Transcript Image Quality - El Camino College

Image Quality
Part II
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Image Quality
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Photographic Quality
Geometric Quality
Image Quality
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The films or images have different levels of density –
different shades of gray
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X-rays show different features of the body in various
shades of gray.
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The gray is darkest in those areas that do not absorb Xrays well – and allow it to pass through
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The images are lighter in dense areas (like bones) that
absorb more of the X-rays.
Why you see what you see…
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Terminology
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Density, contrast
Detail
Distortion
Image Sharpness
spatial resolution
Lp/mm
Blur
Motion
SID
OID
Focal spot size
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Image receptor
Magnification
Penumbra
Size distortion
Shape distortion
Focal Spot size
Density
Contrast
Detail
Distortion
Image quality
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detail
Resolution, ability to
distinguish shapes, ability
to distinguish lines on
image
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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
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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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Recorded Detail
Factors that affect detail
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SID
Focal spot size
OID
Image receptor type
Motion
Focal Spot Geometry
Angle of anode
size
Focal Spot Geometry
Focal spot is not
really a single point
Dependent on filament size
and anode angle.
SID
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Shine a flashlight on a 3-D object, shadow borders
will appear “fuzzy”
-On a radiograph called penumbra
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Penumbra (fuzziness) obscures true border
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Farther the flashlight from object = sharper
borders. Same with radiography.
Recorded Detail: Penumbra and SID
Recorded Detail: Penumbra and Focal Spot Size
Recorded Detail: Penumbra and OID
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
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The closer the object to the film, the sharper the
detail.
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OID , penumbra , sharpness 
OID , penumbra , sharpness 
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Structures located deep in the body, radiographer
must know how to position to get the object closest
to the film.
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Recorded Detail: Image Receptor Type
Film/Screen Imaging
excellent spatial resolution-smallest detail
that can be detected in an image
Computed Radiography (cassettes)
Digital Radiography (cassette-less)
improved contrast resolution
Motion
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Can be voluntary or involuntary
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Best controlled by short exposure times
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Use of careful instructions to the patient
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Suspension of patient respiration
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Immobilization devices
Blurring of image
due to patient
movement during
exposure.
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distortion
Misrepresentation of size or shape of
anatomic part; when part is distorted,
detail is reduced
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Distortion
An increase of decrease in the size of an object : magnification or reduction
Three types: size, shape, placement of part in body
Types of Distortion
FACTOR INFLUENCING
DISTORTION
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SID-size distortion
OID-size distortion
Beam Angulation-shape
distortion
Body Part-Beam alignmentshape distortion
Distortion: SID
40” SID VS 72” SID
Which one is which?
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Distortion: OID
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Elongation
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Foreshortened
Normal
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