Calculation of Patlak plot for regional TACs with reference tissue input
Multiple-time graphical analysis (MTGA) for irreversible tracers (Patlak plot, or Gjedde-Patlak plot) with reference region input is used to estimate tracer net uptake (influx) rate of the PET tracer, Kiref, if there exists a region (usually cerebellum) in the PET image where the tracer does not bind irreversibly. There are no such regions for [18F]FDG.
The units of Kiref are min-1.
Note that although it is possible to do Patlak analysis with plasma input from late-scan imaging only, that is not possible with reference tissue input! For MTGA methods the input data must be measured starting from the time of tracer administration.
ROI drawing, calculation of regional TACs, and calculation of Patlak plot, can all be done in Carimas or PMOD.
As an alternative to Carimas, Patlak plot can also be calculated using in-house command-line tools:
2. Preparation of regional tissue TAC data
Save the regional TAC files in the image analysis program, in DFT format with Carimas, or in TAC format in PMOD. Calculate averages over planes and regions if needed.
Reference tissue region can be included in the datafile with other ROIs, or kept in a separate TAC file.
In brain [18F]FDOPA studies with reference region input (cerebellum or occipital cortex) you must not subtract the reference region from other regional TACs (subtraction is only done if plasma input is used).
3. Computing the net uptake rate (Kiref)
The patlak program can then be run with (at least) the following command-line parameters:
- regional tissue TAC file
- name of reference region inside the previous file, or, name of TAC file which contains only the reference region TAC
- start time for the line fit (time where linear phase starts)
- end time for the line fit (time where linear phase ends, or end time of study)
- name for result file
Control the linearity of plots
MTGA methods produce correct results only if the slope is calculated from the linear phase of the plot, excluding the curvature in the beginning. You should always draw the Patlak plots and control the linearity and quality of the data visually.
Steps of Patlak plot calculation using the old SUN/Solaris tool:
Preparation of regional tissue TAC data
Convert the regional TACs in DFT format (*.dft) older *.roi.kbq format using dft2nci.
Computing the uptake rate
The Patlak program can be found in the menu of SUN/Solaris workstations:
- Patlak plot using plasma input
- Patlak plot and long time frames
- Calculation of Patlak plot for images
- Reference region input compartmental models
Logan J. Graphical analysis of PET data applied to reversible and irreversible tracers. Nucl Med Biol. 2000; 27:661-670.
Patlak CS, Blasberg RG. Graphical evaluation of blood-to-brain transfer constants from multiple-time uptake data. Generalizations. J Cereb Blood FlowMetab 1985; 5: 584-590.
Created at: 2013-12-11
Updated at: 2018-03-15
Written by: Vesa Oikonen