A study of an emission subtraction method for post-injection single transmission in PET

An accurate emission contamination (EC) correction method for postinjection single transmission without increasing scan time is highly required in clinical PET study. We have proposed a new correction method by using emission single counts (Es) acquired at the detectors behind the shielded transmission source. However, these counts include some transmission components such as penetrated through the source holder (Tp), and back-scattered (Ts) in the object. The scattered component can\´t be estimated simply because of its geometrical dependence property such as the object size, detector axial FOV, and the diameter ratio between detector ring and transaxial FOV. On the other hand, the penetrated component can be estimated directly by blank scan data. The feasibility of this method will be confirmed if the Ts/(Ts+Es) ratio is sufficiently low. In this work, we estimated the EC ratio at the detectors at the opposite side of the source. Then we evaluated the energy window dependence and axial FOV dependence by calculating Ts/(Ts+Es) ratio detected behind the source in some different conditions. As a results, the Ts/(Ts+Es) ratio has shown to be negligible in different lower energy threshold and in different axial FOV conditions. So we came to the conclusion that our proposed method has a usefulness and possibility to correct emission contamination accurately even if the energy threshold is low, and axial FOV is large. The main advantages of this method are needless of additional scan time only for EC correction, and accurate estimation of EC due to its simultaneous acquisition without "mock-scan".