Comparison of Noise Equivalent Count Rates (NECRs) for the PET Systems With Different Ring Diameter and Electronics

Because the sensitivity of positron emission tomography (PET) system increases in proportion to the inverse of the diameter of the detector ring, brain PET systems are being planned and developed. However, count losses due to the dead-time of the detector blocks increases as the ring diameter decreases. Since the count losses decrease the noise equivalent count rate (NECR) of the system, the NECR of brain PET system may be lower than that of a whole-body PET system in clinical dose range. In this paper, we compared the NECRs of brain PET systems with that of a whole-body PET system using a Monte Carlo simulation. We simulated the PET system for a 27-cm-diameter detector ring, a 54-cm-diameter detector ring, and an 89-cm-diameter detector ring and evaluated the NECRs. In the clinical dose range, the NECR of the small-diameter brain PET system was lower than those of the whole-body PET system unless the electronics was advanced. We conclude that the small-diameter brain PET system with conventional electronics has not so much advantage except for the lower cost and the higher spatial resolution. However, advanced electronics can reduce degradation of NECR, so the small-diameter brain PET system with advanced electronics will be useful for clinical studies.