Contrast. Contrast: the difference in density on adjacent areas of a radiograph or other image receptor. Subjective. Long Scale (Low Contrast)

Transcription

1 Contrast Contrast: the difference in density on adjacent areas of a radiograph or other image receptor. Subject Subjective Radiographic Long Scale (Low Contrast) Short Scale (High Contrast)

2 Factors affecting contrast 1. Kilovoltage peak (kvp) 4. Pathology 2. Contrast media 5. Scattered radiation 3. Bodyparts 6. Viewingcondition

3 Density Density: the amount of blackening darkness on the radiograph Controlling factors: 1. Milliamperage x time (mas) 2. Distance, source image receptor distance (SID) 3. Kilovoltage peak (kvp)

4 mas Density mas Density

5 Recorded Detail Detail: The degree of sharpness in an object s borders and structural details. Other names: sharpness h of detail definition resolutionl degree of noise

6 Detailcontrolling factors 1) kvp & mas 2) Focal Spot Size 3) SID (Source to Image Distance) 4) OID (Object to Image Distance) 5) Movement unsharpness 6) Object Unsharpness (Geometric) 7) Material Unsharpness (Photographic)

7 Focal Spot Size Focal spot: the area on the anode where the source of x ray coming out. o Fine detail = small focal spot (i.e. small bones) o General radiography uses large focal spot

8 What Is Penumbra? Partial shadows at the edge of the object Shine a flashlight on a 3 D object, shadow borders will appear fuzzy On O a radiograph called Penumbra

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10 SID (Source toimagedistance) o The greater the distance between the source of the x ray (tube) and the image receptor (cassette), the greater the image sharpness. o Standard distance = 40 in. most exams o Exception = Chest radiography 72in in.

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12 OID (Object toimagedistance) o The closer the object to the film, the sharper the detail. o OID, penumbra, sharpness o OID, penumbra, sharpness

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14 Movement unsharpness o o Due to patient, equipment or film movement during the exposure. Patient movement can be voluntary or involuntary. Bestcontrolled by: 1. Use of careful instructions to the patient. 2. Suspension ofpatientrespiration respiration. 3. Immobilization devices. 4. Use a faster film screen combination 5. short exposure time ( mas kvp)

15 Blurring of imagedue to Blurring of image due to patient movement during exposure.

16 Object Unsharpness (Geometric) o Main problem is trying to image a 3 D object on a 2 D film. o Compensation for object unsharpness with factors that can be controlled dby: 1. focal spot size 2. SID 3. OID

17 Material Unsharpness (Photographic) Fast film/screen combinations = image sharpness Slower film/screen combinations = image sharpness Good film/screen contact = image sharpness Single sided emulsion = image sharpness

18 Distortion Distortion: Misrepresentation of the true size or shape of an object Two types: 1. MAGNIFICATION (i (size distortion) i 2. TRUE DISTORTION (shape distortion)

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20 MAGNIFICATION (size distortion) Major influences: SID & OID o As SID, magnification o As OID, magnification Magnification large OID

21 TRUE DISTORTION (shape distortion) o Controlled by alignment of the Beam (x ray) part (object) image receptor (film) o Influences: 1. Central ray angulation 2. body part rotation

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23 General radiography Conventional Radiography Applications Application Types of film - Single emulsion, direct exposure, low sensitive speed for extremities. - Double emulsion, screen/film, high sensitive speed for other exams e.g. CXR and Abdomen. Mammography - Single emulsion, screen/film, low sensitive speed Old Type Ultrasonography Dental radiography Single emulsion screen/film low sensitive speed fine grains. Single emulsion, non-screen grey tone transparency film use Multi-Format Camera (MFT). Double emulsion, different film speeds whether direct exposure (intraoral) or indirect screen type exposure (extraoral) Duplication Films Laser Films Subtraction Films Single emulsion, blue or clear polyester base coated, UV light sensitive, positive film. High speed, high contrast, single-emulsion emulsion red light sensitive film coated on blue or clear polyester base. It s used with laser printers employing infrared solid state lasers. single-sided monochromatic emulsion, polyster base, low contrast film

24 Old US Films Mammography Film Intraoral Film Intraoral Films (Periapical, Bitewing, Occlusal)

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