Dead-time correction method for block detector based ultra-long axial FOV PET scanner

The application of PET technology in preclinical studies and tumor diagnosis relies on accurate quantitative image reconstruction. For an ultra-long axial FOV PET scanner, a position dependent dead-time correction is necessary due to different relative count rate load on different part of the detector system. Therefore, a component dead time correction model taking into account singles losses, coincidence losses, and the mismatch between the fixed LLD/ULD energy window and drifting energy spectrum is proposed to compensate the coincidence event losses in scan process. In this method, a block based non-paralyzable dead time model is used to compensate the single losses, a global paralyzable model as a function of module event rates is used to compensate the coincidence losses, we use a least squares fit to get the correction factor for each block because the detectors at ends of the scanner cannot get enough counts to ignore the background, and we also consider the variation of the correction factor for objects with different single-to-coincidence ratio. Additional correction related to the scatter fraction was performed to ensure the linearity of real coincidence events vs effective activity concentration. A series of decaying source experiments were finished to verify the validity of this method. Good response linearity is obtained for uniform water cylinder and NEC scatter phantoms with different length.