Radioactivity measurement of blood samples
The total radioactivity of blood, plasma and urine samples is obtained by two automated gamma counters (1480 Wizard 3", Wallac, Turku). Plasma is separated from blood by centrifuging, and then measured. Procedures for taking manual blood samples is documented in the quality system in intranet.
Arterial whole blood radioactivity concentration can be measured with an on-line blood sampler and detector system ("blood pump", ABSS). Currently, there are four systems installed, two made by Scanditronics/GEMS and two made by Allogg.
Manual plasma and blood samples
The radioactivity concentrations in manual samples of blood or plasma are corrected for physical decay to the injection time, and calibrated to units kBq/mL. Laboratory personnel copies the plasma and/or blood TAC datafiles to the PETO system. From there, the datafiles can be extracted to your group disks. In other PET centers the unit is often given per mass (gram) because the samples may have been weighted. In Turku PET Centre, the plasma samples are pipetted by known volume, which allows the same unit in plasma and tissue data. Blood samples can not be pipetted because of very high viscosity; sample tubes are weighted and converted to kBq/mL applying the population mean blood density.
Datafiles are in ASCII format (File format of time-radioactivity curves), that can be imported e.g. to Excel, Origin or OpenOffice Calc. See also plotting of TACs.
Blood on-line samplers
Each on-line sampler is normally used only with a certain PET scanner, but they can be swapped if necessary.
It may be necessary to collect a few blood samples while the on-line sampler is still working. These may be needed for example for metabolite analysis or for determining the blood-to-plasma ratio. These manual samples can usually be taken from the end of the tubing, so that they do not cause any disturbance in the on-line data, but the timing of samples need to be adjusted based on tubing and flow rate.
Please not that the clocks on ABSSs may not always be synchronized with PET scanner clocks.
Samplers on PET scanners
On-line detector that is normally located at GE Advance PET scanner, is manufactured by GEMS. Raw on-line detector data is stored in a specific format. After the necessary processing and correction steps, the data format is the same as in any other TAC files.
The raw blood data is written in the PETO system. From there the original data can be extracted to group data disks.
Studies conducted before 2000-02-03
Blood data files from GE Advance studies which date back to 2000-02-02 and before that, do not contain the date of the study. The date has to be added manually to the data file in international format; without it, wrong calibration coefficients will be applied (the first measured calibration coefficients). Files are in ASCII text format, and can be edited for example with Notepad. For example, if the study date was Sep 24 1999, add the following line to the beginning of the data file:
Raw on-line detector data of Allogg ABSS (Allogg AB, Mariefred, Sweden, http://www.allogg.se/) is stored in a specific ASCII text format. After the necessary processing and correction steps, the data format is the same as in any other TAC files.
The raw blood data is written in the PETO system. From there the original data file can be extracted to group data disks. Data that was collected before PETO system was in use can be found in S:\Lab\plasma\archive\hrplus_kevat2004_2005\ or S:\Lab\plasma\HRplus\.
A second-generation Allogg ABSS is installed and used with HRRT; before that other systems were temporarily used.
Scanditronics on-line sampling system is used normally with PET-CT. This system was previously used with ECAT 931. The raw blood data is written in the PETO system. From there the original data file can be extracted to group data disks.
ECAT 931 (put out of operation in the end of April 2005)
Scanditronics on-line detector was located at ECAT931 during the years it was in operation.
Raw on-line detector data is stored in a specific format. After the necessary processing and correction steps, the data format is the same as in any other TAC files.
The raw blood data were written in directory S:\Lab\plasma\ecat\*_blo.lis. From this directory the original data may have been moved to group disks and MO or CD-ROM disks.
Processing on-line blood sampler data in TPC
Usually, on-line detector (ABSS) data is processed by different software (scripts or batch files) for each tracer (oxygen-15 and carbon-11 and fluorine-18 tracers).
If you need to calibrate ABSS 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,
- with option -d to correct the data for physical decay,
- option -i with isotope code 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, a GE Advance study might be processed with this command in Windows XP command prompt window:
blo2kbq -c=S:\Lab\plasma\bsampler_calibration\pump_cal.dat -d -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 S: disk.
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.
Delay and dispersion
Arterial curve is dispersed in the sample tubing and the arrival times to the region of interest and to the sampling point may be different. Thus the input curve may need to be corrected for time delay and dispersion.