Estimation of the noise contributions from blank, transmission and emission scans in PET

This work determines the relative importance of noise from blank (B), transmission (T) and emission (E) scans in PET using a GE Advance scanner on a 20 cm cylinder, a brain phantom, and a torso-like ellipse (18/35 cm) with examples of human scans (brain O-15 water and F-18 FDG, heart FDG). Phantom E scans were acquired in both 2D and 3D modes as decay series with C-11 or F-18 over 3-6 decades of noise equivalent counts (NEC). B and T scans were made using two pin sources (389+134 MBq) with times 16-32,768 sec. In humans only a limited subset was available. In homogeneous phantoms normalized variance (var) was estimated from pixel distributions in single images. In other objects, including the human studies, calculations were performed on differences of paired images. In all cases a fit was made to a simple noise model. The cylinder data shows expected relations of T to B noise proving the adequacy of B scan times <30 min for most purposes. For cylinder and brain phantom, contour plots are provided for var(E,T). In a typical 3D O-15 water study with 0.5 M counts per central slice, a 10 min T-scan ensures that var(T)<0.1*var(E). Using 10 min T scan for a static 3D FDG brain study of 10 min having 5 M counts yields equal E and T variance contributions. In human body scans T noise has a relative larger importance and is often dominated by effects of line artefacts from (clusters of) zeros in the T-scan, not included in the simple model.