The cellular origins of relaxation and diffusion contrast

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. 

Possible correlations between cross-polarization rates and quality factors are an additional aspect that appears to have been overlooked, yet image contrast 

In the limit of zero gradient, the sequence reduces to the Hahn echo, and it is conventional to expand the echo amplitude as a multiple exponential function of T, and define, the usual transverse relaxation times, T, 

As already discussed, modelling this multiple exponential decay function with the numerical cell model gives valuable information about cell morphology and membrane permeability. Similar information is available 

The Ti q) behave as wavevector-dependent relaxation times and the form of the wavevector dependence can provide a useful check on the consistency of models. Table 5 shows a comparison of the experimental coefficients for fresh apple tissue with those calculated with the numerical cell model. The agreement is quite reasonable and supports the general theoretical framework. It would be interesting to apply this approach to mealy apple and to other types of fruit and vegetable. 

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