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1.  Application of F-18-Sodium Fluoride (NaF) Dynamic PET-CT (dPET-CT) for Defect Healing: A Comparison of Biomaterials in an Experimental Osteoporotic Rat Model 
The aim of the current study was to measure and compare the effect of various biomaterials for the healing of osteoporotic bone defects in the rat femur using 18F-sodium fluoride dPET-CT.
Osteoporosis was induced by ovariectomy and a calcium-restricted diet. After 3 months, rats were operated on to create a 4-mm wedge-shaped defect in the distal metaphyseal femur. Bone substitution materials of calcium phosphate cement (CPC), composites of collagen and silica, and iron foams with interconnecting pores were inserted. Strontium or bisphosphonate, which are well known for having positive effects in osteoporosis treatment, were added into the materials. Eighteen weeks after osteoporosis induction and 6 weeks following femoral surgery, dPET-CT studies scan were performed with 18F-Sodium Fluoride. Standardized uptake values (SUVs) and a 2-tissue compartmental learning-machine model (K1-k4, vessel density [VB], influx [ki]) were used for quantitative analysis.
k3, reflecting the formation of fluoroapatite, revealed a statistically significant increase at the biomaterial-bone interface due to the Sr release from strontium-modified calcium phosphate cement (SrCPC) compared to CPC, which demonstrated enhanced new bone formation. In addition, k3 as measured in the porous scaffold silica/collagen xerogel (Sc-B30), showed a significant increase based on Wilcoxon rank-sum test (p<0.05) as compared with monolithic silica/collagen xerogel (B30) in the defect region. Furthermore, ki, reflecting the net plasma clearance of tracer to bone mineral measured in the iron foam with coating of the bisphosphonate zoledronic acid (Fe-BP), was enhanced as compared with plain iron foam (Fe) in the defect region.
k3 was the most significant parameter for the characterization of healing processes and revealed the best differentiation between the 2 different biomaterials. PET scanning using 18F-sodium fluoride seems to be a sensitive and useful method for evaluation of bone healing after replacement with these biomaterials.
PMCID: PMC4210358  PMID: 25317537
Aortopulmonary Septal Defect; Biomarkers; Pharmacological; Osteoporosis
2.  Quantitative approaches of dynamic FDG-PET and PET/CT studies (dPET/CT) for the evaluation of oncological patients 
Cancer Imaging  2012;12(1):283-289.
Objectives: The use of dynamic positron emission tomography/computed tomography (dPET/CT) studies with [18F]deoxyglucose (FDG) in oncological patients is limited and primarily confined to research protocols. A more widespread application is, however, desirable, and may help to assess small therapeutic effects early after therapy as well as to differentiate borderline differences between tumour and non-tumour lesions, e.g., lipomas versus low-grade liposarcomas. The aim is to present quantification approaches that can be used for the evaluation of dPET/CT series in combination with parametric imaging and to demonstrate the feasibility with regard to tumour diagnostics and therapy management. Methods: A 60-min data acquisition and short acquisition protocols (20-min dynamic series and a static image 60 min post injection) are discussed. A combination of a modified two-tissue compartment model and non-compartmental approaches from the chaos theory (fractal dimension of the time–activity curves) are presented. Fused PET/CT images as well as regression-based parametric images fused with CT or with PET/standardised uptake value images are demonstrated for the exact placement of volumes of interest. Results: The two-tissue compartmental method results in the calculation of 5 kinetic parameters, the fractional blood volume VB (known also as the distribution volume), and the transport rates k1 to k4. Furthermore, the influx according to Patlak can be calculated from the transport rates. The fractal dimension of the time–activity curves describes the heterogeneity of the tracer distribution. The use of the regression-based parametric images of FDG helps to visualise the transport/perfusion and the transport/phosphorylation-dependent FDG uptake, and adds a new dimension to the existing conventional PET or PET/CT images. Conclusions: More sophisticated quantification methods and dedicated software as well as high computational power and faster acquisition protocols can facilitate the assessment of dPET/CT, and may find use in clinical routine, in particular for the assessment of early therapeutic effects or new treatment protocols in combination with the new generation of PET/CT scanners.
PMCID: PMC3485644  PMID: 23033440
Dynamic PET; oncology; compartment modelling; non-compartment modelling; parametric imaging; feature extraction
3.  Dynamic PET with 18F-Deoxyglucose (FDG) and quantitative assessment with a two-tissue compartment model reflect the activity of glucose transporters and hexokinases in patients with colorectal tumors 
Dynamic PET (dPET) with 18F-Deoxyglucose (FDG) provides quantitative information about distribution of the tracer in a predefined volume over time. A two-tissue compartment model can be used to obtain quantitative data regarding transport of FDG into and out of the cells, phosphorylation and dephosphorylation rate of intracellular FDG, and fractional blood volume in the target volume, also named vessel density. Aim of the study was the correlation of glucose transporters expression and hexokinases with the corresponding compartment parameters.Patients with colorectal tumors were examined with dynamic PET prior to surgery. Afterwards, tumor samples were obtained during surgery and gene expression was assessed using gene arrays. The dynamic PET data were evaluated to quantify the parameters of a two tissue compartment model for colorectal tumors using a Volume-of-Interest (VOI) technique. A multiple correlation/regression analysis was performed using glucose transporters as independent variables and k1 as the dependent variable. A correlation of r=0.7503 (p=0.03) was obtained for the transporters SLC2A1, SLC2A2, SLC2A4, SLC2A8, SLC2A9, SLC2A10 and k1. The correlation of r=0.7503 refers to an explained variance of data of 56.30 %, therefore more than 50 % of data changes are associated with the gene expression. An analysis of the hexokinases HK1-HK3 and k3 revealed a correlation coefficient of r=0.6093 (p=0.04), which is associated with an explained variance of 37.12 %. Therefore, parameters k1 and k3 reflect gene activity. The results demonstrate that k1 and k3 of the two-tissue compartment model are correlated with glucose transporters and hexokinases.
PMCID: PMC3784805  PMID: 24116350
Dynamic PET; compartment model; glucose transporter; hexokinase
4.  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
5.  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
6.  Correlation of Dynamic PET and Gene Array Data in Patients with Gastrointestinal Stromal Tumors 
The Scientific World Journal  2012;2012:721313.
Introduction. The results obtained with dynamic PET (dPET) were compared to gene expression data obtained in patients with gastrointestinal stromal tumors (GIST). The primary aim was to assess the association of the dPET results and gene expression data. Material and Methods. dPET was performed following the injection of F-18-fluorodeoxyglucose (FDG) in 22 patients with GIST. All patients were examined prior to surgery for staging purpose. Compartment and noncompartment models were used for the quantitative evaluation of the dPET examinations. Gene array data were based on tumor specimen obtained by surgery after the PET examinations. Results. The data analysis revealed significant correlations for the dPET parameters and the expression of zinc finger genes (znf43, znf85, znf91, znf189). Furthermore, the transport of FDG (k1) was associated with VEGF-A. The cell cycle gene cyclin-dependent kinase inhibitor 1C was correlated with the maximum tracer uptake (SUVmax) in the tumors. Conclusions. The data demonstrate a dependency of the tracer kinetics on genes associated with prognosis in GIST. Furthermore, angiogenesis and cell proliferation have an impact on the tracer uptake.
PMCID: PMC3373132  PMID: 22701369
7.  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.
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.
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.
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.
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.
PMCID: PMC3292467  PMID: 22214362
68Ga-bombesin; 68Ga-RGD tetramer; PET; kinetic modeling; neuroendocrine tumors

Results 1-7 (7)