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Ultrafast timing enables reconstruction-free positron emission imaging
Nature Photonics  (IF38.771),  Pub Date : 2021-10-14, DOI: 10.1038/s41566-021-00871-2
Sun Il Kwon, Ryosuke Ota, Eric Berg, Fumio Hashimoto, Kyohei Nakajima, Izumi Ogawa, Yoichi Tamagawa, Tomohide Omura, Tomoyuki Hasegawa, Simon R. Cherry

X-ray and gamma-ray photons are widely used for imaging but require a mathematical reconstruction step, known as tomography, to produce cross-sectional images from the measured data. Theoretically, the back-to-back annihilation photons produced by positron–electron annihilation can be directly localized in three-dimensional space using time-of-flight information without tomographic reconstruction; however, this has not yet been demonstrated due to the insufficient timing performance of available radiation detectors. Here we develop techniques based on detecting prompt Cherenkov photons, which, when combined with a convolutional neural network for timing estimation, resulted in an average timing precision of 32 ps, corresponding to a spatial precision of 4.8 mm. We show this is sufficient to produce cross-sectional images of a positron-emitting radionuclide directly from the detected coincident annihilation photons, without using any tomographic reconstruction algorithm. The reconstruction-free imaging demonstrated here directly localizes positron emission and frees the design of an imaging system from the geometric and sampling constraints that are normally present for tomographic reconstruction.