1. A method for merging and displaying images captured by a first and a second imaging device, comprising: recording first image information including a plurality of two-dimensional images of an examination area comprising fluorescent and non-fluorescent areas, the recording of the first image information comprising fluorescence-based images using a medical instrument adapted to perform light-excitation of fluorescent areas of the examination area, the medical instrument introduced invasively into the examination area, by a first imaging device; generating a three dimensional fluorescence image data record related to the examination area using the plurality of two-dimensional images; recording a further three dimensional image data record of the examination area using a further medical examination procedure, by a second imaging device, wherein the medical examination procedure by the second imaging device is based on electromagnetic radiation; generating a further three dimensional image related to the examination area using the further three dimensional image data record; registering the three dimensional fluorescence image data record and the further three dimensional image data record with each another, wherein the registering of the three dimensional fluorescence image data record and the further three dimensional image data record with each another is based on anatomical landmarks present in both the three dimensional fluorescence image data record and the further three dimensional image data record; processing the fluorescence image data record of the examination area to identify at least one dark area corresponding to at least one non-fluorescent area of the examination area unresponsive to the light-excitation and at least one bright area corresponding to at least one fluorescent area of the examination area responsive to the light-excitation, said processing based on respective voxel values indicative of said at least one dark area and said at least one bright area; superimposing the three dimensional fluorescence image data record over the further three-dimensional image, wherein voxels indicative of said at least one dark area are omitted to mask out said at least one dark area; and displaying a fluorescence-optically marked relevant area of the examination area on a screen, wherein the fluorescence-optically marked relevant area consists only of said at least one bright area responsive to the light-excitation and is positioned in the further three-dimensional image so that its position in the further three-dimensional image is anatomically correct relative to the further three-dimensional image using mapping rules included in the registering of the three dimensional fluorescence image data record with the further three dimensional image data record.