The radiographic contrast, when using hydrosoluble uro-angiographic contrast media, depends on several factors. A phantom and a new method are proposed to assess and optimize the contrast. The phantom allows to simulate three pseudovessels with diameter of 2 mm, 5 mm, and 10 mm, placed in a water-equivalent layer of 20/cm thickness. The phantom is exposed to a photon beam produced by a conventional X ray tube, and the images are obtained using conventional screen film system. The aim of the study is to assess the radiographic contrast between the vessel and the background when modifying the optical density of the radiograph (by different settings of the mAs switching), the X-ray tube high voltage and the diameter of the vessels; the contrast was studied with four different contrast media (Uromiro 24%, Conray 36%, Iopamiro 300 and Iomeron 400) and three X-ray tube high voltages (60 kV, 80 kV, 100 kV). The curve fitting the contrast as a function of the optical density of the background (in each condition of high voltage, diameter of the vessel and contrast media used) is a parabola. A quite narrow distribution of abscissas of the maxima of the parabolas was found, ranging from the minimum optical density 1.21 in the case of 100 kV high voltage and 2 mm diameter to the maximum optical density 1.58 in the case 60 kV and 10 mm. The mean value (1.40) is proposed as the optical density of the background optimizing the contrast according to the screen-film system used. In conclusion, the authors suggest to optimize the use of contrast media, trying to obtain radiographs with an optical density approaching the optimal value in any clinical situation. Therefore tables of the settings of the X-ray tube and generator are required; the tables must take into account the main parameters influencing the settings, such as the source-film distance, the water-equivalent thickness of the patient and the film-screen system used.
|Titolo:||A method of image enhancement in the use of hydrosoluble uro-angiographic contrast media [Un metodo di ottimizzazione dell'immagine nell'impiego di mezzi di contrasto idrosolubili uro-angiografici]|
|Data di pubblicazione:||1995|
|Appare nelle tipologie:||Articolo su Rivista|