Table 6.

PET imaging studies assessing TSPO tracers in psychiatric disorders.

Disorder	Population	Radioligand	Main Findings	References
BD	14 patients with BD-I vs. 11 HC	11C-PK11195	No significant difference in the whole-brain gray matter BP in patients with bipolar I disorder versus healthy subjects Significantly increased tracer binding in hippocampus of BD-I patients, compared to normal controls	Haarman et al. (2014, 2016) [155,170]
MDE	10 patients with mild to moderate depression vs. 10 HC	11C-PBR28	No statistically significant difference in 11C-PBR28 VT between individuals with depression and healthy volunteers 7/10 patients exhibited lower tracer VT in cortical regions (frontal, temporal, parietal and occipital), striatum, thalamus and cerebellum than normal controls	Hannestad et al. (2013) [167]
	20 MDE drug-free patients vs. 20 HC	18F-FEPPA	In MDE patients, significant elevation of TSPO VT in the prefrontal cortex, anterior cingulate cortex and insula, of 26%, 32% and 33%, respectively, compared to normal controls Anterior cingulate cortex TSPO VT correlated with total 17-item HDRS score	Setiawan et al. (2015) [168]
SCZ	10 patients with recent-onset SCZ vs. 10 HC	11C-PK11195	Significantly greater total gray matter tracer BP in SCZ patients than in healthy volunteers No statistical correlation between total gray matter 11C-PK11195 BP and PANSS	Van Berckel et al. (2008) [171]
	7 SCZ patients vs. 8 HC	11C-PK11195	Significantly higher radioligand BP was observed in the hippocampus of SCZ patients than in HC Although the difference did not reach a significance level, the whole-brain gray matter and white matter were, respectively, 30% higher and 20% greater in SCZ patients than in HC	Doorduin et al. (2009) [172]
	14 SCZ patients vs. 14 HC	11C-DAA1106	No clear difference in either regional or total cortical radioligand BPND values between the two groups	Takano et al. (2010) [173]
	16 SCZ patients vs. 27 HC	18F-FEPPA	No significant effect of clinical group (SCZ vs. HC) detected on tracer VT in hippocampus, medial prefrontal cortex, dorsolateral prefrontal cortex, temporal cortex and striatum or in white matter tracts None of the disease parameters (PANSS, AES and RBANS) statistically correlated with regional radioligand VT	Kenk et al. (2015) [174]
	14 UHRP subjects (APT-naive), 14 SCZ patients and 28 HC	11C-PBR28	Significantly increased tracer DVr in total gray matter and frontal and temporal lobes in UHRP subjects and SCZ patients, compared to age-matched controls No statistical difference in tracer binding values between UHRP and SCZ patients In UHRP subjects, statistical positive correlation was found between CAARMS and 11C-PBR28 DVr in total gray matter	Bloomfield et al. (2016) [175]
	12 recent onset SCZ patients vs. 14 HC	11C-DPA713	Significantly increased 11C-DPA713 VT in amygdala and cingulate cortex in SCZ patients compared healthy volunteers	Coughlin et al. (2016) [176]
	12 recent onset SCZ patients vs. 14 HC	11C-DPA713	Relative to HC, there was a strong trend towards reduce 11C-DPA713 VT in the middle frontal gyrus of patients with recent onset SCZ	Notter et al. (2017) [177]

AES, Apathy Evaluation Scale; APT, antipsychotic therapy; BD, bipolar disorder; BP, binding potential; BP_ND, binding potential; CAARMS, comprehensive assessment of the at-risk mental states; CDS, calgary depression scale; DVr, distribution volume ratio; IDC-C₃₀, inventory of depressive symptoms—clinician version; HDRS, Hamilton depression rating scale; HC, healthy control; MDE, major depressive episodes; PANSS, positive and negative syndrome scale; RBANS, repeatable battery for the assessment of neuropsychological status; SCZ, schizophrenia; UHRP, ultra-high risk of psychosis; V_T, total distribution volume.