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 scan ner 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, h eart FDG). Phantom E scans were acquired in both 2D and 3D modes as de cay series with C-11 or F-18 over 3-6 decades of Noise Equivalent Coun ts (NEC). B and T scans were made using two pin sources (approximate t o 500 MBq total) over 64-32768 sec. In humans only a Limited subset wa s available. In homogeneous phantoms normalized variance (var) was est imated from pixel distributions in single images. In other objects, in cluding 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 show expected relations of T to B noise proving the adequacy of B scan times less than or equal to 20 min for most purpos es. For the brain phantom, a contour plot is provided for var(E,T). In a typical 3D O-15 water study with 0.5M counts per central slice, a 1 0 min T-scan adds less than 10% to the total noise level. An example s hows how to split a total scan time between E and T scans, in order to minimize the variance.