COMBINED MRI-PET SCANNER - A MONTE-CARLO EVALUATION OF THE IMPROVEMENTS IN PET RESOLUTION DUE TO THE EFFECTS OF A STATIC HOMOGENEOUS MAGNETIC-FIELD

Positron emission tomography (PET) relies upon the detection of photon s resulting from the annihilation of positrons emitted by a radiopharm aceutical. The combination of images obtained with PET and magnetic re sonance imaging (MRI) have begun to greatly enhance the study of many physiological processes, A combined MRI-PET scanner could alleviate mu ch of the spatial and temporal coregistration difficulties currently e ncountered in utilizing images from these complementary imaging modali ties. In addition, the resolution of the PET scanner could be improved by the effects of the magnetic field. In this computer study, the uti lization of a strong static homogeneous magnetic field to increase PET resolution by reducing the effects of positron range and photon nonco llinearity was investigated. The results reveal that significant enhan cement of resolution can be attained, For example, an approximately 27 % increase in resolution is predicted for a PET scanner incorporating a 10-Tesla magnetic field. Most of this gain in resolution is due to m agnetic confinement of the emitted positrons, Although the magnetic fi eld does mix some positronium states resulting in slightly less photon noncollinearity, this reduction does not significantly affect resolut ion, Photon noncollinearity remains as the fundamental limiting factor of large PET scanner resolution.