Assessment of [18F]PI-2620 Tau-PET Quantification via Non-Invasive Automatized Image Derived Input Function

Radiosynthesis, In Vitro Characterization, and In Vivo PET Neuroimaging of [18F]F-4 for Tau Protein: A First-in-Human PET Study

[18F]PI-2620 is a promising radiopharmaceutical for positron emission tomography (PET) imaging of both Alzheimer's disease (AD) and non-Alzheimer's disease (non-AD) tauopathies in humans. An array of fluorinated derivatives of the carbazole scaffold of PI-2620 were synthesized and evaluated. In vitro binding assays with [3H]PI-2620 in human tissues with AD, progressive supranuclear palsy, and corticobasal degeneration, combined with in silico predictions of blood-brain barrier permeability, led to the selection and radiosynthesis of [18F]F-4 as a promising radiotracer. In vivo PET imaging with [18F]F-4 in healthy rats showed brain uptake and kinetics suitable for neuroimaging, similar to those of [18F]PI-2620. A first-in-human PET imaging study in a healthy subject as well as a patient with AD, in comparison with [18F]PI-2620 in the same AD subject, confirmed that [18F]F-4 is an alternative radiopharmaceutical for imaging tau protein.

Kinetic modeling of 18 F-PI-2620 binding in the brain using an image-derived input function with total-body PET

Accurate quantification of tau binding from 18 F-PI-2620 PET requires kinetic modeling and an input function. Here, we implemented a non-invasive Image-derived input function (IDIF) derived using the state-of-the-art total-body uEXPLORER PET/CT scanner to quantify tau binding and tracer delivery rate from 18 F-PI-2620 in the brain. Additionally, we explored the impact of scan duration on the quantification of kinetic parameters. Total-body PET dynamic data from 15 elderly participants were acquired. Time-activity curves from the grey matter regions of interest (ROIs) were fitted to the two-tissue compartmental model (2TCM) using a subject-specific IDIF derived from the descending aorta. ROI-specific kinetic parameters were estimated for different scan durations ranging from 10 to 90 minutes. Logan graphical analysis was also used to estimate the total distribution volume (V T ). Differences in kinetic parameters were observed between ROIs, including significant reduction in tracer delivery rate (K 1 ) in the medial temporal lobe. All kinetic parameters remained relatively stable after the 60-minute scan window across all ROIs, with K 1 showing high stability after 30 minutes of scan duration. Excellent correlation was observed between V T estimated using 2TCM and Logan plot analysis. This study demonstrated the utility of IDIF with total-body PET in investigating 18 F-PI-2620 kinetics in the brain.