Delayed PET scan must be corrected to injection time
By default, all PET images are decay corrected to the scan start time. If scan was started after the injection, the frame times and decay correction must be corrected to the true injection time prior to any other calculation with the dynamic image or sinogram.
If PET scanning was performed in separate session, and you only need to combine these together, then follow this link: Catenation of PET images or sinograms.
Correction procedure
Use program ecattime.
You need to feed the program with the actual injection time (hh:mm:ss) or
the time delay between the injection and scan start time in minutes.
If another scan (for example another organ) was started at the time of injection, you can get the start time from that time using the same program ecattime.
Not recommended: Instead of correcting the image or sinogram, the corrections can
be applied to the time-activity curves (TACs), either when the TACs are calculated using program
img2kbq with option -t, or later using program
dfttime with option -d.
This has to be done to all *.roi.kbq or *.dft files, also when additional ROIs are drawn later on,
but correction of dynamic image or sinogram needs to be done only once for one study.
Do not correct twice
Unless you are sure that the image/sinogram is not yet corrected to the injection time,
you can check this by entering the command ecattime yourfilename ; if the scan
start time matches the injection time, or the start time of the first frame is later than 0,
then the image/sinogram has already been corrected.
It is always safe to make the correction by entering the injection time (hh:mm:ss).
You must not correct the TACs (*.dft or *.roi.kbq), if the image or sinogram was already corrected to injection time.