Regional MTGA for irreversible tracers with reference region input

Theory

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, 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 Gjedde-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 always be measured starting from the time of tracer injection.

Regional Kiref calculation

The following steps can be done in MS Windows command prompt window or Solaris terminal window. If you insist on working with the old Sun/Solaris version of Patlak, instructions for that are here.

1. Preparation of regional tissue TAC data

This is explained in detail elsewhere. In short: draw ROIs and calculate regional TACs from dynamic images, and calculate averages over planes and regions if required.

Make sure that reference tissue region is included in the datafile.

In brain [18F]FDOPA studies with reference region input (cerebellum or occipital cortex) you must not subtract the reference region from other regional TACs, although this is done if plasma input ise used.

2. Computing the net uptake rate (Kiref)

The patlak program can then be run with (at least) the following command-line parameters:

  1. regional tissue TAC file
  2. name of reference region inside the previous file
  3. start time for the line fit (time where linear phase starts)
  4. end time for the line fit (time where linear phase ends, or end time of study)
  5. name for result file

Read the more detailed instructions on patlak usage by entering command patlak --help.

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 control the linearity and quality of the data visually.


Steps of Patlak plot calculation using the old SUN program:

1. Preparation of regional tissue TAC data

As above, but when you have regional TACs in new format (*.dft), you have to convert those to back to old *.roi.kbq format using dft2nci.

2. Computing the uptake rate

The Patlak program can be found in the menu of Solaris and SunOS workstations:

oldpatlak_ref_demo.gif (90702 bytes)


See also:

References:

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.


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