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chapter 10 bushong
Terms in this set (86)
whether a radiograph is made with long or short exposure, as long as it is the same mAs, OD will be the same.
Important in very short or very long exposure times.
1.) IR contrast
2.) Subject Contrast
determined by size, shape, anatomy, and Kvp
Range of exposure.
Margin of error. With wider latitude Mas can vary more and still produce and image.
ability to image 2 seperate objects and visually distingusih one from the other.
How easily details can be percieved on a radiograph.
Minimum distortions, magnification, and positioning.
ability to image small objects that have high subject contrast.
calcified lung nodule
All images on radiograph are larger than the objects they represent.
(image size/ object size)
Size and Shape
Controlled by tech. Random nature in which X-rays interact with the IR
Similar in film graininess, but refers to phosphur, Inherent in screenfilm IR (in phosphors of IR) '
Tech does not have control.
Visibility of Detail
ability to visualize recorded detail.
Degree of sharpness od structural lines (Fine lines/Bony Structures.)
Random fluctuation in the OD of the image.
(Lower noise= better image)
Optical Density (OD)
Degree of blackening on radiograph
OD clear area= _________
OD Black area=__________
not apparent when viewing an image but it influences noise and resolution.
ability to distinguish anatomical structures of similar subject contrast
(gray matter-white matter)
SID in Magnification
Increasing SID reduces Mag and improves spatial resolution and decreases patient dose.
100cm= MF 1.1
object appears smaller than it really is
Misrepresentation in the image of the actual spatial relationships among objects.
Focal Spot Blur
-Not a point source, a rectangle tht varies in size depending on the tube.
-blurred region on an image
-Tech can not control
-resulted because of the effective FS size.
Anode Heel effect
Varying radiation intensity across the x-ray field in the anode to cathode direction caused by attenuation of x-rays in heel of anode
associated with patient size and shape and tissue composition.
Tissue Mass Density
Body sections may have smililar thickness but different attenuating characteristics, different mass densities.
Function of IR contrast and subject contrast
Measured in relation to beam attenuation
affects subject contrast
reduces spatial resolution and contrast resolution of any anatomical structure.
Higher atomic number =increased attenuation=diffrential absorption
Subject Factors: KVP
gives radiographer control of subject contrast
What technique selection will improve image quality?
shortest exposure time
Tools radiographers can employ to improve image quality are:
-CR centered to anatomy part close to the IR
-detail films for extremities
-grid vs. non grid
what procedures reduce motion unsharpness?
-communication / restraining
-short exposure time
Caused by x-ray tube moving during radiography?
(tomography does on purpose)
what is usually the cause of motion blur?
Patient motion (voluntary + involuntary)
low subject contrast (long scale)
high subject contrast (short scale)
Size and shapes of organs have different absorption blur which _________________________
decreases subject contrast especially at edges
Anatomic structure that concides with the shape of the beam has the maximum____________
What is the most important influence on subject contrast?
What happens when effective atomic number of adjacent tissues is very different?
Subject contrast is very high
In tissue mass density what does the image show differently on a finished radiograph?
Fat , muscle
In the Heel effect is the size of the effective FS constant across the image?
In subject contrast:
more x-rays are trasnmitted through a thin section, leaving the thinner section darker
TRUE or FALSE
In terms of subject contrast:
What will a thick body section do compared to a thin body section?
Attenuate more x-rays than a thin section of the body.
how should the tube be for a femur exam?
cathode @ the hip
anode @ the knee
how should the tube be for a T-spine exam?
cathode @ the abdomen
anode @ the neck
Where is the FS greater?
on the Cathode side
on what side of the tube is the FS blur greater on?
because the effective focal spot size is largest oncathode side
What is the most important factor for determing spatial resolution?
Focal spot Blur
Where is the FS larger?
on the cathode side
When is focal spot blur small?
when OID is small
If an object has a long OID what happens to the FS blur?
it is increased
What will reduce FS blur
keeping the object close to the IR using smallest FS possible.
Why does Focal Spot blur occur?
Because the FS is not a point, the x-rays aren't coming from a point source.
Why are x-ray exams performed 2 or more projections?
because of spatial distortion.
An inclined object positioned lateral to the CR may be distorted severly by________________
elongation or foreshortening
What does inclination of an object result in?
A foreshortened image.
What will happen to irregular anatomy located off the CR?
it will be distorted.
Film screen images always have higher contrast compared w/ direct film exposure images
T OR F
How is magnification determined?
Ratio of SID to SOD
What affect does object thickness have?
thick objects are more distorted than thin ones
What 3 conditions contribute to image distortion?
How would you minimize magnification?
use largest SID an smallest OID possible.
What 2 factors affect magnification?
What are 3 geometric factors?
focal spot blur
long gray scale
short gray scale
Latitude and contrast are inversly proportional?
T or F
more black and whites (more OD)
Reciprocity Law works for ________ and doesn't work for __________
intensifying screens 10 ms or longer than 2s
What does higher fog density do?
reduces contrast on image
better detail (extremities)
Less Detail (abdomen)
Faster IR's have increased quantum mottle
T or F
What causes a greater chance of quantum mottle?
The lower the number of x-rays striking the IR. (image is produced with few x-rays)
What are the 4 components of noise?
What are the 4 most important characteristic of radiographic image quality?
What reduces quantum mottle?
use of high mas, low kvp and slower IR reduces quantum mottle. (controlled by adjusting mas)
1st basic quality rule:
Fast Irs have increased noise decreased spatial resolution and decreased contrast resolution
2nd basic quality rule:
high spatial resolution and high contrast resolutionrequire low noise and slow IR's
3rd basic quality:
Low noise accompanies slow IR's with high spatial resolution and contrast resolution.
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