Sensitivity of SPECT with rotating slat collimators

SPECT acquisition with rotating slat collimators does not have a constant sensitivity over the field of view, like in parallel hole collimated SPECT. Therefore knowledge of the sensitivity variation is required to be able to correct for this effect during reconstruction. The variation of the sensitivity in the field of view for SPECT imaging with planar collimation is determined by different factors. A primary factor are the collimator properties, but there is also an influence of the type of detector and its dimensions. The geometric sensitivity is derived from the collimator dimensions using some assumptions. It is shown that this is a valid prediction for the sensitivity when the point is far enough from the collimator. Close to the collimator the assumptions for calculating the sensitivity are not fulfilled any more, and a modified calculation method is used. It is shown that after using this modified method a constant error between the calculated and experimental (Monte Carlo simulation)values for the different distances is obtained. After calculating the sensitivity in one plane it is easy to obtain the tomographic sensitivity. This is done by rotating the maps for spin and camera rotation. The method allows to obtain an expression for the resolution of these systems. It is shown that for the same collimator dimensions the same resolution-distance relationship is obtained as for parallel hole collimators. The accuracy is shown by comparison with the resolution values from Monte Carlo simulation. Close to the detector a correction factor is needed.