Simultaneous measurements of single gamma ray of 131I and annihilation radiation of 18F with Compton PET hybrid camera

In internal 131I therapy for thyroid cancer, a decision to continue treatment is made by comparing 131I scintigraphy and [18F]FDG-PET. However, with current SPECT and PET systems, simultaneous imaging of diagnostic PET nuclides and therapeutic 131I nuclides has not been achieved so far. Therefore, we demonstrated that the recently developed Compton PET hybrid camera with Ce:Gd3(Al,Ga)5O12 (GAGG)- Silicon Photomultiplier(SiPM) scintillation detectors can be used to simultaneously image 131I Compton image and 18F PET image.

Fully Automated Synthesis of Novel TSPO PET Imaging Ligand [18F]Fluoroethyltemazepam

Introduction: Benzodiazepines, including temazepam are described as TSPO antagonists. In fact, TSPO was initially described as a peripheral benzodiazepine receptor (PBR) with a secondary binding site for diazepam. TSPO is a potential imaging target of neuroinflammation because there is an amplification of the expression of this receptor. Objectives: Herein, we developed a novel fluorinated benzodiazepine ligand, [¹⁸F]Fluoroethyltemazepam ([¹⁸F]F-FETEM), for positron emission tomography (PET) imaging of translocator protein (18 kDa). Methods: [¹⁸F]F-FETEM was radiolabelled with an automated synthesizer via a one-pot procedure. We conducted a [¹⁸F]F-aliphatic nucleophilic substitution of a tosylated precursor followed by purification on C18 and Alumina N SPE cartridges. Quality control tests was also carried out. Results: We obtained 2.0–3.0% decay-uncorrected radiochemical activity yield (3.7% decay-corrected) within the whole synthesis time about 33 min. The radiochemical purity of [¹⁸F]F-FETEM was over 90% by TLC analysis. Conclusions: This automated procedure may be used as basis for future production of [¹⁸F]F-FETEM for preclinical PET imaging studies.

Quantification of Macrophage-Driven Inflammation During Myocardial Infarction with 18F-LW223, a Novel TSPO Radiotracer with Binding Independent of the rs6971 Human Polymorphism

Myocardial infarction (MI) is one of the leading causes of death worldwide, and inflammation is central to tissue response and patient outcomes. The 18-kDa translocator protein (TSPO) has been used in PET as an inflammatory biomarker. The aims of this study were to screen novel, fluorinated, TSPO radiotracers for susceptibility to the rs6971 genetic polymorphism using in vitro competition binding assays in human brain and heart; assess whether the in vivo characteristics of our lead radiotracer, 18F-LW223, are suitable for clinical translation; and validate whether 18F-LW223 can detect macrophage-driven inflammation in a rat MI model. Methods: Fifty-one human brain and 29 human heart tissue samples were screened for the rs6971 polymorphism. Competition binding assays were conducted with 3H-PK11195 and the following ligands: PK11195, PBR28, and our novel compounds (AB5186 and LW223). Naïve rats and mice were used for in vivo PET kinetic studies, radiometabolite studies, and dosimetry experiments. Rats underwent permanent coronary artery ligation and were scanned using PET/CT with an invasive input function at 7 d after MI. For quantification of PET signal in the hypoperfused myocardium, K1 (rate constant for transfer from arterial plasma to tissues) was used as a surrogate marker of perfusion to correct the binding potential for impaired radiotracer transfer from plasma to tissue (BPTC). Results: LW223 binding to TSPO was not susceptible to the rs6971 genetic polymorphism in human brain and heart samples. In rodents, 18F-LW223 displayed a specific uptake consistent with TSPO expression, a slow metabolism in blood (69% of parent at 120 min), a high plasma free fraction of 38.5%, and a suitable dosimetry profile (effective dose of 20.5-24.5 μSv/MBq). 18F-LW223 BPTC was significantly higher in the MI cohort within the infarct territory of the anterior wall relative to the anterior wall of naïve animals (32.7 ± 5.0 vs. 10.0 ± 2.4 cm3/mL/min, P ≤ 0.001). Ex vivo immunofluorescent staining for TSPO and CD68 (macrophage marker) resulted in the same pattern seen with in vivo BPTC analysis. Conclusion:18F-LW223 is not susceptible to the rs6971 genetic polymorphism in in vitro assays, has favorable in vivo characteristics, and is able to accurately map macrophage-driven inflammation after MI.

Radionuclide calibrator intercomparison study of clinical PET centres in England to a single traceable 68Ge syringe source

OBJECTIVES

The aim of this study was to characterize national variation in radionuclide calibrator activity response to a single National Institute of Standards and Technology (NIST) traceable reference Ge source used as a surrogate for F at clinical PET centres in England using National Physical Laboratory approved techniques.

METHODS

Readings from 20 instruments at 13 centres using local F and Ge factor settings were recorded with the source located in vial and syringe positions. Ten repeat measurements were conducted to investigate repeatability using % coefficient of variability (COV). Comparison ratios to investigate accuracy were made between calibrator responses and decay-corrected NISTref reference activity for syringe and vial position measurements.

RESULTS

The maximum %COV was 0.79%, while 90, 95 and 80% of calibrators conformed to 5% accuracy for F syringe, Ge syringe and Ge vial position readings, respectively. We revealed a trend towards reduced bias in measurements using Veenstra devices for F and using Capintec devices for Ge factor settings.

CONCLUSIONS

This study demonstrated good repeatability in local device measurements. In total, 70% of English calibrators tested and 88% of all measurements performed achieved 5% accuracy. While statistically significant bias was exhibited between different vendor equipment dependent upon radioisotope selected, our study recommends regular traceability checks for optimum instrument performance conducted within National Metrology Institutes guidelines.

NEUTRON FLUX DISTRIBUTION IN THE RADIOISOTOPES TARGET ROOMS AND MAZE IN SYRIAN CYCLOTRON

Gold activation foils were used in this work to measure thermal, epithermal and fast neutron fluxes in the 18F, 123I, (201Tl, 67Ga) production units in Syrian cyclotron. The neutron flux distribution around the targets were determined. It shows that, the maze thermalizes the fast neutrons and reduces the flux about four orders of magnitudes. The results can be adopted by medical centers to identify radioactive hot spots and develop radiation protection.

Alcohol-Supported Cu-Mediated 18F-Fluorination of Iodonium Salts under "Minimalist" Conditions

In the era of personalized precision medicine, positron emission tomography (PET) and related hybrid methods like PET/CT and PET/MRI gain recognition as indispensable tools of clinical diagnostics. A broader implementation of these imaging modalities in clinical routine is closely dependent on the increased availability of established and emerging PET-tracers, which in turn could be accessible by the development of simple, reliable, and efficient radiolabeling procedures. A further requirement is a cGMP production of imaging probes in automated synthesis modules. Herein, a novel protocol for the efficient preparation of ¹⁸F-labeled aromatics via Cu-mediated radiofluorination of (aryl)(mesityl)iodonium salts without the need of evaporation steps is described. Labeled aromatics were prepared in high radiochemical yields simply by heating of iodonium [¹⁸F]fluorides with the Cu-mediator in methanolic DMF. The iodonium [¹⁸F]fluorides were prepared by direct elution of ¹⁸F^- from an anion exchange resin with solutions of the corresponding precursors in MeOH/DMF. The practicality of the novel method was confirmed by the racemization-free production of radiolabeled fluorophenylalanines, including hitherto unknown 3-[¹⁸F]FPhe, in 22-69% isolated radiochemical yields as well as its direct implementation into a remote-controlled synthesis unit.

Molecular Imaging of Vascular Calcification with 18F-Sodium-Fluoride in Patients Infected with Human Immunodeficiency Virus

¹⁸F-Sodium Fluoride (NaF) accumulates in areas of active hydroxyapatite deposition and potentially unstable atherosclerotic plaques. We assessed the presence of atherosclerotic plaques in 50 adult patients with HIV (HIV+) who had undergone two cardiac computed tomography scans to measure coronary artery calcium (CAC) progression. CAC and its progression are predictive of an unfavorable prognosis. Tracer uptake was quantified in six arterial territories: aortic arch, innominate carotid artery, right and left internal carotid arteries, left coronary (anterior descending and circumflex) and right coronary artery. Thirty-one patients showed CAC progression and 19 did not. At least one territory with high NaF uptake was observed in 150 (50%) of 300 arterial territories. High NaF uptake was detected more often in non-calcified than calcified areas (68% vs. 32%), and in patients without than in those with prior CAC progression (68% vs. 32%). There was no correlation between clinical and demographic variables and NaF uptake. In clinically stable HIV+ patients, half of the arterial territories showed a high NaF uptake, often in the absence of macroscopic calcification. NaF uptake at one time point did not correlate with prior progression of CAC. Prospective studies will demonstrate the prognostic significance of high NaF uptake in HIV+ patients.

Experimental validation of estimated spatially variant radioisotope-specific point spread functions using published positron range simulations and fluorine-18 measurements

In this work we compare spatially variant radioisotope-specific point spread functions (PSFs) derived from published positron range data with measured data using a high resolution research tomograph (HRRT). Spatially variant PSFs were measured on a HRRT for fluorine-18, carbon-11 and gallium-68 using an array of printed point sources. For gallium-68, this required modification of the original design to handle its longer positron range. Using the fluorine-18 measurements and previously published data from Monte-Carlo simulations of positron range, estimated PSFs for carbon-11 and gallium-68 were calculated and compared with experimental data. A double 3D Gaussian function was fitted to the estimated and measured data and used to model the spatially varying PSFs over the scanner field of view (FOV). Differences between the measured and estimated PSFs were quantified using the full-width-at-half-maximum (FWHM) and full-width-at-tenth-maximum (FWTM) in the tangential, radial and axial directions. While estimated PSFs were generally in agreement with the measured PSFs over the entire FOV better agreement was observed (FWHM and FWTM differences of less than 10%) when using one of the two sets of positron range simulations, especially for gallium-68 and for the FWTM. Spatially variant radioisotope specific PSFs can be accurately estimated from fluorine-18 measurements and published positron range data. We have experimentally validated this approach for carbon-11 and gallium-68, and such an approach may be applicable to other radioisotopes such as oxygen-15 for which measurements are not practical.

Synthesis and evaluation of a radiolabeled bis-zinc(II)-cyclen complex as a potential probe for in vivo imaging of cell death

The exposition of phosphatidylserine (PS) from the cell membrane is associated with most cell death programs (apoptosis, necrosis, autophagy, mitotic catastrophe, etc.), which makes PS an attractive target for overall cell death imaging. To this end, zinc(II) macrocycle coordination complexes with cyclic polyamine units as low-molecular-weight annexin mimics have a selective affinity for biomembrane surfaces enriched with PS, and are therefore useful for detection of cell death. In the present study, a ¹¹C-labeled zinc(II)-bis(cyclen) complex (¹¹C-CyclenZn2) was prepared and evaluated as a new positron emission tomography (PET) probe for cell death imaging. ¹¹C-CyclenZn2 was synthesized by methylation of its precursor, 4-methoxy-2,5-di-[10-methyl-1,4,7,10-tetraazacyclododecane-1,4,7-tricarboxylic acid tri-tert-butyl ester] phenol (Boc-Cyclen2) with ¹¹C-methyl triflate as a prosthetic group in acetone, deprotection by hydrolysis in aqueous HCl solution, and chelation with zinc nitrate. The cell death imaging capability of ¹¹C-CyclenZn2 was evaluated using in vitro cell uptake assays with camptothecin-treated PC-3 cells, biodistribution studies, and in vivo PET imaging in Kunming mice bearing S-180 fibrosarcoma. Starting from ¹¹C-methyl triflate, the total preparation time for ¹¹C-CyclenZn2 was ~40 min, with an uncorrected radiochemical yield of 12 ± 3% (based on ¹¹C-CH₃OTf, n = 10), a radiochemical purity of greater than 95%, and the specific activity of 0.75-1.01 GBq/μmol. The cell death binding specificity of ¹¹C-CyclenZn2 was demonstrated by significantly different uptake rates in camptothecin-treated and control PC-3 cells in vitro. Inhibition experiments for ¹⁸F-radiofluorinated Annexin V binding to apoptotic/necrotic cells illustrated the necessity of zinc ions for zinc(II)-bis(cyclen) complexation in binding cell death, and zinc(II)-bis(cyclen) complexe and Annexin V had not identical binding pattern with apoptosis/necrosis cells. Biodistribution studies of ¹¹C-CyclenZn2 revealed a fast clearance from blood, low uptake rates in brain and muscle tissue, and high uptake rates in liver and kidney, which provide the main metabolic route. PET imaging using ¹¹C-CyclenZn2 revealed that cyclophosphamide-treated mice (CP-treated group) exhibited a significant increase of uptake rate in the tumor at 60 min postinjection, compared with control mice (Control group). The results indicate that the ability of ¹¹C-CyclenZn2 to detect cell death is comparable to Annexin V, and it has potential as a PET tracer for noninvasive evaluation and monitoring of anti-tumor chemotherapy.

Incidental focal colonic uptake in studies 18F-FDG PET/CT

OBJECTIVES

To assess the frequency of focal colonic uptake as an incidental observation in ¹⁸F-FDG PET/CT studies, and to correlate this finding with histopathological results.

MATERIAL AND METHODS

Out of a total of 3,176 PET/CT studies with ¹⁸F-FDG systematic analysis was carried out on 30 studies in which colonic focal uptake was observed. Patients with known colorectal neoplasia were excluded. The maximum standardised uptake values (SUVm) and the morphological findings provided by the CT were recorded. The studies were reported by a radiologist and a nuclear medicine doctor. The findings were compared with endoscopy and pathology findings.

RESULTS

Of the 30 patients with focal hypermetabolic lesions of the colon (0.94%), 15 were men and 15 were women with ages between 27 and 73 (mean 55 years). The reasons for PET/CT were bronchopulmonary cancer (4), breast cancer (4), tumour of unknown origin (4), melanoma (3), renal carcinoma (3), cervical neoplasia (2), adenocarcinoma of ovary (2), and others (8). Of the 23 colonoscopies performed, 10 patients (43.4%) had malignant lesions, 6 (26.1%) had pre-malignant lesions, and in 7 patients (30.4%) no lesion was identified or was benign. No endoscopy was performed on 7 patients for various reasons (patient refusal to perform the study, advanced oncological disease). An analysis was performed with the SUVm, with no statistically significant differences being found between malignant-premalignant lesions and benign lesions.

CONCLUSIONS

Focal uptake in the colon of ¹⁸F-FDG has clinical relevance, and is mainly associated with morphological lesions in CT. It should be evaluated, as it may be a second tumour or a pre-malignant lesion. It is recommended that all focal uptakes of the colon be evaluated with endoscopy.

DOSE MEASUREMENTS TO THE LENS IN NUCLEAR MEDICINE AND IN FLUOROSCOPY-GUIDED INTERVENTIONAL PROCEDURES: ANALYSIS OF THE RESULTS AND ASSESSMENT OF THE EFFECTIVENESS OF PROTECTIVE EYEWEAR ANTI-X

The new limit of 20 mSv to the lens raises the need for further assessment of the equivalent dose to the lens for nuclear medicine and interventional radiology operators. (a) A measurement campaign was performed in nuclear medicine, (b) a routine monitoring was organised in interventional procedures and (c) the effectiveness of protective eyewear was assessed. In nuclear medicine, for photon fields, the adequacy of Hp(0.07) of dosemeter worn on the trunk is confirmed; with (90)Y, the annual values of Hp(3) measured in therapeutic session are <5 mSv. In interventional procedures, routine monitoring of the dose to the lens must be maintained where the values of Hp(0.07) dosemeter worn on the trunk are higher than one-third of the new limits. The measures carried out have shown that the attenuation factor mean of the protective glasses is equal to ∼4 (range 1.7-11.4).

EYE LENS DOSES IN NUCLEAR MEDICINE: A MULTICENTRIC STUDY IN BELGIUM AND POLAND

This study aimed to investigate the level of the eye lens (EL) doses in nuclear medicine in the light of the new International Commission on Radiological Protection limit. In 7 Belgian and 1 Polish hospitals, 45 staff members were monitored for EL (Hp(3)) and whole-body (WB) (Hp(10)) doses using dedicated dosemeters. Weekly measurements were carried out and used to estimate annual doses. Mostly diagnostic procedures involving radionuclides such as (99m)Tc and (18)F were monitored; measurements were also performed for therapeutic procedures. The cumulative doses showed important variation across the participants. The weekly EL and WB doses ranged from 0.02 to 0.27 and 0.03 to 0.17 mSv, respectively; the annual EL and WB doses ranged from 0.6 to 9.3 and 0.9 to 8.0 mSv, respectively. Some correlation was found between the EL and the WB doses. No significant correlation with the manipulated activities was found.

Design, Synthesis, and In Vitro and In Vivo Evaluation of an (18)F-Labeled Sphingosine 1-Phosphate Receptor 1 (S1P1) PET Tracer

Sphingosine 1-phosphate receptor 1 (S1P1) plays a pivotal signaling role in inflammatory response; because S1P1 modulation has been identified as a therapeutic target for various diseases, a PET tracer for S1P1 would be a useful tool. Fourteen fluorine-containing analogues of S1P ligands were synthesized and their in vitro binding potency measured; four had high potency and selectivity for S1P1 (S1P1 IC50 < 10 nM, >100-fold selectivity for S1P1 over S1P2 and S1P3). The most potent ligand, 28c (IC50 = 2.63 nM for S1P1) was (18)F-labeled and evaluated in a mouse model of LPS-induced acute liver injury to determine its S1P1-binding specificity. The results from biodistribution, autoradiography, and microPET imaging showed higher [(18)F]28c accumulation in the liver of LPS-treated mice than controls. Increased expression of S1P1 in the LPS model was confirmed by immunohistochemical analysis (IHC). These data suggest that [(18)F]28c is a S1P1 PET tracer with high potential for imaging S1P1 in vivo.

Tracking Transitions in Spider Wrapping Silk Conformation and Dynamics by (19)F Nuclear Magnetic Resonance Spectroscopy

Aciniform silk protein (AcSp1) is the primary component of wrapping silk, the toughest of the spider silks because of a combination of high tensile strength and extensibility. Argiope trifasciata AcSp1 contains a core repetitive domain with at least 14 homogeneous 200-amino acid units ("W" units). Upon fibrillogenesis, AcSp1 converts from an α-helix-rich soluble state to a mixed α-helical/β-sheet conformation. Solution-state nuclear magnetic resonance (NMR) spectroscopy allowed demonstration of variable local stability within the W unit, but comprehensive characterization was confounded by spectral overlap, which was exacerbated by decreased chemical shift dispersion upon denaturation. Here, (19)F NMR spectroscopy, in the context of a single W unit (W1), is applied to track changes in structure and dynamics. Four strategic positions in the W unit were mutated to tryptophan and biosynthetically labeled with 5-fluorotryptophan (5F-Trp). Simulated annealing-based structure calculations implied that these substitutions should be tolerated, while circular dichroism (CD) spectroscopy and (1)H-(15)N chemical shift displacements indicated minimal structural perturbation in W1 mutants. Fiber formation by W2 concatemers containing 5F-Trp substitutions in both W units demonstrated retention of functionality, a somewhat surprising finding in light of sequence conservation between species. Each 5F-Trp-labeled W1 exhibited a unique (19)F chemical shift, line width, longitudinal relaxation time constant (T1), and solvent isotope shift. Perturbation to (19)F chemical shift and nuclear spin relaxation parameters reflected changes in the conformation and dynamics at each 5F-Trp site upon addition of urea and dodecylphosphocholine (DPC). (19)F NMR spectroscopy allowed unambiguous localized tracking throughout titration with each perturbant, demonstrating distinct behavior for each perturbant not previously revealed by heteronuclear NMR experiments.

Radionuclidic purity tests in (18)F radiopharmaceutIcals production process

Radionuclidic purity tests of (18)F radiopharmaceuticals (Na(18)F and fluorodeoxyglucose [(18)F]FDG) and radionuclide composition analysis of irradiated water [(18)O]H2O were performed. The measurements were conducted using a High-Purity Germanium (HPGe) detector and a liquid scintillation counter. Radionuclide identification and activity measurements were performed for samples from different stages of the production process. Most of the impurities were detected on QMA (quaternary methylammonium) anion exchange columns and in liquid wastes. Using liquid scintillation counting, the activity of (3)H resulting from the (18)O[p, (3)H](16)O reaction was determined. It was shown that all of the impurities were efficiently determined and eliminated in the radiopharmaceuticals synthesis process and that the final products meet the requirements set by relevant regulations.

Detection of bone metastases in breast cancer patients in the PET/CT era: Do we still need the bone scan?

AIM

To examine the value of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) for the detection of bone metastasis in breast cancer patients and assess whether whole body bone scan (BS) with (99m)Tc-methylene diphosphonate provides any additional information.

MATERIAL AND METHODS

Study group comprised 150 patients, mean age 52 years (range 27-85) with breast cancer, suspected of having bone metastases. All patients had undergone both FDG-PET/CT and BS with or without single photon emission tomography/computed tomography (SPECT/CT) within a period of 6 weeks. The final diagnosis of bone metastasis was established by histopathological findings, additional imaging, or clinical follow-up longer than 10 months. Cancer antigen 15-3 (CA15-3) and carcinoembryogenic antigen (CEA) were measured in all patients.

RESULTS

Histologically 83%, 7% and 10% had infiltrating ductal, lobular and mixed carcinoma respectively. Confirmed bone metastases were present in 86 patients (57.3%) and absent in 64 (42.7%). Mean CA15-3 and CEA values in patients with bone metastases were 74.6ng/mL and 60.4U/mL respectively, compared to 21.3ng/mL and 3.2U/mL without metastases (p<0.001). The sensitivity of FDG-PET/CT for the detection of bone metastases was 97.6% compared to 89.5% with SPECT/CT. In 57 patients, FDG-PET/CT correctly identified additional pulmonary, hepatic, nodal and other soft tissue metastases, not detected by BS.

CONCLUSION

Our findings suggest that FDG-PET/CT is superior to BS with or without SPECT/CT.

18F-fluorodeoxyglucose Positron Emission Tomography in Kaposi Sarcoma Herpesvirus-Associated Multicentric Castleman Disease: Correlation With Activity, Severity, Inflammatory and Virologic Parameters

BACKGROUND

Kaposi sarcoma herpesvirus (KSHV)-associated multicentric Castleman disease (MCD) is a lymphoproliferative inflammatory disorder commonly associated with human immunodeficiency virus (HIV). Its presentation may be difficult to distinguish from HIV and its complications, including lymphoma. Novel imaging strategies could address these problems.

METHODS

We prospectively characterized (18)F-fluorodeoxyglucose positron emission tomography (PET) findings in 27 patients with KSHV-MCD. Patients were imaged with disease activity and at remission with scans evaluated blind to clinical status. Symptoms, C-reactive protein level, and HIV and KSHV loads were assessed in relation to imaging findings.

RESULTS

KSHV-MCD activity was associated with hypermetabolic symmetric lymphadenopathy (median maximal standardized uptake value [SUVmax], 6.0; range, 2.0-8.0) and splenomegaly (3.4; 1.2-11.0), with increased metabolism also noted in the marrow (2.1; range, 1.0-3.5) and salivary glands (3.0; range, 2.0-6.0). The (18)F-fluorodeoxyglucose PET abnormalities improved at remission, with significant SUVmax decreases in the lymph nodes (P = .004), spleen (P = .008), marrow (P = .004), and salivary glands (P = .004). Nodal SUVmax correlated with symptom severity (P = .005), C-reactive protein level (R = 0.62; P = .004), and KSHV load (R = 0.54; P = .02) but not HIV load (P = .52).

CONCLUSIONS

KSHV-MCD activity is associated with (18)F-FDG PET abnormalities of the lymph nodes, spleen, marrow, and salivary glands. These findings have clinical implications for the diagnosis and monitoring of KSHV-MCD and shed light on its pathobiologic mechanism.

18F-EF5 PET Is Predictive of Response to Fractionated Radiotherapy in Preclinical Tumor Models

We evaluated the relationship between pre-treatment positron emission tomography (PET) using the hypoxic tracer ¹⁸F-[2-(2-nitro-1-H-imidazol-1-yl)-N-(2,2,3,3,3- pentafluoropropyl) acetamide] (¹⁸F-EF5) and the response of preclinical tumor models to a range of fractionated radiotherapies. Subcutaneous HT29, A549 and RKO tumors grown in nude mice were imaged using ¹⁸F-EF5 positron emission tomography (PET) in order to characterize the extent and heterogeneity of hypoxia in these systems. Based on these results, 80 A549 tumors were subsequently grown and imaged using ¹⁸F-EF5 PET, and then treated with one, two, or four fraction radiation treatments to a total dose of 10–40 Gy. Response was monitored by serial caliper measurements of tumor volume. Longitudinal post-treatment ¹⁸F-EF5 PET imaging was performed on a subset of tumors. Terminal histologic analysis was performed to validate ¹⁸F-EF5 PET measures of hypoxia. EF5-positive tumors responded more poorly to low dose single fraction irradiation relative to EF5-negative tumors, however both groups responded similarly to larger single fraction doses. Irradiated tumors exhibited reduced ¹⁸F-EF5 uptake one month after treatment compared to control tumors. These findings indicate that pre- treatment ¹⁸F-EF5 PET can predict the response of tumors to single fraction radiation treatment. However, increasing the number of fractions delivered abrogates the difference in response between tumors with high and low EF5 uptake pre-treatment, in agreement with traditional radiobiology.

Noninvasive Evaluation of Metabolic Tumor Volume in Lewis Lung Carcinoma Tumor-Bearing C57BL/6 Mice with Micro-PET and the Radiotracers 18F-Alfatide and 18F-FDG: A Comparative Analysis

Purpose

To explore the value of a new simple lyophilized kit for labeling PRGD₂ peptide (¹⁸F-ALF-NOTA-PRGD₂, denoted as ¹⁸F-alfatide) in the determination of metabolic tumor volume (MTV) with micro-PET in lewis lung carcinoma (LLC) tumor-bearing C57BL/6 mice verified by pathologic examination and compared with those using ¹⁸F-fluorodeoxyglucose (FDG) PET.

Methods

All LLC tumor-bearing C57BL/6 mice underwent two attenuation-corrected whole-body micro-PET scans with the radiotracers ¹⁸F-alfatide and ¹⁸F-FDG within two days. ¹⁸F-alfatide metabolic tumor volume (V_RGD) and ¹⁸F-FDG metabolic tumor volume (V_FDG) were manually delineated slice by slice on PET images. Pathologic tumor volume (V_Path) was measured in vitro after the xenografts were removed.

Results

A total of 37 mice with NSCLC xenografts were enrolled and 33 of them underwent ¹⁸F-alfatide PET, and 35 of them underwent ¹⁸F-FDG PET and all underwent pathological examination. The mean ± standard deviation of V_Path, V_RGD, and V_FDG were 0.59±0.32 cm³ (range,0.13~1.64 cm³), 0.61±0.37 cm³ (range,0.15~1.86 cm³), and 1.24±0.53 cm³ (range,0.17~2.20 cm³), respectively. V_Path vs. V_RGD, V_Path vs. V_FDG, and V_RGD vs. V_FDG comparisons were t = -0.145, P = 0.885, t = -6.239, P<0.001, and t = -5.661, P<0.001, respectively. No significant difference was found between V_Path and V_RGD. V_FDG was much larger than V_RGD and V_Path. V_RGD seemed more approximate to the pathologic gross tumor volume. Furthermore, V_Path was more strongly correlated with V_RGD (R = 0.964,P<0.001) than with V_FDG (R = 0.584,P<0.001).

Conclusions

¹⁸F-alfatide PET provided a better estimation of gross tumor volume than ¹⁸F-FDG PET in LLC tumor-bearing C57BL/6 mice.

The patient as a radioactive source: an intercomparison of survey meters for measurements in nuclear medicine

In this work, the radiation exposure in nuclear medicine is evaluated by measuring dose rates in the proximity of patients and those in close contact to sources like capsules and syringes. A huge number of different survey meters (SMs) are offered commercially. This topic has recently gained interest since dosemeters and active personal dosemeters (APD) for the new dose quantities (ambient and directional dose equivalent) have become available. One main concern is the practical use of SMs and APD in daily clinical routines. Therefore, the radiation field of four common radiopharmaceuticals containing (18)F, (90)Y, (99m)Tc and (131)I in radioactive sources or after application to the patient was determined. Measurements were carried out with different SMs and for several distances. Dose rates decline significantly with the distance to the patient, and with some restrictions, APD can be used as SMs.

Eukaryotic resistance to fluoride toxicity mediated by a widespread family of fluoride export proteins

Fluorine is an abundant element and is toxic to organisms from bacteria to humans, but the mechanisms by which eukaryotes resist fluoride toxicity are unknown. The Escherichia coli gene crcB was recently shown to be regulated by a fluoride-responsive riboswitch, implicating it in fluoride response. There are >8,000 crcB homologs across all domains of life, indicating that it has an important role in biology. Here we demonstrate that eukaryotic homologs [renamed FEX (fluoride exporter)] function in fluoride export. FEX KOs in three eukaryotic model organisms, Neurospora crassa, Saccharomyces cerevisiae, and Candida albicans, are highly sensitized to fluoride (>200-fold) but not to other halides. Some of these KO strains are unable to grow in fluoride concentrations found in tap water. Using the radioactive isotope of fluoride, (18)F, we developed an assay to measure the intracellular fluoride concentration and show that the FEX deletion strains accumulate fluoride in excess of the external concentration, providing direct evidence of FEX function in fluoride efflux. In addition, they are more sensitive to lower pH in the presence of fluoride. These results demonstrate that eukaryotic FEX genes encode a previously unrecognized class of fluoride exporter necessary for survival in standard environmental conditions.

Extremity exposure in nuclear medicine: preliminary results of a European study

The Work Package 4 of the ORAMED project, a collaborative project (2008-11) supported by the European Commission within its seventh Framework Programme, is concerned with the optimisation of the extremity dosimetry of medical staff in nuclear medicine. To evaluate the extremity doses and dose distributions across the hands of medical staff working in nuclear medicine departments, an extensive measurement programme has been started in 32 nuclear medicine departments in Europe. This was done using a standard protocol recording all relevant information for radiation exposure, i.e. radiation protection devices and tools. This study shows the preliminary results obtained for this measurement campaign. For diagnostic purposes, the two most-used radionuclides were considered: (99m)Tc and (18)F. For therapeutic treatments, Zevalin(®) and DOTATOC (both labelled with (90)Y) were chosen. Large variations of doses were observed across the hands depending on different parameters. Furthermore, this study highlights the importance of the positioning of the extremity dosemeter for a correct estimate of the maximum skin doses.

Frequency-swept pulse sequences for 19F heteronuclear spin decoupling in solid-state NMR

Heteronuclear spin decoupling pulse sequences in solid-state NMR have mostly been designed and applied for irradiating 1H as the abundant nucleus. Here, a systematic comparison of different methods for decoupling 19F in rigid organic solids is presented, with a special emphasis on the recently introduced frequency-swept sequences. An extensive series of NMR experiments at different MAS frequencies was conducted on fluorinated model compounds, in combination with large sets of numerical simulations. From both experiments and simulations it can be concluded that the frequency-swept sequences SWf-TPPM and SWf-SPINAL deliver better and more robust spin decoupling than the original sequences SPINAL and TPPM. Whereas the existence of a large chemical shift anisotropy and isotropic shift dispersion for 19F does compromise the decoupling efficiency, the relative performance hierarchy of the sequences remains unaffected. Therefore, in the context of rigid organic solids under moderate MAS frequencies, the performance trends observed for 19F decoupling are very similar to those observed for 1H decoupling.

1H-19F spin-lattice relaxation spectroscopy: proton tunnelling in the hydrogen bond studied by field-cycling NMR

Proton tunnelling in the hydrogen bonds of two fluorine substituted benzoic acid dimers has been investigated using field-cycling NMR relaxometry. The close proximity of the (19)F nuclei to the hydrogen bond protons introduces heteronuclear (19)F-(1)H dipolar interactions into the spin-lattice relaxation processes. This renders the (1)H magnetisation-recovery biexponential and introduces multiple spectral density components into the relaxation matrix characterised by frequencies that are sums and differences of the (19)F and (1)H Larmor frequencies. Using field-cycling NMR pulse sequences that measure the spin-lattice relaxation and cross-relaxation rates we demonstrate how some of these multiple spectral density components can be separately resolved. This leads to an accurate determination of the correlation times that characterise the proton tunnelling motion. A broad spectrum of relaxation behaviour is illustrated and explored in the chosen samples and the investigation is used to explore the theory and practise of field-cycling NMR relaxometry in cases where heteronuclear interactions are significant.

Factors affecting the specific activity of [18F]fluoride from a [18O]water target

AIM

Characterisation of the influence of different polymeric tube materials of a water target system, used for the production of 18F activity, on the specific activity of radiotracers.

MATERIAL, METHODS

Target water samples taken from different locations of the 18F water target system of a Cyclone 18/9 cyclotron, equipped with Teflon (PTFE) or polypropylene (PP) tubes, were analyzed for non-radioactive [19F]fluoride content. [19F]Fluoride content was measured by ion chromatography (IC20, Dinoex) with suppressed conductivity detection. Both the ion chromatographic results and the amount of 18F activity produced were used for the calculation of the specific activity (SA) of [18F]fluoride at the start of the labelling synthesis. To check these results, the SA of the labelled receptor ligand [18F]ZK811460 was also determined by using the different tubing materials.

RESULTS

Dose-exposed PTFE tubes of the target dispensing (loading) system were identified to be a major source of [19F]fluoride contamination.

CONCLUSION

By replacing PTFE tubes of the target dispensing system with PP tubes, the content of 19F was reduced considerably resulting in an increase of SA of the radiotracer [18F]ZK811460 by factor of two.

Standardization of 18F by coincidence and LSC methods

The nuclide 18F disintegrates to 18O by beta+ emission (96.86%) and electron capture (3.14%) with a half-life of 1.8288 h. It is widely used in nuclear medicine for positron emission tomography (PET). A radioactive solution of this nuclide has been standardized by two techniques: coincidence measurements with a pressurized proportional counter and liquid scintillation counting using the CIEMAT/NIST method. One ampoule containing a solution calibrated in activity was sent for measurement at the International Reference System maintained by the BIPM. Results are in excellent agreement with SIR values.

Calibration of the Capintec CRC-712M dose calibrator for 18F

Primary standardisation was performed on a solution of (18)F using the 4pibeta-gamma coincidence counting efficiency-tracing extrapolation method with (60)Co used as a tracer nuclide. The result was used to calibrate the ANSTO secondary standard ionisation chamber which is used to disseminate Australian activity standards for gamma emitters. Using the secondary activity standard for (18)F, the Capintec CRC-712M dose calibrator at the Australian National Medical Cyclotron (NMC) Positron Emission Tomography (PET) Quality Control (QC) Section was calibrated. The dial setting number recommended by the manufacturer for the measurement of the activity of (18)F is 439. In this work, the dial setting numbers for the activity measurement of the solution of (18)F in Wheaton vials were experimentally determined to be 443+/-12, 446+/-12, 459+/-11, 473+/-15 for 0.1, 1, 4.5 and 9ml solution volumes, respectively. The uncertainties given above are expanded uncertainties (k=2) giving an estimated level of confidence of 95%. The activities determined using the manufacturer recommended setting number 439 are 0.8%, 1.4%, 4.0% and 6.5% higher than the standardised activities, respectively. It is recommended that a single dial setting number of 459 determined for 4.5ml is used for 0.1-9ml solution in Wheaton vials in order to simplify the operation procedure. With this setting the expended uncertainty (k=2) in the activity readout from the Capintec dose calibrator would be less than 6.2%.

Characterisation of fluorine containing glasses by 19F, 27Al, 29Si and 31P MAS-NMR spectroscopy

OBJECTIVE

The aim of this study is to characterise a range of model and commercially available glasses used to form glass (ionomer) polyalkenoate cements.

METHODS

A range of model fluoro-alumino-silicate glasses that form the basis of glass (ionomer) polyalkenoate cements and five commercial glasses have been characterised by 29Si, 27Al, 31P and 19F Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR).

RESULTS

The 29Si spectra indicate a predominantly Q33Al and Q44Al structure where the Q33Al species represents a silicon with one non-bridging oxygen and three Si-O-Al linkages and the Q44Al species a silicon with four Si-O-Al bonds. Aluminium was found in predominantly four coordinate sites, but glasses with high fluorine contents showed an increasing proportion of five and six coordinate aluminium. In phosphate containing glasses the phosphorus was present as Al-O-PO3(2-) type species indicating local charge compensation of Al3+ and P5+ in the glass structure. 19F MAS-NMR indicated the presence of F-Ca(n), Al-F-Ca(n), F-Sr(n), Al-F-Sr(n) and Al-F-Na(n) species where F-M(n) indicates a fluorine surrounded by n next nearest neighbour cations and Al-F-M(n) represents a fluorine bonded to aluminium with the metal, M in close proximity charge balancing the tetrahedral AlO3F species. The proportion of Al-F-M(n) species increased with increasing fluorine content of the glass and lower non-bridging oxygen contents. There was no evidence of Si-F bonds in any of the glasses.

CONCLUSIONS

The local structure of the phosphate containing glasses with regard to fluorine, calcium, strontium and phosphate is similar to that of fluorapatite the mineral phase of tooth. This may explain the ease with which these glasses crystallize to fluorapatites and the recently observed mineralization of glass polyalkenoate cements found in vivo.

Radioactive byproducts in [18O]H2O used to produce 18F for [18F]FDG synthesis

Potential radioactive byproducts in [(18)O]H(2)O irradiated with 9.6 MeV protons to produce (18)F were analyzed theoretically and experimentally. Twenty two nuclear reaction cross sections included in the National Nuclear Data Center's (NNDC) data base were selected from the possible nuclear reactions between 9.6 MeV protons and a silver havar target. Ten radionuclides: (52)Mn, (55)Fe, (55)Co, (56)Co, (57)Co, (58)Co, (59)Ni, (95)Tc, (96)Tc and (109)Cd were detected experimentally in [(18)O]H(2)O by using high purity germanium semiconductor detectors. The activities of the 10 radionuclides were distributed between 4B q and 1.2k Bq. These activities were less than the reference values given in the International Basic Safety Standards. The radionuclides derived from nuclear reactions between a silver target body and 9.6 MeV protons at a beam current 25 microA for 60 min irradiation would be exempt from restrictions for radioactive waste. The purified [(18)F]FDG prepared from (18)F produced by irradiating a silver havlar target with 9.6 MeV protons was not contaminated by the radionuclides.

NCA nucleophilic radiofluorination on substituted benzaldehydes for the preparation of [18F]fluorinated aromatic amino acids

Nucleophilic aromatic substitution is a challenging task in radiochemistry. Therefore, a thorough evaluation and optimisation of this step is needed to provide a satisfactory tool for the routine preparation of [(18)F]fluorinated aromatic amino acids. Two methods, already proposed elsewhere, were evaluated and improved. The yields for the radiofluorination were increased whereas activity loss during solid phase extraction was observed. Radiochemical yields for the two methods were 92.7+/-5.5% (method 1) and 92.1+/-12.3% (method 2) for conversion and 11.1+/-2.8% (method 1) and 34.8+/-0.6% (method 2) for purification, respectively. In total, we demonstrate an optimised method for the preparation of this important class of [(18)F]fluorinated synthons for PET.

[Influence of radioactive concentration and storage time on radiochemical purity of 18F-FDG]

OBJECTIVE

To study the influence of the 18F-FDG radioactive concentration and the usual greatest storage time of the radiopharmaceutical at the Radiopharmacy Unit (RU) over its radiochemical purity.

MATERIAL AND METHODS

Thirty 18F-FDG preparations coming from different batches were studied. The radiochemical purity was determined at the RU by means of TLC to saline-diluted (1:10) and undiluted samples of each preparation, in the early 30 minutes since its arrival and 5 hours later. The radiochemical purity of the original 18F-FDG was determined at the PET radiopharmaceutical producer Laboratory (PETL) by means of HPLC in the early hour since the 18F-FDG dispensing.

RESULTS

The increase of 18F-Fluoride found in the (5 h-30 min) period was significantly greater in the samples without diluting than in the diluted ones (p < 0.0001). We found a significant correlation between the percent of this increase of 18F-Fluoride (y) and the radioactive concentration of the 18F-FDG (x): y = 0.00061x + 0.1759 (R2 = 0.198; p < 0.0005). The percent of 18F-Fluoride determined at the RU was significantly higher than the percent of 18F-Fluoride determined at the PETL (p < 0.0001). A significant correlation between the differences of the percent of 18F-Fluoride determined by TLC and HPLC (y) and the radioactive concentration (x) was found: y = 0.0139x + 0.3146 (R2 = 0.196; p = 0.016). A significant correlation among the differences of percent 18F-Fluoride determined by TLC and HPLC ([%F] RU - [%F] PETL), the radioactive concentration (RC) and the time since the radiopharmaceutical dispensing (t) was found: [%F] RU - [%F] PETL = 0.01159*RC (mCi/mL) + 0.250*t (h) - 0.01903 (R2 = 0.226; p < 0.014).

CONCLUSIONS

The stability of the 18F-FDG preparations with time increases when diminishing its concentration. We recommended the dilution of these preparations with physiological saline solution.

Using 19F NMR spectroscopy to determine trifluralin binding to soil

Trifluralin is a widely used herbicide for the control of broad leaf weeds in a variety of crops. Its binding to soil may result in significant losses in herbicidal activity and a delayed pollution problem. To investigate the nature of soil-bound trifluralin residues, 14C-labeled herbicide was incubated for 7 weeks with four soils under anoxic conditions. As determined by radiocounting, trifluralin binding ranged between 10 and 53% of the initial 14C depending on the soil tested. 19F NMR analyses of the methanol extracts and different fractions of the extracted soil suggested that bound residue formation largely involved reduced metabolites of the herbicide. A 2,6-diamino product of trifluralin reduction with zero-valent iron (Fe-TR), and the standard of a 1,2-diaminotrifluralin derivative (TR6) formed covalent bonds with fulvic acid (FA), as indicated by the 19F NMR spectra taken periodically over a 3-week contact time. At short contact times, TR6 and Fe-TR formed weak physical bonds with FA, as the respective spin-lattice relaxation times (T1) decreased from the range 1300-1831 ms for TR6 or Fe-TR analyzed in the absence of FA to the range 150-410 ms for TR6/FA or Fe-TR/FA mixtures. In general, the results indicated that trifluralin immobilization involved a variety of mechanisms (covalent binding, adsorption, sequestration), and with time it became increasingly stable.

Tritium in [18O]water containing [18F]fluoride for [18F]FDG synthesis

The presence of tritium in enriched [18O]water irradiated with 9.6 MeV protons used to produce [18F]fluoride by the 18O(p, n)18F reaction was inferred from the cross sections and threshold energies of the 18O(p, t)16O reaction, and the existence of tritium was confirmed experimentally. Tritium was also detected in both [18O]water recovered for recycling and waste acetonitrile solutions. The purified [18F]FDG was not contaminated with 3H. The amount of 3H discharged into the air was far less than the International Basic Safety Standard Level.

18F-Fluorothiols: A New Approach To Label Peptides Chemoselectively as Potential Tracers for Positron Emission Tomography

[(18)F]Fluorothiols are a new generation of peptide labeling reagents. This article describes the preparation of suitable methanesulfonyl precursors and their use in no-carrier-added radiosyntheses of (18)F-fluorothiols. The preparations of (3-[(18)F]fluoropropylsulfanyl)triphenylmethane, (2-[2-[2-(2-[(18)F]fluoroethoxy)ethoxy]ethoxy]ethylsulfanyl)triphenylmethane, and 4-[(18)F]fluoromethyl-N-[2-triphenylmethanesulfanyl)ethyl]benzamide starting from the corresponding methanesulfonyl precursors were investigated. Following the removal of the triphenylmethane protecting group, the (18)F-fluorothiols were reacted with the N-terminal chloroacetylated model peptide ClCH(2)C(O)-LysGlyPheGlyLys. The corresponding radiochemical yields of (18)F-labeled isolated model peptide, decay-corrected to (18)F fluoride, were 10%, 32%, and 1%, respectively. These results indicate a considerable potential of (18)F-fluorothiols for the chemoselective labeling of peptides as tracers for positron emission tomography (PET).

Structural properties of perfluorinated linear alkanes: a 19F and 13C NMR study of perfluorononane

Liquid perfluorocarbons exhibit unique physical-chemical characteristics such as extraordinary stability, combined hydrophobia and lipophobia, low surface tension and a capacity to carry large quantities of gas. They have found widespread use in industry, medicine and biology even though the molecular origin of these properties is not fully understood. The objective of the present work was to elucidate the physical behavior of perfluorinated linear alkanes by investigating their intramolecular electronic environment using 13C and 19F NMR techniques in combination with theoretical calculations of molecular orbitals. Particular advantage was taken of 19F-19F through-space couplings, which led us to propose a molecular model in which delocalized p-electrons of the fluorines cover the entire surface of the molecule in two pairs of intertwined helices. Experimental data are presented for n-perfluorononane and supported by corresponding measurements with shorter and longer perfluorinated alkanes.

Measurement of the residual radioactivity induced in the front foil of a target assembly in a modern medical cyclotron

The levels of residual radioactivity induced in Havar foils at the entrance of a high-pressure 18O-enriched water target used for the production of 18F- in a medical cyclotron with 16 MeV protons have been determined using high-resolution gamma-ray spectrometry. Whole body and skin dose rates arising from exposure to these foils during their periodic replacement have been estimated. The results indicate that irradiated foils do not represent a significant radiological hazard for the cyclotron operating staff and that no waste disposal difficulties should be encountered after an appropriate 'cooling' period of 2 years.

Establishing equivalence for activity standards of short-lived radionuclides using the NPL secondary standard radionuclide calibrator

Conventional comparison techniques used between National Metrology Institutes are not practicable for short-lived radionuclides because of geographical separations and transport difficulties. The NPL Secondary Standard Radionuclide Calibrator provides an alternative approach and a comparison was conducted with 18F to investigate its feasibility. The exercise was successful and the paper details the protocol used, the quality assurance mechanisms introduced to underpin the comparison and an analysis of the results. It was also demonstrated that this approach could be linked to the BIPM SIR system. Recommendations are presented for the extension of this work to other suitable, short-lived radionuclides.

Calculation of 18F, 99mTc, 111In and 123I calibration factor using the penelope ionization chamber simulation method

A new method using the Monte Carlo code PENELOPE for ionization chamber simulation has already been successfully used for calculating calibration factors needed for the measurements of radionuclides with photon emission (2003, Appl. Radiat. Isot., to be published). This work has been continued at (Laboratoire National Henri Becquerel) in order to calculate the calibration factors for radionuclides with short half-lives used in medical services. Activity measurements of 18F, 99mTc,111In and 123I using the calculated calibration factors were obtained with standard uncertainties equal to 0.6% for 18F, 99mTc and 1.5% for 111In and 123I.

Neutron measurements in the vicinity of a self-shielded PET cyclotron

The radionuclides used in positron emission tomography (PET) are short-lived and generally must be produced on site using a cyclotron. A common end product of the nuclear reactions used to produce the PET radionuclides is neutron radiation. These neutrons could potentially contribute to the annual effective dose received by hospital personnel. A Bonner sphere spectrometer was used to measure neutron energy spectra at three locations near a self-shielded PET cyclotron. This cyclotron accelerates protons to 11 MeV. The neutron measurements reported were made during the production of 18F via the 18O(p,n)18F reaction (Q = -2.4 MeV). Neutron spectra were obtained with the BUMS unfolding code and converted to dose equivalent rates.

Radioassays and experimental evaluation of dose calibrator settings for 18F

The positron emitter 18F continues to be one of the most important imaging radionuclides in diagnostic nuclear medicine. Assays of radiopharmaceuticals containing this nuclide are often performed in the clinic using commercial reentrant ionization chambers, or "dose calibrators". Meaningful quantitative clinical studies require accurate knowledge of the injected activity which requires proper calibration of these instruments. Radioassays were performed at the National Institute of Standards and Technology (NIST) on a solution of 18F produced at the National Institutes of Health (NIH) using 4pibeta liquid scintillation (fS) counting with 3H-standard efficiency tracing. Cocktails containing water fractions of approximately 0.9 and 9% (both as saline) were used. The massic activity values were measured to be 2.52+/-0.06 and 2.50+/-0.03 MBq g(-1), respectively, for the 0.9 and 9% water cocktails as of the reference time. The uncertainties on the activity measurements are expanded (k = 2) uncertainties. The largest uncertainty component was found to be the repeatability on a single LS source, with the cocktails containing 0.9% water fraction exhibiting a larger variability by nearly a factor of two. Reproducibility between LS cocktails with the same water fraction was also found to be a large uncertainty component, but with a value less than half that due to measurement repeatability. Radionuclidic impurities consisted of 48V and 46Sc, at levels of 0.11+/-0.08% (expanded uncertainties) and approximately 2 x 10(-3)% (upper limit) relative to the activity of the 18F, as of the reference time. Dose calibrator dial settings for measuring solutions of 18F were experimentally determined for Capintec CRC-12 and CRC-35R dose calibrators in three measurement geometries: a 5-ml standard NIST ampoule (two ampoules measured), a 12-ml plastic syringe containing 9 ml of solution and a 10-ml Mallinckrodt molded dose vial filled with 5 ml of solution. The experimental dial settings (and the corresponding expanded uncertainties) for these geometries were found to be 477+/-7, 474+/-6, 482+/-6 and 463+/-7 for the two ampoules, the syringe and the dose vial, respectively, in the CRC-12. The dial settings determined for the CRC-35R were 472+/-7, 470+/-7, 464+/-6 and 456+/-6 for the two ampoules, the syringe, and the dose vial, respectively. The uncertainties in the dial settings are expanded uncertainties. Comparisons between the empirically determined dial settings and the manufacturer's recommended setting of "439" indicate that use of the manufacturer's setting overestimates the activity by between 3 and 6%, depending upon the geometry used.

REDOR-determined distances from heterospins to clusters of 13C labels

The use of rotational-echo double resonance NMR to measure distances from an observed tightly coupled cluster of 13C spins to a distant 15N, 31P, or 19F is practical if all homonuclear 13C-13C dipolar interactions are suppressed by multiple-pulse decoupling during heteronuclear dipolar evolution. This scheme is first calibrated by experiments performed on multiply labeled alanines and then applied in the measurement of 19F-13C distances in p-trifluoromethylphenyl [1,2-13C2]acetate.

Identification and quantitation of gaseous compounds of fluorine generated in [18F]F2 target systems

The first direct evidence for the chemical identity of the electrophilic fluorinating agents generated in 20Ne(d, alpha)18F (single-step), 18O(p,n)18F (single-step and two-step) and 16O(3He2+, p)18F (single-step) gas target systems, utilizing aluminum, silver, copper, nickel and gold plated copper target bodies, has been established with multinuclear NMR and mass spectral techniques. The major components of the reactive fraction from these targets were also quantitated using 19F NMR. Fluorine-19 NMR data of the reactive fraction of all proton and 3He2+ irradiated oxygen gas target systems showed the presence of oxygen difluoride in various proportions. Samples from the single-step method contained up to 20% OF2 while those from the two-step process had 0-5%. Fluorine nitrate (FONO2) was observed only as a minor component (0-3%) in the reactive fraction. The presence of OF2 and FONO2 was further confirmed by 17O and 15N NMR, respectively, using [17O]O2 and [15N]N2 spiked oxygen gas targets. The NMR results were supported by mass spectral data collected with a residual gas analyzer (RGA). Both 19F NMR and mass spectroscopy showed CF4 as the only major inert component in the single-step oxygen target products. As expected, the 19F NMR and mass spectral data showed that the reactive fraction of the neon gas target constituted only F2 and the inert fraction comprised of CF4 and NF3.

48V radionuclidic impurity in product streams from liquid cyclotron targets with titanium windows

Vanadium-48, a positron emitter with a 16.0 day half-life, was observed in the aqueous product stream from a liquid cyclotron target equipped with a titanium window, a type of target system commonly used for preparing [13N]NH3 at PET centers. The amount of 48V activity is directly related to bombardment time and beam current. It is apparently present as vanadate ion, and it is efficiently removed by anion exchange cartridges. More generally, it is likely that the specie would be present in the product stream of any titanium-window-equipped liquid target which contains water and which is bombarded with protons or deuterons. Incidental to the 48V investigation, was quantitation of 18F in the system under study.

Detection and quantitation of 17F formation during the cyclotron production of 13N

The positron emitter 17F has been identified for the first time as a radioactive contaminant formed during 13N production. It was determined that 17F made up 18% of the short-lived radioactivity previously thought to be exclusively 15O. Mathematical deconvolution of decay curve data was employed as a complement to radioanalytical techniques. The nuclidic composition of the effluents from the proton bombardment of (a) water, (b) dilute ethanol and (c) 13C powder/water slurry was determined and compared with previous literature values.

Rapid, inexpensive quality control of fluorine-18 2-deoxy-2-fluoro-D-glucose preparations using the hexokinase reaction in vitro

A rapid enzymatic method for determining the purity of 2FDG preparations has been devised. A small aliquot of the preparation is incubated with a hexokinase/adenosine triphosphate/Mg+2 mixture and passed through a Dowex 1 ion-exchange column, which retains the 2FDG-6-phosphate. Another aliquot, without prior incubation, is passed through an identical column and the 2FDG radioactivity is found in the eluant. The criteria for purity are quantitative retention of the 2FDG-6-phosphate on the column and no retention of 2FDG. Comparison of the HK method with thin layer and high performance liquid chromatography assays indicate that the HK method can serve as a rapid, simple and inexpensive alternative to these other methods. It can be used in a routine quality control program and may be easily adaptable to automated 2FDG synthetic methods.