Figure 1 MARVIS (Medical AR VISualizer) augmented reality navigation system at work. (A) A marker on the operator’s head allowing video cameras to locate a head position. (B) Over-the-field projector displays anatomical features and the tumor view on the surface of the real, 3-dimensional model of the liver. (C) Targeting an aim hidden within the model with the needle connected to an electrical circuit. The closure of the circuit turns on the diode, which confirms the perfect placement of the needle.