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D1 Radiology > OMR LEcture 4 > Flashcards

OMR LEcture 4 Flashcards

(66 cards)

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1
Q

film has 2 principal components

A
  1. emulsion - coats both sides

2. base - supporting b=plastic materia

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2
Q

what the is the emulsion?

A

-(chemical coating) it is the photon sensitive silver halide grain and suspension vehicle

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3
Q

what type of film is used intra-orally?

A

direct exposure

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4
Q

what is sheet film used for?

A
  • intensifying screens

- used for Panographic, TMJ and Cephalometric x-rays

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5
Q

how should the film dot be oriented?

A
  • dot oriented toward the tube head (radiation source) and the dot goes toward the slot
  • the raised bump points to the source of radiation
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6
Q

what is intra-oral film size 0?

A

0 = pedo

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7
Q

what is intra-oral film size 1?

A

1= adult anterior

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8
Q

what is intra-oral film size 2?

A

2= adult posterior

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9
Q

what is intra-oral film size 3?

A

3 = long posterior

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10
Q

what is intra-oral film size 4?

A

4= occlusal

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11
Q

how does the size of the silver halide crystals affect the speed of the film?

A

-the larger the crystals of silver halide the faster the film speed

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12
Q

what film is the slowest?

A

c film = slowest
-has smaller grains
need more light and photons to expose this

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13
Q

what film is the fastest?

what does it look like?

A

F film is the fastest

-it it more grainy

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14
Q

D fil is ASA about?

A

100

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15
Q

benefit of cassettes?

A

Cassettes require less radiation to expose film

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16
Q

radiographic dentist is influenced by what 6 things?

A
  1. mA
  2. kVp
  3. exposure time
  4. focal spot to film distance
  5. subject density
  6. subject thickness
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17
Q

in the film packet where is the lead place?

A

in the back

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18
Q

how to know by the radiograph id the film was in backwards?

A

-if a pattern is evident- means the lead film backing was in front

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19
Q

what is the order or contents of the film packet from the back to the front?

A 
outer package
lead foil backing
inner paper wrap
dental film
inner paper 
outer package
-tube head
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20
Q

what is the function of a grid in a cassette?

A

grids reduce scatter and “fog” radiation

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21
Q

what are the 5 steps of processing film in the dark

A
  1. developer- converts exposed silver halide crystals (latent image) to metallic silver grains
  2. wash - removes developer
  3. fixer - removes undeveloped silver halide crystals and then hardens and shrinks the emulsion
  4. wash - removes the fixer
  5. drying - makes it safe to handle
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22
Q

what does the developer do?

A

the developer converts the exposed silver halide crystals to metallic silver grains

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23
Q

what does the fixer do?

A

fixer - removes undeveloped silver halide crystals and then hardens and shrinks the emulsion

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24
Q

the intraoral film is ___________?

the cassette film is ___________?

A

intraoral film = monochromatic

cassette film = polychromatic

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25
what happens to very 10 degrees celsius increase in the processing temperature?
the rate of the reaction dubles
26
number 1 vs number 2 introral film sizes for the # of radiographs taken
``` #1 - 21 radiographs taken #2 - 18 radiographs taken -less exposure ```
27
at 68 degrees how long does it take to process the film?
5 minutes
28
at 80 degrees how long does it take to develop film?
2.5 minutes
29
what is the most economical means of developing films?
manual processing - but its most time consuming - produces the best radiographs
30
what is the most efficent way to process film?
automatic processors
31
what type of film requires less exposure time and why?
- fast film because it has larger silver halide crystals | - downside is it is grainy
32
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
33
what type of speed films are more used in dentistry and why?
fast speed film b/c of decreased exposure
34
what are the 3 advantages of digital x-rays?
1. lower patient exposure 2. faster radiographs 3. more eco friendly
35
digital films reduce the amount of exposure by how much?
50-80 percent
36
what type of film is placed in a cassette?
panoramic or TMJ film
37
cassettes have increased or decreased definition?
decreased definition - bc angle of light photons (cascading effect from photon interaction with rare earth intensifying screen)
38
intensifying screens are used in cassettes
decrease the exposure or radiation
39
what are 3 things that decrease the quality of radiographs from cassettes and degrade the cassette.
- dirt - light leakage - static electricity
40
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.
41
under exposed looks what color?
white
42
over exposed looks what color?
black
43
what is the standard language for the electronic communication of digital images?
DICOM
44
what does DICOM stand for?
digital image and communication in medicine
45
how is most digital data stored?
in DICOM format
46
what is contract resolution?
the ability to distinguish different densities in an image
47
what are densities limited by?
noise of the film
48
computer monitors are only able to display how many bits?
- only 8 bits - they can not display the accuracy of the sensor
49
what is spatial resolution?
the ability to distinguish fin detail
50
what is the pixel size of CCD and CMOS ? | pixel size of film?
``` digital = 20 um film = 8 um ```
51
what is the sensor latitude?
the ability to capture a range of exposures
52
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
53
What are the 3 types of digital sensors?
1. Photostimulable storage phosphor plate (PSP) 2. Charge-coupled devices (CCD) - early sensors 3. Complementary Metal Oxide Semiconductor (CMOS)
54
disadvantage of automatic processor for film?
-have to use a lot more chemicals
55
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)
56
CCD, CMOS and PSP require a dose equal to what film speed?
200 | -F-speed film has a speed of 125
57
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.
58
x-rays hit the _______ and are converted to visible light?
CSI scintillator
59
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
60
what leads to blooming in digital x-rays?
overexposure (distortion and burned out)
61
spatial resolution is determined digitally by _______
the size of the pixels (20 um) | vs film of 8 um
62
the average grayscale value of _____ adjacent pixels in a high resolution image is assigned to create on pixel in a high contrast image.
4
63
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
64
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 ```
65
how to optimize the grayscale?
use computer to take away some of the shades of gray to increase contrast -loose detail to increase contrast
66
what does smoothing do?
it averages the gray scale

D1 Radiology (1 decks)

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