Patent ID: 8022368

Claim:
A method for reducing randoms variance in a Positron Emission Tomograph (PET) or Positron Emission Tomograph combined with another Medical Imaging device, wherein an averaged estimate of an element, R ij , of a randoms event (delayeds) sinogram corresponding to detectors i and j in a detector ring of the PET or PET/Medical Imaging device is expressed as R ^ ij = R i ⁢ R j 2 ⁢ τ ( ∑ i ′ ∈ I j ⁢ s i ′ ) ⁢ ( ∑ j ′ ∈ J i ⁢ s j ′ ) wherein R i and R j are fan sums for detectors i and j ; 2 T is the coincidence time window; the randoms relate to single rates s i and s j in the detectors by R ij =2 TS i S j ; I j is a set of detectors corresponding to the fan of detector j ; and J i is a set of detectors corresponding to the fan of detector i ; the method comprising the steps of: estimating the numerator from fan sums in the delayeds sinogram of the PET or PET/Medical Imaging device; estimating the denominator from recorded singles rates; using the resulting averaged estimate of R ij as a randoms event (delayeds) sinogram.