Abstract
PurposeThe simplified reference tissue model (SRTM) is commonly applied for the quantification of brain positron emission tomography (PET) studies, particularly because it avoids arterial cannulation. SRTM requires a validated reference region which is obtained by baseline-blocking or displacement studies. Once a reference region is validated, the use should be verified for each new subject. This verification normally requires volume of distribution (VT) of a reference region. However, performing dynamic scanning and arterial sampling is not always possible, specifically in elderly subjects and in advanced disease stages. The aim of this study was to investigate the use of non-invasive standardised uptake value (SUV) approaches, in comparison to VT, as a verification of the previously validated grey matter cerebellum reference region for [18F]flortaucipir and [18F]florbetapir PET imaging in Alzheimer’s disease (AD) patients and controls.ProceduresDynamic 130-min [18F]flortaucipir PET scans obtained from nineteen subjects (10 AD patients) and 90-min [18F]florbetapir dynamic scans obtained from fourteen subjects (8 AD patients) were included. Regional VT’s were estimated for both tracers and were considered the standard verification of the previously validated reference region. Non-invasive SUVs corrected for body weight (SUVBW), lean body mass (SUL), and body surface area (SUVBSA) were obtained by using later time intervals of the dynamic scans. Simulations were also performed to assess the effect of flow and specific binding (BPND) on the SUVs.ResultsA low SUV corresponded well with a low VT for both [18F]flortaucipir and [18F]florbetapir. Simulation confirmed that SUVs were only slightly affected by flow changes and that increases in SUV were predominantly determined by the presence of specific binding.ConclusionsIn situations where dynamic scanning and arterial sampling is not possible, a low SUV(80–100 min) for [18F]flortaucipir and a low SUV(50–70 min) for [18F]florbetapir may be used as indication for absence of specific binding in the grey matter cerebellum reference region.
Highlights
In quantitative dynamic brain positron emission tomography (PET) studies, the simplified reference tissue model (SRTM) is one of the most frequently used models, because it avoids arterial cannulation and metabolite measurements [1, 2]
For [18F]flortaucipir, a strong positive correlation was found between the standardised uptake value (SUV) and volume of distribution (VT) for both the Alzheimer’s disease (AD) patients (r2 = 0.97) and the controls (r2 = 0.95)
For [18F]florbetapir, a high positive correlation between VT and all the SUVs was observed for the AD patients (r2 = 0.96), whereas for the controls, a bit lower positive correlation was found (r2 = 0.77)
Summary
In quantitative dynamic brain PET studies, the simplified reference tissue model (SRTM) is one of the most frequently used models, because it avoids arterial cannulation and metabolite measurements [1, 2]. The use of SRTM requires a validated reference region. Validation of the reference region is done using blocking or displacement studies along with histopathological assessments on postmortem tissue samples. A non-invasive approach such as the standardised uptake value (SUV) would be desirable for QC of the previously validated reference region in situations where dynamic scanning and arterial sampling is not feasible. SUV metrics are already commonly used in clinical oncology imaging [4]. It ideally removes variability introduced by differences in patient size and amount of injected tracer [4, 5], and is not influenced by differences in injected doses and population
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