Table 1.

Preclinical and in-vivo properties of tau PET tracers. IC₅₀: half-maximal inhibitory concentration; K_d: dissociation constant; ARG: determined by autoradiography; Ref: region of reference; CER: cerebellum; PSP: progressive supranuclear palsy; CBD: corticobasal degeneration; CTE: chronic traumatic encephalopathy; † Conference abstract

Radiotracer	Affinity	SUVR in AD tau-rich areas (min post-injection)	Reported off-target binding? (region or substrate-specific binding)	Off-target binding to MAO-A or MAO-B?	Binding to non-AD tauopathy?	References
11C-PBB3	Kd =2.5 nM in NFT-rich AD brain tissue Method: ARG	0.75–1.6 (30–70 min) Ref.: CER	Yes : Dural venous sinuses, basal ganglia, thalamus	Not reported	Yes: PSP, CBD, and Pick’s disease	Maruyama et al. 2013; Kimura et al. 2015; Ono et al. 2017a, b.
18F-THK5351	Kd =2.9 nM in hippocampal AD brain homogenates Method: in-vitro saturation binding	1.7–2.5 (50–60 min) Ref.: CER gray	Yes: Basal ganglia (including striatum and substantia nigra), thalamus, midbrain, and periaqueductal gray matter	Yes: very high affinity to MAO-B	Yes: PSP and CBD	Harada et al. 2015, 2017: Betthauser et al. 2017.
18F-AV-1451	Various values reported: [1] Kd =14.6 nM in AD brain sections Method: ARG, saturation binding studies (Xia et al., 2013) [2] Kd =1.4–3.72 nM (enthorhinal cortex)  Kd =0.63–1.70 nM (frontal cortex) in NFT-rich AD brain homogenates Method: saturation binding studies (Hostetler et al. 2016)	1–4 (80–100 min) Ref.: CER gray	Yes: Basal ganglia (including striatum and substantia nigra), choroid plexus, midbrain, meninges, scalp. Binds to: melanin-containing cells, leptomeningeal melanin, vessels, brain hemorrhagic lesions, iron-associated regions and calcifications.	Yes: low affinity to MAO-A; mixed results for MAO-B.	No (evaluated in PSP, CBD, MAPT P301L mutation, Pick’s disease, CTE)	Xia et al. 2013; Vermeiren et al. 2015; Marquie et al. 2015, 2017, 2018; Ikonomovic et al. 2016; Lowe et al. 2016; Hostetler et al. 2016; Lee et al. 2017†; Lemoine 2017; Hansen et al. 2017.
18F-RO6958948	IC50=18.5 nM in late AD brain tissue (Braak V-VI) Method: ARG, displacement of [3H] T808	1–3 (60–90 min) Ref.: CER gray	None reported	No	No (evaluated in Pick’s, PSP, and CBD)	Honer et al. 2017; Wong et al. 2015†
18F-GTP1	binding affinity: 14.9±0.43 nM in tau-positive brain tissue Method: ARG	1–3 (90–120 min) Ref: CER gray	In some subjects, signal in basal ganglia (may be non-tau age-related)	No	Not reported	Marik et al. 2016†; Sanabria-Bohorquez et al. 2016†, 2017†; Alzforum 2017.
18F-PI-2620	IC50 =1.8 nM in AD brain tissue Method: competition-assays	2.5–2.8 (90–100 min)	None reported	No	Yes: Pick’s and PSP	Mueller et al. 2017†; Barret et al. 2017†
18F-MK-6240	Kd ~0.3 nM in NFT-rich AD brain homogenates Method: saturation binding studies	2.5–4 (90–120 min)	Left leptomeningeal region, nasal sinus and red nucleus, meninges, superior anterior vermis, and focal hemangiomas.	No	Unlikely (binds to same site as AV-1451)	Walji et al. 2016; Hostetler et al, 2016; Alzforum 2017; Betthauser et al. 2018†.