Carr-Purcell-Meiboom-Gill CPMG experiment

We can perform spatially resolved Carr-Purcell-Meiboom-Gill (CPMG) experiments, and then, for each voxel, use magnetization intensities at the echo times to estimate the corresponding number density function, P(t), which represents the amount of fluid associated with the characteristic relaxation time t. The corresponding intrinsic magnetization for the voxel, M0, is calculated by... 

Carr-Purcell-Meiboom-Gill (CPMG) experiment. An experiment wherein the net magnetization is allowed tipped into the xy plane, and subjected to a series (or train) of RF pulses and delays to refocus the net magnetization. Maintaining the net magnetization in the xy plane allows the measurement of the T2 relaxation time. 

Since R2 is the only observable that provides information about the /(O) spectral density contribution, accurate measurement of this observable is of particular importance. Transverse relaxation rates are typically measured by either a spin-lock (f ip) or a Carr-Purcell-Meiboom-Gill (CPMG) experiment. In the following, advantages and disadvantages of the two experiments are described with particular consideration of... 

Figure 12 Pulse sequence and detected signal for the Carr-Purcell-Meiboom-Gill (CPMG) experiment used to measure the spin-spin relaxation time, T2.

T2 measurements usually employ either Carr-Purcell-Meiboom-Gill (CPMG) [7, 8] spin-echo pulse sequences or experiments that measure spin relaxation (Tlp) in the rotating frame. The time delay between successive 180° pulses in the CPMG pulse sequence is typically set to 1 ms or shorter to minimize the effects of evolution under the heteronuc-lear scalar coupling between 1H and 15N spins [3]. 

Ti reports on fast dynamics on a timescale of ps-ns, whereas T2 relaxation depends on both fast and slower dynamics (ps-ns and xs-ms). The experimentally measured T2 relaxation times include an exchange contribution that can be measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse train (25, 26) or an effective spin-lock field (27-29). The combination of T2 and Tip measurements allows determination of the contribution of chemical exchange to the relaxation time. Eurthermore, relaxation dispersion experiments have been developed to measure slow time-scale xs-ms dynamic processes (30-35). 

Static imaging experiments conducted on fluid-saturated samples are used to determine porosity distributions. Carr-Purcell-Meiboom-Gill (CPMG) imaging is used to evaluate the spin density. The local relaxation is modeled in order to estimate the intrinsic magnetization intensity, which is proportional to the amount of saturating fluid. 

Deuterium NMR experiments were performed at 13.7 MHz on a JEOL FX 90Q spectrometer. The Ti measurements were performed using an inversion recovery sequence and the T2 values were estimated from the line widths. Because the resonances are relatively broad for the polymers in concentrated solutions, the Ta s measured were virtually the same as those measured from the Carr-Purcell-Meiboom-Gill (CPMG) method. In this case, measuring the line widths was much faster than measuring the T2 s by the CPMG method. Thus the T2 measurements were taken to be equivalent to the T2 s. 

The trick introduced by Meiboom and Gill (14) is to dephase all n pulses in the Carr Purcell train by an angle of 90° with respect to the initial ti/2 pulse. It is easily shown that, without this phase change, imperfections of the 71 pulses are cumulative, whereas with the 90° phase change, a self-compensation occurs for all echoes of even number. The CPMG (Carr-Purcell-Meiboom-Gill) experiment can be handled in two ways ... 

While many NMR active nuclei such as JH, 13C, 31P, and 15N have been used to analyze metabolites (19-21), JH NMR analysis is the most widely used in the field because of the ubiquitous nature of JH and its high NMR sensitivity. Furthermore, ease of analysis and high-throughput capabilities make onedimensional (ID) NMR experiments, including the ID NOESY (nuclear Over-hauser enhancement spectroscopy) and CPMG (Carr-Purcell-Meiboom-Gill)... 

CPMG (Carr-Purcell-Meiboom-Gill) pulse sequence to odd-half-integer quadrupolar spin systems. It was found that QCPMG (controlled CPMG) can be one order of magnitude more sensitive than quadrupolar echo MAS experiments. Assisted by numerical simulation, the QCPMG MAS experiments can be used to determine the quadrupolar as well as chemical shift tensors. ... 

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