Nuclear imaging is a commonly used tool in today's diagnostics and therapy planning. For interventional
use however it suffers from drawbacks which limit its application. Freehand SPECT was developed to overcome
these limitations and to provide 3D functional imaging during an intervention. It combines a nuclear
probe with an optical tracking system to obtain its position and orientation in space synchronized with its
reading. This information can be used to compute a 3D tomographic reconstruction of an activity distribution.
However, as there is no fixed geometry the system matrix has to be computed on-the-fly, using ad-hoc
models of the detection process. One solution for such a model is a reference look up table of previously
acquired measurements of a single source at different angles and distances. In this work two look up tables
with a one and four millimeter step size between the entries were acquired. Twelve datasets of a phantom
with two hollow spheres filled with a solution of Tc99wm were acquired with the Freehand SPECT system.
Reconstructions with the look up tables and two analytical models currently in use were performed with these
datasets and compared with each other. The finely sampled look up table achieved the qualitatively best
reconstructions, while one of the analytical models showed the best positional accuracy.