Evaluation of the ECAT EXCAT HR with ACSII for clinical routine 3D measurements

In recent years considerable interest has been given to 3D PET because of the advantage of increased sensitivity by acquiring radiation in a larger solid angle. Recent commercial PET scanners have the possibility to acquire data in full 3D mode by removing the septa and acquiring data in all possible detector combinations. On the early ECAT EXACT HR systems, the hardware and software only supported 3D data acquisition and reconstruction was done offline on a separate reconstruction workstation. The high computational burden for the reconstruction process and the huge amount of data acquired on the 24 ring system made it difficult to use this scanner for routine 3D PET. For this reason the ECAT EXACT HR system was upgraded recently with new hardware (ACSII) and software (ECAT version 7.0). The major features of the new configuration include: 8 processor reconstruction engine for short image reconstruction times (down to 6 minutes per frame); smart memory board to improve counting performance at higher count rates; data reduction by variable axial slice rebinning (VARB); faster memory-to-disk transfers for fast 3D dynamic scans (sustained frame rate of 5 seconds per frame) In the present paper we report on the evaluation of the new system (referred to as ACSII) which also includes the new operating software with regard to count rate performance, spatial resolution in reconstructed images with respect to the new data reduction scheme, image homogeneity, scatter correction and data handling/reconstruction times. In this work we also compare the factory supplied scatter correction method with the approach we used in reconstructing 3D data acquired with the previous hardware configuration (referred to as ACSI) and the previous reconstruction code (referred to as LB code).