Oncological patient care requires long term follow-up in order to estimate effectiveness of existing and new treatment choices. Image-based assessment of whole body tumour burden is commonly used for that purpose. The WHO response criteria were established in 1979 proposing bi-dimensional tumor measurements. New RECIST guidelines appeared in 2000 relying on only the longest diameter (uni-dimensional) measurements. Obviously, a change in tumour size is only one potential surrogate for therapy response which not necessarily reflects the biologic activity of the tumour or the effect of particular therapy. Thus, the evaluation of biological, metabolic or molecular properties of a tumor and its changes might be an attractive means to assess the response to therapy sensitively and early.