Quantitative PET imaging and modeling of molecular blood-brain barrier permeability

The Prevalence and Significance of Incidental Positron Emission Tomography Findings in the Brain Using Radiotracers Other than [18F]FDG: A Systematic Review and Meta-Analysis

Background: Incidental brain imaging findings could be clinically relevant, and advancements in molecular imaging could lead to their more frequent identification. The aim of this review is to establish the prevalence and clinical significance of brain incidentalomas at PET (BIPs) using radiotracers other than [18F]FDG. Methods: A comprehensive literature search of studies about BIPs was carried out. Four different databases (PubMed/MEDLINE, EMBASE, the Cochrane library, and Google Scholar) were screened up to December 2024. Only original articles about BIPs using radiotracers other than [18F]FDG were selected. A proportion meta-analysis of the prevalence of BIPs was carried out using a random-effects model. Results: Fourteen studies were included in the review, using somatostatin receptor (SSTR) PET (n = 6), radiolabeled choline PET (n = 5), prostate-specific membrane antigen (PSMA) ligands PET (n = 1), [18F]Fluciclovine PET (n = 1), and [18F]FDOPA PET (n = 1). The pooled prevalence of BIPs was 4.6% for SSTR PET, 1.1% for choline PET, 1.2% for PSMA ligands PET, 2.5% for [18F]Fluciclovine PET, and 3.9% for [18F]FDOPA PET. When BIPs were further evaluated using MRI, meningiomas were the most frequent lesions detected, but both benign and malignant lesions could be incidentally diagnosed. Conclusions: BIPs using radiotracers other than [18F]FDG are not rare, in particular at SSTR PET, further justifying the extension of PET scans to the brain when radiotracers other than [18F]FDG are used. When detected, a BIP should be further evaluated using brain MRI. Both benign and malignant lesions could be incidentally detected in the brain. Further studies are warranted to better clarify the clinical impact of BIP detection.

Quantitative Total-Body Imaging of Blood Flow with High-Temporal-Resolution Early Dynamic 18F-FDG PET Kinetic Modeling

Past efforts to measure blood flow with the widely available radiotracer 18F-FDG were limited to tissues with high 18F-FDG extraction fraction. In this study, we developed an early dynamic 18F-FDG PET method with high-temporal-resolution (HTR) kinetic modeling to assess total-body blood flow based on deriving the vascular phase of 18F-FDG transit and conducted a pilot comparison study against a 11C-butanol flow-tracer reference. Methods: The first 2 min of dynamic PET scans were reconstructed at HTR (60 × 1 s/frame, 30 × 2 s/frame) to resolve the rapid passage of the radiotracer through blood vessels. In contrast to existing methods that use blood-to-tissue transport rate as a surrogate of blood flow, our method directly estimated blood flow using a distributed kinetic model (adiabatic approximation to tissue homogeneity [AATH] model). To validate our 18F-FDG measurements of blood flow against a reference flow-specific radiotracer, we analyzed total-body dynamic PET images of 6 human participants scanned with both 18F-FDG and 11C-butanol. An additional 34 total-body dynamic 18F-FDG PET images of healthy participants were analyzed for comparison against published blood-flow ranges. Regional blood flow was estimated across the body, and total-body parametric imaging of blood flow was conducted for visual assessment. AATH and standard compartment model fitting was compared using the Akaike information criterion at different temporal resolutions. Results: 18F-FDG blood flow was in quantitative agreement with flow measured from 11C-butanol across same-subject regional measurements (Pearson correlation coefficient, 0.955; P < 0.001; linear regression slope and intercept, 0.973 and -0.012, respectively), which was visually corroborated by total-body blood-flow parametric imaging. Our method resolved a wide range of blood-flow values across the body in broad agreement with published ranges (e.g., healthy cohort values of 0.51 ± 0.12 mL/min/cm3 in the cerebral cortex and 2.03 ± 0.64 mL/min/cm3 in the lungs). HTR (1-2 s/frame) was required for AATH modeling. Conclusion: Total-body blood-flow imaging was feasible using early dynamic 18F-FDG PET with HTR kinetic modeling. This method may be combined with standard 18F-FDG PET methods to enable efficient single-tracer multiparametric flow-metabolism imaging, with numerous research and clinical applications in oncology, cardiovascular disease, pain medicine, and neuroscience.