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Other version: http://linkinghub.elsevier.com/retrieve/pii/S1053811918303835
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Title 
Dualradiotracer translational SPECT neuroimaging. Comparison of three methods for the simultaneous brain imaging of D 2/3 and 5HT 2A receptors 

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Published in  NeuroImage. 2018, vol. 176, p. 528540  
Abstract  PURPOSE: SPECT imaging with two radiotracers at the same time is feasible if two different radioisotopes are employed, given their distinct energy emission spectra. In the case of (123)I and (125)I, dual SPECT imaging is not straightforward: (123)I emits photons at a principal energy emission spectrum of 143.1179.9keV. However, it also emits at a secondary energy spectrum (1545keV) that overlaps with the one of (125)I and the resulting crosstalk of emissions impedes the accurate quantification of (125)I. In this paper, we describe three different methods for the correction of this crosstalk and the simultaneous in vivo [(123)I]IBZM and [(125)I]R91150 imaging of D2/3 and 5HT2A receptors in the rat brain. METHODS: Three methods were evaluated for the correction of the effect of crosstalk in a series of simultaneous, [(123)I]IBZM and [(125)I]R91150 in vivo and phantom SPECT scans. Method 1 employs a dualenergy window (DEW) approach, in which the crosstalk on (125)I is considered a stable fraction of the energy emitted from (123)I at the principal emission spectrum. The coefficient describing the relationship between the emission of (123)I at the principal and the secondary spectrum was estimated from a series of singleradiotracer [(123)I]IBZM SPECT studies. In Method 2, spectral factor analysis (FA) is applied to separate the radioactivity from (123)I and (125)I on the basis of their distinct emission patterns across the energy spectrum. Method 3 uses a modified simplified reference tissue model (SRTMC) to describe the kinetics of [(125)I]R91150. It includes the coefficient describing the crosstalk on (125)I from (123)I in the model parameters. The results of the correction of crosstalk on [(125)I]R91150 binding potential (BPND) with each of the three methods, using cerebellum as the reference region, were validated against the results of a series of singleradiotracer [(123)I]R91150 SPECT studies. In addition, the DEW approach (Method 1), considered to be the most straightforward to apply of the three, was further applied in a dualradiotracer SPECT study of the relationship between D2/3 and 5HT2A receptor binding in the striatum, both at the voxel and at the regional level. RESULTS: Average regional BPND values of [(125)I]R91150, estimated on the crosstalk corrected dualradiotracer SPECT studies provided satisfactory correlations with the BPND values for [(123)I]R91150 from singleradiotracer studies: r=0.92, p<0.001 for Method 1, r=0.92, p<0.001 for Method 2, r=0.92, p<0.001, for Method 3. The coefficient describing the ratio of the (123)Iemitted radioactivity at the (125)Iemission spectrum to the radioactivity that it emits at its principal emission spectrum was 0.34 in vivo. Dualradiotracer in vivo SPECT studies corrected with Method 1 demonstrated a positive correlation between D2/3 and 5HT2A receptor binding in the rat nucleus accumbens at the voxel level. At the VOIlevel, a positive correlation was confirmed in the same region (r=0.78, p<0.01). CONCLUSION: Dualradiotracer SPECT imaging using (123)I and (125)Ilabeled radiotracers is feasible if the crosstalk of (123)I on the (125)I emission spectrum is properly corrected. The most straightforward approach is Method 1, in which a fraction (34%) of the radioactivity emitted from (123)I at its principal energy spectrum is subtracted from the measured radioactivity at the spectrum of (125)I. With this method, a positive correlation between the binding of [(123)I]IBZM and [(125)I]R91150 was demonstrated in the rat nucleus accumbens. This result highlights the interest of dualradiotracer SPECT imaging to study multiple neurotransmitter systems at the same time and under the same biological conditions.  
Keywords  5HT(2A) receptor — D(2/3) receptor — Dualradiotracer — Ibzm — Spect — Simultaneous SPECT  
Identifiers  PMID: 29723640  
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Research groups  Imagerie de la transmission dopaminergique dans les troubles addictifs (989) Neuroimagerie moléculaire en psychiatrie (983)  
Project  FNS: 310030_156829  
Citation (ISO format)  TSARTSALIS, Stergios et al. Dualradiotracer translational SPECT neuroimaging. Comparison of three methods for the simultaneous brain imaging of D 2/3 and 5HT 2A receptors. In: NeuroImage, 2018, vol. 176, p. 528540. doi: 10.1016/j.neuroimage.2018.04.063 https://archiveouverte.unige.ch/unige:104851 