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1.  Evaluation of bone remodeling with 18F-fluoride and correlation with the glucose metabolism measured by 18F-FDG in lumbar spine with time in an experimental nude rat model with osteoporosis using dynamic PET-CT 
Rats with osteoporosis were involved by combining ovariectomy (OVX) either with calcium and Vitamin D deficiency diet (Group D), or with glucocorticoid (dexamethasone) treatment (Group C). In the period of 1-12 months, dynamic PET-CT studies were performed in three groups of rats including Group D, Group C and the control Group K (sham-operated). Standardized uptake values (SUVs) were calculated, and a 2-tissue compartmental learning-machine model (calculation of K1-k4, VB and the plasma clearance of tracer to bone mineral (Ki) as well as a non-compartmental model based on the fractal dimension (FD) was used for quantitative analysis of both groups. The evaluation of PET data was performed over the lumbar spine. The correlation analysis revealed a significant linear correlation for certain dPET quantitative parameters and time up to 12 months after induction of osteoporosis. Based on the 18F-Fluoride data, we noted a significant negative correlation for K1 (the fluoride/hydroxyl exchange) in the Group C and a significant positive correlation for k3, SUV (bone metabolism) and FD in the Group K. The evaluation of the 18F-FDG data revealed a significant positive correlation for SUV (glucose metabolism) only in Group C. The correlation between the two tracers revealed significant results between K1 of 18F-Fluoride and SUV of FDG in Group K as well as between FD of 18F-Fluoride and FDG in Group D and C and between k3 of 18F-Fluoride and SUV of FDG in Group C.
PMCID: PMC3601472  PMID: 23526138
dPET-CT; 18F-FDG; 18F-fluoride; osteoporosis
2.  18F-Deoxyglucose (FDG) kinetics evaluated by a non-compartment model based on a linear regression function using a computer based simulation: correlation with the parameters of the two-tissue compartment model 
Parametric imaging with a linear regression function of the tracer activity curve fit is a non-compartmental method, which can be used for the evaluation of dynamic PET (dPET) studies. However, the dependency of the slope of the regression function fit on the 18F-Deoxyglucose (FDG) 2-tissue compartment parameters (vb, k1-k4) is not known yet. This study is focused on the impact of the 2-tissue compartment parameters on the slope of the curve. A data base of 1760 dynamic PET FDG studies with the corresponding 2-tissue compartment model parameter solutions were available and used to calculate synthetic time-activity data based on the 2-tissue compartment model. The input curve was calculated from the median values of the input curves of the 1760 dynamic data sets. Then, sequentially each of the five parameters (vb, k1-k4) of the 2-tissue compartment model was varied from 0.1 to 0.9 and tracer activity curves were calculated (60000 curves/parameter). A linear regression function was fitted to these curves. The comparison of the slope values of the regression function with the corresponding compartment data revealed a primary dependency on k3, which is associated with the intracellular phosphorylation of FDG. The squared correlation coefficient was high with r2=0.9716, which refers to 97 % explained variance of the data. k2 and vb had only a minor impact, while k1 and k4 had no impact on the slope values. The results demonstrate, that k3 has a major impact on the slope values calculated by the linear regression function.
PMCID: PMC3484418  PMID: 23145361
FDG; non-compartment model; parametric imaging
3.  Comparison between 68Ga-bombesin (68Ga-BZH3) and the cRGD tetramer 68Ga-RGD4 studies in an experimental nude rat model with a neuroendocrine pancreatic tumor cell line 
EJNMMI Research  2011;1:34.
Objectives
Receptor scintigraphy gains more interest for diagnosis and treatment of tumors, in particular for neuroendocrine tumors (NET). We used a pan-Bombesin analog, the peptide DOTA-PEG2-[D-tyr6, β-Ala11, Thi13, Nle14] BN(6-14) amide (BZH3). BZH3 binds to at least three receptor subtypes: the BB1 (Neuromedin B), BB2 (Gastrin-releasing peptide, GRP), and BB3. Imaging of ανβ3 integrin expression playing an important role in angiogenesis and metastasis was accomplished with a 68Ga-RGD tetramer. The purpose of this study was to investigate the kinetics and to compare both tracers in an experimental NET cell line.
Methods
This study comprised nine nude rats inoculated with the pancreatic tumor cell line AR42J. Dynamic positron emission tomography (PET) scans using 68Ga-BZH3 and 68Ga-RGD tetramer were performed (68Ga-RGD tetramer: n = 4, 68Ga-BZH3: n = 5). Standardized uptake values (SUVs) were calculated, and a two-tissue compartmental learning-machine model (calculation of K1 - k4 vessel density (VB) and receptor binding potential (RBP)) as well as a non-compartmental model based on the fractal dimension was used for quantitative analysis of both tracers. Multivariate analysis was used to evaluate the kinetic data.
Results
The PET kinetic parameters showed significant differences when individual parameters were compared between groups. Significant differences were found in FD, VB, K1, and RBP (p = 0.0275, 0.05, 0.05, and 0.0275 respectively). The 56- to 60-min SUV for 68Ga-BZH3, with a range of 0.86 to 1.29 (median, 1.19) was higher than the corresponding value for the 68Ga-RGD tetramer, with a range of 0.78 to 1.31 (median, 0.99). Furthermore, FD, VB, K1, and RBP for 68Ga-BZH3 were generally higher than the corresponding values for the 68Ga-RGD tetramer, whereas k3 was slightly higher for 68Ga-RGD tetramer.
Conclusions
As a parameter that reflects receptor binding, the increase of K1 for 68Ga-BZH3 indicated higher expression of bombesin receptors than that of the ανβ3 integrin in neuroendocrine tumors. 68Ga-BZH3 seems better suited for diagnosis of NETs owing to higher global tracer uptake.
doi:10.1186/2191-219X-1-34
PMCID: PMC3292467  PMID: 22214362
68Ga-bombesin; 68Ga-RGD tetramer; PET; kinetic modeling; neuroendocrine tumors

Results 1-3 (3)