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Why you see what you see…
The films or images have different levels of density – different shades of gray
X-rays show different features of the body in various shades of gray.
The gray is darkest in those areas that do not absorb X-rays well – and allow it to pass through
The images are lighter in dense areas (like bones) that absorb more of the X-rays.
Terminology Density, contrast Detail Distortion Image Sharpness spatial resolution Lp/mm Blur Motion SID OID Focal spot size
Image receptor Magnification Penumbra Size distortion Shape distortion Focal Spot size
RECORDED DETAIL
The degree of sharpness in an object’s borders and structural details.
How “clear” the object looks on the radiograph
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Recorded detail Image sharpness Spatial resolution Smallest separation
of two lines or edges Measured by lp/mm
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RESOLUTION TEST
TOOLS
LINE PAIRS/ MM
Depicts how well you can see the differences in structures
More lines=more detail
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Focal Spot Geometry
Focal spot is notreally a single point
Dependent on filament size and anode angle.
SID
Shine a flashlight on a 3-D object, shadow borders will appear “fuzzy”
-On a radiograph called penumbra
Penumbra (fuzziness) obscures true border
Farther the flashlight from object = sharper borders. Same with radiography.
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The position of the structure in the body will influence how magnified it will be seen on the image
The farther away – the more magnified
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Recorded Detail: OID and Penumbra
The closer the object to the film, the sharper the detail.
OID , penumbra , sharpness OID , penumbra , sharpness
Structures located deep in the body, radiographer must know how to position to get the object closest to the film.
Recorded Detail: Image Receptor Type
Film/Screen Imagingexcellent spatial resolution-smallest
detail that can be detected in an imageComputed Radiography (cassettes)Digital Radiography (cassette-less)
improved contrast resolution
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Motion Can be voluntary or involuntary
Best controlled by short exposure times
Use of careful instructions to the patient
Suspension of patient respiration
Immobilization devices
Misrepresentation of size or shape of anatomic part; when part is distorted,
detail is reduced
distortion
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Distortion
An increase of decrease in the size of an object : magnification or reductionThree types: size, shape, placement of part in body
Types of Distortion
SID-size distortion OID-size distortion Beam Angulation-
shape distortion Body Part-Beam
alignment-shape distortion
FACTOR INFLUENCING DISTORTION
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