Real-time imaging system for a small OpenPET prototype

The “OpenPET” geometry has potential for real-time tracking of targeted tumors and in situ visualization of dose distribution in radiation therapy. For the real-time imaging system, we are intending to use one-pass list-mode dynamic row-action maximum likelihood algorithm (DRAMA) and implement it using general-purpose computation on graphics processing unit techniques. However, it is difficult to consistently reconstruct in real-time because the amount of list-mode data acquired in PET scan can be large depending on the activity and reconstruction speed depends on the amount of the list-mode data. In this study, we developed a system to control the data used in the reconstruction step keeping quantitative performance. In the proposed system, data transfer control system limits the event count to be used in the reconstruction step according to the reconstruction speed, and the reconstructed images are properly intensified by using ratio of the used count to the total count. We implemented the system on a small OpenPET prototype system and evaluated the performance in terms of the real-time tracking ability by displaying reconstructed images in which the intensity was compensated. The intensity of the displayed image was properly correlated with the original count rate and a frame rate of 2 frames per second was achieved without significant delay.