Echo spacing

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... 

Our method is demonstrated with experiments on a Bentheimer sandstone sample. The sample was prepared to be cylindrically shaped with a diameter of 2.5 cm and a length of 2.0 cm. The sample was fully saturated with de-ionized water under vacuum. We performed the CPMG imaging experiment described in the previous section to measure the magnetization intensity at 50 echoes spaced by 4.6 ms for each of 32 x 16 x 16 voxels within the field of view of 3.0 cm x 3.0 cm x 3.0 cm. The corresponding voxel size is 0.938 mm x 1.88 mm x 1.88 mm. We used 1 s of repetition time (TR) and the total imaging time was 4.3 min. 

Fig. 7.3.1 Principle of spectroscopic Fourier imaging. To separate spatial and spectroscopic responses, the spectroscopic evolution must be constant during the space encoding period f i, or it can be refocused by formation of an echo. Space is encoded during the evolution time fi and the spectroscopic response is acquired during the detection time t2.

Figure 8.9 (a) The pulse sequence for the 2-D deuteron exchange experiment where is the incremented period for the first-time domain, t2 is the aquisition period for the second time domain, t is the quadrupole echo spacing and is the mixing time period, (b) A 2-D exchange spectrum of crystalline i-PP. This confirms the 120° jump motion for the helix shown in the chain model. (Reprinted from D. Schaefer, H.W. Spiess, U.W. Sutter and W.W. Fleming, Macromolecules 23 (1992) 3431-3439 by permission of the publishers, American Chemical... 

TE is the inter-echo spacing used in the CPMG sequence. 

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