Two Eppendorf tubes served as the navigation targets, to be scanned with (fh)SPECT imaging, and were placed at roughly 5 cm apart. With a volume of , the Eppendorf tubes should resemble a typical lymph node size found in lymph node dissection for prostate cancer; KleinJan et al.25 reported a range of 80 to , with a median of . These tubes were filled with a mixture of ICG and of an ICG solution and of a solution (). The ICG solutions used, in this study, consisted of ICG (ICG-Pulsion, Pulsion Medical Systems, Munich, Germany) dissolved in human serum albumin (Albuman , Sanquin, Amsterdam, The Netherlands). With this as stock solution, the effective ICG solutions used in the phantom experiments range from 9.62 to . This quantity was chosen based on both clinical relevance (0 to typically found in lymph nodes during prostatectomy25) and best visibility during fluorescence guidance (best visibility found between 2.44 and 26). The solutions used, in this study, were obtained from a pertechnetate solution ( saline, Technekow, Mallinckrodt Medical BV, Petten, The Netherlands). Two additional Eppendorf tubes were hidden on the sides of the tissue mimicking structure to serve as “anatomical reference” in the CT images. These tubes were filled with CT contrast agent [Ultravist (Bayer AG, Leverkusen, Germany) 50% diluted with demineralized water].