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A single-scan protocol for absolute D2/3 receptor quantification with [123I]IBZM SPECT
Stergios Tsartsalis1, Benjamin B Tournier2, Karl Aoun2
1Vulnerability Biomarkers Unit, Division of Adult Psychiatry, Department of Mental Health and Psychiatry, University Hospitals of Geneva, Switzerland; Division of Addictology, Department of Mental Health and Psychiatry, University Hospitals of Geneva, Switzerland; Department of Psychiatry, University of Geneva, Switzerland.
A novel partial saturation protocol allows separate, non-invasive estimation of D2/3 receptor availability (Bavail) and affinity (1/appKd) in molecular imaging. This method aids in understanding dopaminergic system variations in research.
Area of Science:
- Neuroscience
- Radiochemistry
- Pharmacology
Background:
- Molecular imaging of D2/3 receptors is crucial in neuropsychiatric research.
- Non-displaceable binding potential (BPND) is a common quantitative index, but its accuracy is affected by endogenous neurotransmitter dynamics.
- A simplified method for absolute quantification of receptor concentration (Bavail) and affinity (1/appKd) is needed.
Purpose of the Study:
- To describe and validate a partial saturation protocol for in vivo Scatchard plotting.
- To enable separate estimation of Bavail and appKd using a single SPECT session.
- To compare this method with established kinetic modeling and BPND estimation techniques.
Main Methods:
- A partial saturation protocol was developed and applied at regional and voxel levels in rats.
- Validation involved a multi-injection protocol with a 3-tissue compartment, 7-parameter (3T-7k) model for [123I]IBZM.
- The protocol was tested after D2 receptor overexpression and during amphetamine-induced dopamine release.
Main Results:
- The partial saturation protocol yielded results comparable to the 3T-7k model.
- D2 receptor overexpression increased striatal Bavail by ~18%.
- Amphetamine administration decreased Bavail by ~17% and increased appKd by ~39%.
- BPND estimates from SRTM, LNIGA, and SUR methods correlated well with 3T-7k Bavail values.
Conclusions:
- The partial saturation protocol offers a non-invasive, time-efficient method for estimating Bavail and appKd separately.
- This technique can differentiate changes in receptor density from changes in receptor-ligand interaction.
- It holds potential for in-depth studies of the dopaminergic system in translational molecular imaging.
