1. A method for an image registration process, comprising: creating a first 3D image data set of a patient by a first image acquisition system, wherein the first 3D image data set comprises imaging of a part of the body of the patient comprising soft tissue, wherein one or more imaging parameters of the first image acquisition system are selected for soft tissue imaging; creating a second 3D image data set of the patient by the first image acquisition system, wherein the second 3D image data set comprises imaging of a part of the body of the patient comprising an skeletal structure, wherein one or more imaging parameters of the first image acquisition system are selected for skeletal imaging; transmitting the first and the second 3D image data set of the patient to a second image acquisition system, which is not suitable for soft tissue imaging; creating a third 3D image data set of the patient by the second image acquisition system, wherein the third 3D image data set comprises imaging of the part of the body of the patient comprising the skeletal structure imaged by the first image acquisition system; determining a mapping rule for a coordinate transformation from the second 3D image data set to the third 3D image data set based on a registering of the skeletal structure having been respectively imaged by the first image acquisition system in the second 3D image data set and by the second image acquisition system in the third 3D image data set; processing the determined mapping rule to relate the first 3D image data set which comprises imaging of the part of the body of the patient comprising soft tissue, to a coordinate system of the second image acquisition system, which is not suitable for soft tissue imaging; and generating a representation of the part of the body of the patient comprising soft tissue from the first 3D image data set related to the coordinate system of the second image acquisition system, and effective for registering the representation of the part of the body of the patient comprising soft tissue with a 2D image recorded by second image acquisition system.