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physics spring semester 2015 > test 2 Intro and computed radiography > Flashcards

test 2 Intro and computed radiography Flashcards

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1
Q

analog computers

A

handle data composed of continuously varying electrical currents

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2
Q

digital computers

A

handle data composed of definite quantities of current

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3
Q

Analog to digital converter

ADC

A

needed to convert analog input into digital data for processing
converts analog signal into sequence of numbers

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4
Q

digital to analog converter

DAC

A

converts this info back into analog signals so it can be interpreted by analog display device

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5
Q

the computer operates in what system?

A

binary system

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6
Q

binary system

A

two symbol alphabet

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7
Q

bit

A

each binary number or a single binary digit

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8
Q

teleradiology

A

transfer of images and patient reports to remote sites

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9
Q

digital

A

an image constructed from numerical data

ex: CT, MRI

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10
Q

film digitizers

A

used to convert analog image into digital

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11
Q

disadvantages of conventional

A

image is permanent
increased pt. exposure
difficulty seeing structures within the same image
processing time, storage, etc

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12
Q

advantages of digital

A

can be obtained, processed, stored, etc in a more timely manner
can be manipulated without re exposing the pt.

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13
Q

dynamic range

A

the range of exposures a system can retain to create the visible image
refers to the number of shades of gray
greater the range greater the ratio

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14
Q

the greater the dynamic range, the better

A

contrast resolution

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15
Q

matrix

A

a combination of rows and columns

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16
Q

pixel

A

smallest component picture element

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17
Q

the larger the matrix, the better

A

the quality

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18
Q

increasing the number of pixels will

A

improve the quality of the image

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19
Q

quantization

A

assigning of a unique value to each pixel

AKA the value of each pixel

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20
Q

bit depth

A

the number of bits used to reproduce image gray levels

bit number is always expressed as the exponent of 2

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21
Q

a system that can display a greater number of shades of gray has better image quality
true or false

A

TRUE

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22
Q

voxel

A

each pixel value corresponds to a 3 dimensional volume of tissue
the voxel size depends on the thickness of the slice and the matrix size and field of view

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23
Q

In CT the numeric value of each pixel is called a

A

Hounsifeld unit (HU)

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24
Q

field of view

A

the diameter of image reconstruction
think of pieces of a puzzle
the more puzzle pieces the better the picture will be

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25
Q

spatial resolution

A

the degree of geometric sharpness or accuracy of structural lines actually recorded in the image
also called detail, definition, sharpness, or recorded detail

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26
Q

spatial resolution formula

A

spatial resolution = FOV/Matrix

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27
Q

4 steps of acquiring the image

A
  1. radiation exits the pt. and interacts with the IR
  2. photons absorbed by photostimulable phosphor in plate
  3. image formed within crystals to produce latent image
  4. IP is erased for future use
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28
Q

Imaging plate

A

thin sheet of plastic that records the image

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29
Q

5 layers of the imaging plate

A
  1. protective layer
  2. phosphor layer
  3. reflectivve layer
  4. conductive layer
  5. light shield layer
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30
Q
  1. protective layer
A

thin tough clear plastic that protects the phosphor layer

insulates imaging plate from handling trauma

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31
Q
  1. phosphor layer
A

active layer (where image is created)
holds photostimulable phosphor (PSP)
traps electrons during exposure

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32
Q

what is the phosphor used to create the picture

A

barium fluorohalide with europium

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33
Q

photostimulable luminescence

A

the phosphor emits light when exposed to xrays and then again when when exposed to another light source
releases light twice

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34
Q

europium acts as an activator

without this activator, there would be no

A

latent image

35
Q

storage phosphor

A

the latent image is stored electrons

36
Q

structured phosphors

A

needle phosphors lined up and packed together tightly

gives nice resolution

37
Q

turbid phosphors

A

a phosphor layer with a random distribution of phosphor crystals
randomly scattered doesn’t give as good resolution

38
Q
  1. reflective layer
A

sends light in a forward direction when released in cassette reader
may be black to reduce spread of light
helps to prevent blur

39
Q

conductive layer

A

grounds the plate to eliminate electrostatic problems

40
Q

color layer

A

some newer plates contain color layer to absorb light

41
Q

support layer

A

base on which to coat other layers

gives the imaging plate some strength

42
Q

light shielding layer

A

prevents light from erasing data on the imaging plate or leaking through the backing and decreasing spatial resolution

43
Q

backing layer

A

soft polymer that protects the back of the cassette

where the barcode label is found

44
Q

imaging plate is scanned with a laser beam and releases stored energy as visible light

A

TRUE

45
Q

photomultiplier tube

A

collects, amplifies and converts light to electrical signal

46
Q

how does an IP get erased

A

residual electrons are removed by intense light

47
Q

plates should be erased

A

every day

48
Q

plates should be left no more than

A

48 hours

49
Q

CR imaging plate is equivalent to a

A

200 speed system and mAs must be adjusted because film screen was a 400 speed system

50
Q

estimated life of an IP

A

10000 readings

51
Q

image acquisition

A
  1. the remnant beam interacts with electron in the barium fluorohalide crystals
  2. this interaction gives energy to electron in the crystals
  3. this allows them to enter the conductive layer
  4. here they are trapped in an area of the crystal known as the phosphor center
  5. this trapped signal remains there for some time, but does begin to deteriorate
  6. some of the exposure still remains trapped even after you read it.
52
Q

the reader

A

cassette fed into reader
removes imaging plate
scans with laser to release stored electrons

53
Q

LASER

Light Amplification of Stimulate Emission of Radiation

A

creates and amplifies a narrow intense beam of light
scans the imaging plate
scans the plate in a raster pattern

54
Q

beam shaping optics

A

keep the size, shape, speed and intensity constant

55
Q

translation

A

as the imaging plate moves through the reader the laser scans across multiple times
the translation speed must be coordinated with the scan direction of the laser

56
Q

beam deflector

A

moves the laser beam rapidly back and forth across the IP to stimulate the phosphors

57
Q

light collection optics

A

direct the released phosphor energy to an optical filter and then to the photodetector

58
Q

T or F

the smaller the laser beam, the better the resolution

A

True

59
Q

T or F

the wider the laser beam the more speed

A

True

60
Q

photomultiplier tubes and photodiodes

A

light detectors of choice for CR

photomultiplier amplifies light signal and sends it to a digitizer

61
Q

pixel pitch

A

the space from teh center of a pixel to the center of the adjacent pixel
determines the pixel density (pixels per mm)

62
Q

digitizing the signal

A

assigning the image a number

63
Q

quantization

A

the value of each sample

64
Q

sampling frequency

A

the frequency at which the analog sample is taken

how much data the laser is obtaining during a certain amount of time

65
Q

T or F

as receptor size decreases sampling frequency increases

A

True

66
Q

as sampling frequency increases, spatial resolution

A

increases

67
Q

nyquist frequency

A

the highest spatial frequency that can be recorded by a digital detector
determined by the pixel density
nyquist frequency is half the number of pixels/mm

68
Q

moire effect

A

occurs when the grid frequency is equal to he nyquist frequency

69
Q

spatial resolution

A

the amount of detail present in any image

ex: the thinner the phosphor layer the higher the resolution

70
Q

image acquisition

A

exposure
artifacts
imaging plate artifacts

71
Q

quantum mottle

A

grain condition as a result of not enough mAs

72
Q

grid frequency

A

refers to the number of grid lines per inch

the higher the frequency the finer the grid lines in the image therefore the less interference

73
Q

grid ratio

A

the relationship between the height of the lead strips and the space between them

74
Q

sampling rate

A

the number of bits of output it provides

the number of times a second that it can sample and digitize the input signal

75
Q

shuttering

A

putting a black background around the collimation during postprocessing
DOES NOT TAKE THE PLACE OF COLLIMATION

76
Q

exposure indicator

A

the amount of light given off by the IP is a result of the radiation exposure the plate has received
the light is converted to a signal that’s used to calculate the exposure index

77
Q

Dose Area Product (DAP)

A

the volume of tissue irradiated (not just the dose)

used to monitor radiation output from radiographic and fluoroscopic imaging systems

78
Q

factors that produce low contrast

A

no grid
inadequate grid efficiency
inadequate beam limitation
increased part size or tissue thickness

79
Q

histogram

A

graphic representation of numerical tone values on an xray exposure

80
Q

advantages of CR

A

compatible with existing film screen xray equipment

useful in mobile imaging

81
Q

disadvantages of CR

A

amount of time necessary to process and image readout
more exposure needed to avoid quantum mottle
appropriate kVp used to achieve optimal images

82
Q

binary notation

A

used to describe image size, image shades of gray, and image storage capacity

83
Q

two systems available for digitizers

A

laser and CCD linear array

physics spring semester 2015 (5 decks)

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