Today’s surgical navigation systems are difficult to use for deformable organs. State of the art technology struggles to continuously update and display preoperative information such that it corresponds to the actual position of the organ. An update method is presented in this pro ject that uses pre-operative CT phantom data to extract a virtual organ model and calculate the position of inner landmarks. The virtual model is based on a mass-spring system. Surface data is processed to calculate forces that are applied on the model. The accuracy of the obtained inner landmark positions is verified by tracking navigation aids that are inserted in the phantom organ. Three different mass-spring models are created and compared to each other. Accuracy below 1cm was achieved but the method needs to be further tested with different deformations.