 The development of a new automated method of measurement of the volume of the hippocampus allows confirming these results in patients presenting with pre-dementia Alzheimers Disease AD, treated with donepezil in order to verify if this product is capable of stopping the speed of the atrophy of the hippocampus in patients and more specifically in those who will evolve to AD, compared to a placebo. This method is a semi automatic segmentation of the hippocampus from MRI, made by competitive region growing. 