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Image Formation

End of chapter 11 (Fosbinder)

QuestionAnswer
What is recorded detail? Distinctness or unsharpness
What is umbra? Pure, true, complete shadow.
An increase in detail causes a ________ in unsharpness (blur) Decrease
What is blur? Also referred to as penumbra, edge gradient and geometric unsharpness, partial shadow of the edge of an object.
What is the controlling factor for recorded detail? Focal spot size
What are the influencing factors of recorded detail. SID OID Film Screen Speed Patient Motion
How does focal spot size effect recorded detail? Inversely. Increased focal spot size = decreased recorded detail
How is focal spot size and blue related? Directly. Increase focal spot size, decrease in recorded detail = increase of blur
What is the size range of a small focal spot? .5mm-.6mm
What is the size range of a large focal spot? 1.0mm-1.2mm
How does SID influence recorded detail? Increased SID, decrease in blur = increased recorded detail
How does OID influence recorded detail? Increased OID, increased blur = decrease in recorded detail
Blur Formula? Focal Spot Size x OID = _____mm SOD
How do you fine SOD? SID-OID=SOD
When there is an excessive amount of OID the amount of blur can be decreased by? Increasing SID
What is image receptor blur? Variations in construction and composition of film screen systems affect photographic properties and geometric properties
How does film screen speed effect recorded detail? High speed screens required less X-rays, decrease patient dose, increase blur = decrease in recorded detail.
What is quantum mottle? Blotchy appearance of a radiograph that has been exposed by means of a fast intensifying screen. Looks like salt and pepper ****faster screen = more artificial light***
What tool do you use to test film screen contact? Wire mesh
What is resolution? Ability of the image system to resolve or distinguish between two adjacent structures.
What is spatial resolution? Minimum distance between two objects at which they can be recognized as two separate objects. (Physical distance)
What is contrast resolution? The ability of the imaging system to distinguish between small objects having similar subject contrast. (Depends on your system)
What is a line pair? A line and a space
How many line pairs can the human eye discern? 5Lp/mm
2 types of blur 1. Voluntary (within patient control) 2. Involuntary (outside patient control)
What 3 things can you do to limit patient movement? 1. Communication 2. Immobilization 3. Short exposure time
What is distortion? Radiographic misrepresentation of size or shale compared to the actual size and shape of the structure.
What factors influence distortion? SID OID Central ray angle
What is spatial distortion? The intentional distortion used to avoid superimposition Ex: inlet/outlet pelvis, lateral knee, sacrum/coccyx
Define magnification The equal enlargement (both length and width) of the recorded image as compared to the actual size to the structure
How is magnification and OID related? Directly. Increase OID = increase magnification
How is magnification and SID related? Inversely. Decrease magnification = increase SID
Formula to calculate image and object size. Image size = SID Object size SOD
What is magnification factor? Indicates how much he size distortion is demonstrated on the image
What is the magnification factor formula? SID Or Image SOD Object
Formula to calculate object size using magnification factor. Object = Image Magnification factor
Formula to calculate percent of magnification Image - object x 100 Object
2 types of shape distortion 1. Elongation 2. Foreshortening
Elongation happens when... The tube is angled
Foreshortening happens when... When the part is angled
When angling the tube you must decrease your SID by... 1inch for every 5 degrees
Created by: Aborys88