Sciences Unit 1 Flashcards
Radiographic quality=
balance between the photographic and geometric characteristics of our image
2 Geometric properties of an image
Detail
Distortion
Detail
degree of accuracy of the structural lines actually recorded on the image
Distortion
Misrepresentation of the size or shape of the structures
What properties control geometric detail
recorded detail
What properties control photographic properties
Visibility of detail
Recorded Detail def
accuracy of structural lines actually recorded
Recorded Detail AKA
Sharpness geometric sharpness definition spatial resolution umbra
Umbra def
Distinctly sharp area of a shadow
Penumbra def
imperfect
unsharp shadow
Term used for measuring detail with film screen
resolution
How is resolution measured
Line pairs per mm, resolution tool
3 Factors affecting detail
Geometry
Image Receptor
Motion
3 Things we have control over to “fix” detail
eliminate motion
reduce OID
reduce FSS
What 2 factors affect detail
Distance(OID/SID)
FSS
Why does FSS cause geo unsharpness
beam diverges as they leave the target
How does distance affect geo unsharpness
^distance = ^divergence
Geometric blur
area where beam diverges
Which distace issue is most important to fix if you have to choose 1
OID
Geometric blur/OID relationship
Direct
Geo blur/SID relationship
inverse
What distance options will give you the highest resolution
decreased OID and increased SID
FSS is controlled by
the line-focus principle
SFS= _______ geo blur
less
LFS=________ geo blur
more
What controls penumbra
FSS
Where does penumbra come from
fact that photons do not come from a point source
FSS/Penumbra relationship
direct
Typical SFS mm
.6mm
Typical LFS mm
1.2 mm
To min geo unsharpness use what focal spot
smalles
to min geo unsharpness use what SID
greatest practical
To min geo unsharpness use what OID
lowest
What shape would produce a perf sharp image
trapezoidal
unsharpness/detail relationship
inverse
GUS formula
FSSxOID / SOD
F/S Image Receptor faster combo = ____ resolution
less
slow combo f/s image receptors
increased resolution and dose
What do you use to test cassette quality
wire mesh
Matrix
the whole picture/all pixels combined
^matrix size=___ resolution
increase
smaller pixel pitch=______ resolution
higher
What IR size should be used for greater detail
smallest IR positive
Monitor quality test used
Monitor quality assurance
used to see that all four corners look alike
What is printer resolution determined by
dpi, dots per inch
Higher dpi=___ resolution
higher
1 Cause of image unsharpness
Motion
3 Types of motion
Voluntary
Involuntary
Equipment
Best way to reduce motion
Communication
2 other ways to reduce motion
Exposure time reduction
Immobilization
List of immobilizers in order
- Male relatives
- Female relatives
- non-tech staff
- techs
- students
Distortion
Misrepresentation of size and/or the shape of the object being imaged
2 Types of distortion
- Size distortion
2. Shape distortion
What is seen with size distortion
Magnification
What 2 things is size distortion affected by
SID
OID
2 things seen with shape distortion
elongation
foreshortening
What is elongation affected by
CR/IR Misalignment
what is foreshortening affected by
part being misaligned
Elongation makes objects appear (2)
longer and thinner
Foreshortening makes objects appear (2)
shorter and wider
size distortion/OID relationship
directly proportional
size distortion/ SID relationship
inversely
Magnification formula
Image width/ object with or
SID/OID
Define macroradiography
When we mag intentionally for very small anatomy
What is Macroradiography AKA?
Magnification
What does macro use to image
microfocus tubes
What benefit does a fractional FSS have?
helps gain back some of the detail lost by the magnification
What is a risk of fractional FSS?
Increased OID increases pt skin dose
What is size distortion referred to
“true distortion”
What causes elongation
tube
IR alignment
What causes Foreshortening
Part not aligned
What is size distortion dependent on
CR/part/image receptor relationship
What should always be perpendicular to the part
CR
What should always be // to the part
IR
What is foreshortening most often caused by
the part not being parellel with iR
What may distortion lead to diagnostically
incorrect dx, not seen or make a fx seem worse
2 bones are superimposed, what will get thrown the furthest when a tube is angled?
The furthest one from the IR, or closest to the tube
2 reasons why we intentionally distort
trying to “undistort” anatomy that may not be parallel to the IR
To prevent superimposition of one anatomical structure over another
What is intentional distorment AKA
Displacement