The dynamics of β-amyloid deposition and related second-order physiological effects, such as regional cerebral blood flow (rCBF), are key factors for a deeper understanding of Alzheimer's disease (AD). We present longitudinal in vivo data on the dynamics of β-amyloid deposition and the decline of rCBF in two different amyloid precursor protein (APP) transgenic mouse models of AD. Using a multiparametric positron emission tomography and magnetic resonance imaging approach, we demonstrate that in the presence of cerebral β-amyloid angiopathy (CAA), β-amyloid deposition is accompanied by a decline of rCBF. Loss of perfusion correlates with the growth of β-amyloid plaque burden but is not related to the number of CAA-induced microhemorrhages. However, in a mouse model of parenchymal β-amyloidosis and negligible CAA, rCBF is unchanged. Because synaptically driven spontaneous network activity is similar in both transgenic mouse strains, we conclude that the disease-related decline of rCBF is caused by CAA.

Although T cells can be labeled for noninvasive in vivo imaging, little is known about the impact of such labeling on T-cell function, and most imaging methods do not provide holistic information about trafficking kinetics, homing sites, or quantification. Methods: We developed protocols that minimize the inhibitory effects of 64 Cupyruvaldehyde-bis(N4-methylthiosemicarbazone) ( 64 Cu-PTSM) labeling on T-cell function and permit the homing patterns of T cells to be followed by PET. Thus, we labeled ovalbumin (OVA) T-cell receptor transgenic interferon (IFN)-g-producing CD4 1 T (Th1) cells with 0.7-2.2 MBq of 64 Cu-PTSM and analyzed cell viability, IFN-g production, proliferation, apoptosis, and DNA double-strand breaks and identified intracellular 64 Cu accumulation sites by energy dispersive x-ray analysis. To elucidate the fate of Th1 cell homing by PET, 10 7 64 Cu-OVA-Th1 cells were injected intraperitoneally or intravenously into healthy mice. To test the functional capacities of 64 Cu-OVA-Th1 cells during experimental OVA-induced airway hyperreactivity, we injected 10 7 64 Cu-OVA-Th1 cells intraperitoneally into OVA-immunized or nonimmunized healthy mice, which were challenged with OVA peptide or phosphate-buffered saline or remained untreated. In vivo PET investigations were followed by biodistribution, autoradiography, and fluorescence-activated cell sorting analysis. Results: PET revealed unexpected homing patterns depending on the mode of T-cell administration. Within 20 min after intraperitoneal administration, 64 Cu-OVA-Th1 cells homed to the perithymic lymph nodes (LNs) of naive mice. Interestingly, intravenously administered 64 Cu-OVA-Th1 cells homed predominantly into the lung and spleen but not into the perithymic LNs. The accumulation of 64 Cu-OVA-Th1 cells in the pulmonary LNs (6.8 6 1.1 percentage injected dose per cubic centimeter [%ID/cm 3 ]) 24 h after injection was highest in the OVA-immunized and OVA-challenged OVA airway hyperreactivity-diseased littermates 24 h after intraperitoneal administration and lowest in the untreated littermates (3.7 6 0.4 %ID/cm 3 ). As expected, 64 Cu-OVA-Th1 cells also accumulated significantly in the pulmonary LNs of nonimmunized OVA-challenged animals (6.1 6 0.5 %ID/cm 3 ) when compared with phosphate-buffered saline-challenged animals (4.6 6 0.5 %ID/cm 3 ). Conclusion: Our protocol permits the detection of Th1 cells in single LNs and enables temporal in vivo monitoring of T-cell homing over 48 h. This work enables future applications for 64 Cu-PTSM-labeled T cells in clinical trials and novel therapy concepts focusing on T-cell-based immunotherapies of autoimmune diseases or cancer.

Purpose: Great advances have recently been made in treating patients with metastatic melanoma. However, existing therapies are less effective on cerebral than extracerebral metastases. This highlights the potential role of the brain environment on tumor progression and drug resistance and underlines the need for "brain-specific" therapies. We previously showed that the PI3K-AKT survival pathway is hyperactivated in brain but not extracerebral melanoma metastases and that astrocyte-conditioned medium activates AKT in melanoma cells in vitro. We therefore tested the PI3K inhibitor buparlisib as an antitumor agent for melanoma brain metastases. Conclusions: These results emphasize the value of targeting the PI3K pathway as a strategy to develop drugs for melanoma brain metastases.

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The increasing use of genetically engineered mice as animal models of human disease in biomedical research, latest advances in imaging technologies, and development of novel, highly specific radiolabeled biomarkers provide great potential to study receptor expression and gene function in vivo in mice. 11 C-raclopride is a widely used PET tracer to measure striatal D 2 receptor binding and was used to test the feasibility of the multiple-ligand-concentration receptor assay for D 2 receptor quantification. Methods: Mice underwent a total of 4 scans with decreasing specific activities from 141 to 0.4 GBq/mmol, corresponding to 11 C-raclopride injected doses of 2.4 to 1,274 nmol/ kg, using either a standard bolus injection protocol (n 5 12) or a bolus-plus-constant infusion protocol to attain true equilibrium conditions (n 5 7). Receptor occupancy was plotted as a function of raclopride dose, and D 2 receptor density and raclopride affinity were calculated using linear and nonlinear regression analysis, respectively. In addition, we used ex vivo autoradiography, a more spatially accurate imaging technology, to validate the in vivo PET measurements, and we performed test-retest experiments to determine the reproducibility and reliability of the PET-derived measures. Results: The receptor occupancy curves showed that an injected tracer dose of 4.5 nmol/kg induces approximately 10% receptor occupancy, whereas 1% receptor occupancy will be achieved at tracer doses of approximately 0.45 nmol/kg. Using the bolus injection protocol and nonlinear regression analysis, we determined that the average D 2 receptor density was 9.6 6 1.1 pmol/mL, and the apparent raclopride affinity was 5.0 6 0.6 pmol/mL. These values agreed well with those obtained at true equilibrium conditions. In contrast, linear Scatchard analysis did not lead to the expected linear relationship because nonsaturable binding was observed at high raclopride concentrations, and thus, it seems to be unsuitable for quantitative 11 C-raclopride analysis in mice. Conclusion: Our data showed that the tracer mass, if higher than 4 nmol/kg, can strongly affect binding parameter estimations and must be considered when performing kinetic analysis, specifically in mice. We also demonstrated that the in vivo determination of D 2 receptor density and raclopride affinity is feasible in mice using multiple-injection protocols and nonlinear regression analysis. The interest in noninvasive functional and metabolic imaging of transgenic animal models of human disease has increased tremendously over the last several years. For this purpose, dedicated small-animal PET systems with improved spatial resolution and highly specific radiolabeled biomarkers have become available. Among them is the benzamide dopamine antagonist 11 C-raclopride, a widely used PET biomarker to measure D 2 receptor binding characteristics in humans (1-3), nonhuman primates (4-6), and rats (7-11). Given the small size of the mouse brain and, in particular, the D 2 receptor-rich striatum, which has a volume ...

Differential diagnosis and therapy of heterogeneous breast tumors poses a major clinical challenge. To address the need for a comprehensive, non-invasive strategy to define the molecular and functional profiles of tumors in vivo, we investigated a novel combination of metabolic positron emission tomography (PET) and diffusion-weighted (DW) magnetic resonance imaging (MRI) in the polyoma virus middle T transgenic mouse model of breast cancer. The implementation of a voxelwise analysis for the clustering of intra- and intertumoral heterogeneity in this model resulted in a multiparametric profile based on [18F]FDG-PET and DW-MRI which identified 3 distinct tumor phenotypes in vivo, including solid acinar and solid nodular malignancies as well as cystic hyperplasia. To evaluate the feasibility of this approach for clinical use, we examined estrogen receptor-positive (ER+) and progesterone receptor-positive (PR+) breast tumors from 5 patient cases using DW-MRI and [18F]FDG-PET in a simultaneous PET/MRI system. The post-surgical in vivo PET/MRI data was correlated to whole-slide histology using the latter traditional diagnostic standard to define phenotype. By this approach, we showed how molecular, structural (microscopic, anatomic) and functional information could be simultaneously obtained non-invasively to identify precancerous and malignant subtypes within heterogeneous tumors. Combined with an automatized analysis, our results suggest that multiparametric molecular and functional imaging may be capable of providing comprehensive tumor profiling for non-invasive cancer diagnostics.

Non-invasive imaging of β-cells represents a desirable preclinical and clinical tool to monitor the change of β-cell mass and the loss of function during pre-diabetic stages. Although it is widely accepted that manganese (Mn) ions are actively gated by voltage-dependent calcium channels (VDCC) in response to glucose metabolism, little is known on its specificity in vivo for quantification of islet β-cell function using Mn and magnetic resonance imaging (MRI). On the other hand, glucagon-like-peptide-1 receptor (GLP-1R) represents a validated target for the estimation of β-cell mass using radiolabeled exendin-4 (Ex4) and positron emission tomography (PET). However, a multiparametric imaging workflow revealing β-cell mass and function quantitatively is still missing.Methods: We developed a simultaneous PET/MRI protocol to comprehensively quantify in vivo changes in β-cell mass and function by targeting, respectively, GLP-1R and VDCC coupled with insulin secretion. Differences in the spatial distribution of Mn and radiolabeled Ex4 were monitored overtime in native and transgenic pancreata, characterized by spontaneous pancreatic neuroendocrine tumor development. Follow-up with mass spectrometry imaging (MSI) and autoradiography allowed the ex vivo validation of the specificity of Mn and PET tracer uptake and the detection of endogenous biometals, such as calcium and zinc, throughout the endocrine and exocrine pancreas.Results: Our in vivo data based on a volumetric PET/MRI readout for native pancreata and insulinomas connects uptake of Mn measured at early imaging time points to high non-specific binding by the exocrine tissue, while specific retention was only found 24 h post injection. These results are supported by cross-validation of the spatial distribution of exogenous 55Mn and endogenous 44Ca and 64Zn as well with the specific internalization of the radiolabeled peptide targeting GLP-1R.Conclusion: Simultaneous PET/MR imaging of the pancreas enabled the comprehensive in vivo quantification of β-cell function and mass using Mn and radiolabeled Ex4. Most important, our data revealed that only late time-point measurements reflect the Mn uptake in the islet β-cells, while early time points detect non-specific accumulation of Mn in the exocrine pancreas.

Quantification accuracy and partial volume effect (PVE) of the Siemens Inveon PET scanner were evaluated. The influence of transmission source activities (40 and 160 MBq) on the quantification accuracy and the PVE were determined. Dynamic range, object size and PVE for different sphere sizes, contrast ratios and positions in the field of view (FOV) were evaluated. The acquired data were reconstructed using different algorithms and correction methods. The activity level of the transmission source and the total emission activity in the FOV strongly influenced the attenuation maps. Reconstruction algorithms, correction methods, object size and location within the FOV had a strong influence on the PVE in all configurations. All evaluated parameters potentially influence the quantification accuracy. Hence, all protocols should be kept constant during a study to allow a comparison between different scans.