MEASUREMENT OF POSITRON RANGE IN MATTER IN STRONG MAGNETIC-FIELDS

Positron range is one factor that places a limitation on Positron Emis sion Tomography (PET) resolution. The distance a positron travels thro ugh matter before it annihilates with an electron is a function of its initial energy and the electron density of the medium. A strong magne tic field limits positron range when momentum components are transvers e to the field. Measurement of positron range was determined by deconv olving the effects of detector response and radioactivity distribution from the measured annihilation spread function. The annihilation spre ad function for a 0.5 mm bead of Ga-68 was measured with 0.2 and 1.0 m n wide slit collimators. Based on the annihilation spread function FWH M (Full Width at Half Maximum) for a 1.0 mm wide slit the median posit ron range in tissue equivalent material. is 0.87, 0.50, 0.22 mm at 0, 5.0 and 9.4 T, respectively.