Dose inhomogeneities on surfaces of different dental implants during irradiation with high-energy photons.

OBJECTIVES: The aim of this study was to determine the radiation doses in mucosa and bone close to the surface of different dental implant materials. METHODS: Radiation dose was measured at the interface of bone or soft tissue and various implant materials for 6 MV photons generated by a medical linear accelerator using a phantom and ultrathin thermoluminescent dosemeters. RESULTS: Increasing thickness of implant materials resulted in a dose decrease in bone immediately behind the implants. Directly in front of titanium implants, dose increases of 18.2% and 30.4% were found in bone and soft tissue, respectively, independent of implant thickness and surface structure (polished/plasma coated). Even a titanium coating with 70 microm hydroxyapatite did not affect the scattering dose. In contrast, for aluminium oxide ceramics, a scatter-induced notable dose increase could not be assessed. CONCLUSIONS: During irradiation with high-energy photons, an implant-induced dose enhancement could be reduced in bone using the technique of multiple fields and in soft tissue using ceramic abutments.

Dose reduction in thorax radiography in simulated neonates with additional filtration and digital luminescence radiography.

PURPOSE: To determine the minimum acceptable radiation dose for an adequate image quality in thorax a.p. radiographs of neonates using mobile X-ray equipment. MATERIAL AND METHODS: The influence of additional filtration (1.0 mm Al + 0.1 mm Cu) on image quality and radiation dose was determined for the speed class 400 screen-film system (SFS) and digital luminescence radiography (DLR) by making radiographs of a test phantom. Conventional and digital thorax a.p. radiographs of a rabbit were produced using various tube current-time products. The quality of the rabbit radiographs was judged by eight radiologists applying image quality criteria according to the German guidelines and the recommendations of the European Community. RESULTS: The added filter resulted in a dose reduction of 39% at 66 kV. DLR gave a further dose reduction of 25% in comparison to the speed class 400 SFS while maintaining adequate image quality, i.e. the radiographs were clinically acceptable with regard to quality criteria. CONCLUSION: The radiation dose resulting from thorax a.p. radiographs of neonates can be reduced by approximately 50% with the use of additional filtration and DLR.

Patient doses from standard and spiral CT of the head using a fast twin-beam system.

Investigations were carried out on a novel type of CT scanner, the Elscint CT-Twin, for comparison and optimization of the patient dose caused by standard and spiral CT of the head. For selected CT parameters, organ doses of the Alderson head phantom were measured with thermoluminescent dosemeters. Organ doses were also calculated using the normalized computed tomography dose index (CTDIn) combined with organ dose conversion factors. Then effective doses were deduced. For standard and spiral head CT examinations brain, red bone marrow and bone surface receive the main contributions to effective dose. This amounts to 0.9 and 0.8 mSv for routine standard and spiral CT, respectively, if the combination "dual-slice" mode, 250 mAs per rotation, 5 mm nominal slice width and a packing factor of 1.0, is applied. In clinical practice, for spiral CT head examinations the effective dose has been reduced to 0.7 mSv while guaranteeing adequate image quality, as assessed by determination of low and high contrast resolution. The effective dose values obtained are in the lower part of the range of values published in the literature. The dose determinations showed that, from the aspect of radiation protection of the patient, CT examinations with nominal slice widths between 0.5 and 1 mm as well as packing factors greater than 1.0 should be restricted to really necessary cases.

[Radiation exposure in abdominal radiography with digital luminescence radiography and conventional screen-film system: an experimental animal study]. / Die Strahlenexposition bei der Abdomen-Ubersichtsaufnahme mit digitaler Lumineszenzradiographie und konventionellem Film-Folien-System--eine tierexperimentelle Untersuchung.

PURPOSE: To determine and compare the minimum required radiation exposure for a.-p. abdominal radiographs with digital luminescence radiography (DLR) and a screen-film system (SFS) providing adequate image quality in clinical routine. MATERIAL AND METHOD: Abdominal radiographs a.-p. of a pig were produced with DLR and SFS systematically varying the tube current-time product. The image quality was assessed by eight experienced radiologists according to the criteria of visual resolution, mean optical density, perceptibility of the lateral edge of the psoas, the caudal edge of the liver, bone structures and intestinal wall. RESULTS: The image quality of the digital radiographs was better for each criterion except visual resolution if the same current-time product was used for both techniques. From the minimum tube current-time products providing an adequate image quality it follows that a dose reduction of 57% can be achieved by applying DLR instead of speed class 200 SFS. CONCLUSION: The recently published guide-lines for quality assurance in x-ray diagnostics issued by the German Federal Board of Physicians recommend using speed class 400 SFS. Since in that case an approximately halved radiation dose is necessary, dose reduction is hardly to be expected with DLR.

The radiation exposure of the patient from stable-xenon computed tomography.

For stable-xenon computed tomography (CT), an X-ray examination for measurement of cerebral blood circulation in the brain, the radiation exposure of the patient was determined in order to estimate the risk of inducing cancer. Organ doses of brain, eyelenses, thyroid and gonads have been calculated using the measured air kerma free-in-air on the axis of rotation and organ-specific conversion factors calculated with the Monte Carlo method. Dose measurements with TLD-100 rods using a humanoid Alderson phantom were carried out for verification of the calculated organ doses. In the case of brain partially located in the region of primary radiation a mean organ dose of 39 mSv was calculated. The dose measurements showed dose equivalents between 6 and 68 mSv in different regions of the brain and consequently an inhomogeneous dose distribution. From an estimation of the radiation-induced risk using the effective dose of 1.6 mSv it follows that one additional fatal cancer per 12,500 stable-xenon CT examinations has to be expected. The organ doses of eyelenses and thyroid located in the region of scattered radiation are so low that biological effects are hardly to be expected. The calculated dose equivalents of 6.5 mSv and 0.5 mSv, respectively, are in good agreement with measurements. The organ dose of gonads amounted to less than 0.07 mSv.

[The determination of the ovarian dosage in defecography on a digital C-arm unit]. / Zur Bestimmung der Ovarialdosis bei der Defäkographie an einem digitalen C-Bogen.

When using defaecography as a radiological tool for diagnosing the anorectal function in female patients, the ovaries are inevitably directly exposed. With the aim of minimising the ovarian dose applied both the area-dose product and the surface dose above the ovaries were measured during investigations of female patients with a digital C-arm unit. These values were converted into ovarian doses using tissue-air ratios. From the surface dose measured with TLD-100 a mean ovarian dose of 15.6 +/- 8.6 mGy was derived. The contributions of screening and film exposures were similar. A reduction of screening time by 10 seconds or omission of 60 film exposures results in a decrease of ovarian dose by values between 0.7 and 2 mGy. Employing a greater focus-skin distance during defaecography, however, made it possible to reduce the ovarian dose by 26%.

Frequency distribution of D1S80 alleles in the German population.

The locus D1S80 is a very useful genetic marker system for forensic DNA analysis. It consists of a variable number of tandem repeats (VNTR) and can be analyzed by the polymerase chain reaction (PCR). As accurate data about the distribution of the alleles is one of the most important prerequisites for the application in forensic biology we studied the allele distribution in the German population.

Age-related retinal vasculopathy.

Second and third order retinal arterioles and venules were studied by immunohistochemistry and electron microscopy in the uncomplicated ageing process and in association with central retinal vascular occlusive disease (CRVOD). Tissue was obtained from eight enucleated human eyes (4 control, 4 with manifestations of CRVOD) and the investigation was directed towards abnormalities in the myocytes and the nature of collagenous materials which are deposited during the process of hyalinization. In normal ageing and in two cases of CRVOD, the endothelial cell monolayer and the underlying cells (subendothelial myocytes) were preserved in arterioles and venules: there was no evidence of fibrin leakage. Degenerative changes were found in the medial myocytes in control tissue from the fifth decade and these included myocyte shrinkage, accumulation of intracytoplasmic membranous structures, cytoplasmic vacuolation and fragmentation. The 'hyalinized' acellular vessel wall seen in CRVOD contains scattered activated fibroblast-like myocytes and macrophages lying within a matrix of fibronectin, 65 nm collagen and multilayered basement membrane material. Endothelial cells and cohort subendothelial myocytes are involved in the formation of capillaries which bud into the hyalinized vessel wall in CRVOD. In two cases of CRVOD there was extensive cellular degeneration and cell debris accumulated within the degenerate stroma: this was attributed to superadded total ischaemia. The pathogenesis of hyalinization remains obscure but a subtle age-related dysfunction of the morphologically intact lining endothelium could be responsible for metabolic damage to myocytes in the media.