Chapter 14 Geometrical qualities of the image -megs class

in the projection geometry of an x-ray beam, unsharpness is controlled by what 3 things:

1. SOD 2. OID 3. focal spot size

define overall image resolution, and list its 2 primary components

1. high visibility 2. optimum recognizability resolution is defined as the ability to distinguish any 2 adjacent details in the image as being separate and distinct from each other.

for ratios up to a doubling, to convert the magnification factor into a percentage, simply subtract 1 and multiply by _______

100

what is the geometrical unsharpness forumla (penumbra formula)

FS x OID/ SOD

what is SID, OID, SOD

SID- source to image receptor distance OID- object to image receptor distance SOD- source to object distance sid-oid = sod

magnification in any radiographic image is controlled by the _______/_______ ratio

SID/OID

what is the magnification formula?

SID/SOD = image/object size

what is the sharpness formula?

SOD/OID

The sharpness of recorded detail may be described as the ________ with which the edges of a particular image stop

abruptness

partial shadows occur because any given edge of the object is actually projected at several different ________ from several different points within an area light source.

angles

if shadows could be cast from a point source of light, there would never be any ________ present.

blur

in a radiograph, high _______ is easy to mistake for high sharpness.

contrast

for shape distortion to be present, the length and the width of the image must have been altered by _______ degrees

different

severe penumbra has the effect of making it impossible to distinguish two adjacent objects in an image as being ________ objects.

distinct and separate

if the image of an object in the direction of any angling or off-centering of the x-ray beam measures longer than that of the real object, while its width remains unchanged, _______ distortion is present.

elongation

what is the distinction between shape distortion and magnification

for shape distortion to be present, the length and the width of the image must have been altered by different degrees

the opposite of elongation is _______

foreshortening

in a given axis of direction, (lengthwise or crosswise) shape distortion will consist of either _______ of the image or _______ of the image

foreshortening, elongation

what is elongation

if the length measures longer than that of the real object, while its width remains unchanged

what is foreshortening

if the length measures shorter than that of the real object

define and describe the cause of geometrical penumbra

is the region of the field that receives radiation from some parts of the source but not the whole source,, leads to variation in dose.

in a magnified image, both axes of the image, that is , both its _______ and its _______ will measure larger than the real object by equal projections.

length, width

an image has a length 3 times longer than the projected object, while the width is only 2 times wider. the image is both distorted and magnified. the magnification is simply the _______ of the two amounts.

lesser

we define ________ as the difference between size of the real object and the size of its projected image

magnification

the width of the penumbra can actually be ________, and can also be predicted geometrically.

measured

the human eye tends to locate the visual edge of the bone in the _______ of the penumbal shadow

middle

sharpness is destroyed not only by geometrical penumbra s described above, but also by ________ penumbra.

motion

the two general factors that primarily control sharpness within the image carried by the remnant x-ray beam to the imaging plate are the occurrence of _______ and beam projection geometry

motion

if the heart size is magnified because of the way the radiographer positioned the patient, it can simulate a _______ condition. Magnification can lead to misinformation.

pathological

the blurry, fading partial shadow projected at each edge is referred to as the ________

penumbra

the spread of penumbra is precisely indicated by drawing out the relationship of these three variable in a _______ diaphragm

penumbra

at an extreme distance it is possible to make the pure umbra portion of the shadow actually disappear, so that the remaining image is all ________ shadows

prenumbra

the shape _______ of an object is simply defined as its length divided by its width

ratio

The _________ or geometrical integrity of a image is made up of its sharpness of recorded detail, magnification, and shape distortion.

recogizability

mathematical expressions of sharpness are always indirectly derived and expressed as _______ numbers

relative

the difference between the shape of the real object and the shape of its projected image is referred to as _______

shape distortion

the most important component of the recognizablility of an image is its _______

sharpness of detail

list and define the 3 recognizability or geometrical components of every image

sharpness, magnification, shape distortion

the spreading of the penumbra (blur) in an image can actually cause the umbra to _______ in size

shrink

like sharpness, magnification is based solidly on the geometry of _______ triangles.

similar

penumbra can be precisely predicted because in terms of plane geometry at each edge of the projected object a penumbra diagram shows two _______ triangles, (inverted and reversed to each other.)

similar

magnification is often referred to as ________ distortion

size

in angiography, magnification techniques are sometimes intentionally used when blood clots or other anomalies may be too _______ to recognize

small

what is the "penumbra"

the blurry, fading partial shadow projected at each edge

what is shape distortion

the difference between the shape of the real object and the shape of its projected image

what is magnification (size distortion)

the difference between the size of the real object and the size of its projected image.

what is the "umbra"

the inner portion of a shadow has a uniform darkness, considered to be the "true/pure" portion of a shadow

define image sharpness (spatial resolution)

the sharpness of detail may be described as the abruptness with which the edges of a particular image stop,

for magnification to be present, the pure shadow, the _______ of the image must be enlarged.

umbra

the inner portion of a shadow has a uniform darkness and is called the ________

umbra

the scattering process is _______ to the formation of penumbra at the edges of an image.

unrelated

_______, on the other hand is an objective quantity that can be directly measured, geometrically predicted and mathematically calculated

unsharpness

just like the rest of an image, the edges of anatomy also have both _______ and recognizability functions. just because they are more visible does not mean they are also more sharp.

visibility