1) and (2.6.2) to estimate the sensitivity gain obtained by remote detection, knowledge of the relative sensitivity of the detector and the encoding circuit, A, is required. Here we discuss the sensitivity of an rf coil detector as an example, because all the experiments presented in this text use inductive detection at high field. The signal-to-noise ratio of inductive NMR detection can be approximated by the following simplified equation [12] ... 

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