Fig. 1

From invasive to non-invasive imaging. It took more than 500 years to establish non-invasive imaging from the pencil drawings of Da Vinci to routine tomographic imaging. Fifty years were needed to introduce hybrid imaging. With the availability of stand-alone anatomical and functional imaging, the first attempts to fuse separately acquired images were made as early as the 1960s. Computer-assisted software fusion can be regarded as a main incubator of hardware fusion, first introduced in the late 1980s, a decade before prototype hardware-fusion became available