Correction/Calibration of twilite Measurements

Raw data acquired with the twilite (and LYSO detector head) represents a combination of background counts from the LYSO crystals, constant (with noise) at all activities, and counts (coincidences) resulting from decay of activity in the whole blood within the catheter. The number of counts from blood varies not only due to physiological kinetics, but also due to radioactive decay. Typically in quantitative PET studies we are only interested in physiological kinetics, meaning that counts in PET and blood should be corrected for decay. Thus, the following corrections have to be applied to raw twilite data in order to convert it into a whole blood arterial input function:

1.Subtraction of the intrinsic LYSO background.

2.Decay correction to the same time as the PET data, typically the PET scanner start time (DICOM Acquisition Time).

3.Correction for the isotope branching ratio.

4.Multiplication with the calibration factor.