Radiotracer

Radionuclide imaging using (111)In, (99m)Tc and (153)Sm is commonly undertaken for the clinical investigation of gastric emptying, intestinal motility and whole gut transit. However the documented evidence concerning internal radiation dosimetry for such studies is not readily available. This communication documents the internal radiation dosimetry for whole gastrointestinal transit studies using (111)In, (99m)Tc and (153)Sm labeled formulations. The findings were compared to the diagnostic reference levels recommended by the United Kingdom Administration of Radioactive Substances Advisory Committee, for gastrointestinal transit studies.

A series of radiolabeled peptides have been designed and optimized for tumor-targeted peptide receptor radionuclide therapy (PRRT). Pre-clinical and clinical applications of PRRT have shown promising results on tumor response, overall survival, and quality of life in patients with several kinds of tumors. 90Y-DOTA-TOC and 177Lu-DOTA-TATE are two of the most common radiopharmaceuticals with symptomatic improvements and complete clinical data. In addition to somatostatin analogs, radiolabeled peptides have been developed to target the relative receptors overexpressed in the tumors, such as integrin α vβ 3, gastrin-releasing peptide receptor (GRPR), melanocortin-1 receptor (MC1-R), cholecystokinin (CCK) receptor, and glucagon-like peptide-1 receptor (GLP-1R). Several strategies have been designed to improve the therapeutic efficacy of PRRT. For instance, radiolabeled peptides could be optimized by the amino acid modification and radionuclide selection. Healthy tissue protective agents and multi-cycle procedures could effectively decrease the side effects of PRRT. Furthermore, combination treatments, including PRRT combined with surgery, chemotherapeutic agents, or radiosensitizing agents could be applied to increase the effectiveness of PRRT. In this review, the current progress of peptide-based radiopharmaceuticals for tumor-targeted PRRT was summarized. Radiopharmaceuticals currently under clinical investigation were also described.

Simultaneous measurements of airborne radionuclides 7Be and 210Pb, together with aerosol mass load PM10, have been routinely carried out at the Global WMO-GAW station of Mt. Cimone (Italy, 2165m a.s.l., 44° 12' N, 10° 42' E) from 1998 to 2011. The experimental activity was started with the purpose of gaining a better understanding of the vertical and horizontal transports taking place at this site affecting the atmospheric chemical composition. The time series of the collected data is presented and discussed in this paper. The 7Be concentrations in this period are in the range 0.05-15.8mBqm-3 with the presence of two distinct relative maxima during winter/spring and summer, suggesting an origin from different physical processes. The 210Pb concentrations collected during the period are in the range 0.05-2.30mBqm-3 and are characterized by a single maximum during the warm period. The 7Be/210Pb ratio was in the range 0.5-127.8 and is characterized by a maximum during the cold period. The frequency distributions of the three parameters and the seasonal/interannual variabilities are investigated and presented.

The present paper deals with the characterization of ion exchange resins Dowex 550A LC and Indion-930A based on kinetics of ion-isotopic exchange reactions for which the short lived radioactive isotopes 131 I and 82 Br were used as a tracers. The study was performed for different concentration of ionic solution varying from 0.001 mol/L to 0.004 mol/L and temperature in the range of 30.0 °C to 45.0 °C. The results indicate that as compared to bromide ion-isotopic exchange reaction, iodide exchange reaction take place at the faster rate. For both the ion-isotopic exchange reactions, under identical experimental conditions, the values of specific reaction rate increases with increase in the ionic concentration and decreases with rise in temperature. It was observed that at 35.0 0 C, 1.000 g of ion exchange resins and 0.002 mol/L labeled iodide ion solution for iodide ion-isotopic exchange reaction, the values of specific reaction rate (min-1), amount of ion exchanged (mmol), initial rate of ion exchange (mmol/min) and log K d were 0.270, 0.342, 0.092 and 11.8 respectively for Dowex 550A LC resin, which was higher than the respective values of 0.156, 0.241, 0.038 and 7.4 as that obtained for Indion-930A resins. From the results, it appears that Dowex 550A LC resins show superior performance over Indion-930A resins under identical experimental conditions.

The present study analyses the peak 210Pb activity concentrations observed all over the 1998-2011 period at the WMO-GAW high altitude site of Mt. Cimone (44.18N, 10.7E, 2165masl; Italy) in terms of meteorological conditions, links with other atmospheric species and population dose rate associated with this radiotracer. The highest 210Pb events mainly occurred in the warm period and were associated with prolonged anticyclonic conditions, high temperatures, and low relative humidity values. A correlation with the seasonal pattern of the mixing height was also observed, suggesting the importance of thermal convection promoting uplift of warm air from the atmospheric boundary layer (ABL), transporting high concentrations of 222Rn and thus 210Pb. The main sources of high 210Pb concentrations were identified by means of clusters of back-trajectories applied at three different heights. Sources located at east (central Europe), at west (Spain and France) and south (northern Africa) of Mt. Cimone were distinguished. The clusters obtained at the three heights were compared in order to study the extent between ABL and free troposphere during the highest 210Pb events: a wide influence of the strong coupling among atmospheric vertical layers on 210Pb activity concentrations increases was demonstrated. The annual effective dose from the potential inhalation of this radionuclide during the peak concentration episodes was also calculated. The average dose increase during the selected events represents only a small fraction of the total dose from all sources; these results are nevertheless useful for providing information on natural background dose contribution from inhalation which is required for the accurate assessment of dosimetric conditions in the case of nuclear emergencies.

The author discusses the feasibility of PET measurements of rHct using 68Ga-labelled plasma albumin and 15O- or 11C-labelled red blood cells, administered either simultaneously or sequentially. The effects of regional cerebral haematocrit, amount of administered radioactivity and the timing and duration of PET scans on measurement error are examined. The radiation dose to various organs resulting from several protocols estimated and compared. The consideration of both absorbed radiation dose and effects of protocol on measurement errors are generally applicable to any physiological measurements requiring determination of more than one parameter.

ABSTRACT In the phosphoric acid production process, the time a particle spends inside the chemical reactor (residence time) is of paramount importance to process engineers. Residence time distribution (RTD) gives information on the efficiency of the chemical reactor, on the efficiency of the process, and also the availabilities of the reactive volume for the reaction (active volume vs. dead volume). Traditionally, chemical engineers used chemical tracer to determine the RTD. However, first disadvantage is that the chemical tracer could not allow an online diagnosis: the samples containing chemical tracer have to go to a lab for analysis, second disadvantage is that the chemical tracer is less sensitive than radioactive ones because of its adsorption onto strata or its retention in rocks. Consequently, chemical tracer results are not always precise and cannot convincingly explain the multiple flow-path model. Radioactive tracers are the only tracers capable of measuring the active RTD with high degree of precision and give information on the internal recirculation rate. In this work, we will describe the application of radiotracer method for RTD measurement in the phosphoric acid production process and give results and discussion of each case encountered.

Positron Emission Tomography (PET) is a powerful imaging technique exploring in vivo brain functions. Today PET is becoming an essential tool in specialist clinical neurology settings particularly for diagnosing Alzheimer’s, Parkinson’s and epilepsy disease states. This inaugural article aims to deliver a brief insight into PET techniques in the diagnosis of neurological diseases including multiple sclerosis.

Example question: An investigator starts with 300 mCi of fluorine-18 (half-life 109.7m) to prepare a radiotracer. The radiotracer synthesis was completed in 94 minutes. The reaction conversion was 74%. How much fluorine-18 product will be produced at the end of the synthesis?

The present paper deals with application of short-lived radiotracer isotopes to understand the performance of Purolite NRW-5050 (nuclear grade) and Indion-870 (non-nuclear grade) anion exchange resins. The performance evaluation was done based on thermodynamics of iodide and bromide ion-isotopic exchange reactions. It was observed that for Purolite NRW-5050 resins during the bromide ion-isotopic exchange reaction, the enthalpy and energy of activation values calculated were 3287.8 and 5869.3 J.mol −1 respectively, which were less than the respective values of 8486.7 and 11068.2 J.mol −1 obtained for the same reaction using Indion-870 resins. The identical trend was observed for the two resins during the iodide ion-isotopic exchange reaction. The thermodynamic data suggest that Purolite NRW-5050 resins were more efficient than Indion-870. This was further confirmed from the fact that for 0.003M iodide ion solution, as the temperature of solution increases from 30.0 to 45.0 ° C, the percentage of iodide ions exchanged increases from 82.80 to 78.00% using Purolite NRW-5050 resins and from 51.45 to 48.32% using Indion-870 resins. Similarly, when the temperature of ionic solution was kept constant at 40.0 ° C, as the concentration of labeled iodide ion solution increases from 0.001 to 0.004 mol/L, the percentage of iodide ions exchanged increases from 76.44 to 80.90% using Purolite NRW-5050 resins and from 45.80 to 51.05% using Indion-870 resins. The overall results of the present investigation reveal superior performance of Purolite NRW-5050 over Indion-870 resins under identical experimental conditions.

Although the [18F]-2-fluoro-2-deoxyglucose positron emission tomographic technique for measuring regional glucose metabolic rate has been successfully employed for neurobehavioral studies, the long (>30 min) equilibration time required may complicate the interpretation of experimental results. Positron emission tomography neurobehavioral protocols employing the continuous inhalation of CO15O and 19Ne were developed for measuring regional cerebral blood flow during multiple control and stimulation periods. Timing, lung absorbed dose, statistical accuracy, and resolution were considered. Studies with 19Ne require shorter equilibration and stimulation times than do CO13O studies but entail higher absorbed doses and yield poorer imaging statistics.

The aim of this work was to study the absorption, distribution through the hemolymph, and bioaccumulation of arsenic by the freshwater Pomacea canaliculata using a short-lived tracer (76As, t1/2: 1.07 d) with high specific activity. Arsenic travels mainly dissolved in the plasma of the snail's hemolymph. This element is transferred from the hemolymph to the tissues (87%) 4  after the inoculation of 50 μL of a 0.04 g/L of 76As radiotracer solution, being the digestive gland, kidney, and head-foot the main places of arsenical inventories. Snails exhibited a rapid arsenic accumulation response in a wide range of concentrations (from 1 to 1000 μg/L) of the metalloid dissolved in water and in a concentration-dependent manner. Also, snails incorporated As from the digestive system when they received a single safe dose of ~2 μg of 76As inoculated in a fish food pellet. The (semi) physiologically based toxicokinetic model developed in this study is based on anatomical and physiological parameters (blood flow, irrigation, tissue volume and other). Together, these findings make P. canaliculata an excellent sentinel organism to evaluate freshwater bodies naturally contaminated with As.

Regional cerebral blood volume and blood flow may be determined using PET and C15O, 11CO, and CO15O. Detailed estimates of radiation absorbed dose for 22 organs and the whole body are reported and compared for these gases administered by continuous or bolus inhalation and by infusion techniques.