A suitable quantity for evaluating the image quality in mammography is the smallest visible size of an object. This quantity, called the image quality index (IQI), can be derived from the basic image parameters: contrast, MTF, Wiener spectrum. Several evaluation methods of the IQI, all based on statistical decision theory, have been considered. An experimental visibility test using simulated microcalcifications has been performed in order to compare the results obtained with different IQI models. A previous approach, based on simplifying assumptions, yields a good correlation with the visibility test but fails to predict the actual size of the visible objects. Improved models have been derived for an ideal observer and for a 'quasi-ideal' one with perfect or with realistic visual characteristics. The experimental visual results are well modelled by the IQI method, provided that a suitable threshold signal-to-noise ratio is used for each of these models.
The influence of anode and filter materials on the performance (image quality and dose) of a mammography system is investigated. The image quality is evaluated with the image quality index method. A computer simulation has been developed to calculate the physical parameters of the image quality index (contrast, resolution and noise) as well as the mean glandular dose. The calculations take into account the successive steps of the process: x-ray production, filtration, interaction with the test object, anti-scatter grid, interaction with the image detector (screen-film system). An excellent correlation is obtained between the results predicted by the model and those of experimental measurements, suggesting that the model may be used for the prediction of the performance of mammographic equipment. The experimental conclusions are confirmed: the use of a tungsten anode with a rhodium filter allows a dose reduction without a significant degradation of image quality. The computer program can also be used to simulate the influence of factors which are difficult to combine in practice, e.g., various anode and filter materials, monoenergetic x-rays, etc.
The authors have developed an experimental method for simultaneous determination of dose and image parameters in mammography. A global and objective quality concept, the image quality index, is proposed and its reliability demonstrated by tests of reproducibility. Objective quality tests and subjective evaluation by radiologists showed good correlation.
A quality control program for mammography units was carried out, based on objective tests of image quality and dose. Results are reported for 31 units, including correlation between various parameters. Satisfactory results were obtained in the case of 21 installations; for the other 10, comparison between measured quality parameters and those of the reference system suggested ways in which quality might be improved.
The diagnosis of Graves’ ophtalmopathy (GO) is based on clinical examination, laboratory tests (indicating thyroid dysfunction and inflammatory and autoimmune unbalance) and imaging studies (such computed tomography, magnetic resonance imaging, ultrasound and colour Doppler imaging). Imaging studies can be helpful in establishing the certain diagnosis of GO, because they provide objective morphological findings of the orbital structures. An important role of imaging studies is revealed in differential diagnosis versus other orbital diseases and can be also used to evaluate the progression of the disease and follow-up after clinical or surgical treatment.
Graves ophtalmopathy (GO), thyroid eye disease (TED) and thyroid - associated orbitopathy (TAO) are terms referring to an autoimmune inflammatory process that affects the adipogenesis of orbital fat and periorbital tissue, associated with dysthyroidism. On imaging, such as computed tomography (CT) thyroid -associated orbitopathy (or thyroid -associated ophtalmopathy) is characterised by symmetrical and bilateral proptosis, secondary to extra-ocular muscle (EOM) enlargement and expansion of orbital fat. Imaging studies ca be useful in identifying patients risk to develop dysthyroid optic neuropathy and initiating early treatment of the condition, avoiding permanent visual loss. The purpose of this study was to reveal the prevalence of thyroid ophtalmopathy imaging considerations in Graves disease patients. A total of 19 patients were evaluated on computed tomography scanning the diameters and density of extra-ocular muscles, muscular index, proptosis, width of the optic nerve, width of superior ophthalmic vein and lacrimal gland position.
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