Improving the sensitivity of radionuclide particulate monitoring stations

A worldwide radionuclide network of 80 stations, part of the International Monitoring System, is being setup to monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The radioactivity sampled at these stations is primarily ²²⁰Rn progenies. Using the knowledge of the diurnal change of the ²²⁰Rn progeny ²¹²Pb the sampled activity at the end of the sampling process can be minimised by choosing the right collection start time. It is shown that improvements of several percents in the minimum detectible concentration (MDC) for CTBT relevant nuclides can be achieved.     

A ultra low level laboratory for nuclear test ban measurements.

The radionuclide laboratory at the Austrian Research Centers Seibersdorf (ATL03) was installed to support the international monitoring system for verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT and Text of the establishment of a Preparatory Commission for the Comprehensive Test-Ban-Treaty Organization, 1996). Therefore, the background of a high-purity germanium detection system has been reduced by developing a high sophisticated active and passive detector shielding. The entire system is encapsulated in an iron-castle and placed into a fall-out shelter. The final count rate, achieved over the energy interval from 40 to 2700 keV, amounts to 0.18 counts s(-1) kg(-1) (Ge).     

Use of the reference source method to determine the half-lives of radionuclides of importance in nuclear medicine.

The reference source method associated with HPGe gamma-ray spectrometric techniques has been applied to half-life determinations of radionuclides used in nuclear medicine. Simultaneous measurements were undertaken for radiopharmaceutical nuclides such as 67Ga, 99Tcm, 123I, 131I and another radionuclide as reference. Besides optimizing the analysis time, this procedure was shown to be independent of the instrumental technique, environmental and radiochemical impurity interferences for most radionuclides. However, some restrictions were observed in samples that contained impurities with the same emission energy or an energy that was very close to the energy of the radionuclide to be measured. The measurement conditions improved the quoted accuracy of the half-life by reducing the type B component uncertainty.     

Intercomparison experiments of systems for the measurement of xenon radionuclides in the atmosphere

Radioactive xenon monitoring is one of the main technologies used for the detection of underground nuclear explosions. Precise and reliable measurements of ^131mXe, ^133gXe, ^133mXe, and ^135gXe are required as part of the International Monitoring System for compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). For the first time, simultaneous testing of four highly sensitive and automated fieldable radioxenon measurement systems has been performed and compared to established laboratory techniques. In addition to an intercomparison of radioxenon monitoring equipment of different design, this paper also presents a set of more than 2000 measurements of activity concentrations of radioactive xenon made in the city of Freiburg, Germany in 2000. The intercomparison experiment showed, that the results from the newly developed systems agree with each other and the equipment fulfills the fundamental requirements for their use in the verification regime of the CTBT. For 24-h measurements, concentrations as low as 0.1 mBq m⁻³ were measured for atmospheric samples ranging in size from 10 to 80 m³. The ¹³³Xe activity concentrations detected in the ambient air ranged from below 1 mBq m⁻³ to above 100 mBq m⁻³.     

Measurement of the activity of 11C and 22Na sources using a 4pi-beta-gamma coincidence system.

Many radiation applications, including positron emission tomography (PET) studies and activation dosimetry, require the knowledge of the activity of short-lived radionuclide samples, whereas relative measurements may be hampered by the absence of a reference source. Using 11C radionuclide as an example, an analytical model based on a probabilistic approach has been set up to predict the activity of a pure positron emitter measured using the 4pi-beta-gamma coincidence technique. The model has been extended to describe the measurement on a 22Na source used to test the measurement technique. Comparison of the modeled results with the measurements confirms the general validity of the model. The model has also been studied for the effect of the variation of key measurement conditions, such as nominal source activity, detector efficiency, detector background levels, and coincidence resolving time. The 4pi-beta-gamma coincidence technique and the results of modeling allow the activity measurements on 22Na and 11C sources with an estimated relative standard uncertainly on the order of one percent.     

Estimation of ascitic fluid volume using 99Tcm labelled macroaggregated albumin

We have assessed the usefulness of a radionuclide dilution method for estimation of ascitic fluid volume. 99Tc(m) macroaggregated albumin (10 MBq) was injected into the peritoneal fluid. Multiple samples were taken using a trocath peritoneal dialysis catheter over a 4-h period. Blood samples were taken at the same time and a 4-h urine collection was made during the study. At 4 h a controlled drainage of ascitic fluid, followed by suction drainage, was used and a total drained volume measured. For comparison, peritoneal volumes were measured from the radioactivity of peritoneal fluid activity samples using dilution techniques. The estimated peritoneal fluid volume using the radionuclide method was consistently higher than the drained volume. This was attributed to either a lack of uniform distribution of the activity in the peritoneal cavity by 4 h or early breakdown and absorption of activity from the peritoneal cavity. In two patients it was not possible to measure a volume due to poor distribution of the radionuclide in the peritoneal fluid. We found that in our group of patients the radionuclide dilution is of little value in estimating the peritoneal fluid volume.     

Distribution coefficients (Kd's) for use in risk assessment models of the Kara Sea.

As a prerequisite for most evaluations of radionuclide transport pathways in marine systems, it is necessary to obtain basic information on the sorption potential of contaminants onto particulate matter. Kd values for use in modeling radionuclide dispersion in the Kara Sea have been determined as part of several international programs addressing the problem of radioactive debris residing in Arctic Seas. Field and laboratory Kd experiments were conducted for the following radionuclides associated with nuclear waste: americium, europium, plutonium, cobalt, cesium and strontium. Emphasis has been placed on two regions in the Kara Sea: (i) the Novaya Zemlya Trough (NZT) and (ii) the mixing zones of the Ob and Yenisey Rivers (RMZ). Short-term batch Kd experiments were performed at-sea on ambient water column samples and on samples prepared both at-sea and in the laboratory by mixing filtered bottom water with small amounts of surficial bottom sediments (particle concentrations in samples = 1-30 mg/l). Within both regions, Kd values for individual radionuclides vary over two to three orders of magnitude. The relative particle affinities for radionuclides in the two regions are americium approximately equal to europium > plutonium > cobalt > cesium > strontium. The values determined in this study agree with minimum values given in the IAEA Technical Report [IAEA, 1985. Sediment Kd's and Concentration Factors for Radionuclides in the Marine Environment. Technical Report No. 247. International Atomic Energy Agency, Vienna.]. Given the importance of Kd's in assessments of critical transport pathways for radionuclide contaminants, we recommend that Kd ranges of values for specific elements rather than single mean values be incorporated into model simulations of radionuclide dispersion.     

Inhomogeneous deposition of radiopharmaceuticals at the cellular level: experimental evidence and dosimetric implications

We have undertaken an experimental examination of the conventional internal dosimetry assumptions of homogeneity of radionuclide deposition in tissues. The distribution of radiolabeled Microlite has been quantitated in mouse liver at the millimeter (multicellular) and the micrometer (cellular) levels. Measurements of radioactivity in 1-mm3 tissue samples indicate homogeneous radionuclide distribution; those derived from autoradiographs of 0.5-micron tissue sections show that, relative to other cells, the colloid was concentrated 200- to 1000-fold in liver macrophages. The dosimetric implications of such inhomogeneous radionuclide distribution in human liver, where similar radionuclide distribution is expected, are discussed on the basis of a recently developed model for calculating the dose at the cellular level, and the estimates are compared to conventional internal dosimetry predictions. It is demonstrated that during routine diagnostic examinations with 99mTc-Microlite, conventional dosimetry underestimates the dose to labeled human liver cells by factors of 8-30.     

Pre-operative radionuclide localization of intracerebral lesions: a five-year experience

Intracerebral lesions demonstrated by computerized tomography usually require histological confirmation to determine subsequent management. Tissue samples are generally obtained by craniotomy or burr hole biopsy; either procedure can prove negative if a lesion is small, deep, or very superficial. Pre-operative imaging and localization reduce biopsy failures. Before the introduction of this straight forward radionuclide technique, our biopsy success rate using conventional localization methods was 88%. In a 5-year period, 200 patients underwent pre-operative radionuclide localization, with an improvement in the overall biopsy success rate to 92.7% (95.5% for lesions which took up radionuclide). Patients have benefitted from reduced operating time and improved post-operative recovery rates. About 85% of all intracerebral lesions may be expected to accumulate radionuclide. However in our series, 93.2% were sufficiently well visualized for a siting marker to be placed with confidence. Within this group, low grade astrocytomas (Kernohan Grades I and II) showed a predictably low incidence of imaging (30.8%). For the majority of lesions which present difficulties in biopsy due to size or site, the radionuclide method is a simple procedure which increases the chance of obtaining positive tissue with the minimum of surgical intervention.     

Radionuclide accumulation in near-shore sediments along the Bulgarian Black Sea coast

The accumulation of radionuclides in Black Sea marine ecosystems was investigated by low level gamma spectrometry. Artificial as well as natural radionuclides were determined in bottom sediments samples from 35 reference locations along the Bulgarian Black Sea coast, evenly distributed from the Rumanian to the Turkish border including the main Black Sea resorts and rivers. The measurement of radionuclides in sea bed sediments was carried out during six consecutive seasons using a HPGe detector. The data obtained show that the nuclide concentrations depend strongly on the sediment nature. Results for sandy sediments are within close range, while those for slime and silt vary to a much greater extent. The radionuclide content in the sandy sediments of the main Black Sea resorts is at the lowest limit of the determined values. Small seasonal changes of radionuclide concentration in sandy sediments were observed while greater variations in slime and silt occur. From the data obtained ¹³⁴Cs/¹³⁷Cs and ¹³⁷Cs_meas/¹³⁷Cs_Chern ratios are calculated to determine the Chernobyl part of the measured ¹³⁷Cs. The activities determined in the sediments for natural radionuclides correspond to those cited in the literature for natural levels, showing no additional anthropogenic contamination. A data base for the nuclide concentration values was created which will enable the modeling of radionuclide transfers by estimation of their concentration variations, accumulation and influence on the marine ecosystems.     

CT renal planimetry: effectiveness in the evaluation of individual renal function.

Computed tomographic (CT) renal planimetry was used to study individual renal function in 32 adult patients with urologic disease. CT results were well-correlated to reference methods (r = 0.88, P < 0.001), which were radionuclide studies (N = 9) or separate creatinine clearance (N = 23). The difference between planimetric data and reference methods did not exceed 14% in any case and was less than 10% in 26 cases.     

Validity of tissue paste standards for quantitative whole-body autoradiography using short-lived radionuclides

A method of preparing radioactive standards for quantitative whole-body autoradiography (WBARG) using short-lived radionuclides is described and evaluated. Radioactive standards were prepared from bovine brain paste which was mixed with serial dilutions of the radionuclide being studied. Homogeneous distribution of the radionuclide in the brain paste was verified by direct counting and autoradiographic techniques. In addition, there was good agreement between the amounts of radioactivity obtained from quantitative WBARG and tissue counting in all of the major tissues sampled. Therefore, this method is effective for quantitative analysis of WBARG using short-lived radionuclides, for which permanent reference standards are unavailable.     

Determination of radium-226 in environmental and personal monitoring samples.

Radium-226 is a member of the Uranium-238 natural decay series and is the most hazardous radionuclide released to the environment from uranium mining and milling. Due to its long half-life (1600 years) and radiological effects it is one of the most important isotopes to be determined among the naturally occurring nuclides in environmental samples. It is also among the most toxic long-lived alpha-emitters present in environmental samples, as well as one of the most widespread. The requirement for the determination of radium has become a matter of interest in public health due to its hazardous nature with respect to internal exposure. It is concentrated in bones, thus increasing the internal radiation dose of individuals. The methodology developed involves dissolving solid samples by microwave digestion. The radium is then separated from matrix interferents by cation exchange chromatography and subsequently electrodeposited onto a stainless steel disc. Alpha-Spectrometry is employed to determine the activity in the sample. A limit of detection of 20 mBq l(-1) for ground water samples (100 ml) and 20 mBq g(-1) for solid samples (0.1 g) is achievable. The method has been validated via an intercomparison exercise and analysis of a marine sediment reference material. Samples analysed include run off waters from uranium mines, coal and fly ash and also trapping media such as silica gel, charcoal and activated carbon.     

Verifying the operational set-up of a radionuclide air-monitoring station.

A worldwide radionuclide network of 80 stations, part of the International Monitoring System, was designed to monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty. After installation, the stations are certified to comply with the minimum requirements laid down by the Preparatory Commission of the Comprehensive Nuclear-Test-Ban Treaty Organization. Among the several certification tests carried out at each station, the verification of the radionuclide activity concentrations is a crucial one and is based on an independent testing of the airflow rate measurement system and of the gamma detector system, as well as on the assessment of the samples collected during parallel sampling and measured at radionuclide laboratories.     

Thermal-ionization mass spectrometry for small sample analysis of uranium and plutonium

Thermal-ionization mass spectrometry (TIMS) offers the unique capability of measurement of all isotopes of a radionuclide with equal sensitivity and with sufficient precision to enable differences in isotopic compositions to be observed even for picogram size samples.     

Split renal function testing using Tc-99m DTPA. A rapid technique for determining differential glomerular filtration

The fractional renal uptake of intravenously administered Tc-99m DTPA, within 2 to 3 minutes following radiotracer arrival in the kidneys, is proportional to the glomerular filtration rate (GFR). Thus it is possible to determine total, as well as individual kidney, GFR by a radionuclide technique which needs only six minutes of patient time and requires neither blood nor urine samples. The radionuclide computed GFR correlates extremely well with 24-hour creatinine clearance determinations, and is highly reproducible. This method has been used in nearly 500 split renal function determinations and has provided valuable, accurate information.     

Validation of radionuclide cardiac output measurements during exercise

A nongeometric radionuclide technique with correction for attenuation was used for the determination of cardiac output and stroke volume during exercise in nine normal subjects and in ten hypertensive patients. Simultaneous reference stroke volume (range 48-159 ml) and cardiac output (range 3.6-23.8 l/min) measurements were obtained by the Fick method. Data were collected at rest and during 60 degrees upright exercise, at two or three levels of increasing severity. Three statistical measurements were used for the comparison of both methods: correlation, precision, and accuracy. Radionuclide and Fick cardiac output measurements (n = 67, rest and exercise data) correlated well (r = 0.90). For stroke volume, the correlation was less (r = 0.64); however, the precision or random variability of both methods was similar for stroke volume (radionuclide: 8 ml or 9%; Fick: 16 ml or 16%). The accuracy or systematic error was defined as the mean difference between radionuclide and Fick measurements. The radionuclide method underestimated the Fick measurements. The systematic error was 18 +/- 18 ml for stroke volume and 2.4 +/- 2.4 l/m for cardiac output. A similar comparison of both methods was made on the absolute changes of stroke volume (r = 0.61; range -19 + 70 ml) and cardiac output (r = 0.82; range +1.6 + 16.4 l/m) between rest and exercise. The precision of the two methods was similar; the systematic error was 1.9 +/- 2.2 l/m for cardiac output and 6 +/- 17 ml for stroke volume. Thus, in these two groups of patients, although radionuclide and Fick cardiac output measurements at rest and during exercise correlated well, the radionuclide values were systematically and significantly lower.     

Two-compartment, two-sample technique for accurate estimation of effective renal plasma flow: theoretical development and comparison with other methods

Discordance between effective renal plasma flow (ERPF) measurements from radionuclide techniques that use single versus multiple plasma samples was investigated. In particular, the authors determined whether effects of variations in distribution volume (Vd) of iodine-131 iodohippurate on measurement of ERPF could be ignored, an assumption implicit in the single-sample technique. The influence of Vd on ERPF was found to be significant, a factor indicating an important and previously unappreciated source of error in the single-sample technique. Therefore, a new two-compartment, two-plasma-sample technique was developed on the basis of the observations that while variations in Vd occur from patient to patient, the relationship between intravascular and extravascular components of Vd and the rate of iodohippurate exchange between the components are stable throughout a wide range of physiologic and pathologic conditions. The new technique was applied in a series of 30 studies in 19 patients. Results were compared with those achieved with the reference, single-sample, and slope-intercept techniques. The new two-compartment, two-sample technique yielded estimates of ERPF that more closely agreed with the reference multiple-sample method than either the single-sample or slope-intercept techniques.     

Radiotracer imaging in a case of diffuse skeletal hemangiomatosis

The hospital course of a patient with diffuse skeletal hemangiomatosis is presented with reference to the role of radionuclide imaging procedures in the diagnosis and evaluation of this disorder. In addition to static scans of liver, bone, and bone marrow, flow studies using Tc-99m-sulfur colloid and methylene diphosphonate (MDP) were performed.     

First-pass left ventricular ejection fraction with 95mAu on a 1/4 in. crystal gamma camera

First-pass left ventricular ejection fraction was determined in 21 patients using 195mAu. The technical aspects of the application are discussed with particular reference to the thin crystal (1/4 in.) gamma camera. The use of diverse catheter types and combinations were also investigated so that optimal administration of the radionuclide could be achieved.