Multi-spin echo

Duyn JH, Frank JA, Moonen CT (1995) Incorporation of lactate measurement in multi-spin-echo proton spectroscopic imaging. Magn Reson Med 33 101-107 Duyn JH, Moonen CT (1993) Fast proton spectroscopic imaging of human brain using multiple spin-echoes. Magn Reson Med 30 409-414... 

T2 maps were obtain fiom multi spin echo (MSE) images with 32 consecutive echoes, 30 ms inter-echo time and TR=10 s. Ti maps were measured using the TOMROP sequence with 32 consecutive echoes, Tl=210 ms and TR=10 s. T2 and T maps were calculated on a pixel-by-pixel basis using corresponding monoexponential fimctions, via the Levenberg-Marquardt criterion for chi-square minimization... 

Fig. 2.1.16 Trabecular bone structure, muscle after removal of the soft tissue (right). Image and tendon of a mouse tail in vitro at 21.14T, parameters multi-slice spin-echo method,...

It must be stressed that the spin-echo sequence is applied only during the detection period and its unique purpose is to estimate the signal amplitude (in a sense, it is a replacement for the simple 90° pulse). Consequently, in an arrayed multi-block experiment whose purpose is to measure Ti(Br), only the X value is varied, while the delays 5 and 8 are kept constant in order to make sure that no T2(Ba) effects leak into the experimental relaxation curves. Moreover, to avoid contamination of the echo by FID residues due to imprecise settings of RF pulses and to Bi inhomogeneity, proper phase cycling is highly recommended. 

The result is an enhancement of all the advantages of spin-echo detection. The number of usable data points in each acquired data array can in this case exceed in an FID by a factor much larger than two. Since T2 relaxation is going on during the detection, it is again important to keep 8 rigorously constant during the whole multi-block experiment. 

Abstract We use Nuclear Magnetic Resonance relaxometry (i.e. the frequency variation of the NMR relaxation rates) of quadrupolar nucleus ( Na) and H Pulsed Gradient Spin Echo NMR to determine the mobility of the counterions and the water molecules within aqueous dispersions of clays. The local ordering of isotropic dilute clay dispersions is investigated by NMR relaxometry. In contrast, the NMR spectra of the quadrupolar nucleus and the anisotropy of the water self-diffusion tensor clearly exhibit the occurrence of nematic ordering in dense aqueous dispersions. Multi-scale numerical models exploiting molecular orbital quantum calculations, Grand Canonical Monte Carlo simulations, Molecular and Brownian Dynamics are used to interpret the measured water mobility and the ionic quadrupolar relaxation measurements. 

For a two-pulse (90° - t - 180°), or primary echo experiment, the integrated intensity of the spin echo, which occurs at time t after the 180° pulse, is measured as a fimction of increasing t from the probe s dead-time ( 100 ns) to a time where the echo amplitude has decayed to a few percent of its initial amplitude (2-8 ps for most powder samples). A two-pulse ESE decay envelope for the type-1 Cu(II) site of a multi-copper oxidase, Fet3p, is shown in Figure 1(a). The data show an overall decay characterized by a phase memory time, Tm or T, of < 1.0 ps. Superimposed on this decay are echo modulations that arise ft om hyperfine coupling to the N nuclei of two histidyl imidazole ligands and the protons of the snrronnding matrix. 

Static spin echo decay spectroscopy also forms the basis for the measurement of magnetic dipole-dipole interactions between two unlike nuclei I and S. While this interaction is refocused by the Hahn spin echo, it can be recoupled by applying a 7i-pulse to the S-spins during the dipolar evolution period [12]. This manipulation inverts the sign of the heterodipolar Hamiltonian, and thereby interferes with the ability of the Hahn spin echo technique to refocus this interaction. The corresponding pulse sequence, termed SEDOR spin echo double resonance) shown in Fig. 4, compares the I-spin echo intensity as a function of dipolar evolution time (a) in the absence and (b) in the presence of the ti(S) pulses. Experiment (a) produces a decay F(2ti)/Fo, which is dominated by homonuclear dipole-dipole interactions, while experiment (b) results in an accelerated decay, reflecting the contribution from the heteronuclear I-S dipole-dipole interaction, which is now re-introduced into the spin Hamiltonian. For multi-spin systems, a Gaussian decay is expected ... 

Fio. 7,2.30 [Sch 13 Multi-quantum filtered images of a phantom made from Pt samples with different cross-link densities. The cross-link density varies from left to right according to medium, high and low. The top image is a conventional spin-echo image for reference. 

Stilbs, P. and Moseley, M.E. (1979) Nuclear spin-echo experiments on standard Fourier-transform NMR spectrometers - Application to multi-component self-diffusion studies. Chem. Scripta., 13, 26-28. 

In this section the simple one-pulse experiment and different multi-pulse ID experiments and the 2D coupling resolved experiment will be discussed. By means of the one-pulse experiments several concepts are introduced such as pulse length calibration or delay calculation which must be kept in mind when successfully setting up an n dimensional experiment. The J-resolved 2D experiment is included in this section because it is based on the simple but extremely useful spin echo unit whereby the chemical shift evolution is refocused by a 180° pulse applied in the centre of the free precession evolution. 

Mansfield P 1977 Multi-planar image formation using NMR spin echoes J. Rhys. C Solid State Phys. 10 L55-L58... 

Abstract Multi-resonance involves ENDOR, TRIPLE and ELDOR in continuous-wave (CW) and pulsed modes. ENDOR is mainly used to increase the spectral resolution of weak hyperfine couplings (hfc). TRIPLE provides a method to determine the signs of the hfc. The ELDOR method uses two microwave (MW) frequencies to obtain distances between specific spin-labeled sites in pulsed experiments, PELDOR or DEER. The electron-spin-echo (ESE) technique involves radiation with two or more MW pulses. The electron-spin-echo-envelope-modulation (ESEEM) method is particularly used to resolve weak anisotropic hfc in disordered solids. HYSCORE (Hyperfine Sublevel Correlation Spectroscopy) is the most common two-dimensional ESEEM method to measure weak hfc after Fourier transformation of the echo decay signal. The ESEEM and HYSCORE methods are not applicable to liquid samples, in which case the FID (free induction decay) method finds some use. Pulsed ESR is also used to measure magnetic relaxation in a more direct way than with CW ESR. 

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