The switchable phantom was designed as composed of two parts: a homogeneous host phantom and a movable rod. The host phantom has a cylindrical hole in which the rod can be inserted (see Fig. 1). By moving the rod which carries a black cylindrical inclusion, the phantom can be switched from a homogeneous to an inhomogeneous phantom. The host phantom is manufactured from a solid homogeneous base material consisting of epoxy resin (NM500/H179B; Nils Malmgren AB, Ytterby, Sweden) to which black toner (black 46/I, part No. 885 983 06, Infotec, France) and particles (T-8141, Sigma–Aldrich, St. Louis, Missouri) were added as absorption and scattering components, respectively. The phantom recipe was taken from the work of Swartling et al.,38 but we introduced some improvements to better control the reproducibility and the quality of the final product. One hundred twenty mg of black toner powder was dispersed in 100-g hardener by sonicating for 20 min (B220, Branson Ultrasonics, Danbury) to prepare the absorption base from which the required amount was taken and added to the final volume of hardener. The powder was directly weighted to the proper amount. The resin was poured in the mold (Jars Nalgene style 2118, 500 ml, Sigma–Aldrich, St. Louis, Missouri), the particles were added and then mechanically dispersed in the resin by means of a laboratory homogenizer (OV5, VELP Scientifica, Italy) operating for 3 to 5 min at 10,000 rpm. To this suspension, the mixture of hardener and black toner were added, and then a mechanical stirring was performed for 2 to 3 min at 12,000 rpm. A vacuum pump (XDS5, Edwards Ltd, Crawley, UK), operating at 10 to 20 mbar was used to eliminate air bubbles (usually 4 to 5 min pumping). Since the mechanical stirring overheats the mixture, following the bubble removal, the mold was kept partially immersed in running water for about 10 min to bring the mixture to room temperature. Then, the phantom was cured in a ventilated oven (UTP 20, Heraeus, Heraeus Holding GmbH, Hanau, Germany) at 50°C for 6 to 8 h. The phantom was then extracted from the mold, ready to be machined in the proper shape, and polished. A cylindrical hole (diameter 14 mm) was finally drilled parallel to the largest surface at a depth of 15 mm (Fig. 1). The concentration of black toner and for the host phantom were chosen so as to yield an absorption coefficient, , of and a reduced scattering coefficient, , of at 690 nm, representative of average biological tissue optical properties in the 600 to 1000 nm spectral range.