1. Comparison of methodologies for the assessment of dopamine receptor binding in subregions of the striatum Functional Neuroimaging Lab School of Psychology University of Newcastle Schizophrenia Research Institute Darlinghurst, Australia Sharna Jamadar Mentor: Julie Price PET Modality Coordinator: Jonathan Carney

2. Project Aims Become familiar with the basics of PET radioligand methods –Compartmental models –Logan graphical method (arterial input function) –Logan graphical method (cerebellum reference tissue) Become familiar with two types of dopamine radioligands –Raclopride –CFT –How do these differ? Understand utility of PET radiotracer methods for the study of behaviour

3. PET Methodology Compartmental models –Model parameters determined by iterative non-linear least-squares fitting, used to obtain receptor binding measures, use arterial blood as model input Outcome measures: –Distribution volume (V T ) the ratio of the concentration of radioligand in a region of tissue to that in plasma (at equilibrium) –Distribution volume ratio (DVR) is related to receptor density x affinity, and equal to V T / V ND –Binding potential (BP) proportional to receptor density x affinity 1T 2T V T = free + nonspecific + specific V ND = free + nonspecific (non-displaceable reference uptake)

4. PET Methodology Logan Graphical Methods –Linear alternative, use arterial blood as input (V T ), possible to use reference-tissue (DVR) –Transforms multiple time measurements of plasma and tissue uptake into a linear plot, the slope related to receptor binding measures –Appropriate for radiotracers for which a constant relationship between blood and brain tissue radioactivity is established during the study (steady-state) –Advantages Simpler calculations (non-iterative) Not reliant upon definition of underlying compartments

5. Radiotracers for Dopamine [C-11]Raclopride –D 2/3 receptors –Benzamide that shows selective and moderate affinity for D 2 receptors and binds reversibly to postsynaptic D 2 receptors [C-11]CFT 2-carbomethoxy-3-(4-[18F]-fluorophenyl)tropane –Dopamine transporter –Cocaine analogue that shows good selectivity for the dopamine transporter over other transporters and shows little non-specific binding in the brain –Dopamine transporter is present exclusively in dopamine-synthesising neurons, thus is an index of presynaptic dopaminergic function. –(Almost) irreversible binding

6. Project N=4 Assess compartmental modeling and graphical methods for [C-11]raclopride & [C-11]CFT Estimate binding potential: BP  (V T /V ND ) – 1 –Cerebellum used as reference tissue to estimate VND Free of dopamine receptors, good estimate of non-displaceable (i.e., free + non-specific) uptake –Which method(s) are acceptable? 1 tissue compartment model 2 tissue compartment model Logan (arterial) Logan (reference tissue)

7. Project Dorsal caudate (DCA) Anteroventral striatum (AVS) accumbens, ventromedial caudate + anteroventral putamen Middle caudate (MCA) Dorsal putamen (DPU) Ventral putamen (VPU) First defined in Drevets et al. (1999) in baboon, used in humans Drevets et al. (2001)

8. CER 1 Tissue Compartment [C-11]RAC 0.1 0.35 K1 = 0.116Err = 0.0134%Err = 11.5 k2 = 0.300Err = 0.0307%Err = 10.2 V T = 0.387 = V ND SS=0.057 Receptor free region = free + unspecific binding µCi/mL obs-fit Time (min)

9. CER 1 Tissue Compartment CER 2 Tissue Compartment [C-11]RAC 0.1 0.35 0.1 K1 = 0.130Err = 0.0221%Err = 17.0 k2 = 0.383Err = 0.612%Err = 42.4 k3 = 0.036Err = 0.130%Err >100 k4 = 0.232Err = 0.397%Err > 100 V T = 0.39 SS=0.055 K1 = 0.116Err = 0.0134%Err = 11.5 k2 = 0.300Err = 0.0307%Err = 10.2 V T = 0.387 = V ND SS=0.057 Receptor free region = free + unspecific binding Similar VT Slightly lower SS in 2T Better k estimation in 1T µCi/mL obs-fit Time (min)

10. CER 1 Tissue Compartment CER 2 Tissue Compartment [C-11]RAC 0.1 0.35 K1 = 0.116Err = 0.0134%Err = 11.5 k2 = 0.300Err = 0.0307%Err = 10.2 V T = 0.387 SS = 0.057 0.35 0.1 K1 = 0.130Err = 0.0221%Err = 17.0 k2 = 0.383Err = 0.612%Err = 42.4 k3 = 0.036Err = 0.130%Err >100 k4 = 0.232Err = 0.397%Err > 100 V T = 0.39 SS=0.055 DPU K1 = 0.097Err = 0.0040%Err = 4.1 k2 = 0.055Err = 0.0027%Err = 4.9 V T = 1.77 SS = 0.087 0.5 0.14 Receptor-rich region = free + unspecific + specific binding Differences in curve shapes = differences in clearance & specific binding

11. CER 1 Tissue Compartment CER 2 Tissue Compartment [C-11]RAC 0.1 K1 = 0.116Err = 0.0134%Err = 11.5 k2 = 0.300Err = 0.0307%Err = 10.2 V T = 0.387 SS = 0.057 0.1 K1 = 0.130Err = 0.0221%Err = 17.0 k2 = 0.383Err = 0.612%Err = 42.4 k3 = 0.036Err = 0.130%Err >100 k4 = 0.232Err = 0.397%Err > 100 V T = 0.39 SS=0.055 DPU K1 = 0.097Err = 0.0040%Err = 4.1 k2 = 0.055Err = 0.0027%Err = 4.9 V T = 1.77 SS = 0.087 0.5 0.14 DPU 0.5 0.14 K1 = 0.121Err = 0.091%Err = 15.6 k2 = 0.143Err = 0.120%Err = 84.1 k3 = 0.139Err = 0.218%Err >100 k4 = 0.123Err = 0.051%Err = 41.1 V T = 1.81 SS=0.072 Differences in curve shapes = differences in clearance & specific binding Similar VT Lower SS in 2T Better k estimation in 1T 0.35

12. DPUCER 1 Tissue Compartment DPUCER 2 Tissue Compartment [C-11]RAC µCi/mL obs-fit Time (min)

13. DPUCER 1 Tissue Compartment DPUCER 2 Tissue Compartment DPUCER Logan Arterial DPU Logan Cerebellum [C-11]RAC V T = 1.87 V T = 0.459 V T = 1.81V T = 0.39 DVR = 4.02 DVR = 1.87/0.459 = 4.08 DVR=4.64 µCi/mL obs-fit Time (min)  Cp/ROI  ROI/ROI

14. CER 1 Tissue Compartment [C-11]CFT K1 = 0.347Err = 0.009%Err = 2.6 k2 = 0.042Err = 0.001%Err = 2.8 V T = 8.34 SS = 0.092 0.6 0.08 µCi/mL obs-fit Time (min)

15. CER 1 Tissue Compartment [C-11]CFT K1 = 0.347Err = 0.009%Err = 2.6 k2 = 0.042Err = 0.001%Err = 2.8 V T = 8.34 SS = 0.092 CER 2 Tissue Compartment 0.6 0.08 0.6 0.14 K1 = 0.401Err = 0.012%Err = 3.1 k2 = 0.056Err = 0.040%Err = 8.0 k3 = 0.005Err = 0.030%Err = 69.2 k4 = 0.012Err = 0.014%Err > 100 V T = 10.36 SS=0.063 VT 1T < 2T Lower SS in 2T Better k estimation in 1T µCi/mL obs-fit Time (min)

16. CER 1 Tissue Compartment [C-11]CFT K1 = 0.347Err = 0.009%Err = 2.6 k2 = 0.042Err = 0.001%Err = 2.8 V T = 8.34 SS = 0.092 CER 2 Tissue Compartment 0.6 0.08 0.6 0.14 K1 = 0.401Err = 0.012%Err = 3.1 k2 = 0.056Err = 0.040%Err = 8.0 k3 = 0.005Err = 0.030%Err = 69.2 k4 = 0.012Err = 0.014%Err > 100 V T = 10.36 SS=0.063 DPU 1.0 0.06 K1 = 0.307Err = 0.003%Err = 1.0 k2 = 0.005Err = 0.0002%Err = 5.0 V T = 68.0 SS = 0.037 DPU 1.0 0.12 K1 = 0.275Err = NA%Err < -8000 k2 < 0Err = 0.002%Err < -100 k3 = 0.051Err = 0.021%Err = 40.7 k4 < 0Err = 0.069%Err < -100 V T < 0 SS=0.194 Irreversible binding

17. CER 1 Tissue Compartment [C-11]CFT CER 2 Tissue Compartment 0.6 0.08 0.6 0.14 DPU 1.0 0.06 DPU 1.0 0.12 V T = 68 V T = 8.34 µCi/mL obs-fit Time (min)

18. CER 1 Tissue Compartment [C-11]CFT CER 2 Tissue Compartment 0.6 0.08 0.6 0.14 DPU 1.0 0.06 DPU 1.0 0.12 DPUCER Logan Arterial DPU Logan Cerebellum V T = 68 V T = 8.34 V T = 65V T = 8.84 DVR = 3.03 DVR = 65/8.84 = 7.45 DVR=8.14  Cp/ROI  ROI/ROI 

19. Interim Summary [C-11]Raclopride 2Tcomp better fit [C-11]CFT 1Tcomp better fit Conclusions consistent with known properties of the radiotracers: –[C-11]Raclopride shows reversible binding during the PET study. Thus k 3 and k 4 can be determined –[C-11]CFT shows irreversible binding in receptor-rich regions during the PET study. Thus k 4 cannot be accurately determined RAC - DPU CFT - DPU

20. Comparison of binding potential between methods Simplified methods are appropriate for raclopride

21. Comparison of binding potential between methods

22. Utility of PET radioligand methods for the study of behaviour Or, I’m a psychologist, why do I care?

23. Utility of PET radioligand methods for the study of behaviour Or, I’m a psychologist, why do I care?

24. Utility of PET radioligand methods for the study of behaviour Sequential motor learning –[ C-11]Raclopride BP in dorsal striatum decreases during finger sequence learning task –Both implicit & implicit learning of complex motor sequences increase [C-11]raclopride displacement in the caudate & putamen Reward-related processes –Decreased striatal [C-11]raclopride BP during an active but not passive reward task Cognition –Decreases in [C-11]raclopride BP when planning a set shift, during spatial planning and spatial working memory Variability in BP outcomes are related to behaviour

25. Utility of PET radioligand methods for the study of behaviour Variability in BP outcomes are related to behaviour Variability in BP outcomes are related to EEG synchrony

26. Acknowledgements PET Facility –Julie Price –Jonathan (Eoin) Carney –Carl Becker –Amy Wagner MNTP –Seong-Gi Kim –Bill Eddy –Tomika Cohen –Rebecca Clark Schizophrenia Research Institute, Australia University of Newcastle, Australia

27. Comparison of binding potential between methods

29. BP = K 3 /k 4 BP=V T ROI /V T CER -1 = K 1 /k 2 (1+k 3 /k 4 )-1

30. Interim Summary Logan –Susceptible to bias –Bias is worse in CFT because of slower reference tissue clearance relative to plasma –Bias not so bad in RAC because of similar clearance in reference tissue relative to plasma