Count-rate (CR) data
What is count-rate data
"Count-rate" data file contains the true counts per second collected by the PET scanner during each second of the scanning. It is used for time-delay correction.
CR data is stored in an ASCII text file with two columns, time (s) and true count rate (units may differ). In Turku PET Centre, CR curves are corrected for physical decay. The filename extension is usually .cr or .head ("head curve").
However, the count-rate data is saved in different formats by the PET scanners and may need to be converted to this format before use.
Where does CR data come from
GE Advance
In Turku PET Centre, when ECAT 6.3 format images are extracted from
GE Advance database, the CR data is also extracted (program
crexport via dbExtr), and written in the
same directory than the PET image with extra extension .cr. The CR data
is corrected for physical decay and dead-time.
Originally the .cr file does not contain time column, which must be
added before any use withaddtimes; however, many
software do this automatically.
HR+
Count-rate data is routinely saved in all PET studies beginning in the autumn 2005. The placement and naming of data files will be determined later.
Count-rate data ("head-curve") in HR+ is originally saved in format like this:
time prompt delayed p_rate d_rate dtime frame singles 1050 148 131 0 0 0 1 184302 3066 1165 1084 504 472 1 1 622488 4133 2060 1889 838 754 1 1 622488 5866 3858 3715 1037 1053 0 2 0 6916 5260 5010 1335 1233 3 2 1284090
Before any use, this data must be converted to normal count-rate data format using tocr. However, batch files and scripts for processing blood and plasma curves will in future do this step automatically for the often used tracers.
HRRT
Head-curve files (*.hc) will be placed in PETO system with the images, and they are also located in pet-storage disk in folder HRRT\rawdata. Data is originally in comma-separated table format, like this:
Singles,Randoms,Prompts,Time(ms) 1913508,4936,5580,761 2017637,6025,6437,1975 2570950,28844,29498,3299 3133375,59768,60599,4545 4867737,67194,67184,5587 ...
Before any use, this data must be converted to normal count-rate data format using tocr. However, batch files and scripts for processing blood and plasma curves may in future do this step automatically for the often used tracers.
PET-CT
Not considered yet.
ECAT 931
Count-rate data was written in the same directory as the dynamic PET image with extension *.head; the files did not originally contain the time column, which may have to be added withaddtimes; however, many software do this automatically, and some very old software may work only if there is no time column.
If CR data is not available
Count-rate curve can be replaced in time delay fitting with regional TACs or "head curve", an average TAC from the dynamic image or sinogram made withecathead, in case that PET time frames are short enough (10-15 s or less) in the beginning of the PET scan.
Software for processing CR data
- Add time column into count-rate file
- Create a "head curve" if count-rate file does not exist
- Make a SVG or PostScript (PS) graph for viewing the count-rate curve; count-rate curve can be scaled to fit better in the same graph.
