Positron range is one factor that places a limitation on Positron Emission Tomography (PET) resolution. The distance a positron travels through matter before it annihilates with an electron is a function of its initial energy and the electron density of the medium. A strong magnetic field limits positron range when momentum components are transverse to the field. Measurement of positron range was determined by deconvolving the effects of detector response and radioactivity distribution from the measured annihilation spread function. The annihilation spread function for a 0.5 mm bead of 68Ga was measured with 0.2 and 1.0 mm wide slit collimators. Based on the annihilation spread function FWHM (Full Width at Half Maximum) for a 1.0 mm wide slit the median positron range in tissue equivalent material is 0.87, 0.50, 0.22 mm at 0, 5.0 and 9.4 T, respectively.
Bibliographical noteFunding Information:
The authors gratefully acknowledge Intermagnetics General Corporation, Latham, NY for loaning the nuclear instrumentation. Dr.'s K. Ugurbil, M. Garwood and H. Merkle for 9.4 T magnet access at the Center for Magnetic Resonance Research, University of MN, Minneapolis, MN. Supported by U.S. Public Service Grant (1 R03 RR07042-01).