mAs controls:
quantity
kVp controls:
quality
How dose OID affect contrast?
it uses the air gap technique
As SID increases, spatial resolution
increases
As grid ratio increases, receptor exposure
decreases
What is APR?
Anatomically Programmed Radiography
What dose APR do?
provides choices of anatomical parts with suggested exposure factors
-factors can be modified
What is an example of APR?
picking a chest on a portable, the suggested technique pops up and can be modified
What are calipers?
device used to measure part thickness
Who developed the fixed kVp system
Fuchs (during WW2 in 1943)
What are the advantages of fixed kVp system
-reduction in pt dose
-provides more info within image
-increased consistency in receptor
-lengthens exposure altitude
-reduces x-ray tube wear
-allows shorter exposure times
-easier to memorize
What is the disadvantage of fixed kvp system
higher amount of scatter results in reduced image contrast
What does "lengthens exposure latitude" mean
it gives you more room for error
Who developed the variable kVp system
Ed Jerman (1925)
When is variable kVp systems used
when kVp range is limited by equipment generators
What are the advantages of variable kVp systems
-allows for small changes in exposure for small changes in part thickness
-higher contrast
What are the disadvantages of variable kVp systems
-more pt dose
-higher repeat rate
-tube wear
What does the 15% rule state
an increase in kVp by 15% will cause a doubling in exposure, the same effect as doubling the mAs
How much kVp should you increase for a wet plaster cast?
10-15 kVp
How much kVp should you increase for a fibercast cast
3-4 kVp
How much kVp do you use for barium?
for barium with air?
110
90
How much kVp do you use for iodine based contrast?
for air?
75
70
Massive body build, broad chest & abdomen, and short lungs represents?/
Hypersthenic body habitus
Long narrow lungs and low diaphragm represents
Hyposthenic body habitus
average bod build =
Sthenic habitus
All backup timers have to stop at:
600 mAs
Using AEC, the radiographer loses control over:
mAs (the time)
The most important part of using AEC is
the appropriate anatomic alignment (positioning)
When would you use -1 for the density control?
if the patient has emphysema
Density control should not:
be used to compensate for changes in part thickness
Physical distance from the center of one pixel to another
pitch
As pixel size decreases,
the pitch decreases
As pixel pitch decreases,
spatial resolution increases
What is a matrix made up of
pixels and voxels
As matrix size increases,
pixel size decreases
What does TFT stand for
Thin Film Transistor
TFT are used in both
indirect and direct detectors
What dose DEL stand for
detector elements
DEL size is expressed in
micrometers
bit depth determines
the number of assigned gray shades to pixel values;
number of density values
Greater bit depth =
increased size of data set and volume of data for image processing;
(MORE SHADES OF GRAY)
Modulation transfer function (MTF) measures
accuracy of image to actual object (range form 0 to 1)
MTF of ______ represents "perfect" reproduction of original
one
Detective Quantum Efficiency (DQE)
measure of the sensitivity and accuracy by which the image receptor converts the incoming data to the output viewing device
DQE of ______ = 100% or no loss of info
one
Higher DQE =
lower dose
What is quantum noise
Lack of sufficient incoming data for processing;
an insufficient number of x-ray photons reaching the image receptor
Noise is measured in
signal-to-noise ratio (SNR)
A high SNR indicates
little noise in the image
Image noise has an _____ relationship to contrast.
inverse
What is the contrast-to-noise ratio (CNR)
the difference in signal contribution between different tissues, divided by the background noise
CNR is the measure of
the detectors ability to distinguish between objects in an image and the image noise
All radiographs must include
-date
-name or ID number
-R or L marker
-institution
What are the two types of imaging equipment
diagnostic
therapeutic
What is the minimum response time normally for AEC?
.001 seconds
Federal law requires automatic termination at _______ mAs
600
What is the piece of equipment that converts mechanical energy to electrical energy
the generator
What are the components of an x-ray generator
armature, magnets, slip rings, brushes
What are the 3 transformers in the x-ray circuit
autotransformer, step-up transformer, step-down transformer
What are the two types of rectification?
Half wave
full wave
What is the mA range for typical fluoro
0.5-5.0 mA
What is the minimum SOD in fixed fluoro equpiment
15