Processing ABSS data
Researcher has to preprocess the arterial blood data collected using an on-line detector ("blood pump") (*.alg, *.bld or *.blo.lis), before using it as the input in his/her data analyses. This page contains instructions on what needs to be done and how to do that.
As a rule, there are tracer specific (and sometimes both tracer and organ specific) software (scripts) which do most of the required steps, and new scripts can be written when needed, based on the general step-by-step instructions given below.
These scripts work only in Windows computers in TPC/hostpital network:
Inside TPC network, the scripts can be executed from command-line by giving the name of the script.
1. ABSS file format conversion, calibration, and correction for radioactive decay
If you need to do the preprocessing steps (calibration, decay correction, file format conversion) to the "blood pump" data by yourself, use blo2kbq in Windows command prompt window with the following command-line options and arguments:
- with option -c the location and name of datafile containing the calibration coefficients,
- to correct the data for radioactive decay, specify the isotope code with option -d,
- option -i with isotope code (again) to select the correct calibration coefficient and branching ratio,
- optionally, the name of the output file may be specified with option -o,
- the name of the original on-line detector ("blood pump") data file.
As an example, an oxygen-15 labeled tracer data might be processed with this command in Windows command prompt window:
blo2kbq -c=S:\Lab\plasma\bsampler_calibration\pump_cal.dat -d=O -i=O -o=uo268blo.kbq uo268.bld
If you copy the calibration file (pump_cal.dat) to your own data directory, make sure that it contains an up-to-date calibration coefficient for all of your studies, because PET physicists can update only the original calibration file in \\pet-storage disk system.
Detailed information on how on-line detector raw data is processed is given with the raw data file format descriptions for Scanditronics/GEMS and Allogg ABSS.
2. Dispersion correction
Correction for dispersion in the ABSS assembly and possibly in vasculature is necessary in 15O studies, and may be useful with other tracers if the peak shape of the input curve is important in the analysis method.
3. Blood curve must be converted to plasma
The blood and plasma curves of most tracers are different, for the most analysis modes the plasma curve is needed as input. Therefore the blood curve must be converted to plasma curve. This is never needed for 15O tracers.
4. ABSS and manual sample data must be combined
After the "blood pump" data is converted to plasma TAC, it usually has to be combined with the plasma TAC measured from manual blood samples (in 15O studies usually only ABSS is used). This catenation of the two curves can be accomplished with dftcat.
There is often an overlap in "blood pump" and manual samples, and in those cases dftcat will automatically ignore the end of ABSS. This can be changed with options. In some cases it may be necessary to select and remove the overlapping samples manually in a text editor.
Manual blood samples are pre-processed by the personnel of blood laboratory, and the necessary corrections for manually sampled blood and plasma TACs are made to the data before the datafiles are copied to the PETO system or directory S:\Lab\plasma\.
When you have the combined plasma TAC, you can proceed with the pre-processing of the input curve as usual.
5. Metabolite correction
Metabolite correction of the plasma or blood curve is required for most of the tracers, but not for the most commonly used tracers [18F]FDG and [15O]H2O.
[15O]O2 and [13N]NH4+ studies may require metabolite correction. However, some model analysis software make these corrections automatically; look for the specific analysis program documentation.
6. Delay time correction
The difference between the tracer arrival times to tissue (PET measurement) and blood sampling site ("blood pump") may have to be corrected (delay correction). Result of delay time correction must always be controlled visually!
These command-line tools are used by the scripts, but can be used separately, if needed. These programs are available for both Windows and Linux. Installation to computers outside TPC/hospital network is possible but not supported.
See example on handling on-line detector data.