The simplified reference tissue model for SPECT/PET brain receptor studies

Abstract

SummaryAim: The SRTM (simplified reference tissue model) of brain receptor imaging assumes that the time activity curve in the receptor-rich region of interest can be fitted satisfactorily by the 1-tissue compartment model. This assumption has been formulated by a rather restrictive constraint on the rate constants. Empirically, the SRTM might well describe also tracers which do not fulfil this constraint, such as [11C]raclopride, for example. However, this has not been justified rigorously. Methods: The requirements for the SRTM to be applicable are analyzed in detail. Results: The SRTM is applicable under a less restrictive constraint than described previously. The interpretation of the SRTM parameters R1 and K2 in physiological terms depends on the constraint, while the interpretation of BPND does not. Conclusion: Correct interpretation of the results of the SRTM is tracer specific. In particular, the parameter R1, which in case of compliance with the original constraint might be used to detect perfusion and/or extraction effects, might not be appropriate for this purpose in case of raclopride-like tracers.