An improved analytical detector response function model for multilayer small-diameter PET scanners.

The optimization of spatial resolution is a critical consideration in the design of small-diameter positron emission tomography (PET) scanners for animal imaging, and is often addressed with Monte Carlo simulations. As a faster and simpler solution, we have developed a new analytical model of the PET detector response function, and implemented the model for a small single-slice, multilayer PET scanner. The accuracy of the model has been assessed by comparison with both Monte Carlo simulations and experimental measurements published in the literature. Results from the analytical model agreed well with the Monte Carlo method, being noise free and two to three orders of magnitude faster. The only major discrepancy was a slight underestimation of the width of the point spread function by the analytical method as inter-crystal scatter is neglected. We observed good agreement between the predictions of the model and experimental measurements. For two large-diameter scanners additional discrepancies were seen due to photon acollinearity, which is not considered in the model. We have shown that the simple and fast analytical detector response function model can provide accurate estimates of spatial resolution for small-diameter PET scanners, and could be a useful tool for several applications, complementing or cross-validating other simulation methods.

A study of artefacts in simultaneous PET and MR imaging using a prototype MR compatible PET scanner.

We have assessed the possibility of artefacts that can arise in attempting to perform simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) using a small prototype MR compatible PET scanner (McPET). In these experiments, we examine MR images for any major artefacts or loss in image quality due to inhomogeneities in the magnetic field, radiofrequency interference or susceptibility effects caused by operation of the PET system inside the MR scanner. In addition, possible artefacts in the PET images caused by the static and time-varying magnetic fields or radiofrequency interference from the MR system were investigated. Biological tissue and a T2-weighted spin echo sequence were used to examine susceptibility artefacts due to components of the McPET scanner (scintillator, optical fibres) situated in the MR field of view. A range of commonly used MR pulse sequences was studied while acquiring PET data to look for possible artefacts in either the PET or MR images. Other than a small loss in signal-to-noise using gradient echo sequences, there was no significant interaction between the two imaging systems. Simultaneous PET and MR imaging of simple phantoms was also carried out in different MR systems with field strengths ranging from 0.2 to 4.7 T. The results of these studies demonstrate that it is possible to acquire PET and MR images simultaneously, without any significant artefacts or loss in image quality, using our prototype MR compatible PET scanner.