X-ray的基本知识PPT.ppt

X-RAY IMAGING ;Who discovered the X-ray?;What is X-Ray ? High energy electromagnetic radiation produced in an X-ray tube with a much shorter wavelength and a higher frequency than visible light Wavelength range:0.0006nm ~ 50nm(10-9 m) For medical diagnosis: 0.008nm ~ 0.031nm ;Production of X-rays;X-ray tube ;Fluorescenct effect Exciting fluorescent material to transform short wave rays in to long wave visible lights (fluorescence). Foundation of fluorescopy ;Photosensitivity Silver bromide（Ag+） latent image(Ag, black） Development and fixation wash out silver bromide Amount of deposited Ag ? absorption of X-ray Foundation of X-ray photography;Ionizing effect — biological effect Molecule ionization Breakdown of the molecular structure Foundation of radiotherapy Reason for medical radiation protection ; ② Tissues with different density or thickness different X-ray absorption;Film1 unexposed to X-ray;Influecne of tissue density and thickness on X-ray imaging Density (Specific gravity) ? Absorption of X-ray ? Gray scale on radiograph or brightness on the fluorescent screen;;加试管图;Tissues with different densities: natural difference — natural contrast;The shape of the cross section?;Fluorescent screen;补穿透正常的胸片;Chest film with inadequate penetrating effect of X-ray（kV is too low);;Consolidation (↑) in the lung appears as white shadow due to its higher density than normal pulmonary tissue containing air.;Shortcomings of radiograph Overlapping of organs and tissues that X-ray beam passing through ② Magnification: shorter distance between the focus and examined object, less magnification ③ Distortion: like the shadow of human figure under the sun; X-ray production Devices ① X ray tube ② Transformer ③ Control table;X-ray tube; Conventional X-ray detection devices X-ray film: varying degrees of blacking (varying density of the microscopic black silver granules) Fluorescent screen: emitting visible light (Imaging i