
164 Statistical Computing in Nuclear Imaging
PMT
PMT
PMT
a1
a2
a3
a4
b2
b1
b3
b4
a b
PMT
true paths of photons
assigned LOR
location of radioactive decay
LFI
LFI
DOI DOI
FIGURE 5.24 Detection of a direct (true) coincidence by two detector blocks (a and
b).
In the other stage (typically during the data ana lysis/reconstruct
ion) the
approximation is made about the LFI within the volume of the crystal. For
example, the assumption is made that LORs begin a nd end in the ce nters of
the crystals. The inner surface of the crystal or average depth o f interaction
can also be used as beginnings and ends of LORs.
The uncertainty of unknown LFI is the cause of parallax error.