Image Production 1 Flashcards
In DR, what is the main controlling factor of spatial resolution?
Pixel size and pixel pitch
Spatial resolution
- Recorded detain
- measured in line pairs per mm
Receptor exposure
Overall amount of radiation to reach IR
Contrast resolution
Visual detail
Size distortion
Distance creates magnification
Shape distortion
Foreshortening or elongation
Main controlling factor of receptor exposure
mAs
5:1
2
6:1
3
8:1
4
10:1/12:1
5
16:1
6
FAT CAT
Proximal joint will always be thicker
What is the primary controlling factor of subject contrast
kVp
Umbra
Area of image sharpness
Penumbra
Geometric unsharpness surrounding image
Magnification
Image size/object size= SID/SOD
What causes shape distortion
Angulation of tube, angulation of part, angulation of IR, and motion
What causes size distortion
Changes in object to image receiver and source to image receiver distances
2 kV change is made for each centimeter in part thickness when operating at what kVp
80
Wet plaster casts require what
- doubling of exposure
- 100% increase in mAs
- 8-10 increase in kVp
Dry plaster casts require what
- 50-60% increase in mAs
- 5-7 increase in kVp
Fiberglass casts require what
- 25-30% increase in mAs
- 3-4 inches in kVp
Parts measuring how much require a grid
10-13 cma
How does tech adjust the rate of the exposure when using an AEC device
Adjust density control
How does higher kVp technique influence contrast
Results in Reduction of contrast
Higher mAs will result in what
Longer exposure time and possibly motion
When can quantum mottle occur with AEC techniques
If mAs is too low
For thin or pediatric patients what kind of receptor exposure control may be selected to prevent overexposure
Negative
For large patients what kind of receptor exposure control may be selected to prevent underexposure
Positive
DEL (detector element size)
- used with direct capture radiography (cassette less)
- uses flat panel detector
Spatial resolution is determined by what
- DEL size
- as DEL increases SR decreases
Fill factor is a ratio of what
Of pixels light sensitive area vs a pixels total area
Matrix size
- is the total number of pixels
- dependent on the FOV and pixel density
Increase in IR size results in what for matrix size
Increase in matrix size
Decreasing pixel size results in what
- increased matrix size
- increased SR
- increased visibility of small structures
Is SR related to exposure amount
No
What is the main controlling factor of SR for CR
Sampling frequency
Sampling frequency
Number of pixels sampled per millimeter as the laser scans each line of the imaging plate
The more pixels sampled per millimeter, the greater the
Sampling frequency
Increasing the sampling frequency results in the laser moving a smaller distance and there is a what in special resolution
Increase
What is the minimum rate at which a signal can be sampled without introducing errors?
Nyquist frequency
Nyquist frequency
Relationship between the sampling frequency (# of pixels/mm scanned by the laser, at a rate that is 2x the highest frequency present) and the spatial resolution (image detail)
Contrast resolution (equipment related)
Ability to detect subtle changes in the grayscale
Image signal (exposure related)
Results from x-ray deposition of energy in a detector
Dynamic range
Series of exposure values used to produce an acceptable image
Greater dynamic range will yield what kind of contrast resolution
Greater contrast resolution
Quantum noise/quantum mottle
Insufficient quantity
Exposure latitude
Ability of a system to over and underexpose, yet still produce an acceptable image
Signal to noise ratio (SNR)
Desirable to have high SNR
What minimum info must be present on radiograph
- patient data (name and id #)
- examination data (markers)
- examination date
- institution data
What is the minimum kVp change necessary to see a noticeable receptor exposure change within the radiographic image
10%
What is the minimum mAs change necessary to see a noticeable receptor exposure change within the radiographic image
30%
Conscious decreases proportionally as kVp
Increases
Image contrast will decrease as filtration
Increases
Increasing kVp=
Decreasing contrast, increased noise and increased scatter
The unintended absorption of primary beam
Grid cut off
Moire pattern
-wave like or watery appearance of an image, when two linear grids are placed on top of one another but the lead lines are not aligned at right angles to one another
Moire pattern may also occur with what
Digital subtraction images if there is a misalignment of the pixels
Static (type of image artifact)
Black spider like artifact on the image
Grid lines (type of image artifact)
Appears as parallel opaque lines on the radiograph
Ghost image
When there is insufficient erasure of an image and a ghost image is seen on the new image