Comparison of dual- and triple-head hybrid PET systems using estimation task performance

The precision of quantitative analysis in hybrid PET is affected by the spatial sensitivity profile of the imaging system and by patient attenuation. Dual- and triple-head (2H and 3H, respectively) systems have different sensitivity profiles: the 2H profile being triangular and centrally peaked, whereas the 3H configuration tends to concentrate sensitivity in the peripheral field-of-view (FOV). The authors quantify how the degradation in performance of an estimation task is related to the joint action of the system sensitivity profile and patient attenuation. Their analysis involved ideal-observer models of performance in non-linear tasks involving the simultaneous (maximum-likelihood) estimation of the amplitude, size, and location of a focal lesion in a torso-sized attenuator, as well as the attenuator's background activity. The hybrid-PET system simulated was the Marconi IRIX, operating in either 2H or 3H coincidence mode. The 3H configuration had more than a two-fold greater sensitivity across the entire field of view than the 2H; however, the 3H outperformed the 2H only in the peripheral FOV. Task performance was relatively constant across the FOV for the 2H configuration because its sensitivity profile tended to mitigate count loss due to attenuation.