With this motivation behind, Wendler et. al. introduced the Freehand SPECT technology, which allows to do 3D reconstructions with tracked 1D gamma probes [29]. In a pre-operative validation study they achieved mapping of at least one SLN in 87.5% of the 85 patients, with a sensitivity of 83.33% compared to the SPECT/CT [30]. After this initial success, Freehand SPECT system has been brought to the operating room (OR) for feasibility studies in SLNB procedures in breast cancer and melanoma patients [8, 14, 4].