[en] One of the latest transverse-axial single-photon tomography machines is the Cleon 710 Radionuclide Brain Imager. This system was developed by Union Carbide Inc. The performance of the Cleon system has been compared with two systems which have both been developed in Professor Mallarel's department at Aberdeen University: (i) the Aberdeen Section Scanner which is the prototype of the Tomogscanner and consists of two opposing 8.9 cm diameter detectors with 20 cm focal length collimators, (ii) a rotating γ-camera system, using a Nuclear Enterprises (NE 5LF) γ-camera with a high resolution parallel-hole collimator (NE 8961) connected to a Nuclear Data 50. (WU)

[en] Factors contributing to poor outcome following treatment of non-small-cell lung cancer include hypoxia, which contributes to radioresistance, and poor perfusion, which limits drug access. Following earlier animal studies showing good correlation with Rb-86 uptake into tumors and normal tissue, clinical single photon emission studies have been performed following intravenous administration of TC-99m HMPAO. Good reproducibility was seen in eight duplicate studies. A strong relationship between tumor-lung uptake ratio and tumor volume on chest radiographs was observed, suggesting poorer perfusion and worsening hypoxia with increasing tumor size

[en] In order to destroy thyroid cancer metastases by radio-iodine an average tissue dose of 80-300 Gy is needed. Such high doses can be expected, following the administration of the conventional 5.5 GBq of ¹³¹I, only if both the percentage uptake pergram in the target tissue and the effective half life of the radio-iodine in it are higher than well-defined threshold values, and if every dimension of the tissue exceeds several millimeters. The fulfilment of such favourable conditions in actual clinical cases can only be confirmed by in vivo quantitation of the absorbed dose achieved as a result of the administration of radio-iodine. (author). 31 refs.; 2 tabs

[en] A revised method of correcting for attenuation has been investigated through experiments using discrete sources within a radioactive background. The effects of changing the source size, the source position relative to the central axis, and the ratio of the concentrations in the source and background have been studied. A comparison of the results obtained using old and new attenuation corrections show marked improvement. The measurement of radioactive concentration on the central axis had a typical systematic error of -14%, compared to -60% previously, but is generally dependent on source size, source position, and source and background concentrations. An allowance can be made for this error using experimental data

[en] The PETRRA positron camera consists of two 60x40 cm² detectors mounted on a rotating gantry. The detectors each contain 1 cm thick BaF₂ crystals interfaced to a MWPC filled with tetrakis dimethylamino ethylene (TMAE) vapour. PETRRA acquires data in 3D only and images can contain high levels of scatter and random coincidences. Scatter comes from the patient and the detector support structure whereas randoms rates depend on the detector count rates and coincidence timing resolution. The camera has little energy resolution but low energy scattered photons produce a smaller range of pulses and can be discriminated against using signal thresholding. Scatter can also be reduced by shielding the camera from radioactivity outside of the field of view and by minimising the amount of scattering material in the camera itself. We conclude that the most effective way of reducing scatter and randoms count rates is to minimise the support structures in the detectors and shield the detectors from out-of-field activity. Energy thresholding does reduce scatter and randoms but severely reduces the numbers of true events

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No abstract available

[en] Single photon emission computed tomogrpahy (SPECT) has been shown to be of value in estimating the radiation dose to the peritoneum from ³²P therapy. Simple dosimetry calculations, assuming uniform irradiation of tissue, indicate that radiation doses of proportional40 Gy to the peritoneal surface are achieved. However, the images show that the radionuclide distribution is non-uniform, giving rise to radiation dose variations of at least a factor of 10. (orig.)

[en] The orthohole test pattern (OHTP) has been useful for weekly comparative tests of spatial distortion differential non-uniformity, spatial resolution and image pixel size and its use has minimised the camera time needed for quality control. By analysing the images obtained, it has been possible to provide quantitative information for comparing weekly performances and for the intercomparison of two systems. It should be stressed though that the measurements described are non-standard and hence the OHTP should be used only for observing general trends in performance which may indicate that the camera needs adjusting. When standard measurements are required, for example when checking camera performance with the manufacturer's specifications, NEMA phantoms should be used. (author)

[en] A comparison of two methods of scatter compensation in single photon emission computed tomography (SPECT) imaging is made on the basis of improvements in quantification. The methods, scatter-window subtraction and constrained deconvolution of an average point source response function (PSRF), are described; the theoretical basis of each method is also briefly assessed. Improvements in relative quantification offered by each method are measured by examining ratios of counts in hot cylinders to counts in a slightly radioactive background. The cylinder/background concentration ratio was varied by a factor of five; the sizes of the cylinders remained constant. Keeping the diameter of the cylinders constant allowed for an assessment of the effect of concentration differences, without the conflicting effect of variation in the size of the hot source. Results showed that while both scatter-window subtraction and constrained deconvolution offer quantification improvements in the final image, the method of prereconstruction deconvolution of a planar PSRF from each planar projection is substantially more successful than either scatter-window subtraction or other methods of implementing the deconvolution procedure