My apologies for asking elementary question as I am a beginner. I am in the process of creating input data for reconstruction. I have generated .cdf file for PET list mode that contains only crystal ids and the time. I am trying to calculate other fields in the list mode as well. However, I am a little bit at a loss. Any help with the following would be appreciated.

1- Why is the scatter intensity rate dependent on TOF while the random intensity rate is not? What do a normalized and un-normalized random/scatter mean?

2- How can I compute, un-normalized random/scatter intensity rate, attenuation factor, and normalization factor for a simple event/LOR? I mean image I have just only Event or LOR, How can I compute each factor for this specific event. I am trying to get an intuition of these notions.

I have seen some related topics like the following topics. However, I would like to see how one can calculated the factors manually just for only one event/LOR to understand the concept better.

Can someone help me to find out an answer to the following questions?

1- Why is the scatter intensity rate dependent on TOF while the random intensity rate is not? What do a normalized and un-normalized random/scatter mean?

2- How can I compute, un-normalized random/scatter intensity rate, attenuation factor, and normalization factor for a simple event/LOR? I mean image I have just only Event or LOR, How can I compute each factor for this specific event. I am trying to get an intuition of these notions.

A random coincidence is the accidental detection of two photons coming from two distinct decays. These photons are not correlated in time, hence the rate of random coincidences does not depend on the detection time difference.

A scattered coincidence is the detection of two photons coming from the same decay. These photons are correlated in time, hence the rate of scattered coincidences depend on the detection time difference

Un-normalized random : you can use a delayed coincidence window or compute the product of the single rates, times the full coincidence window

Un-normalized scatters : you can estimate them with a Monte Carlo simulation

Attenuation factor : forward project a map of the attenuation coefficients at 511 keV

Normalisation factor : see previous discussions about this specific hot topic

I’m afraid that a comprehensive answer to your questions is outside the scope of this mailing list. I can only recommend you to read a basic article about PET.