Week 15. DISTORTION
OID (object to image receptor distance)
Another critical factor in both magnification and resolution.
true
Some radiographic tubes can also be angled transversely (sometimes referred to as "roll"). true or false
true
This misrepresentation can be classified as either size or shape distortion. true or false
Photographic Properties
-Visibility- contrast and density
SID (Source-to-Image Receptor Distance)
has a major effect on magnification
true
Any structure that will is not positioned at the central ray will be distorted because of the divergence of the beam - the farther from the central ray, the greater the distortion. true or false
true
Shape distortion can be caused or avoided by careful alignment of the central ray with the anatomical part and the image receptor. true or false
true
Shape distortion is a more subjective evaluation than size. true or false
false Shape distortion is the misrepresentation by unequal magnification of the actual shape of the structure being examined
Shape distortion is the misrepresentation by equal magnification of the actual shape of the structure being examined. true or false
false Shape distortion often results because structures lie normally at different levels within the body. It also occurs due the divergence of the x-ray beam.
Shape distortion often results because structures lie normally at same levels within the body. It also occurs due the divergence of the x-ray beam. true or false
true
Since it is not possible to reflect or refract x-ray photons by ordinary methods, they can only diverge from their point source. true or false
true
The anatomical part is normally positioned with its long axis perpendicular to the central ray and parallel to the image receptor. true or false
false The angulation of the tube is designed to cause a controlled or expected amount of shape distortion to avoid superimpositions.
The angulation of the tube is designed to cause a controlled or expected amount of size distortion to avoid superimpositions. true or false
Longitudinal angulations
are usually termed cephalad when the tube is angled toward the head of the patient, and caudad when it is angled toward the patient's feet.
Magnification
as the x-ray beam diverges, the image produced on the film is always slightly larger than the original image, and this effect is call
Distortion
is a misrepresentation of the size or shape of the structures being examined.
Degree
is simply a method of describing the exact amount of angulation and is usually stated as the angle between the central ray and the image receptor plane from the standard reference point of perpendicularity.
OID (object to image receptor distance)
is the critical distance for magnification and resolution.
ASSESSING DISTORTION
is the second of the 2 geometric properties affecting radiographic image quality
Central ray
is the theoretical photon that exits from the exact center of the focal spot.
false it is much more difficult to assess because there is no effect that can be calculated, as in the magnification factor for size distortion.
it is much more easy to assess because there is effect that can be calculated, as in the magnification factor for size distortion. true or false
Foreshortening
projects the image so it appears shorter than it really is
Elongation
projects the object so it appears to be longer than it really is.
true
shape distortion involves both elongation and foreshortening and is a serious alteration in the projection image. true or false
false size distortion is generally a matter of magnification.
shape distortion is generally a matter of magnification. true false
Geometric properties
sharpness- recorded detail and distortion
cephalad
toward the head
caudad
toward the tail
true
•In 1928 "Modern X-ray Technic", Ed Jerman recommended distances from 25" (63 cm) to 36" (90 cm). true or false
longitudinal
The most common direction of the tube angle is
true
Although 40" (100 cm) has developed as the current routine SID, this was not always so. true or false
false Distortion can be difficult to determine even when normal sizes and shapes are known.
Distortion can be easy to determine even when normal sizes and shapes are known. true or false
false Elongation occurs when there is poor alignment of the tube and/or image receptor.
Elongation occurs when there is poor alignment of the patient. true or false
false For many, many years chest radiography has been performed at 72" (180cm) because the erect positioning arrangement permits horizontal beam to be used and the increased SID effectively minimizes the magnification of the heart shadow
For many, many years chest radiography has been performed at 72" (180cm) because the erect positioning arrangement permits horizontal beam to be used and the decreased SID effectively maximizes the magnification of the heart shadow. true or false
false Foreshortening occurs only when there is poor alignment of the part.
Foreshortening occurs only when there is poor alignment of the tube and/or image receptor. true or false
false Glenn Files' 1945 book, "Medical Radiographic Technic" - 40' (100cm) SID.
Glenn Files' 1945 book, "Medical Radiographic Technic" - 36" (90cm) SID. true or false
false In all instances, reduced magnification size distortion increases the resolution of recorded detail.
In all instances, reduced magnification size distortion decreases the resolution of recorded detail. true or false
Distortion
It creates a misrepresentation of the size and/or shape of the anatomical part being imaged.
false Magnification size distortion is controlled by positioning the body part and tube to maximize SID while minimizing OID.
Magnification size distortion is controlled by positioning the body part and tube to minimizing SID while maximize OID. true or false
Angulation
Refers to the direction and degree the tube is moved from its normal position perpendicular to the image receptor.
true
Size distortion can be only magnified with film/screen radiography. true or false
true
Some institutions are adopting the 48" (120 cm) as a routine distance and the movement appears to be growing. true or false
false The first x-ray techniques book in the United States is generally recognized to be the 1918 "Extract from the United States Army X-ray manual" - 20" or 50 cm is discussed as a reasonable SID.
The first x-ray techniques book in the United States is generally recognized to be the 1918 "Extract from the United States Army X-ray manual" - 40" or 50 cm is discussed as a reasonable SID. true or false
false The long axis of the anatomical part, or object, is intended to be positioned perpendicular to the central ray and parallel to the image receptor.
The short axis of the anatomical part, or object, is intended to be positioned perpendicular to the central ray and parallel to the image receptor. true or false
true
When a part is superimposed, central ray angulation can be a useful tool to provide a projection that would otherwise be impossible to differentiate from overlying structures. true or false
true
When describing objects, it is important to remember the size and distance relationship in a radiographically projected image is the opposite of that perceived visually. true or false
false When the position of the body part or object within the body does not permit this alignment, creative positioning must be utilized.
When the position of the body part or object within the body permits this alignment, creative positioning must be utilized. true or false
true
Whenever the central ray is not perpendicular, some degree of shape distortion will result. true or false
Ideally
is intended to be projected perpendicular to both the anatomical part & the image receptor.