CPMG sequence

Fig. 2.4.4 Profile of a sample made from two latex layers 70 pm thick separated by a 150 pm thick glass spacer. The full profile is the combination of 10 images with an FOV of 50 pm, covering a total depth of 500 pm. Each of these images is the FT of the echo signal obtained as the addition of the first 16 echoes acquired during a CPMG sequence and 512 scans with...

Fig. 2.4.5 Profile of a phantom made of three 2-mm thick rubber layers separated by glass slides of 2- and 1-mm thick. The CPMG sequence was executed with the following parameters repetition time = 50 ms, tE = 0.12 ms, number of echoes = 48 and 64 accumulations. The profile was scanned with a spatial resolution of 100 pm in 5 min.

The skin layers from the palm of the hand were scanned in vivo. A CPMG sequence was applied to sample the echo train decays as a function of depth. The decay was determined by both the relaxation time and the diffusion coefficient. To improve the contrast between the layers, a set of profiles was measured as a function of the echo... 

Fig. 2.4.14 Profile of a multi-layer polymer coating used to protect concrete surfaces from environmental corrosion. The profile is the signal amplitude resulting from the addition of the first 32 echoes acquired with a CPMG sequence with tE = 50 ps. It has an FOV of 8 mm and was measured with a spatial resolution of 100 pm. Using 256 scans per point and a repetition time of 100 ms, the total acquisition time per point was 25 s.

When Tcp is longer in a CPMG sequence under a constant gradient, the diffusion effect can be observed. For the Flahn echo coherence pathway where every jt pulse refocuses the dephasing, the diffusion contribution is,... 

When the measurement of a distribution of diffusivity is desired, improved signal-to-noise is needed. This can be achieved by using a diffusion-editing pulse sequence [7] rather than the CPMG sequence with varying echo spacing. This... 

Figure 15B shows a screenshot displaying the spin echoes of 195Pt in platinum powder acquired by the CPMG sequence. The experiments were performed at a carrier frequency of 50.74 MHz. The 19SPt signal... 

Measurement of a true T2 can be obtained using a spin-echo pulse sequence, such as the Carr-Purcell-Meiboom-Gill (CPMG) sequence, which minimizes the loss of phase coherence caused by inhomogeneities (Kemp, 1986). 

Fig. 14.4 Pulse sequences used for the experiments described in this chapter. A [ N HJ-HSQC with water flip back and PFGs. The shaped pulse on the proton channel is a sine-shaped, 1.5 ms soft pulse all other pulses are hard pulses. Gradients are applied as square or sine-shaped pulses. The sign of the last gradient is reversed for anti-echo selection together with the sign of phase 6. B CPMG sequence. C bpPFGLED sequence. The delay T denotes the diffusion delay. Typically, r is set to 1 ms, T to 50-100 ms and Te to 1.2 ms.

These various processes have several important implications for plant tissue relaxometry. First, the fact that plant cells are compartmentalized means that, in general, the transverse and longitudinal relaxation will be multiple exponential when measured with the CPMG sequence and enough data points to give well characterized decay to the baseline. Such multiple exponential relaxation is observed with apple. 

Figure 11 shows the i 2 dependence on the particle size for systems containing a constant amount of magnetized material, without refocusing pulse (like in a gradient echo sequence), and with 7 different echo times used in CPMG sequences. 

The NMR measurements were performed on systems composed of ca. 25 wt. % samples of aPS (M = 6.6x 10 g/mol, PD = 1.1, Pressure Chemical Company) in either reagent grade toluene (Aldrich) or toluene-d0 (Aldrich). The protonated solvent was used for the diffusion measurements and the deuterated solvent for the relaxation studies. At this concentration, the Tg j for the system was determined to be about -65 °C (i). The NMR spectra were run on a JEOL FX-90Q NMR spectrometer operating at 90 and 14 MHz for protons and deuterons, respectively. The T and T2 measurements were made with the standard inversion-recovery and spin-echo (CPMG) sequences, respectively. 

Fig. 4. Pulse sequences for determining spin-spin relaxation time constants. Thin bars represent 7t/2 pulses and thick bars represent tt pulses, (a) the CPMG sequence, (b) the spin-lock sequence used for determining T p and (c) a two-dimensional proton-detected INEPT-enhanced CPMG. T is the waiting period between individual scans. The pulse train during the T period is used for suppression of cross-correlation effects, and the delay S is set to < (1/2)J. The delay A in (c) is set to (1/4)Jih and A is set to (1/4)Jih to maximize the intensity of IH heteronuclei and to (1 /8) Jm to maximize the intensity of IH2 spins. The phase cycling in (c) is as follows i = y,—y 2 = 2 x),2 —x), i = 8(x), 8(—x) Acq = x, 2(—x), x, —x, 2(x), —x, —x, 2(x), —x,x, 2(—x), x. The onedimensional version the proton-detected experiment can be obtained by omitting the ti delay.

Fig. 2.2.10 Echoes in NMR. (a) Two-pulse Hahn echo, (b) CPMG sequence with multiple refocusing pulses, (c) Stimulated echo sequence showing both, the Hahn echo (HE) or primary echo and the stimulated echo (SE). (d) Gradient echo.

Mei 1]. As a tribute to the inventors (Cair, Purcell, Meiboom, and Gill) of this technique, the pulse train is named the CPMG sequence. 

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