Scattered photons are a major problem in single photon emission computed tomography (SPECT) largely because they degrade the diagnostic information in the image both qualitatively and quantitatively. In order to improve the accuracy of SPECT measurements, correction methods have to be used. Two different scatter correction techniques-the dual-window ( DW) technique and the convolution (CV) technique-were compared using projection data, simulated by the Monte Carlo method. Comparison with measured data was also made to validate the accuracy of the Monte Carlo code. The main goal was to investigate how well the estimated scatter distributions, using these two scatter correction techniques, fit the simulated, true scatter distribution of the projection data obtained in the photo-peak window. The scatter distributions predicted by the CV technique were found to be consistently lower than those simulated by the Monte Carlo method in the part of the scatter distribution corresponding to the locations of the sources. The DW technique gives lower estimates of the scatter distribution. However, the scatter distribution estimated by the DW technique and the simulated scatter distribution bear a close resemblance to each other.
Without appropriate quality control (QC) and preventative maintenance (PM) measures for X‐ray machines in place, the benefits of reduced dose to the patient and early diagnosis will not be realized. Quality control and PM also make it possible to unify X‐ray‐imaging practices in the country using international image quality guidelines. The impetus for the present work resulted from the concern that with the recent increase in the numbers of X‐ray machines in Tanzania, but with limited technical support to maintain and operate them, can increase radiation risk to patients and lower diagnostic accuracy. The aim of this work is to report on the current status of diagnostic X‐ray machines in Tanzania in order to produce the data needed to formulate QC and PM policies and strategies. These policies and strategies are needed to ensure that patients receive the lowest possible radiation risk and maximum health benefits from X‐ray examinations. Four QC tests were performed on a total of 196 X‐ray units. Accurate beam alignment and collimation were tested on 80 (41%) units, the timer accuracy was tested on 120 (61%) units, and a radiation leakage test was performed on 47(24%) units. Preventative maintenance tests were performed on all 196 X‐ray units. The results showed that of the units tested for QC, 59% failed the kilovoltage (kVp) test, 57% failed the timer accuracy test, 60% failed the beam alignment test, and 20% failed the radiation leakage test. Only 13% of the units passed the PM test: 53% of the units were defective, and 34% were out of order. As a result of the PM findings, the government has introduced a rehabilitation project to service X‐ray units and replace nonoperational X‐ray units. The new units have full support service contracts signed by their suppliers. As a result of the QC findings, X‐ray maintenance retraining programs have been introduced.PACS numbers: 87.52.‐g, 87.52.Tr, 87.58.SP, 87.59.Bh
Although the use of CT in medical diagnosis delivers radiation doses to patients that are higher than those from other radiological procedures, lack of optimized protocols could be an additional source of increased dose in developing countries. The aims of this study are, first, to determine the magnitude of radiation doses received by selected radiosensitive organs of patients undergoing CT examinations and compare them with other studies, and second, to assess how CT scanning protocols in practice affect patient organ doses. In order to achieve these objectives, patient organ doses from five common CT examinations were obtained from eight hospitals in Tanzania. The patient organ doses were estimated using measurements of CT dose indexes (CTDI), exposure‐related parameters, and the ImPACT spreadsheet based on NRPB conversion factors. A large variation of mean organ doses among hospitals was observed for similar CT examinations. These variations largely originated from different CT scanning protocols used in different hospitals and scanner type. The mean organ doses in this study for the eye lens (for head), thyroid (for chest), breast (for chest), stomach (for abdomen), and ovary (for pelvis) were 63.9 mGy, 12.3 mGy, 26.1 mGy, 35.6 mGy, and 24.0 mGy, respectively. These values were mostly comparable to and slightly higher than the values of organ doses reported from the literature for the United Kingdom, Japan, Germany, Norway, and the Netherlands. It was concluded that patient organ doses could be substantially minimized through careful selection of scanning parameters based on clinical indications of study, patient size, and body region being examined. Additional dose reduction to superficial organs would require the use of shielding materials.PACS numbers: 87.59 Fm; 87.66Jj; 87.52‐g
Head computed tomography examinations are often accompanied with unnecessary irradiation of superficial organs that are rarely the main target for the investigation. The aim of this work is to demonstrate that lead shields could be effectively used to protect superficial organs without compromising image quality where superficial organ itself is not a target and that the irradiation of the superficial organ is unavoidable. The objective was achieved by first assessing the image quality using phantom measurements made with and without lead shielding in order to determine optimal shielding thickness for patient applications. The entrance surface doses (ESDs) to superficial organs of sixty patients were measured using LiF-thermoluminescent dosemeters without, with one layer, or with two layers of lead shields. Phantom studies demonstrated that the use of modified lead shields of up to 0.25 mm thickness could be used without significant effect on the image quality for central and posterior regions. In these studies, lead shields of 0.25 mm thickness reduce the ESDs to the lens of the eyes and thyroid by 44 and 51%, respectively. The image quality reduction by eye shields was significant to the anterior (i.e. orbital) region but marginal to the central and posterior regions (cerebrum). In view of the above, the use of modified lead shields could reduce the dose to the superficial organs considerably without significantly compromising image quality.
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