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Dose Limits for Ionizing Radiation > Digital imaging week 3 cont.II > Flashcards

Digital imaging week 3 cont.II Flashcards

1
Q

Different frequencies built into the system to allow for more spatial resolution

A

sampling frequency

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2
Q

to match the optical and electronic resolution of system, there should be a sufficient amount of _ to represent the original signal presented

A

samples per horizontal line

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3
Q

Sampling frequency is expressed in

A

pixels/mm

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4
Q

the major factor that limits the recorded detail for indirect digital systems is the

A

size of the detector element

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5
Q

The major factor that limits the recorded detail for direct systems is the

A

size of the detector element

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6
Q

what uses a fine laser beam of variable spot sizes down to 50 um (micrometers)

A

laser scanners

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7
Q

a matrix of data that manipulates the values of gray levels, converting an image input value to a different output value

A

Grayscale rendition or look up table (LUT)

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8
Q

An image processing, lookup tables are often called _

A

LUT’s

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9
Q

LUT’s link _ to output values

A

index #

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10
Q

One common LUT is called the

A

colormap or palette

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11
Q

The color map or palette is used to determine the _

A

colors and intensity values with which a particular image will be displayed

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12
Q

what is a graphic display of the distribution of pixel values

A

Histogram

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13
Q

Each image has its own histogram and is evaluated to determine the

A

adequacy of the image receptor exposure

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14
Q

what is used to identify the edges of the image and assess the raw data prior to image display

A

Histogram

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15
Q

uses processing algorithms and compares it with prestablished histogram for the part

A

Histogram analysis

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16
Q

what is generated with the pixel values on the x-axis and the # of pixels on the y-axis

A

histogram graph

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17
Q

the peeks and valleys represent the

A

subject contrast

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18
Q

the voi is identified with S1 representing the _ and S2 representing the

A

min. useful signal

max. useful signal

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19
Q

computer system automatically adjusts the brightness by comparing the histogram with the LUT

A

automatic rescaling

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20
Q

Overexposures of _ and underexposures of _ can be rescaled without losing image quality

A

12%

6%

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21
Q 
For production of an optimal histogram you need a 
correct
choose
center
collimate
control
cover
A 
technique selection
correct body part
CR to VOI
closely, leaving min background
scatter
at least 3% of IR
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22
Q

grid error that occurs with digital image receptor systems when the grid lines are captured and scanned parallel to the scan lines in the IP reader

A

Moire Effect

23
Q

Digital imaging requires that the spatial resolution frequency signal be sampled twice from each cycle, this is the

A

Nyquist criterion

24
Q

what occurs when the Nyquist criterion is violated; incoming data is sampled less than twice per cycle

A

Aliasing

25
Q

Aliasing appears as a

A

Moire pattern

26
Q

for CR the cassette used is a

A

Photostimulable storage phosphor imaging plate

PSP or IP

27
Q

CR is also called

A

indirect acquistion

28
Q

Two part process

A
  1. Scintillator

2. Photodetector

29
Q

converts photons to light

A

scintillator

30
Q

converts light into an electrical signal

A

photodetector (charged couple device)

31
Q

Layers of an IP

A 
Protective layer
Phosphor layer
conductor layer
support layer
light shield layer
backing layer
32
Q 
what are the layer's function
Protective layer-
Phosphor layer-
conductor layer-
support layer-
backing layer-
A

insulates from trauma

  • active component of IP
  • grounds plate to avoid static
  • support base for other layers
  • prevents light from erasing data
  • attaches to cassette
33
Q

most common IP phosphor is

A

barium flourohalide bromides with europium activators

34
Q

a min. of _ of the IR must be exposed for an accurate exposure index to be obtained

A

3%

35
Q

the latent image will lose _ of its energy in _ hrs.

A

2%

8 hrs.

36
Q

latent image is processed by loading the cassette into an image reader device where the plate is scanned by a

A

helium-neon laser beam

37
Q

the beam scans the _ and emits the latent image in the form of _, which are then converted into an electrical signal, then converted to a _ for that level of luminescence

A

phosphors
light photons
digital value

38
Q

reading the IP requires a finely focused red laser beam hat frees the trapped electrons, allowing them to return to a lower energy state called

A

photostimulated luminescence (PSL)

39
Q

4 CR artifacts

A
  1. Phantom images
  2. Dropout artifacts
  3. Quantum
  4. heat blur
40
Q

Phantom images may appear from

A

incomplete IP erasure

41
Q

reduction in resolution, result of dust

A

dropout artifacts

42
Q

caused from inadequate exposure (mAs)

A

Quantum

43
Q

IR exposure to extreme heat

A

heat blur

44
Q

4 factors that produce low contrast and are prone to cause IP fog

A
  1. high kV
  2. No grid or inadequate grid efficiency
  3. Inadequate beam limitation
  4. Increased part size or tissue density
45
Q

DR is also called

A

direct acquisition

46
Q

for a DR what is not needed

A

cassette

47
Q

direct acquisition directly converts

A

photons to an electrical signal

48
Q

DR uses

A

amorphus selenium or amorphus silicon

49
Q

material lacking crystalline structure

A

Amorphous

50
Q

CR’s advantages vs DR

A

less expensive
can be used portably
compatible w/existing radiographic tables

51
Q

DR’s advantages

A

immediate readout
cassette free
can be re-exposed immediately

52
Q

CR’s disadvantages

A

delayed readout
cassettes needed
plate must be erased before use

53
Q

DR’s disadvantages

A

more expensive

not compatible w/existing equipment

54
Q

what is the greatest advantage of digital imaging over film/screen

A

post-processing

Dose Limits for Ionizing Radiation (16 decks)

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