Distortion
Most common tube angle is longitudinal which are often termed
cephalic or caudal
When the position of the body part or object within in body do not permit alignment, ________ _________ is utilized.
creative alignment
When an image is distorted, spatial resolution is
decreased
This is because as SID increases, the percentage of total distance that makes up OID ___________
decreases
Magnification is assessed by calculation of the magnification factor =
degree of magnification
Angulation in tube will result in some form of _________
distortion
Whenever the central ray is not perpendicular, some degree of _________ will occur -This occurs in every image because the central ray is not truly perpendicular
distortion
Any structure which is not positioned at the central ray will be distorted because of the
divergence of the beam
Shape distortion can be caused or avoided by ___________ of the central ray with the anatomical part and central part
alignment
Farther from the central ray -
greater distortion
Large OID, Small SOD,
high entrance exposure
Angulation will __________ SID, which will __________ exposure to IR
increase; decrease
Magnification size distortion is minimized by ___________ SID.
increasing
All magnification involves a degree of
loss of resolution
Short OID, large SOD,
low entrance skin exposure
Size distortion is generally
magnification
Conventional radiography strives to __________ magnification.
minimize
Objective in radiography is to _________ magnification as much as possible
minimize
Any misalignment of the CR among 3 factors-_____________- alters the shape of the part recorded in the image.
tube, part or image receptor
Refers to the direction and the degree the tube is moved from its normal position perpendicular to the image receptor
Angulation
Factors Affecting Shape Distortion Alignment
Central ray Anatomical part Image receptor
Factors Affecting Shape Distortion Angulation
Degree Direction
It is defined as a misrepresentation of the size and/or shape of the anatomical part being imaged
Distortion
Refers to an increase in the image size of an object compared with its true or actual size.
Distortion (Magnification)
projects the object so it appears to be longer than it really is
Elongation
Shape distortion displaces the projected image of an object from its actual position and can be described as either:
Elongation Foreshortening
projects the object so it appears shorter than it really is
Foreshortening
MF=
Image size/Object Size
Proper positioning is achieved when the central ray is at ________ _______ to the anatomical part and the image receptor -This means the *part* and *image* *receptor* must be ________
right angles; parallel
Unequal magnification of different portions of the same object is called __________
shape distortion
Shape distortion is more subjective than
size
The greater the SID, the __________ the magnification
smaller
Angulation is used to avoid __________ of parts
superimposition
Magnification Radiography deliberately increases ___ to cause magnification.
OID
Distortion depends on:
Object thickness Object position Object shape
Very critical when discussing magnification & resolution
Object to Image Receptor
Use as large a source to image receptor distance as possible
Large SID
Less distorted
Long SID
Magnification is expressed quantitatively by the __
MF
Used in interventional radiology and mammography. -Enhances the visualization of small structures.
Magnification radiography
Some tubes can be angled transversely -
"roll"
_______ has a major effect on magnification
SID
2 factors affect image magnification:
SID AND OID
Radiographic images of objects are always magnified in terms of the true object size.
SID and OID are important factors
Foreshortening and elongation
Shape
More distorted
Short SID
Magnification
Size
This misrepresentation can be classified as either:
Size Shape
Place the object as close to the image receptor as possible
Small SID
Direction of tube angle is dependent on
patient position
Ideally, the central is intended to be projected _____________ to both the anatomical part and the image receptor
perpendicular
The image receptor is intended to be positioned __________ to the central ray and _________ to the anatomical part -If IR is not parallel to object, or if central ray is not centered to part, serious distortion can take place
perpendicular; parallel
The long axis of the anatomical part is intended to be positioned __________ the central ray and _________ to the image receptor
perpendicular; parallel
Reducing magnification, ____________ size distortion, therefore ___________ spatial resolution.
reduces; increasing