Virtual extrapolation technique for retracing line of response of single scattered events in positron emission tomography

Purpose: The scattering phenomenon creates degrading effects in positron emission tomography (PET) and the corresponding events are rejected conventionally. We have proposed a mathematical model to retrace the original line of response of the single-scattered coincident events with the aim to incorporate such events in PET. Methods: We have devised a new Virtual extrapolation technique based on the concept of the probability density functions. Through which we transformed the original two-parameter list mode data for the coincident photon pairs to a one-parameter data set. The procedure of random sampling and sampling distribution - by utilizing some unique properties like a collective difference and the length compensation - was employed in the data analysis. We studied the effect of finite timing and energy resolution of detectors on the performance of the proposed model. Results: We determined the frequency of occurrence of the data values corresponding to real as well as fictitious scattering points { placed on the arc of a circle drawn with the constant scattering angle - to observe the highest counts. As expected, we found the highest counts at the location of real scattering points. The model was evaluated for a uniform attenuating phantom medium. The results were found impressive for the case of ideal time and energy information, less so for the cases of finite resolutions. Conclusions: Our work outlines a completely new approach; though, a lot more sophistication is required for its practical utility. Nonetheless, the technique seems promising in developing a potential approach to improve the sensitivity of PET imaging.

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