Standardization of (18)F using the 4pi(beta+gamma) integral counting technique.

Α 4π(β+γ) integral counting technique using a 4πβ−4πγ detector configuration was adopted for the standardization of ¹⁸F. In this technique, the β-detector is composed of two thin plastic scintillators sandwiching the source, coupled with a slender photomultiplier tube. The β-detector part with the source was inserted into a large well-type NaI(Tl) scintillation detector for γ-ray detection, making a 4πβ−4πγ coincidence counting system. In this work, positron particles were detected with high efficiency in the β-channel and annihilation quanta were also detected with high efficiency in the 4πγ channel. The very small inefficiency of the 4π(β+γ) integral counter for the β-plus branch has been confirmed by EGS5 Monte Carlo simulation. The result using this technique agreed within the uncertainties with the result obtained by the conventional 4πβ−γ coincidence counting with the efficiency extrapolation technique using the same detector configuration and a conventional 4πβ−γ coincidence counter.     

The efficiency variation method for 4pibeta-gamma coincidence counting by ink-jet printing.

In order to vary the counting efficiencies in the 4πβ−γ coincidence extrapolation technique, a radioactive source was coated directly with varying amounts of an electrical conducting pigment using an ink-jet printer. This method can be used to efficiently prepare the multiple sources needed to generate efficiency extrapolation curves, and was successfully applied to the standardization of a ⁵⁴Mn source.     

Standardisation of Co and Co using software coincidence counting system

Activities of the radionuclides ⁵⁶Co and ⁵⁷Co were determined by the efficiency extrapolation method applied to 4π(PC)-γ coincidence counting. Solutions of ⁵⁶Co usually contain a significant amount of ⁵⁷Co and ⁵⁸Co, so the measured activity of ⁵⁶Co requires correction. When the conventional coincidence method is used for ⁵⁶Co standardisation, the corrections are derived from the dependence of Proportional Counter (PC) detection efficiencies for ⁵⁷Co and ⁵⁶Co measured using sources with mixture of ⁵⁶Co and ⁵⁷Co, which is complicated. These difficulties were reduced by means of a software coincidence method, with a HPGe detector in gamma channel, where the detection efficiencies were evaluated directly from the records of coincidence measurements of standardised sources. In the case of ⁵⁷Co standardisation, the software coincidence counting system was applied for the evaluation of optimal setting of coincidence parameters. The results obtained by software coincidence counting system were compared with those obtained by the conventional coincidence method.     

Application of “wet” extrapolation method for activity standardisation of electron capture radionuclides

The activity of electron capture radionuclides is usually determined by 4π(proportional counter, PC)–γ coincidence counting. The corrections necessary for the final activity value calculation are obtained by an extrapolation method. Variation of the PC detection efficiency can be achieved through different methods, e.g. by changing the self-absorption of the source using absorbing foils or by adding carriers. Another possibility is a “wet” extrapolation method, which utilises an absorption change during the drying of a water droplet added onto the source surface. In this paper, slopes of extrapolation curves and resulting activity values obtained by different methods are compared for several radionuclides (⁵⁴Mn, ¹³⁹Ce, ⁸⁸Y, ⁵⁷Co). In some cases a digital coincidence system was used for the analysis of measured data. The “wet” extrapolation, due to its very simple procedure, seems to be convenient for routine measurement and its accuracy is similar to the other methods.     

A liquid-scintillation-based primary standardization of Pb

A new radioactivity solution standard of ²¹⁰Pb has been developed and will be disseminated by the National Institute of Standards and Technology (NIST) as standard reference material (SRM) 4337. This new ²¹⁰Pb solution standard is contained in a 5 mL flame-sealed borosilicate glass ampoule, consists of (5.133±0.002) g of a nominal 1 mol L⁻¹ nitric acid solution, has a density of (1.028±0.002) g mL⁻¹ at 20 °C, has carrier ion concentrations of about 11 μg Pb²⁺ and 21 μg Bi³⁺ per gram of solution, and is certified to contain a massic activity (9.037±0.22) kBq g⁻¹ as of the reference time 1200 EST, 15 June 2006. All of the uncertainties cited above correspond to standard uncertainties multiplied by a coverage factor k=2. The standardization for the ²¹⁰Pb content of the solution was based on 4πβ liquid scintillation (LS) measurements using CIEMAT/NIST ³H-standard efficiency tracing (CNET). Confirmatory determinations were also performed by high-resolution HPGe γ-ray spectrometry, by 2π spectrometry with a Si surface barrier detector of separated ²¹⁰Po, and by 4πβ(LS)–γ(NaI) anticoincidence counting.     

Determination of emission probabilities of gamma photons in the decay of Co

The emission probabilities of gamma photons in the decay of ⁵⁶Co were determined at Czech Metrology Institute (CMI) by means of an HPGe detector. This detector was calibrated experimentally and by MCNP-computation in the energy range from 40 to 2754 keV for a point source geometry and source-to-detector distance of 25 cm. Experimental and computed peak and total efficiencies were compared and calibration curves were determined. Full-peak efficiencies were calculated for all ⁵⁶Co γ-ray energies, and were used to calculate the emission probabilities. A set of point sources was prepared from a ⁵⁶Co solution. The solution was standardized using the 4πβ–γ coincidence method, and an ampoule was sent to international reference system for activity measurement of γ-ray emitting radionuclides (SIR). Each point source was measured with the HPGe detector at a source-to-detector distance of 25 cm. Coincidence emission probabilities of all the gamma photons were calculated and used to determine the summing correction factors.     

Standardization of Fe by tracing method

This work describes the procedure followed by the Laboratório de Metrologia Nuclear (LMN) for the standardization of ⁵⁵Fe by the tracing method. This technique was applied using two radionuclides, which decay by the electron capture process followed by a prompt gamma-ray, namely ⁵¹Cr and ⁵⁴Mn, as tracers. The calibration was performed in a 4πβ–γ coincidence system. The efficiency was obtained by selecting a gamma-ray window set at the 320 keV total absorption peak for ⁵¹Cr and at 834 keV for ⁵⁴Mn.     

Disintegration rate measurement of Ta

Measurement of the activity of ¹⁸²Ta sources produced by irradiation at the IPEN research reactor was performed in a 4πβ−γ coincidence system by using the extrapolation technique. The measurements were undertaken selecting two windows in the γ-channel, in order to check the consistency of the results. A Monte Carlo calculation was performed in order to predict the behavior of the observed activity as a function of the 4πβ detector efficiency and the results were compared with experimental values.     

[Dy]Dy/Ho hydroxide macroaggregates: an in vivo generator system for radiation synovectomy

Radiation synovectomy is an effective treatment in patients suffering from inflammatory-rheumatoid and degenerative joint diseases. The aim of this work was to examine the feasibility of preparing dysprosium-166 (¹⁶⁶Dy)/holmium-166(¹⁶⁶Ho) hydroxide macroaggregates ([¹⁶⁶Dy]Dy/¹⁶⁶Ho-HM) as an in vivo generator for radiation synovectomy evaluating whether the stability of ¹⁶⁶Dy-HM and ¹⁶⁶Ho-HM complexes is maintained when the daughter ¹⁶⁶Ho is formed. The Monte Carlo (MCNP4B) theoretical depth dose profile for the in vivo [¹⁶⁶Dy]Dy/¹⁶⁶Ho generator system in a joint model was calculated and compared with that produced by ⁹⁰Y, ¹⁵³Sm and ¹⁶⁶Ho. ¹⁶⁶Dy was obtained by neutron irradiation of enriched ¹⁶⁴Dy₂O₃ in a Triga Mark III reactor. Macroaggregates were prepared by reaction of [¹⁶⁶Dy]DyCl₃ with 0.5 M NaOH in an ultrasonic bath. [¹⁶⁶Dy]Dy/¹⁶⁶Ho-HM was obtained with radiochemical purity >99.5% and with the majority of particles in the 2–5 μm range. In vitro studies demonstrated that the radio-macroaggregates are stable in saline solution and human serum without a significant change in the particle size over 14 d, suggesting that no translocation of the daughter nucleus occurs subsequent to β⁻ decay of ¹⁶⁶Dy. Biological studies in normal rats demonstrated high retention in the knee joint even 7 d after [¹⁶⁶Dy]Dy/¹⁶⁶Ho-HM administration. The Monte Carlo (MCNP4B) theoretical depth dose profiles in a joint model, showed that the in vivo [¹⁶⁶Dy]Dy/¹⁶⁶Ho generator system would produce 25% and 50% less radiation dose to the articular cartilage and bone surface, respectively, than that produced by ⁹⁰Y or pure ¹⁶⁶Ho in a treatment with the same therapeutic dose to the synovium surface. Despite that ¹⁵³Sm showed the best depth dose profile sparing doses to healthy tissues, the use of ¹⁶⁶Dy could provide the advantage of being applied in patients that cannot be reached within a few hours from a nuclear reactor and to produce less radiation exposure to the medical personnel during the radiopharmaceutical administration.     

Standardization of I by the coincidence method and practical applications

A new coincidence system, based on two thin NaI(Tl) crystals, 50×2 mm², with beryllium windows, 1.5 mg cm⁻², positioned approximately symmetrically from the source holder (at various distances) was constructed. The electronic chains of a classical 4πPC–γ system were utilized. A multichannel analyzer was employed for energy calibration, and an oscilloscope for visualization of the pulses. After calibration, the system was used for the standardization of an ¹²⁵I solution. An energy window of 12–95 keV containing the entire spectrum (single and sum peak) was employed, and a simple demonstration of Taylor's equation [1967. X-ray–X-ray coincidence counting methods for the standardization of ¹²⁵I and ¹⁹⁷Hg. In: Standardization of Radionuclides: Proceedings of a International Atomic Energy Agency Symposium, Vienna, 1966, pp. 341–353, SM-79/65] for whole spectrum counting, was developed. The method and system were tested during the calibration of a LKB 2104 multi-gamma counter, by comparing the detection efficiency values obtained for this prepared standard solution and that utilized in the CIPM-CCRI(II) key comparison. The efficiency of the equipment was calculated as the mean of the two individual values. The result validates the method and demonstrates the accomplishment of the national traceability assurance in nuclear medicine for ¹²⁵I.     

Activity standardization of Na

The activity of a ²²Na solution was measured by means of two 4πβ−γ coincidence-counting techniques. The first method corresponds to the classical 4πβ−γ coincidence counting and requires the β⁺-branching ratio. The second procedure is based on a variation of the distance between source and gamma detector. The efficiency for detecting the sum peak is then extrapolated to zero, giving the total source activity. The combination of both methods yields the β⁺ branching ratio. In addition, liquid scintillation counting using the CIEMAT/NIST-method as well as a secondary standardization by means of calibrated ionization chambers were used for activity determination. The results were checked for consistency and an ampoule was submitted to the BIPM to have the activity result entered into the database of the International Reference System (SIR).     

Production of Ho through Dy(n,γ)Dy(n, γ)Dy(β)Ho and separation of Ho

After irradiation with thermal neutrons ¹⁶⁴Dy produces ¹⁶⁶Ho through the nuclear reaction: ¹⁶⁴Dy(n,γ) ¹⁶⁵Dy(n,γ) ¹⁶⁶Dy ¹⁶⁶Ho. ¹⁶⁶Ho has been separated from the bulk dysprosium target with the help of HPLC using Aminex A7 ion exchanger resin and -hydroxyisobutyric acid (-HIBA) as the mobile phase. The separation was quantitative and without any contamination from the dysprosium target. Method has also been developed to produce holmium free of -HIBA ligands. Attempts have been made to produce no-carrier-added recoiled ¹⁶⁶Ho and ¹⁶⁵Dy in water.     

Optimization of a coincidence system using plastic scintillators in 4pi geometry.

Improvements recently developed at the Nuclear Metrology Laboratory of IPEN-CNEN/SP in São Paulo were performed in order to increase the detector efficiency of a 4πβ−γ coincidence primary system using plastic scintillators in 4π geometry. Measurements were undertaken and compared to the original system and Monte Carlo simulations of the extrapolation curves were calculated for this new system and compared to experimental results. For this purpose, the code Penelope was applied for calculating response functions for each detector and the code Esquema, developed at LMN, was used for simulating the decay scheme processes.     

Facile synthesis of bis(hydroxamamide)-based tetradentate ligands for Tc-radiopharmaceutical

A facile, two-step synthesis of the bis(hydroxamamide)-based tetradentate ligands for ^99mTc-radiopharmaceuticals is described. Firstly, the hydroxamamide was converted to hydroximic acid chloride by reaction with sodium nitrite in hydrochloric acid at 0 °C. Secondly, treating the halide with the ethylenediamine or 1,3-propylenediamine in absolute ethanol formed the desired products, N,N′-ethylene bis(1-(4-nitroimidazole-1-yl)–propan-hydroxyiminoamide) (I) and N,N′-propylene bis(1-(4-nitroimidazole-1-yl)-propanhydroxyiminoamide) (II). The corresponding ^99mTc complexes showed high yields and were found by paper electrophoresis to be electrically neutral under physiological conditions. The partition coefficients indicated a distinct difference between the two complexes.     

A re-evaluation of k0 and related nuclear data for the 555.8 keV gamma-line emitted by the Rh-Rh mother–daughter pair for use in NAA

A re-evaluation is made of the k₀-factor and related nuclear data for the 555.8 keV gamma-ray of the ^104mRh-¹⁰⁴Rh mother–daughter pair that are important in neutron activation analysis (NAA). This study considers that the relevant level is also fed by the 4.34 min ^104mRh mother (with an absolute gamma-ray emission probability γ₂=0.13%) and not only, as assumed in former work, by the 42.3 s ¹⁰⁴Rh daughter isotope (with γ₃=2.0%). In view of this, generalised equations were developed for both the experimental determination and the analytical use of the k₀-factor and of the associated parameters k₀(m)/k₀(g), Q₀(m) and Q₀(g) [(m):^104mRh; (g): ¹⁰⁴Rh], requiring the introduction of the γ₂ and γ₃ data and also of the ^104mRh→¹⁰⁴Rh fractional decay factor F₂(=0.9987). The experimental determinations were based on irradiations performed in the BR1 reactor in Mol and the WWR-M reactor in Budapest. Furthermore, considering the special formation of the 555.8 keV gamma-ray, the procedure for true-coincidence correction was revised as well. All this led to the compilation and recommendation of a new set of ‘k₀-NAA’ data.     

Calibration of Fe activity with a lithium-drifted silicon detector

NMIJ participated in the CCRI (II) key comparison of ⁵⁵Fe activity measurement. A planar-type Si(Li) detector and a liquid-scintillation counter were used to calibrate the activity. The calibration result obtained by the Si(Li) detector agreed with that obtained by the liquid-scintillation counter using the CIEMAT/NIST method within uncertainty. The result was reported to the BIPM in 2006. The activity of ⁵⁵Fe was also measured by using a 2π pressurized proportional counter. The result obtained by the 2π pressurized proportional counter agreed with the above results within uncertainty. The measurement by the Si(Li) detector was very simple and its procedure was a combination of conventional methods. The measurement by the liquid-scintillation counter is most popular to calibrate the activity of ⁵⁵Fe. However the Si(Li) detector is also useful.     

Further investigations of a simple counting technique for measuring mixtures of two pure beta-emitting radionuclides

A simple liquid scintillation counting technique to measure the activity composition of a mixture containing two known pure β-emitting radionuclides was recently developed at the NMISA. The method has been applied to various two-component mixtures of ³²P, ³³P and ³⁵S, primarily to gauge the effect of spectral energy differences on the method's ability to extract the individual activities. Excellent results were obtained for mixtures of ³³P and ³⁵S, radionuclides with similar, low β energies. Mixtures containing the high-energy β-emitter ³²P were more difficult to resolve, although quenching of the counting sources with CHCl₃ improved mixture resolution.     

Determination of uranium in aqueous attenuating samples using gamma-ray spectrometry

In the present work, a method for determination of uranium concentration in aqueous solution in standard geometry from attenuating samples has been developed based on modification of the empirical approach of Venkataraman and Croft [2003. Determination of plutonium mass using gamma-ray spectrometry. Nucl. Instrum. Methods Phys. Res. A 505, 527–530]. The method makes use of the multiple gamma (γ)-rays emitted by ²³⁵U and depends on the empirical relation between apparent mass of the sample and γ-ray energy. It was possible to determine uranium concentration in the range of 12–400 mg/ml rapidly by this method without applying transmission corrections.     

Observation of beta-ray spectra after penetrating absorbing materials.

β-Ray spectra after penetrating absorbing materials of various thicknesses were observed by the use of a scintillation-type β-ray spectrometer equipped with a flat NE-102 plastic scintillator of 5 mm thickness for sources of ⁶⁰Co, ⁹⁰Sr–⁹⁰Y, ¹³⁷Cs, ¹⁴⁷Pm and ²⁰⁴Tl. Although the spectra changed rapidly with increasing absorber thickness, the average β-ray energy was kept nearly constant for a wider range. These results are consistent in that the β-ray absorption curve becomes quasi-linear in a semi-logarithmic plot. Spectra including scattered β-rays from several materials placed behind the source were also measured for ¹³⁷Cs and ²⁰⁴Tl. It may be concluded that mean energy measurements by the use of β-ray spectrometer of this kind is useful for the identification of nuclides in radiation protection purposes even in worse source-conditions.     

Evaluation of novel cationic 99mTc(I)-tricarbonyl complexes as potential radiotracers for myocardial perfusion imaging

This report describes the evaluation of three cationic ^99mTc(I)–tricarbonyl complexes — [^99mTc(CO)₃(L)]⁺ (L=N-methoxyethyl-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (ME-PNP), N-[15-crown-5)-2-yl]-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (15C5-PNP) and N-[18-crown-6)-2-yl]-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (18C6-PNP)) — as potential radiotracers for myocardial perfusion imaging. Biodistribution, imaging and metabolism studies were performed using Sprague–Dawley rats. It was found that bisphosphine ligands have a significant impact on the biodistribution characteristics and clearance kinetics of their cationic ^99mTc(I)–tricarbonyl complexes. Among the three radiotracers evaluated in this study, [^99mTc(CO)₃(15C5-PNP)]⁺ has a very high initial heart uptake and is retained in the rat myocardium for >2 h. It also shows rapid clearance from the liver and lungs. The heart/liver ratio of [^99mTc(CO)₃(15C5-PNP)]⁺ is 2.5 times better than that of ^99mTc-sestamibi at 30 min postinjection. [^99mTc(CO)₃(15C5-PNP)]⁺ is almost identical to ^99mTcN-DBODC5 with respect to heart uptake, heart/lung ratio and heart/liver ratio. Results from metabolism studies show that there is no significant metabolism for [^99mTc(CO)₃(15C5-PNP)]⁺ in the urine, but it does show a small metabolite peak (<10%) in the radio high-performance liquid chromatography chromatogram of the feces sample at 120 min postinjection. Results planar imaging studies demonstrate that [^99mTc(CO)₃(15C5-PNP)]⁺ has a much better liver clearance profile than ^99mTc-sestamibi and might give clinically useful images of the heart as early as 30 min postinjection. [^99mTc(CO)₃(15C5-PNP)]⁺ is a very promising candidate for more preclinical evaluations in various animal models.