Digital Imaging Flashcards
How much of a cut in radiation is usually seen when switching from film to digital?
50%
How can we reduce it even further?
By using a rectangular collimator
What are the 3 types of receptors used in digital imaging?
CCD, CMOS, and PSP
Which one of those is used in clinic?
PSP
PSP stands for?
Photostimulable phosphor plates
How is film resolution measured?
In line pairs per millimeter
How is this determined using film?
Depends on the grain density, smaller grains gives higher density
What is the highest resolution the human eye can see?
12-14 line pairs per millimeter
What is the reported range of resolution?
8-20 lp/mm
When a film has low latitude it means?
That the image will increase in density quickly as the dosage increases
What is the latitude of digital film and what does this mean for exposure time?
High latitude meaning the density will not change much with exposure, thus use less exposure time
What is contrast resolution?
How well the film can show minute differences in intensity
Does digital film have higher or lower contrast resolution than regular film?
Higher
As mentioned before there are three types of receptors. What are they and what do they stand for?
CCD is a charge coupled device
CMOS is a complementary metal oxide sensor
PSP is photostimulable phosphate
Describe the steps in creating an image using CCD/CMOS
- Exposure to radiation electrically charges pixels
- Buildup of charge creates voltage
- Voltage values are converted to binary and sent to computer
What piece of hardware is required for CCD/CMOS?
A cord
What are the 3 types of pixel malfunctions?
Hot, dead, and stuck
What is a hot pixel?
A pixel that reads high on longer exposures and appears white, red, or green
What is a dead pixel?
One that is always off and appears black
What is a stuck pixel?
Reads high on all exposures and appears white
Post processing involves a process called?
Gamma correction, digitally changing the brightness and contrast
How can it be used?
To bring out the characteristics you want from an image, for example low contrast brings out soft tissue outlines whereas high contrast brings out caries. This way we don’t need multiple radiographs
How are PSPs read?
Using a ruby laser
In terms of exposure time, how does PSP compare to CMOs/CCD?
Requires a longer exposure time of approximately 30 seconds
When x-rays hit the phosphors, the electrons get trapped inside and we use the ruby laser to release them. What king of light is released?
Blue light called photo simulated luminescence
What device detects the light?
Photomultiplier tube
Can PSP be reused?
Yes, it is flashed with light using a machine.
What is a precaution to take when using PSP/
Extra careful handling must be used since the plates can be easily scratched
What is the function of the dot on the corner of the film?
Telling left from right
What is better smaller or larger film?
Typically larger because more information can be captured that way
Compare the thickness of CCD/CMOS, PSP, and film
CCD and CMOS are thick, about 3.5mm
PSP and film are 1mm
Can receptors be sterilized?
No
What do we use to avoid contamination?
Barrier protection
What is more expensive CMOS or PSP?
CMOS is considerably more expensive
Is printing digital images useful?
No it severely reduces image quality, never do this
