Carr-Purcell-Meiboom-Gill relaxation

CPMG Carr-Purcell-Meiboom-Gill relaxation... 

In electron spin echo relaxation studies, the two-pulse echo amplitude, as a fiinction of tire pulse separation time T, gives a measure of the phase memory relaxation time from which can be extracted if Jj-effects are taken into consideration. Problems may arise from spectral diflfrision due to incomplete excitation of the EPR spectrum. In this case some of the transverse magnetization may leak into adjacent parts of the spectrum that have not been excited by the MW pulses. Spectral diflfrision effects can be suppressed by using the Carr-Purcell-Meiboom-Gill pulse sequence, which is also well known in NMR. The experiment involves using a sequence of n-pulses separated by 2r and can be denoted as [7i/2-(x-7i-T-echo) J. A series of echoes separated by lx is generated and the decay in their amplitudes is characterized by Ty. ... 

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... 

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]. 

Spin-spin relaxation times T2 are determined by the Carr-Purcell-Meiboom-Gill spin echo pulse sequence and provide information about slower molecular motions (66,67). 

Values of the spin-spin relaxation-time (Tz) for individual spectral lines may be measured by Fourier transformation of the echoes produced by a Carr-Purcell-Meiboom-Gill type of pulse sequence,174 but only in a simple manner, if there is no homonuclear spin-coupling present.175 Refocusing of the dispersing magnetization-vector by... 

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. 

When NMR was performed the media hydrated with 1 1 H20 D20 were packed in 10 mm NMR tubes to reach a sample height of 8 to 10 mm. A 90° pulse WALTZ sequence was used with acquisition parameters 7.45 to 780 /AS pulse width, 1500 to 20,000 Hz pulse width, 0.012 to 0.166 sec acquisition time and recycle delay > 5Ti. Spin-spin relaxation time (T2) was determined with a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence with interpulsed spacing (t) ranging from 5 to 500 ms. At least eight different T values were used for each T2 determination. 

NMR molecular mobility Relaxation times ( H NMR Ti and T2) determination was carried out with a Bruker Avance 300 Spectrometer (Bruker Instruments, Billerica, MA, USA). Samples were packed into 5-mm diameter NMR tubes. Ti was measured using an inversion recovery (Derome, 1987) and T2 with a Carr Purcell Meiboom Gill (CPMG Carr and Purcell, 1954 Meiboom and Gill, 1958) pulse sequences. All data were best fit with mono-exponential relaxation with > 0.99 in all samples. 

Since the present NMR-SIM version also consider transverse relaxation as a proper process, it is possible to simulate the common T2 measurement experiment using the Carr-Purcell-Meiboom-Gill sequence. 

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... 

Loria JP, Ranee M, Palmer AG (1999) A relaxation-compensated Carr-Purcell-Meiboom-Gill sequence for characterizing chemical exchange by NMR spectroscopy. J Am Chem Soc 121 2331-2332... 

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