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

test 2 Intro and computed radiography Flashcards

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
spatial resolution
the degree of geometric sharpness or accuracy of structural lines actually recorded in the image also called detail, definition, sharpness, or recorded detail
26
spatial resolution formula
spatial resolution = FOV/Matrix
27
4 steps of acquiring the image
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
28
Imaging plate
thin sheet of plastic that records the image
29
5 layers of the imaging plate
1. protective layer 2. phosphor layer 3. reflectivve layer 4. conductive layer 5. light shield layer
30
1. protective layer
thin tough clear plastic that protects the phosphor layer | insulates imaging plate from handling trauma
31
2. phosphor layer
active layer (where image is created) holds photostimulable phosphor (PSP) traps electrons during exposure
32
what is the phosphor used to create the picture
barium fluorohalide with europium
33
photostimulable luminescence
the phosphor emits light when exposed to xrays and then again when when exposed to another light source releases light twice
34
europium acts as an activator | without this activator, there would be no
latent image
35
storage phosphor
the latent image is stored electrons
36
structured phosphors
needle phosphors lined up and packed together tightly | gives nice resolution
37
turbid phosphors
a phosphor layer with a random distribution of phosphor crystals randomly scattered doesn't give as good resolution
38
3. reflective layer
sends light in a forward direction when released in cassette reader may be black to reduce spread of light helps to prevent blur
39
conductive layer
grounds the plate to eliminate electrostatic problems
40
color layer
some newer plates contain color layer to absorb light
41
support layer
base on which to coat other layers | gives the imaging plate some strength
42
light shielding layer
prevents light from erasing data on the imaging plate or leaking through the backing and decreasing spatial resolution
43
backing layer
soft polymer that protects the back of the cassette | where the barcode label is found
44
imaging plate is scanned with a laser beam and releases stored energy as visible light
TRUE
45
photomultiplier tube
collects, amplifies and converts light to electrical signal
46
how does an IP get erased
residual electrons are removed by intense light
47
plates should be erased
every day
48
plates should be left no more than
48 hours
49
CR imaging plate is equivalent to a
200 speed system and mAs must be adjusted because film screen was a 400 speed system
50
estimated life of an IP
10000 readings
51
image acquisition
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
the reader
cassette fed into reader removes imaging plate scans with laser to release stored electrons
53
LASER | Light Amplification of Stimulate Emission of Radiation
creates and amplifies a narrow intense beam of light scans the imaging plate scans the plate in a raster pattern
54
beam shaping optics
keep the size, shape, speed and intensity constant
55
translation
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
beam deflector
moves the laser beam rapidly back and forth across the IP to stimulate the phosphors
57
light collection optics
direct the released phosphor energy to an optical filter and then to the photodetector
58
T or F | the smaller the laser beam, the better the resolution
True
59
T or F | the wider the laser beam the more speed
True
60
photomultiplier tubes and photodiodes
light detectors of choice for CR | photomultiplier amplifies light signal and sends it to a digitizer
61
pixel pitch
the space from teh center of a pixel to the center of the adjacent pixel determines the pixel density (pixels per mm)
62
digitizing the signal
assigning the image a number
63
quantization
the value of each sample
64
sampling frequency
the frequency at which the analog sample is taken | how much data the laser is obtaining during a certain amount of time
65
T or F | as receptor size decreases sampling frequency increases
True
66
as sampling frequency increases, spatial resolution
increases
67
nyquist frequency
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
moire effect
occurs when the grid frequency is equal to he nyquist frequency
69
spatial resolution
the amount of detail present in any image | ex: the thinner the phosphor layer the higher the resolution
70
image acquisition
exposure artifacts imaging plate artifacts
71
quantum mottle
grain condition as a result of not enough mAs
72
grid frequency
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
grid ratio
the relationship between the height of the lead strips and the space between them
74
sampling rate
the number of bits of output it provides | the number of times a second that it can sample and digitize the input signal
75
shuttering
putting a black background around the collimation during postprocessing DOES NOT TAKE THE PLACE OF COLLIMATION
76
exposure indicator
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
Dose Area Product (DAP)
the volume of tissue irradiated (not just the dose) | used to monitor radiation output from radiographic and fluoroscopic imaging systems
78
factors that produce low contrast
no grid inadequate grid efficiency inadequate beam limitation increased part size or tissue thickness
79
histogram
graphic representation of numerical tone values on an xray exposure
80
advantages of CR
compatible with existing film screen xray equipment | useful in mobile imaging
81
disadvantages of CR
amount of time necessary to process and image readout more exposure needed to avoid quantum mottle appropriate kVp used to achieve optimal images
82
binary notation
used to describe image size, image shades of gray, and image storage capacity
83
two systems available for digitizers
laser and CCD linear array

physics spring semester 2015 (5 decks)

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