A method to assess the relationship between water diffusivity and water content was developed. This method combines the non-destructive measurement of water distribution in sample by NMR imaging during isothermal drying process and data treatment for shrinking/swelling materials and which needs no a priori on the relationship D = f(X). Gelatine eel samples (60 bloom) were used to test the method. Their initial moisture contents were between 1.8 and 5 kg water/kg dry basis, pH between 4 and 8 and temperature in the range of 10 and 24 degreesC. This first part describes the experiments. A specific assembly adapted to the small microimaging probehead was built to promote isothermal and unidirectional drying of the samples. Successive steps were developed to calculate local moisture contents from independent calibration and sources of error were evaluated. It was shown that 2D NMR signal amplitude images must be recorded to derive the true 1D moisture content profiles although the time acquisition is longer. The time variation of 1D moisture content profiles with a spatial resolution of 49 mum and shrinkage was analysed.