[en] A feasibility study was carried out to determine whether image quality can be improved by the use of time-of-flight (TOF) information in positron emission tomography (PET). The experiment used two fast cesium fluoride detectors followed by constant-fraction discriminators for coincidence-timing resolutions of 600 to 800 psec full width at half maximum, depending on the energy discrimination level. A point source was scanned to study the spatial response of the point spread function with and without the TOF information for nonfiltered back-projected data. Back-projected images of a simplified chest phantom, 42 cm in diameter and filled with relative activity concentrations of 1, 0, and 5, are presented for the unfiltered data to demonstrate the improvement in image quality obtained with the use of TOF. Filtered and reconstructed images of this phantom are also presented to show the relative differences in the images obtained with PET and TOF-PET techniques for similar filter functions