Dead-time correction for an orbiting rod normalization in a cylindrical PET system

Orbiting rod source coincidence acquisitions may exhibit a significant amount of dead-time, depending on the system geometry and the rod source activity. This dead-time is a function of the relative location between the rod source and the crystals in the block detector and, therefore, varies across the sinogram row. Methods: Normalization scans were acquired on a GE Discovery ST positron emission tomography (PET)-CT system using three different rod activities and of duration such that the total acquired counts (T+S+R) were held constant. To develop a model of the dead-time, acquisitions at six static source locations, centered over each crystal in a single block detector, were acquired for each of the rod activity levels. The resultant block busy data were analyzed such that the profile of block busy as the rod traversed all lines-of-response (with respect to the said block) was found. The profile was fit with a Gaussian function and parameterized by full-width at half-maximum and amplitude. For image analysis, a 20 cm uniform cylinder and a whole-body patient scan were analyzed in reconstructed image space. The datasets were reconstructed with each uncorrected normalization, then with the normalization corrected for dead-time. Results: A model has been determined allowing application of dead-time correction to an orbiting rod normalization scan based on measured block-busy in the normalization raw data. Bias and variance effects were removed from reconstructed images. Conclusion : The model corrects for dead-time effects in the normalization. Analysis of image quality impact shows that bias and variance effects can be reduced to insignificant levels.