Optimisation of noise equivalent count rates for brain and body FDG imaging using gamma camera PET

Describes the use of noise-equivalent count (NEC) rates to optimise the clinical use of a modified dual-headed gamma camera for positron emission tomography (PET). Phantoms were used to simulate the distribution and uptake for brain and body ¹⁸F-fluorodeoxyglucose (FDG) imaging, including the presence of activity outside the imaging field of view. Camera count rates were recorded as a function of activity in the field of view in the presence and absence of lead septa. The use of variable numbers and widths of energy windows was also investigated. The results indicate that acquisitions without axial collimators is optimal for brain imaging, while a restriction of 12° in the axial acceptance angle leads to superior NEC rates for torso imaging. The most significant factor affecting the NEC rates for body imaging with no axial collimation is the detection of random coincidences from out-of-field activity. Under most imaging conditions, the use of a Compton-photopeak energy window in addition to the traditional photopeak-photopeak appears to lead to increased NEC rates, although an accurate scatter correction would be necessary to compensate for the associated increase in the scatter fraction