A 2D/3D hybrid PET scanner with rotating partial slice-septa and itsquantitative procedures

Abstract

This paper presents a PET scanner capable of acquiring projection data inthree-dimensional (3D) and two-dimensional (2D) modes simultaneously. Thescanner has rotating partial slice-septa, and coincidence events are storedas 2D data or as 3D data depending on whether the lines of response arecollimated by the septa or not. 68Ge/Ga rod sources can beset on the rotating septa, and a transmission scan for attenuationcorrection is performed in the 2D mode. The scanner allows simultaneous3D-emission/2D-transmission scanning or post-injection transmissionscanning with little cross-talk. A blank scan for detector normalization isalso performed with the rotating rod sources in the 2D mode, from which wecan derive the normalizing factors in both modes. The 3D/2D differencemethod is available for scatter correction, even in a dynamic study wherethe source distribution is changing. A `summation method' is proposed as anew image reconstruction algorithm, in which the high- and low-frequencycomponents of images are reconstructed from the 3D and 2D datarespectively. In this method, most of the scatter contribution in the 3Ddata is removed by high-pass filtering, not by subtracting estimatedscatter distribution, and hence the method is expected to be robust forscatter from outside the axial field of view. Computer simulations revealedthat the rotating partial septa offer a single-scatter to true ratiosimilar to that of the conventional full septa if the depth of the partialsepta is properly lengthened, with a small increase in multiple scattering.