Shadow-shield Whole-body Counter Research Articles

Comparison of Indian BOMAB and ICRP voxel phantom for calibration of shadow shield whole body counter

In-vivo whole body monitors are calibrated with various types of phantoms like Bottle Mannikin absorption phantom (BOMAB), IGOR phantom, Masonite cut sheet phantom, realistic numerical phantoms (NORMAN, ICRP voxel phantom). These phantoms contain either point sources, rod sources, uniform source or radionuclides distributed in soft tissues etc. In this study the efficiency values of Shadow Shield wholebody counter (SSC) for 137Cs and 60Co obtained theoretically using ICRP adult voxel male reference phantom (ICRP-AM) having sources distributed in soft tissues and muscles ICRP-AM(S) are compared with the measured efficiencies of Indian BOMAB phantom having mid axial source distribution (BOM-I(A)). The results show that the efficiency value of BOM-I(A) for 137Cs and 60Co is 30% and 20% lower respectively compared to that of ICRP-AM(S). This is due to the variation in size, composition and source distribution between the two phantoms. Study using Indian Voxel phantom shows that the increase in the size of ICRP-AM contributed to an increase of 14% for 137Cs. In case of 60Co the size did not have any influence. Uniform distribution has 9% and 17% higher efficiency than axial distribution for 137Cs and 60Co respectively as shown by the simulation study using uniformly filled Indian BOMAB phantom (BOM-I(U)). The actual tissue composition and source distribution in soft tissue as shown by Indian voxel has efficiencies 12-14% higher compared to BOM-I(U). The systemic error due to the axial source distribution is recognized and quantified to be 22-25% lower compared to that of a realistic phantom with radionuclides in soft tissue and muscle. This study has resulted in an efficiency of the system using Indian realistic Voxel phantom. The efficiencies are 0.65 CPS/kBq for 137Cs and 0.49 CPS/kBq for 60Co.

Response of a Shadow-Shield Whole-Body Counter to a Variety of Physical Phantoms.

The performance characteristics of a shadow-shield whole-body counter system with an array of four high-resolution germanium detectors using whole-body and organ-specific (lungs, liver, head, knee and thyroid) physical phantoms are described. Detection efficiency and minimum detectable activities for selected radionuclides and several measurement configurations are presented. Results demonstrate that the system meets the requirements for direct radio bioassay and that detection efficiency and minimum detectable activities are similar in magnitude to other whole-body (or organ) counting systems installed in fully shielded structures.

A high-sensitivity multidetector whole-body counter

A prototype multidetector shadow-shield whole-body counter is presented to be used as a monitor of internal contamination and as a tool in clinical research. The counter is equipped with 16 NaI(Tl) detectors located in the central region of a shielded tunnel surrounding the subject to be measured. The accuracy of the counting efficacy predictions was tested in a group of adults with various body shapes and sizes using X-ray absorptiometry. The precision of the total body potassium measurements allows the use of the counter in clinical follow-up studies.

An In-vivo Study on Clearance of Thorium from the Thorax

During routine monitoring of workers of a monazite processing plant, a few subjects were observed to have exceeded the normal levels of internal contamination. These subjects had chronic inhalation exposure at low levels for 25 to 30 years. Subsequently, they were removed from active work and subjected to whole-body counting at the thorax region, using a shadow-shield whole-body counter, over a period of time. Results of repeated counting, extended over a period of more than three years, indicated the clearance half-life for thorium to be 954 ± 97 days. As these subjects had chronic inhalation exposure for 25 to 30 years, the observed elimination may not be considered as lung clearance, but as thorax clearance.

Monitoring of the biodistribution and biokinetics of dysprosium-165 ferric hydroxide with a shadow-shield whole-body counter

Monitoring of the biodistribution and biokinetics of dysprosium-165 ferric hydroxide with a shadow-shield whole-body counter

Monitoring of the biodistribution and biokinetics of dysprosium-165 ferric hydroxide with a shadow-shield whole-body counter.

Radiation synovectomy is indicated when conventional pharmacological treatment of chronic synovitis has proved insufficient. In these cases dysprosium-165 ferric hydroxide (DFH) has been demonstrated to be clinically effective. After application of the agent, blood activity measurements and monitoring of activity distribution by gamma camera imaging over the local lymph nodes and the liver are commonly performed for control of possible leakage. In addition, we have used a shadow-shield whole-body counter with a profile facility to evaluate the biokinetics and biodistribution of 165Dy-DFH. Fifteen intra-articular injections were performed in 13 patients who received a median activity of 6.8 GBq (range 0.5-9.9 GBq) 165Dy-DFH. Activity profiles were obtained with the whole-body counter 2, 4 and 6 h after injection of 165Dy-DFH. The doses to non-target organs were calculated using the software MIRDOSE 3. In 10 of 15 treatments, absence of any leakage could be demonstrated. The effect of scattered rays could be observed in 14 measurements. In three patients small amounts of activity could be detected in the urinary bladder and in three patients activity was detected in the local inguinal lymph nodes, while no leakage could be detected by camera imaging. In these cases the individual doses to the bladder were 15 Gy, 65 mGy and 50 mGy, and those to the lymph nodes, 0.54 Gy, 0.89 Gy and 2.41 Gy. The whole-body counter also enabled the monitoring of activity profiles related to more complex pathological structures. In conclusion, using a whole-body counter activity leakage could be detected with much higher sensitivity than by using a gamma camera. The biodistribution of 165Dy-DFH could be determined, and leakage could be localised and related to organs. These results encourage the use of a whole-body counter to identify the site and extent of activity leakage.

A comparison between the use of a shadow shield whole-body counter and an uncollimated gamma camera in the assessment of the seven-day retention of SeHCAT

We have compared the 7-day retention of the radioisotope bile salt analogue SeHCAT (75Se-23-selena-25-homotaurocholate), by whole body counting and by uncollimated gamma camera measurement, in phantoms and in 25 patients with inflammatory bowel disease. The results correlate with a linear correlation coefficient of 0.96. An uncollimated gamma camera can be used to assess bile acid malabsorption when a whole body radioactivity monitor is not available.

Total body neutron activation analysis of calcium: calibration and normalisation

An irradiation system has been designed, using a neutron beam from a cyclotron, which optimises the uniformity of activation of calcium. Induced activity is measured in a scanning, shadow-shield whole-body counter. Calibration has been effected and reproducibility assessed with three different types of phantom. Corrections were derived for variations in body height, depth and fat thickness. The coefficient of variation for repeated measurements of an anthropomorphic phantom was 1.8% for an absorbed dose equivalent of 13 mSv (1.3 rem). Measurements of total body calcium in 40 normal adults were used to derive normalisation factors which predict the normal calcium in a subject of given size and age. The coefficient of variation of normalised calcium was 6.2% in men and 6.6% in women, with the demonstration of an annual loss of 1.5% after the menopause. The narrow range should make single measurements useful for diagnostic purposes.

Deposition of pressurized suspension aerosols inhaled through extension devices.

Only a small fraction of the dose from a pressurized aerosol inhaler reaches the lung, because most is deposited on the upper airways by inertial impaction. We have investigated the effects on aerosol deposition of two spacer devices (a 10-cm tube and a 22-cm cone) by incorporating teflon particles (mass median aerodynamic diameter, 3.2 micrometer) labeled with 99mTc into pressurized canisters. Ten subjects with obstructive airway disease inhaled the aerosol in a controlled manner from a conventional actuator alone or in combination with the tube or the cone. Radioaerosol distribution was measured using a shadowshield whole body counter. Deposition on the conducting airways was significantly improved by both spacers, but alveolar deposition was unchanged. Initial oropharyngeal deposition was reduced by both spacers in all 10 patients. We conclude that the spacer devices may have a role to play in aerosol therapy by increasing drug availability to the lung, while at the same time decreasing unwanted drug deposition in the oropharynx.

Calibration and evaluation of a system for total body in vivo activation analysis using 14 MeV neutrons

A system has been established for determining the total body contents of calcium, phosphorus, sodium, chlorine and nitrogen by neutron activation analysis using sealed-tube neutron generators and a shadow-shield whole-body counter. The system was calibrated using three anthropomorphic phantoms of different sizes, filled with various mixtures of the activatable elements in amounts similar to those in man. The reproducibility, determined from replicate measurements, was on average +or-2.9% (SD). The average uncertainty in absolute measurements was estimated to be +or-4.2% (68% confidence interval).

Thyroid Disorders and the Distribution of Orally Administered Radioiodine

128 control, thyrotoxic, hypothyroid and goitrous euthyroid children were administered 1-2 muCi Na131I orally and studied in a shadow-shield whole-body counter. 48-hr whole-body counts permitted the differentiation of the first 3 groups (p less than 0.005). Ratio of extrathyroid:excreted 131I was 3 times greater in thyrotoxics than in goitrous euthyroids, but the thyroid:extrathyroid ratio was 3 times greater in the latter group. The whole-body profile scan obtained at 48 hr on an attached strip chart recorder, revealed activity not only in the thyroid but even lower down in the vicinity of the knees and feet.

A high sensitivity dual-detector shadow-shield whole-body counter with an 'invariant' response for total body in vivo neutron activation analysis

The sensitivity and performance of the counter are analysed, with specific references to total body in vivo neutron activation analysis, and shown to be at least comparable with those of many conventional shielded-room counters.

Measurement of total body potassium with a shadowshield whole-body counter: calibration and errors

The calibration procedure for the measurement of total body potassiumwith a high sensitivity shadow-shield whole-body counter is described. The sourcesof error have been analysed and it is shown that the estimated standard error for theprocedure is 2.7% for a subject with 140 g of potassium, when 42K is administeredto the subject as an internal standard. When a calibration factor is obtained froma derived regression equation relating this factor to the subject's weight and height,the estimated standard error is 3.9%. In sequential measurements in the same subjecta change of body potassium equal to 4.6% would be significant.

A shadow shield whole-body counter.

A whole-body counter is discussed that combines shadow shielding with (integral or differential) scanning, weighs only 5 tons, has a background as low as an iron-room counter, has little variation in sensitivity for different size people and has only slightly less sensitivity than an iron-room counter. The light weight of the counter was exploited by placing one in a truck for use in a radiation protection program and by transporting it by air for use in a study of radioactivity in Alaskan Eskimos.