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This paper documents modifications to an older PET system to improve its dead time, scatter fraction, and spatial resolution in high count rate, short duration studies. A new dual-tapered collimator reduces scatter by 33 percent while providing excellent resolution uniformity in all slices. A data encoding scheme produces uniformly sampled parallel projections from the coincidence data in real time while the detector array executes an orbital motion. The image uniformity, scatter compensation and high count-rate performance have been validated up to 40 kBq/cc in a 20 cm flood source. The errors in image quantification due to counting statistics, live time, and random counts are estimated from repeated measurements on a contrast phantom at high count-rates. The effects of two methods of scatter compensation on image contrast are shown in contrast phantoms and a typical glucose utilization study. Blood flow measurements using 0-15 labeled water bolus method, made under different physiological conditions, reflected the changes expected. The true count efficiency of 75 kcps/(uCi/cc) permits these studies to be done with only 500-900 MBq (13-25 mCi) injected activity.