1. A method of registering images of different modalities, comprising: taking a first image of a subject obtained by an imaging process of a first modality; taking a second image of the subject obtained by an imaging process of a second modality, said second image having a known positional relationship with the first image; taking a third image of the subject obtained by an imaging process of a third modality; distinguishing between at least one area of interest and at least one other area not of interest in the second image; on the basis of said known positional relationship identifying said at least one area of interest and other area not of interest in the first image; registering the first and third images by an image matching process based on said at least one area of interest identified in the first image.