Evaluation of external radiation exposure rate from radioiodine-treated hyperthyroid patients and radiation safety considerations

Hyperthyroid patients treated with radioiodine (I-131) pose an external radiation risk to individuals who come into close contact with them. In order to determine changes in levels of external radiation with time in relation to the dose administered, 38 hyperthyroid patients being treated with I-131 were evaluated. Thyroid uptake, plasma T3, T4 and TSH levels were measured prior to treatment. Using a Geiger-Muller probe, levels of external radiation were measured at distances of 0.3, 0.6, 1.0 and 2.0 m from the patient - at the level at which the maximum activity was recorded - 30 min, 1, 3, 7 and 10 days post-therapy. The patients were split into two groups. Group I comprised 22 patients treated with less than or equal to 370 MBq I-131, 5 (23%) of whom registered > 0.46 mC kg(-1) at a distance of 1.0 m 30 min post-therapy. Group II comprised 16 patients treated with > 370 MBq I-131, 13 (81%) of whom registered 0.46 mC kg(-1) at a distance of 1.0 m one day post-therapy. At 3 days in Group I and 7 days in Group II, the estimated total radiation exposure rates were found to exceed the 1994 US Nuclear Regulatory Commission dose limits for children and pregnant women. Based on the results obtained, we present some guidelines intended to prevent the public from unnecessary radiation exposures

Effects of allopurinol, ibuprofen and cyclosporin A on local microcirculatory disturbances due to burn injuries

This experiment was designed to study the reactions in the surrounding area of burn injury that may lead to further necrosis in 24 h. To prevent extension of burn size into the tissue adjacent to burn injury, it was attempted to reduce progressive microvascular damage by different drugs (ibuprofen, allopurinol or cyclosporin A (CyA)) in a rat model. The burn model consisted of a row of four 10x20 mm burn areas separated by three unburned 5x20mm skin bridges (interspaces). To evaluate microcirculation and perfusion of panniculus carnosus muscle which is beneath the burned area of skin, the radioactive agent, technetium-99m methoxyisobutylisonitrile (Tc-99(m)-MIBI) was used 24 h after the burn. Capillary permeability of injured tissue was assessed by the wet and dry weight technique. In all study groups, interspaces showed higher uptakes of Tc-99(m)-MIBI between 40 and 95 per cent, in comparison with burn sites in the first 24 h following burn. Among the treated rats better results were obtained by allopurinol and CyA treatment that commenced before burn than ibuprofen. Wet and dry ratios were found to be significantly lower in interspaces in rats pretreated with allopurinol and CyA. Results of this experiment showed that neutrophils and free radical-mediated injury may be involved in the pathogenesis of local response to thermal injury, and allopurinol and CyA have some effects to prevent progressive ischaemia, capillary compromise and oedema. (C) 1997 Elsevier Science Ltd for ISBI

A comparison of Tl-201 stress-reinjection-prone SPECT and Tc-99m-sestamibi gated SPECT in the differentiation of inferior wall defects from artifacts

The frequency of false positive results obtained from the inferior myocardial region using single photon emission computed tomography (SPECT) myocardial perfusion scintigraphy is significantly higher than that obtained from other regions. Several methods, such as prone-position imaging, have been proposed to overcome this diagnostic problem. The aim of the present study was to compare the results of Tc-99m-sestamibi gated SPECT and Tl-201 prone SPECT in the differentiation of inferior wall artifacts from true defects. For this purpose, 38 subjects, whose coronary anatomies were documented on angiography, underwent same-day stress-rest Tc-99m-sestamibi gated SPECT and Tl-201 stress-reinjection-prone (whose standard supine images demonstrated fixed defects on the inferior wall) SPECT. Gated SPECT was performed by 8 frames per cycle acquisition over a 180 degrees rotation on 30 projections. Four gated SPECT slices were obtained on mid-ventricular vertical long axis, horizontal long axis and apical and basal short axis planes, and displayed in cine-format. Both Tl-201 prone imaging and Tc-99m-sestamibi gated analysis increased the specificity of inferior wall disease detection remarkably from 54% to 85% and 46% to 82%, respectively (P 0.05). The positive predictive values for true defects were 96% for Tl-201 prone imaging and 94% for Tc-99m-sestamibi gated imaging. Based on segmental analysis, the two modalities showed fair agreement (kappa = 0.44 for standard supine protocols, kappa = 0.46 for Tl-201 prone and Tc-99m-sestamibi gated SPECT). It can be concluded that Tc-99m-sestamibi gated SPECT, requiring only two-step acquisition, may potentially increase the test specificity for coronary artery disease (CAD) of the inferior wall as well as does Tl-201 sh ess-reinjection-prone SPECT. By giving functional information, it seems the most practical method in daily use for supplying the most extensive information about patients with suspected or known CAD. ((C) 2000 Lippincott Williams & Wilkins)