Studies of Positron Range in Tissue-Equivalent Materials

In this work microPET scans and Monte Carlo simulations of line sources containing F-18, N-13 and Ga-68 were performed to study the effect that positron range has over the spatial resolution of PET images. The experimental studies were carried out using a microPET Focus 120 scanner with a reported axial spatial resolution of 1.44 mm. Line sources consisted of thin capillary tubes filled with a water solution containing a known activity concentration of the radionuclides and placed inside six different tissue equivalent cylindrical phantoms. Image reconstruction was performed using filtered backprojection and from the axial images, radial profiles were extracted to compute the spatial resolution for all radionuclide-material combinations. One dimensional line sources inside cylinders were simulated using PENELOPE to obtain the line spread functions (LSFs) of all the radionuclide-material combinations. Our results indicate that spatial resolution depends strongly on the radionuclide (positron energy) and the density of the tissue in which they travel before annihilation.