Subject Factors Flashcards
Name all six subject factors
Subject Contrast
Patient Thickness
Tissue mass density
Effective Atomic number
Object shape
Kilovolt peak
-the “third general group” of factors that affect radiographic quality involve the patient
-“associated not so much” with the positioning” of the patient
Subject Factors
The contrast of the radiograph “viewed on an illuminator”
Radiographic Contrast
The degree of subject Contrast is “directly proportional” to the relative number of x-rays leaving those sections of the body
Patient Thickness
“Different sections of the body” may have equal thickness yet different mass densities
-these materials have the same thickness and chemical composition
Tissue mass density
Contrast media are effective because “they accentuate” subject Contrast through enhanced
Photoelectric absorption
When the Effective Atomic number of _______ is very much_________, subject Contrast is___________
Adjacent tissues, different, very high.
The high atomic numbers of _______ and ________ result in extremely _____ subject Contrast
Iodine, barium, high
Subject Contrast can be “enhanced greatly” by the use of
Contrast media
The shape of anatomical structure under investigation influences it’s radiograph quality, not only through its “geometry” but also through its contribution to subject Contrast
Object shape
“The characteristics”of the subject that affects subject contrast is sometimes called
Absorption blur
The shape of the structure under investigation “contributes to”
Absorption blur
It “reduces the spatial resolution and the contrast resolution of any anatomical structure”, but it is most troublesome during interventional procedures in which vessels with small diameters are examined
Object shape
-Is the most important influence on Subject Contrast
-also influences film contrast but not to the extent that it controls subject contrast
kVp
If the kvp is high and the subject contrast is low it is
Long gray scale
If the kvp is low and the subject contrast is high it is
Short gray scale
The “absolute magnitude” of subject contrast, however, is greatly controlled by the
kVp of operation
Movement of the patient or the x-ray tube during exposure results in blurring of the radiographic image.
Motion blur
The radiographer can reduce motion blur by carefully instructing the patient
“Take a deep breath and hold it. Don’t move.”
Usually the cause of motion blur
Patient motion
Voluntary motion of the limbs and muscles is controlled by
Communication or Immobilization
Involuntary motion of the heart and lungs is controlled by
Short exposure time
Procedures for reducing motion blur
-Use the shortest possible exposure time
-restrict patient motion by providing instruction or using a restraining device
-use a large sid
-use a small oid
“Requires that the anatomical structure under investigation” be placed as close to the image receptor
Proper patient positioning
Most other radiographs use
double emulsion films with screens
A ______ of screen film image receptor is used throughout a radiology department for a given type of examination.
Standard type
Use of intensifying screen _______ patient dose by a factor of _______
Decreases, At least 20
As the speed of the image receptor______ radiographic noise _____ and spatial resolution is______
Increases, increases, reduced
Low contrast imaging procedures have________, or _________, in producing an _______
Wider latitude, margin of error, acceptable radiograph
Keep exposure time______
as short as possible
The primary control of radiographic contrast is
kVp
The primary control of OD is
mAs
Before each examination, the radiologic technologist must select the optimum radiographic technique Factors, that is, ______, _____, and ______
kVp, mAs, and exposure time
The radiologic technologist has no control over the four previous factors
kVp
Tools for improved radiographic image quality
Patient positioning and image receptors
