OMR LEcture 4 Flashcards
film has 2 principal components
- emulsion - coats both sides
2. base - supporting b=plastic materia
what the is the emulsion?
-(chemical coating) it is the photon sensitive silver halide grain and suspension vehicle
what type of film is used intra-orally?
direct exposure
what is sheet film used for?
- intensifying screens
- used for Panographic, TMJ and Cephalometric x-rays
how should the film dot be oriented?
- dot oriented toward the tube head (radiation source) and the dot goes toward the slot
- the raised bump points to the source of radiation
what is intra-oral film size 0?
0 = pedo
what is intra-oral film size 1?
1= adult anterior
what is intra-oral film size 2?
2= adult posterior
what is intra-oral film size 3?
3 = long posterior
what is intra-oral film size 4?
4= occlusal
how does the size of the silver halide crystals affect the speed of the film?
-the larger the crystals of silver halide the faster the film speed
what film is the slowest?
c film = slowest
-has smaller grains
need more light and photons to expose this
what film is the fastest?
what does it look like?
F film is the fastest
-it it more grainy
D fil is ASA about?
100
benefit of cassettes?
Cassettes require less radiation to expose film
radiographic dentist is influenced by what 6 things?
- mA
- kVp
- exposure time
- focal spot to film distance
- subject density
- subject thickness
in the film packet where is the lead place?
in the back
how to know by the radiograph id the film was in backwards?
-if a pattern is evident- means the lead film backing was in front
what is the order or contents of the film packet from the back to the front?
outer package lead foil backing inner paper wrap dental film inner paper outer package -tube head
what is the function of a grid in a cassette?
grids reduce scatter and “fog” radiation
what are the 5 steps of processing film in the dark
- developer- converts exposed silver halide crystals (latent image) to metallic silver grains
- wash - removes developer
- fixer - removes undeveloped silver halide crystals and then hardens and shrinks the emulsion
- wash - removes the fixer
- drying - makes it safe to handle
what does the developer do?
the developer converts the exposed silver halide crystals to metallic silver grains
what does the fixer do?
fixer - removes undeveloped silver halide crystals and then hardens and shrinks the emulsion
the intraoral film is ___________?
the cassette film is ___________?
intraoral film = monochromatic
cassette film = polychromatic
what happens to very 10 degrees celsius increase in the processing temperature?
the rate of the reaction dubles
number 1 vs number 2 introral film sizes for the # of radiographs taken
#1 - 21 radiographs taken #2 - 18 radiographs taken -less exposure
at 68 degrees how long does it take to process the film?
5 minutes
at 80 degrees how long does it take to develop film?
2.5 minutes
what is the most economical means of developing films?
manual processing
- but its most time consuming
- produces the best radiographs
what is the most efficent way to process film?
automatic processors
what type of film requires less exposure time and why?
- fast film because it has larger silver halide crystals
- downside is it is grainy
fast or slow film requires more radiation or photons to expose it?
- slow speed film requires more radiation b/c the silver halide crystals are smaller
- higher resolution image
what type of speed films are more used in dentistry and why?
fast speed film b/c of decreased exposure
what are the 3 advantages of digital x-rays?
- lower patient exposure
- faster radiographs
- more eco friendly
digital films reduce the amount of exposure by how much?
50-80 percent
what type of film is placed in a cassette?
panoramic or TMJ film
cassettes have increased or decreased definition?
decreased definition - bc angle of light photons (cascading effect from photon interaction with rare earth intensifying screen)
intensifying screens are used in cassettes
decrease the exposure or radiation
what are 3 things that decrease the quality of radiographs from cassettes and degrade the cassette.
- dirt
- light leakage
- static electricity
direct vs indirect digital
- direct = the sensor connects directly to a computer and provides immediate images
- indirect = a reusable phosphor plate is used instead of film. After x-ray exposure a latent image is scanned in a special scanner. The digitized image is stored and read on a computer.
under exposed looks what color?
white
over exposed looks what color?
black
what is the standard language for the electronic communication of digital images?
DICOM
what does DICOM stand for?
digital image and communication in medicine
how is most digital data stored?
in DICOM format
what is contract resolution?
the ability to distinguish different densities in an image
what are densities limited by?
noise of the film
computer monitors are only able to display how many bits?
- only 8 bits - they can not display the accuracy of the sensor
what is spatial resolution?
the ability to distinguish fin detail
what is the pixel size of CCD and CMOS ?
pixel size of film?
digital = 20 um film = 8 um
what is the sensor latitude?
the ability to capture a range of exposures
sensor latitude of CCD and CMOS vs. film? also PSP?
- CCD and CMOS sensors similar to film
- PPS has greater latitude than other sensors and film
What are the 3 types of digital sensors?
- Photostimulable storage phosphor plate (PSP)
- Charge-coupled devices (CCD) - early sensors
- Complementary Metal Oxide Semiconductor (CMOS)
disadvantage of automatic processor for film?
-have to use a lot more chemicals
sensor sensitivity of PSP systems compared to F speed film?
-PSP systems allow dose reduction of abut 50% compared to F speed film (fastest film)
CCD, CMOS and PSP require a dose equal to what film speed?
200
-F-speed film has a speed of 125
how does a digital sensor work?
-x-ray photons are converted to visible light as they hit the CsI scintillator. This light is channeled via the fiberoptic taper to the CCD.
x-rays hit the _______ and are converted to visible light?
CSI scintillator
what happens to the light photons created by the CSI scintillator?
the light photons hit the silicone layer releasing electrons. The negative electrons are drawn to the positive well
what leads to blooming in digital x-rays?
overexposure (distortion and burned out)
spatial resolution is determined digitally by _______
the size of the pixels (20 um)
vs film of 8 um
the average grayscale value of _____ adjacent pixels in a high resolution image is assigned to create on pixel in a high contrast image.
4
6 bit vs 8 bit vs 16 bit for grayscale
6 bit = 64 shades-our eyes can only view 64 shades of gray
8 bit = 256 shades - the monitor
16 bit = 65.535 shades - the senor
on a grayscale what is the color with the value of 0. What is the color for the value of 65,000
0 = black 65,000 = white
how to optimize the grayscale?
use computer to take away some of the shades of gray to increase contrast
-loose detail to increase contrast
what does smoothing do?
it averages the gray scale
