Determination of Mercury in Seafood by Flow Injection–Cold Vapor Atomic Absorption Spectrometry after Microwave Digestion: NMKL Interlaboratory Study

Ten laboratories participated in an interlaboratory method-performance (collaborative) study of a method for the determination of mercury in foods of marine origin by flow injection–cold vapor atomic absorption spectrometry after wet digestion using a microwave oven technique. The study was preceded by a training round of samples of known identity. The method was tested on a total of 7 seafood products: blue mussel (Mytilus edulis), cod muscle (Gadus morhua), crab (Cancer pagurus), scampi (Nephrops norwegicus), black scabbard fish (Aphnopus carbo), longnose velvet dogfish (Centroscymus crepidater), and Portuguese dogfish (Cenbroscymus coelolepis) with mercury concentrations of 0.14, 0.24, 0.35, 0.59, 1.42, 4.2, and 13.2 μg/g, respectively. The materials were presented to the participants in the study as blind duplicates, and the participants were asked to perform single determinations on each sample. Repeatability relative standard deviations (RSDr) for mercury ranged from 2.4 to 14.0%. Reproducibility relative standard deviations (RSDR) ranged from 7.7 to 16.6%. HORRAT values for all samples were <1.0.

A forced-convection gas target for the production of [11C]CH4

A forced-convection gas target for the production of [¹¹C]CH₄ on a 13 MeV cyclotron was constructed and tested. A small fan was incorporated into the back of the target, which mixes the target gas during irradiation. The effect of the forced convection alone on the target operation and the [¹¹C]CH₄ yield was measured. Forced convection improved the target yield by up to 16 ± 4%. In addition, improvement in heat transfer of up to 70% was observed to be a function of fan speed. Operating with forced convection allowed delivery of 21% higher beam currents while still staying in the acceptable pressure rise during irradiation, providing a 25 ± 7% greater yield.

Graphical user interface for yield and dose estimations for cyclotron-produced technetium

The cyclotron-based (100)Mo(p,2n)(99m)Tc reaction has been proposed as an alternative method for solving the shortage of (99m)Tc. With this production method, however, even if highly enriched molybdenum is used, various radioactive and stable isotopes will be produced simultaneously with (99m)Tc. In order to optimize reaction parameters and estimate potential patient doses from radiotracers labeled with cyclotron produced (99m)Tc, the yields for all reaction products must be estimated. Such calculations, however, are extremely complex and time consuming. Therefore, the objective of this study was to design a graphical user interface (GUI) that would automate these calculations, facilitate analysis of the experimental data, and predict dosimetry. The resulting GUI, named Cyclotron production Yields and Dosimetry (CYD), is based on Matlab®. It has three parts providing (a) reaction yield calculations, (b) predictions of gamma emissions and (c) dosimetry estimations. The paper presents the outline of the GUI, lists the parameters that must be provided by the user, discusses the details of calculations and provides examples of the results. Our initial experience shows that the proposed GUI allows the user to very efficiently calculate the yields of reaction products and analyze gamma spectroscopy data. However, it is expected that the main advantage of this GUI will be at the later clinical stage when entering reaction parameters will allow the user to predict production yields and estimate radiation doses to patients for each particular cyclotron run.

2-Fluoropyridine prosthetic compounds for the 18F labeling of bombesin analogues

Acetylene-bearing 2-[(18)F]fluoropyridines [(18)F]FPy5yne and PEG-[(18)F]FPyKYNE were prepared via efficient nucleophilic heteroaromatic [(18)F]fluorination of their corresponding 2-trimethylammoniumpyrdinyl precursors. The prosthetic groups were conjugated to azide- and PEG3-modified bombesin(6-14) analogues via copper-catalyzed azide-alkyne cycloaddition couplings to yield mono- and di-mini-PEGylated ligands for PET imaging of the gastrin- releasing peptide receptor. The PEG3- and PEG2/PEG3-bearing (18)F peptides showed decreased lipophilicity relative to an analogous non-mini-PEGylated (18)F peptide. Assessment of water-soluble peptide pharmacokinetics and tumour-targeting capabilities in a mouse model of prostate cancer is currently underway.

Poster - Thur Eve - 15: Production and assessment of astatine-211 for targeted alpha therapy

Biologically-targeted alpha-particle radiation is the basis of new and promising treatments for eliminating disseminated micrometastases and the residual microscopic malignancies that remain after surgery or radiation therapy. The short-range alpha-particles are highly cytotoxic and capable of inactivating single, isolated cancer cells which may otherwise cause recurrence. Astatine-211 is a promising alpha emitter for therapy; the 7.2 hour half-life of ²¹¹ At provides sufficient time for biological-targeting to take place. However, this radionuclide is in short supply and future treatment strategies still require extensive preclinical evaluation. The present work aims to develop technologies that (1) increase the world-wide availability of ²¹¹ At for clinical use, and (2) assess the risks of ²¹¹ At-based therapies by quantifying the activity distributions in animal models. At TRIUMF (Vancouver, BC), the feasibility of a novel generator system for ²¹¹ At is under investigation which would allow distribution of ²¹¹ At across Canada and internationally. Briefly, a longer-lived parent radionuclide of ²¹¹ At, radon-211, would be produced and allowed to decay in containment to yield ²¹¹ At in solution. Additionally, a supplementary study is underway in collaboration with the University of Washington to evaluate the sub-organ biodistributions of astatinated targeting biomolecules, with cell-level resolution. These measurements involve high resolution quantitative alpha-particle imaging in thin tissue samples and can be done for a selection of applications (eg. lymphoma, metastatic prostate cancer, etc) using animal models. The planned alpha-camera measurements are primarily designed to predict and assess the risk of toxicity associated with ²¹¹ At-based therapies and aid in developing the future clinical applications.

Non-invasive evaluation of tumour hypoxia in the Shionogi tumour model for prostate cancer with 18F-EF5 and positron emission tomography

OBJECTIVE

To evaluate hypoxia non-invasively in androgen-dependent (AD), regressing (6-days after castration, RG) and androgen-independent (AI) Shionogi tumours, using the radiolabelled tracer for hypoxia, 18F-EF5, and positron emission tomography (PET).

MATERIALS AND METHODS

Groups of mice bearing AD, RG and AI Shionogi tumours were co-injected with 18F-EF5 and unlabelled EF5. The mice were imaged non-invasively with PET to examine the accumulation of 18F-EF5 in hypoxic regions of the tumour. The tumours were subsequently placed in a gamma-counter, or disaggregated for flow cytometry, to determine the levels of 18F-EF5 and the percentage of hypoxic cells present in the tumour, respectively.

RESULTS

The mean (sd) levels of hypoxia in AD Shionogi tumours decreased significantly 6 days after androgen ablation as measured by flow cytometry, from 17.1 (4.77) to 1.74 (0.46)% (P=0.003). There were no significant differences in the levels of 18F-EF5 in the tissue between AD and RG tumours using region-of-interest analysis of PET images or gamma-counting, although the differences were significant when measured by flow cytometry. However, mean (sd) levels of hypoxia in AI Shionogi tumours were significantly higher than in AD tumours regardless of the analysis method; PET, 10.5 (4.93)x10(-5)) Bq/cm2 (P=0.017), flow cytometry, 42.98 (3.35)% (P<0.001), well count, 6.81 (1.17)x10(4) and 13.1 (1.99)x10(4) cpm/g, for AD and AI tumours, respectively (P<0.001).

CONCLUSIONS

Differences in hypoxia between AD and AI, but not RG, Shionogi tumours can be detected non-invasively with 18F-EF5 and PET. As prostate tumours are hypoxic and the oxygen levels can change with androgen ablation, noninvasive imaging of hypoxia with PET and 18F-EF5 might ultimately have a prognostic and/or diagnostic role in the clinical management of the disease.

Elevation of plasma cortisol during the spawning migration of landlocked kokanee salmon (Oncorhynchus nerka kennerlyi)

Kokanee salmon (Oncorhynchus nerka kennerlyi ), a landlocked subspecies of sockeye salmon, exhibited hypothalamic-pituitary interrenal (HPI, adrenal homologue) axis activation and an increase in plasma cortisol concentration up to 639 +/- 55.9 ng/ml in association with upstream migration in the upper Colorado River even though they were not exposed to a change in salinity and lengthy migration. Kokanee salmon were collected at various stages of migration and concomitant sexual maturation. The pattern of cortisol elevation in kokanee is similar to that in ocean-run sockeye salmon (O. nerka nerka). The presence of plasma cortisol elevation in an upstream migrating, landlocked Pacific salmon suggests that stressors previously considered to cause the cortisol increase, such as long-distance migration and changes in salinity, may not be primary causes of the HPI axis activation.

Impaired adrenocortical response to stress by brown trout, Salmo trutta, living in metal-contaminated waters of the Eagle River, Colorado

Brown trout, Salmo trutta, were collected from two sites contaminated with cadmium (Cd) and zinc (Zn) and one uncontaminated site. These fish were subjected to a continuous confinement stressor in wire cages placed in the river (moderate stress) or in 5-gal. plastic buckets on land (severe stress). Plasma cortisol and corticotropin (ACTH) were determined for fish in buckets by radioimmunoassay after 0, 1, 3, 12, or 24 h of confinement. Plasma cortisol and ACTH levels of brown trout from both contaminated and uncontaminated sites initially were the same and increased with time. However, the rise in plasma cortisol was delayed significantly in fish residing in contaminated sites, even though ACTH secretion initially was elevated compared with control trout. Furthermore, secretion of cortisol and ACTH by these fish declined significantly between 3 and 24 h of confinement. Fish from the uncontaminated site responded more rapidly to confinement with increased cortisol secretion and elevated levels of ACTH and continued to exhibit elevated levels of both hormones up to 24 h of confinement. Caged fish examined after 0, 3, 12, and 24 h of confinement exhibited similar plasma cortisol responses regardless of previous exposure to metals. These results suggest that the overall response to severe, short-term confinement stress by the hypothalamo-pituitary-adrenocortical axis of fish chronically exposed to Cd and Zn was depressed and that these fish could not sustain the stress response as readily as fish living in uncontaminated water.

[18FDG in the primary staging of lung tumors. Results with a gamma camera and a 511 keV collimator]

The diagnosis of primary lung tumors requires a precise staging according to the TNM classification. In contrast to established imaging methods 18FDG describes the functional metabolic processes in the tumor tissue due to increased glycolysis. This paper describes the use of 18FDG in the primary staging of lung tumors and metastases. 44 patients were studied with a gamma camera and a 511 keV collimator. In comparison to pulmonary tumors and metastases detected by other imaging methods (107) the accumulation of 18FDG has a sensitivity of 85%, in lesions verified by histology (50) of 89%, in primary tumors (35) of 100% and in metastases (63) of 76%. As an alternative to FDG PET studies, primary staging of lung tumors is possible with a gamma camera, suitable for ECT and fitted with a 511 keV collimator.

[Nuclear medicine diagnosis of focal liver lesions]

Confirmation and exclusion of benign focal liver lesions are the main object of liver studies in nuclear medicine. Hepatobiliary sequence scintigraphy (focal nodular hyperplasia, adenoma), blood pool scintigraphy (hemangioma) and, in some cases, colloid scintigraphy are the methods most frequently employed. Receptor scintigraphy with octreopeptides, immunoscintigraphy with monoclonal antibodies, PET and gamma camera scintigraphy with 18FDG, are used to solve special diagnostic problems, particularly in oncology. A stepwise diagnostic approach needs to be used for a successful classification of focal liver lesions and an extensive knowledge of indications for additional supplementary diagnostic procedures is required.

Nuklearmedizinische Diagnostik fokaler Leberläsionen

Bestätigung und Ausschluß benigner fokaler Leberläsionen sind Hauptaufgabe der nuklearmedizinischen Leberdiagnostik. Es stehen die hepatobiliäre Sequenzszintigraphie (fokale noduläre Hyperplasie, Adenom) und die Blutpoolszintigraphie (Hämangiom), in Einzelfällen die Kolloidszintigraphie im Vordergrund. Neuere Untersuchungsverfahren wie die Rezeptorszintigraphie mit Octreopeptiden, die Immunszintigraphie mit monoklonalen Antikörpern und die 18FDG-Untersuchungen mit PET und Gammakamera sind besonderen Fragestellungen, besonders in der Onkologie, Vorbehalten. Für eine erfolgversprechende artdiagnostische Einstufung fokaler Leberläsionen sind ein schrittweises diagnostisches Vorgehen und umfassende Kenntnisse der Indikationen weiterführender diagnostischer Verfahren erforderlich.

Regional cerebral glucose metabolism in identical twins

The present study reports on the degree of similarity in regional cerebral glucose metabolism in seven sets of female identical twins. All scans were done with subjects at rest. Glucose metabolism was measured with positron emission tomography (PET). Significant intraclass correlations were found for the orbital and prefrontal cortex as well as the basal ganglia (caudate/putamen). It is suggested that these correlations reflect the functional aspects of these areas, namely attention and posturing movements.

The metabolism of [18F]6-fluoro-L-3,4-dihydroxyphenylalanine in the hooded rat

The metabolism of the positron-emitting compound [18F]6-fluoro-L-3,4-dihydroxyphenylalanine (*F-DOPA) was studied in carbidopa-pretreated male hooded rats. Thirty minutes following carbidopa administration (5 mg/kg i.p.), animals received *F-DOPA (500 micrograms/kg; specific activity, 175-230 Ci/mol) as an intrajugular bolus. Blood samples were taken at various times between 5 and 90 min, and the plasma was analyzed by HPLC with gamma counting of fractions. *F-DOPA disappeared rapidly from plasma in concert with the formation of the 3-O-methylated metabolite, Me-*F-DOPA. Animals were killed from 5 to 120 min after injection, and the brains were rapidly dissected. The disappearance of *F-DOPA from both vermis and striatal samples was rapid. Me-*F-DOPA, the sole metabolite observed in the vermis, was the major labeled material in the striatum at greater than or equal to 20 min after injection. Fluorodopamine was an important metabolite in the striatum, making up 25% of total radioactivity at early intervals. Striatal samples also contained fluoro-3,4-dihydroxyphenylacetic acid, which constituted approximately 10% of the total radioactivity, and traces of two radiolabeled compounds, tentatively identified as fluorohomovanillic acid and fluoro-3-methoxytyramine.

Positron emission tomography in the early diagnosis of Huntington's disease

We studied 10 patients with early Huntington's disease and 7 normal age-matched controls with positron emission tomography (PET) using fluorodeoxyglucose. Subjects had little or no caudate nucleus atrophy and had not received any medications. The results demonstrated that hypometabolism of glucose preceded tissue loss. Furthermore, patients with minimal neurologic or psychiatric symptoms and no obvious CT changes may be differentiated from normal persons with high accuracy by PET. PET is helpful in the early diagnosis of Huntington's disease irrespective of the mode of presentation. PET may also be useful for preclinical detection and may supplement information from DNA studies.