Image Characteristics; Dental X-ray; PDF

Image Characteristics  Image Characteristics Visual characteristics Geometric characteristics  Visual Characteristics 1-Density 2-Contrast  1-Density Represents the overall degree of darkening of an exposed x-ray film (white to black) Low density light High density dark ...

Image Characteristics  Image Characteristics Visual characteristics Geometric characteristics  Visual Characteristics 1-Density 2-Contrast  1-Density Represents the overall degree of darkening of an exposed x-ray film (white to black) Low density light High density dark  Density influenced by: Exposure factors (mA, exposure time, kVp) Increasing the milliamperage (mA), exposure time, or kilovoltage peak (kVp) increases the number of photons reaching the film and thus increases the density of the radiograph. Patient size If exposure factors used for adults are used on children or an edentulous patient, the resultant films are dark because a smaller amount of absorbing tissue is in the path of the x-ray beam. Object density (amalgam, bone, etc.; as object density increases, film density decreases) Film fog (scatter, improper safe light, improper film storage, expired film) Low object density, high film density High object density, low film density  Fog Represents increased film density from causes other than exposure to the primary x-ray beam (scatter, improper safelighting, improper film storage, expired film)  2-Contrast The difference in densities between various regions on a radiograph  Low Contrast Long Scale Many shades of gray Best for periapical or periodontal evaluation  High Contrast Short Scale Black and White (Few shades of gray) Best for caries detection Low Contrast High Contrast  Contrast influenced by: 1-kVp The primary factor that affects contrast. It is the only exposure parameter that affects contrast It affects the energy or penetrating ability of x- rays 2-Subject contrast (varying object densities within patient) 3-Film fog (scatter, improper safe light, improper film storage, expired film) kVp High Contrast Low Contrast Subject contrast Geometric Characteristics 1-Sharpness 2-Magnification 3-Distortion Principles of Shadow Casting 1. Radiation source small as possible 2. Source-object (Focal-film, Target-film) distance large 3. Object-film distance small 4. Object and film parallel 5. X-ray beam perpendicular to object & film 1. Radiation source small as possible The smaller the focal spot (target), the sharper the image will be. During x-ray production, a lot of heat is generated. If the target is too small, it will overheat and burn up. Radiation source as small as possible Line Focus Principle Source = target = focal spot = focus  Line Focus Principle Target Anode (+) Cathode (-) Apparent (effective) focal spot size Actual focal spot size PID 2-Source-object, Focal-film, Target-film distance Large distance from target to object produces more parallel rays  3-Object-film distance bisecting paralleling Short distance from object to film decreases magnification 4-Object and film parallel 5-X-ray beam perpendicular to object/film  1-Sharpness Measures how well the details (boundaries/edges) of an object are reproduced on a radiograph  Penumbra Partial shadow Zone of unsharpness along the edge of images in a radiograph Penumbra Umbra Sharpness influenced by: 1. Focal spot size 2. Source – object (teeth) distance 3. Object (teeth) - film distance 4. Intensifying screens 5. Film crystal size 6. Motion Decrease focal spot size, increase sharpness Increase target-teeth distance, increase sharpness Target Teeth Umbra Penumbra film Decrease teeth-film distance, increase sharpness Target Teeth Umbra Penumbra film film Intensifying screens decrease sharpness Patient motion decreases sharpness  2-Magnification Increase in size Magnification affected by: 1.Target-object distance 2.Object-film distance Increase target-teeth distance, decrease magnification Decrease teeth-film distance, decrease magnification  3-Distortion Change in shape or relationship Distortion affected by: 1. Film-object relationship 2. Beam alignment Paralleling Bisecting angle Thank you