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Abstract
The differential equations of compartmental analysis form the basis of the models
describing the uptake of tracers used in imaging studies. Graphical analyses convert
the model equations into linear plots, the slopes of which represent measures of tracer
binding. The graphical methods are not dependent upon a particular model structure
but the slopes can be related to combinations of the model parameters if a model structure
is assumed. The input required is uptake data from a region of interest vs time and
an input function that can either be plasma measurements or uptake data from a suitable
reference region. Graphical methods can be applied to both reversible and irreversibly
binding tracers. They provide considerable ease of computation compared to the optimization
of individual model parameters in the solution of the differential equations generally
used to describe the binding of tracers. Conditions under which the graphical techniques
are applicable and some problems encountered in separating tracer delivery and binding
are considered. Also the effect of noise can introduce a bias in the distribution
volume which is the slope of the graphical analysis of reversible tracers. Smoothing
techniques may minimize this problem and retain the model independence. In any case
graphical techniques can provide insight into the binding kinetics of tracers in a
visual way.