Evaluation of a cone-beam SPECT system for brain imaging

The cone-beam geometry induces variations of the Point Spread Function (PSF) with respect to the point position within the Region Of Interest (ROI). These variations are very important issues for quantitation in SPECT imaging and must be analyzed to further well-interpret clinical images. We present the results of the experimentation we have conducted to measure each of the factors responsible of these variations for a brain imaging protocol. We run a simulation and we performed a series of acquisitions with a point source of Cobalt 57 placed successively at different positions to sample the variations of the PSF. Both simulations and acquisitions have been done with and without attenuation in order to compare the importance of attenuation and scatter with respect to the cone-beam geometry in the variations of the PSF. We use Chang and Jaszczak correction methods to correct respectively the attenuation and the scatter. The reconstructions run the Grangeat algorithm in order to deal with large apertures to supply a good sensitivity within the ROI. The results show that the cone-beam geometry does not significantly degrade the PSF within the brain ROI. This study also points out the necessity of well correcting the scatter to expect a good correction of the attenuation. Nevertheless, these results show that the variations of the PSF are very compatible with most of the SPECT protocols used for brain imaging