title: The simplified reference tissue model for SPECT/PET brain receptor studies. Interpretation of its parameters.
abstract: OBJECTIVE
  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 [(11)C]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 R(1) and k(2) in physiological terms depends on the constraint, while the interpretation of BP(ND) does not.
  
  
  CONCLUSIONS
  Correct interpretation of the results of the SRTM is tracer specific. In particular, the parameter R(1), 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.
authors.affiliation: Department of Nuclear Medicine, University Medical Center Hamburg-Eppendorf, Martinistrase 52, Hamburg, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Buchert
authors.forename: F
authors.initials: F
authors.lastname: Thiele
mesh_terms: D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism; D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007700:Kinetics; D008959:Models, Neurological; D015233:Models, Statistical; D049268:Positron-Emission Tomography / Q000379:methods*; D020891:Raclopride / Q000378:metabolism; D019275:Radiopharmaceuticals; D011954:Receptors, Dopamine / Q000378:metabolism; D018079:Receptors, GABA / Q000378:metabolism; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; D011954:Receptors, Dopamine; D018079:Receptors, GABA; D020891:Raclopride