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RAD 350 > Test 4 > Flashcards

Test 4 Flashcards

1
Q

What is a digital image

A

any imaging process that creates an electronic image that can be viewed and manipulated on a computer

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2
Q

digital vs traditional

A

no more physical film just digital and can be manipulated after exposure

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3
Q

when was the first digital manipulation of angiography

A

1977

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4
Q

when did it become common to use digital manipulations

A

1980

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5
Q

when was the first computerization of CT and ultrasound

A

1970-1990

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6
Q

what helped change radiography to digital? what were the changes?

A

insurance requirements pushed
change: film to digital allowing film processing systems

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7
Q

what is concerned as digital radiography

A

computer radiography and direct capture radiography

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8
Q

what do cassette based systems use?

A

traditional type film
imaging plate stimulated by phosphors and storage

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9
Q

what uses cassette based systems

A

computed radiography

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10
Q

what is indirect digital

A

radiographers have to move imaging plate

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11
Q

is cassette based systems indirect digital? cassette-less?

A

yes
no –> direct digital

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12
Q

what is direct digital

A

detector and reader are permanent part of table or wall unit

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13
Q

why are detectors important for direct digital

A

small detectors = active matrix array = enhanced contrast resolution

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14
Q

where is the matrix visible in

A

IR and monitor

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15
Q

what forms a matrix

A

digital image acquisition
numerical values stored in the computer’s memory
cells in each row and column

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16
Q

what is a pixel

A

picture element –> each cell in the matrix

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17
Q

how do we improve digital image quality

A

larger matrix size

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18
Q

what does a large matrix size give better images

A

more smaller pixels within matrix = more contrast

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19
Q

what is the smallest element in matrix

A

pixel

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20
Q

how does a pixel work

A

each pixel assigned single number to represent brightness by location in matrix

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21
Q

what does a pixel correspond to

A

area of patient’s tissue

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22
Q

what is an analog image

A

captures or measures continuously changing signals

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23
Q

what does analog signals control (3)

A

level of brightness
shapes
colors

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24
Q

difference between analog and digital

A

analog:
- xray enters IR in analog form and converted into digital
- single sample exposure
digital:
- records as multiple numeric values and divides into several small elements to be process in many ways
- multiple sampling

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25
Q

how does an analog system convert to digital

A

xray energy –> light waves

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26
Q

how does a digital system produce an image

A

analog signals –> numbers

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27
Q

what controls digitizing data? how?

A

pixel values limits number values –> difference between white and black

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28
Q

why do we want a limited digitizing data set?

A

for pre-set pixel values –> contrast

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29
Q

what does a analog-to-digital converter (ADC) do

A

digitizes incoming analog data

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30
Q

Steps for digitizing an image

A

scanning
sampling
quantization

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31
Q

what is scanning

A

the field of the image divided into a matrix of small cells

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32
Q

how does scanning work

A

it detect activated cells (pixels) through detector to make up initial matrix
ex. collimator

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33
Q

what is sampling

A

detection and measurement of signal intensity coming into the system from each pixel location

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34
Q

what controls sampling? pro?

A

mAs controls each pixel = better contrast

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35
Q

what is quantization

A

leveling out brightness level for each pixel to nearest available gray level in preset dynamic level

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36
Q

why is quantization vital?

A

compares given data to move/fix to preset values

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37
Q

what is dynamic range

A

range of pixel values (shades of gray) available from computer system (hardware/software) to create final digitalized image

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38
Q

limitation of dynamic range? pro?

A

control: subset of bit depth of system
pro: allows image manipulation

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39
Q

what is a subset of dynamic range

A

grayscale (displayed image) –> contrast

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40
Q

what is pixel bit depth

A
  • max range of pixel values that computer or hardware can store
  • number of bits within a pixel
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41
Q

what is the number of gray tones within a pixel

A

2 to the power of bit depth

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42
Q

what does gray level determine

A

image contrast resolution

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43
Q

____ grayscale = ____ constrast = _____ pixelation

A

more
more
less

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44
Q

spatial resolution

A

distinguishes one dot between another dot

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45
Q

what determines the size of a pixel

A

size of matrix

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46
Q

____ pixel = ___ detail

A

smaller
greater

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47
Q

size of pixel is directly related _____

A

amount of spatial resolution or detail in image

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48
Q

which number of pixels in a matrix is better?
1024 x 1024 or 16 x 16

A

1024 x 1024

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49
Q

what is attenuation coefficient

A

% or ratio of original xray beam intensity absorbed by each different type of tissue area within body

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50
Q

what does attenuation coefficient create

A

3D projection onto 2D IR

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51
Q

voxel

A

volume of tissue to pixel
averaged by dexel

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52
Q

dexel function

A

rounds average attenuation coefficient to nearest preset value in dynamic range

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53
Q

imaging chain of events

A
  1. patient placed between Xray source and IR
  2. technique and geometric factors selected
  3. capture image and latent image is formed
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54
Q

how is a latent image formed?

A

an invisible image is created from the remnant beam altering the atomic structure of photostimulable phosphors

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55
Q

what are the types of digital radiography

A

digital radiography (DR)
computed radiography (CR)

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56
Q

types of DR conversions

A

direct
indirect

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57
Q

difference between DR and CR

A

DR: IR directly connected to digital processor electromagnetically
uses TFT
CR: uses PSP

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58
Q

what is a AMA? what does it contain?

A

active matrix array
flat panel with thousands of individual dexels

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59
Q

what is the main component of all DR detectors

A

AMA

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60
Q

what is the size of one dexel

A

100 microns square or 1/10th of a pinhead

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61
Q

what material is the detection surface of a dexel made of in Direct DR

A

amorphous selenium

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62
Q

why is amorphous selenium good

A

high absorption efficiency for xrays

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63
Q

how does a AMA work in direct DR

A

converts remnant beam directly into electrical charges for computer to read

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64
Q

3 components of dexel

A

radiation-sensitive detector surface (a-Se)
thin-film transistor (TFT)
small capacitor

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65
Q

function of radiation-sensitive detector surface (a-Se)

A

semiconductor sensitive to xrays (direct) or light (indirect)

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66
Q

function of TFT

A

individual switch for each pixel to change states on/off quickly

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67
Q

function of capacitor

A

stores electrical charge

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68
Q

function of amorphous selenium

A

converts xray energy to electrical charge

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69
Q

what does ionization of selenium produce? what ionizes selenium?

A

electron hole pair (+)
dexel electrode (-)
xray ionizes

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70
Q

direction of electrical charge movement in direct DR

A

+ moves down toward dexel electrode and stored in capacitor
- moves up to be collected and drained off

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71
Q

types of wires in AMA in direct DR

A

gate lines
data lines

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72
Q

gate line function

A

reads out information on exposed DR detector by changing bias voltage from -5 to +10 volts

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73
Q

data line function

A

sudden change in gate line = electricity flow and charge stored up in capacitor flows to data line

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74
Q

what material is indirect detector dexel made of?

A

amorphous silicon

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75
Q

indirect vs direct AMA

A

indirect: has phosphorescent screen (aka scintillator) laid over AMA
photodiode (a-Si)
direct: photoconductor (a-Se)

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76
Q

function of phosphorescent screen

A

phosphor converts xray into light –> light goes to hit AMA

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77
Q

how does AMA work in indirect DR

A

remnant beam hits phosphor screen to fluoresce (visible light) when exposed
then same process as direct DR occurs

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78
Q

difference between DR and CR

A

DR uses TFT
CR uses PSP plate

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79
Q

function of amorphous silicon

A

high absorption efficiency of visible light

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80
Q

components of CR

A

cassette
processor (CR reader)
IR –> PSP plate

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81
Q

construction of cassette

A

material: plastic
memory chip in corner for patient/procedure information

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82
Q

components of PSP plate (7)

A

front protective layer
phosphor layer
reflective layer
electroconductive layer
polyester base layer
light-shielding layer
back protective layer

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83
Q

function of protective layer and material

A

function: protects PSP from mechanical damage
material: low absorbing carbon fiber

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84
Q

function of phosphor layer

A

active layer containing europium activated barium fluorohalide (phosphor)

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85
Q

function of reflective layer

A

reflects emitted light photons towards photomultiplier tube during scanning (NO INTERACTIONS OCCUR)

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86
Q

function of electroconductive layer

A

prevents static build up –> no artifacts on image

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87
Q

light shielding layer

A

prevents extra light from erasing later before its scanned

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88
Q

what material would stimulated phosphorescence occur

A

barium fluorochloride and barium fluorobromide

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89
Q

why use barium fluorochloride and barium fluorobromide

A

contains defects (metastable sites) in crystals to trap free electrons in, when ionized

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90
Q

ability of metastable sites

A

traps free electrons and store them until excitation occurs to release electrons

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91
Q

steps for CR processing

A

PSP removed from cassette by processor –> scanned by helium-neon red laser beam moving across plate to index down one row at a time

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92
Q

what occurs during scanning with red laser beam

A

metastable sites activated by electromagnetic energy to emit dim light –> image electronically amplified to be displayed

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93
Q

what is fluorescence and example

A

immediate emission of light by substance under some type of stimulation
ex. xray exposure of phosphor plate

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94
Q

what is phosphorescence and example

A

delated emission of stored energy in the form of light
ex. laser beam

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95
Q

what occurs in CR reader (processor)

A

PSP plate pulled by suction cups and rollers –> fast scan and slow scan

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96
Q

what occurs in fast scan

A

laser beam is deflected off rotating mirror to scan across PSP plate

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97
Q

what occurs in slow scan

A

rollers are used to direct/move PSP plate

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98
Q

what determines pixel size in DR and CR

A

DR –> IR size
CR –> defined during processing

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99
Q

fast scan controls?

A

pixel width

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100
Q

slow scan controls?

A

pixel length

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101
Q

what prevents distortion in CR

A

equal frequency in fast/slow scan

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102
Q

what occurs during erasing process

A

after scanning –> PSP plate moved by rollers into eraser section
PSP plate exposed to intense white light –> removes remaining information
plate reloaded and ejected from machine

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103
Q

cons to PSP plate

A

very sensitive to background radiation –> prefogging
1mGy = noticeable fog
FIX: always erase before use

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104
Q

difference between scatter and background radiation

A

background: can change how image is processed
scatter: can be corrected during processing

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105
Q

what are characteristics for image quality? (5)

A

brightness
grayscale (contrast resolution)
noise
spatial resolution (sharpness)
distortion

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106
Q

what characteristics is classified as visibility

A

brightness
grayscale

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107
Q

what characteristics is classified as sharpness

A

resolution
distortion

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108
Q

what determines the overall quality of a radiographic image

A

visibility
sharpness

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109
Q

what is a photographic property? Geometric property?

A

P: visibility
G: sharpness and distortion

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110
Q

what is brightness

A

luminous intensity of the display monitor’s light emission

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111
Q

what does brightness measure

A

amount of light emission of a display monitor

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112
Q

if an image is too light….

A

excessive brightness to allow visualization of anatomic structures

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113
Q

if an image is too dark…

A

insufficient brightness and anatomic part cannot be seen well

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114
Q

is brightness and IR exposure related? why?

A

no brightness is a monitor control that can change lightness and darkness of an image on a display monitor

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115
Q

what controls brightness

A

window leveling and technique

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116
Q

what is brightness measured in? (unit)

A

candela

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117
Q

how does adjusting window level affect brightness

A

changes average gray level –> center gray shade on dynamic range

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118
Q

what occurs if window leveling is unchanged

A

average brightness level is uncahnged

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119
Q

how can we change brightness without changing window leveling

A

minimum change of mAs by 30%

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120
Q

which post processing method is preferred and why?

A

window leveling because window width has a narrower dynamic range which can cause misdiagnosis and potential legal issues

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121
Q

what does window level correspond to?

A

pixel value

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122
Q

increasing level = _______ image
decreasing level = ______ image

A

darker
brighter

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123
Q

what occurs during underexposure

A

exposure to IR is too low for anatomic area

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124
Q

what effect would underexposure cause

A

excessive quantum noise

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125
Q

what effect would overexposure cause

A

saturation –> super black and white

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126
Q

what does an exposure indicator provide

A

numeric value indicating level of radiation exposure to digital IR

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127
Q

when does dose creep occur? issue?

A

lack of attention to wide dynamic range
issue: overdosing patient

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128
Q

why is digital IR bad?

A

allows exposure errors to occur –> wide range of IR exposures = dose creep

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129
Q

what is contrast resolution

A

ability of digital system to display subtle changes in shades of gray

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130
Q

contrast resolution is directly related to what?

A

bit depth of pixels

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131
Q

high contrast resolution = ?

A

enhanced densities

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132
Q

what is grayscale also known as?

A

image contrast

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133
Q

how is grayscale represented?

A

percentage or ratio of differences between IR exposures

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134
Q

what does grayscale measure

A

differences of clear white through varying shades of gray to black

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135
Q

what does grayscale affect

A

visibility of detail on displayed digital image and differences between IR exposures

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136
Q

what does dynamic range describe

A

describes contrast concept displayed and is a characteristic of overall image system

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137
Q

what is dynamic range

A

the range of brightness of display monitor light emission

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138
Q

what does dynamic range represent? limited by?

A

number of shades of gray
Limited by computer system

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139
Q

what is actual dynamic range

A

max number of shades of gray represented by numeric range of each pixel or bit depth

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140
Q

what does actual dynamic range represent

A

capabilities of the overall system

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141
Q

can the actual dynamic range be less than bit depth

A

yes

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142
Q

what does bit depth represent?

A

hardware components

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143
Q

what is high contrast

A

difference between adjacent IR exposures that greatly affect contrast

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144
Q

how does high contrast affect images

A

less varying grays

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145
Q

high contrast is also known as?

A

short scale

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146
Q

what is low contrast?

A

differences between adjacent IR exposures are minimal

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147
Q

how does high contrast affect images

A

more various shades of gray

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148
Q

low contrast is also known as?

A

long scale

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149
Q

what is the primary method to adjust display contrast?

A

window width

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150
Q

does kVp and mAs affect grayscale?

A

no because image processing will correct

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151
Q

how does the system adjust the grayscale

A

Histogram (linear range algorithm) and look up table (LUT)

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152
Q

what does the look up table do? affect on image?

A

provides proper grayscale
consistent image

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153
Q

what is on the look up table

A

stored data to sub new values for each pixel during processing

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154
Q

look up table limitations?

A

needs correct histogram selection
cannot compensate exposure values outside normal range

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155
Q

what is window width

A

range of pixel values thats incorporated into display width

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156
Q

increasing window width = _______ contrast

A

lower

157
Q

decreasing window width = _______ brightness

A

increase

158
Q

what is subject contrast

A

range of difference in intensity of xray beam after being attenuated by subject

159
Q

how does subject contrast occur

A

differential absorption

160
Q

what is subject contrast dependent on

A

kVp
amount and type of irradiated material

161
Q

what is the primary controller of subject contrast

A

kVp

162
Q

if kVp adequate
low kvp = _____ subject contrast

A

high

163
Q

what is the easiest way to improve contrast

A

use collimator

164
Q

is contrast same throughout the whole body?

A

no because of difference densities

165
Q

what do radiologist want on images

A

uniform contrast

166
Q

can mAs compensate for inadequate kVp

A

no use 15% rule

167
Q

factors that affect final displayed image contrast/grayscale

A

look up table
kVp
mAs

168
Q

how can final displayed image contrast/grayscale be altered

A

window width

169
Q

what is the final displayed image contrast/grayscale mainly affected by

A

look up table

170
Q

collimation affects?

A

contrast
patient dose

171
Q

negatives of noise

A

interferes with formation of image
no useful diagnostic information

172
Q

what type of noise is there? (4)

A

anatomic
radiographic
equipment
quantum (mottle)

173
Q

what is signal to noise ratio

A

the strength of radiation exposure compared with amount of noise apparent in digital image

174
Q

why is SNR important

A

it shows how much noise can be tolerated in an image

175
Q

how to improve image quality with SNR? con?

A

increase SNR (higher signal) –> less noise
CON: increases patient dose

176
Q

how do we get quantum noise?

A

little xray photons reaching IR to reach latent image

177
Q

what other factors can cause mottle? (3)

A

materials such as:
IR
electrical current
computer algorithms

178
Q

ways to lower noise to best capabilities
why do we do this?

A

set appropriate target exposure value (IE#)
routine monitoring
avoid exposure creep

179
Q

what is considered appropriate exposure value

A

image production with acceptable noise level without excessive or unnecessary exposure to the patient

180
Q

optimal image = ______

A

may not be the best image

181
Q

spatial resolution is also known as?

A

definition
sharpness
recorded detail

182
Q

spatial resolution in relation to a system

A

ability for system to show small details of an object

183
Q

how do we know that we have good spatial resolution

A

dots are very distinguishable between each other

184
Q

what does spatial resolution control

A

detail or sharpness of structural lines

185
Q

what is considered as a geometric property

A

spatial resolution
distortion

186
Q

what is spatial resolution

A

the degree of geometric sharpness or accuracy of structural lines actually recorded in a image

187
Q

what is spatial frequency

A

digital imaging recorded detail based on frequency of wavelength

188
Q

what is high spatial frequency?
Pros?

A

high frequency with shorter wavelength
signal pair of lines are closer together
high resolution
better for smaller objects

189
Q

what is low spatial frequency?
Pros?

A

low frequency long wavelength
signal pair of lines are further apart
low resolution
better for larger objects

190
Q

what determines sharpness?

A

matrix size
pixel size
grayscale bit depth

191
Q

how is sharpness measured? (4)

A

point spread function (PSF)
line spread function (LSF)
modulation transfer function (MTF)
system noise

192
Q

what is sharpness

A

characteristic of final displayed digital image

193
Q

what is MTF

A

modulation transfer function
trueness or fidelity of an image

194
Q

what does MFT measure

A

accuracy of image compared to original object (scale 0-1)
percentage of object contrast that is recorded

195
Q

if MFT is 0 ….

A

no image –> no signal

196
Q

if MFT is 1….

A

perfect exactness

197
Q

if spatial frequency increases = MFT _____

A

decreases

198
Q

what does detective quantum efficiency (DQE) measure?

A

efficiency of IR in converting xray exposure it receives to quality radiographic image

199
Q

if we have 1.0 DQE what does that mean?

A

no information lost during conversion –> 100% DQE

200
Q

higher DQE = _____

A

decrease radiation exposure/patient dose

201
Q

factors affecting spatial resolution in order

A

eliminate motion
reduce OID –> affected side close to IR
reduce focal spot size –> penumbra
increase SID –> use 46” instead of 40”

202
Q

what is distortion? types?

A

misrepresentation of size or shape of the structures examined
TYPES: size and shape

203
Q

how can we tell if something is distorted?

A

by understanding normal radiographic anatomy

204
Q

what property is distortion? what does it affect?

A

geometric
affects image quality

205
Q

what are factors that affect size distortion

A

magnification –> SID and OID
post processing –> resizing images

206
Q

to control magnification we want…. SID/OID

A

maximize SID
minimize OID –> further away = increase mag

207
Q

_____ magnification = _____ spatial resolution

A

decrease
increase

208
Q

what is the main effector of magnification

A

SID –> source-IR

209
Q

longer SID = ____ magnification
shorter SID = ____ magnification

A

decreases
increases

210
Q

given spine or chest exam what would we use for SID

A

large SID whenever possible

211
Q

objects _____ to IR = _____ magnification

A

closer
decreases

212
Q

magnification factor?

A

M = SID/SOD

213
Q

what does magnification radiography do? how?

A

enhances visualization of small structures by purposely increasing OID while keeping SID constant
HOW: use magnification factor

214
Q

when would magnification radiography be uses

A

interventional radiography
mammography

215
Q

Pros and cons of magnification radiography? Fix for con?

A

PRO: no grid necessary
CON: increased patient dose and decrease in image detail/spatial resolution
FIX: use small focal spot to reduce loss of image detail

216
Q

what is shape distortion

A

misrepresentation by unequal magnification of actual shape of structure examined

217
Q

how does shape distortion occur? how is the degree of distortion determined?

A

object plane and image plane are not parallel
Determined: object’s angle of incline and lateral position from central axis

218
Q

how to reduce shape distortion?

A

making body part and IR parallel with CR perpendicular

219
Q

factors that affect shape distortion

A

object thickness
object position
object shape

220
Q

types of shape distortion and affect

A

elongation –> longer than it really is
foreshortening –> shorter than it really is

221
Q

thick object = ____ OID = ______

A

increased
increased distortion

222
Q

how do we get elongation effect

A

tube angle or IR is improperly aligned

223
Q

how do we get foreshortening effect

A

body part is improperly aligned

224
Q

what is spatial distortion

A

misrepresentation in image of the actual spatial relationships among objects

225
Q

how do we get spatial distortion

A

when object positioned shifted laterally from CR

226
Q

how do we fix spatial distortion

A

by getting 2 or more projections to get more 3D examination

227
Q

do we ever want distortion?

A

Yes –> controlled distortion
removes superimposition by tube angulation

228
Q

what does conventional film measure

A

how much chemical changes occurred within exposure through ionization

229
Q

conventional vs digital processing

A

conventional: development, fixing, washing and drying
digital: pre/post processing

230
Q

what does digital film measure

A

how much electrical charge is built up within exposure

231
Q

digital imaging is recorded as what?

A

pixel values

232
Q

preprocessing steps (4)

A

Field uniformity corrections
Noise and del drop-out corrections
Image and histogram analysis
Rescaling (processing)

233
Q

what is preprocessing

A

all computer operations that compensate for flaws in image acquisition

234
Q

what is preprocessing also known as

A

basic image acquisition

235
Q

postprocessing steps (3)

A

gradation processing (LUTs)
detail processing
preparation for display

236
Q

what is postprocessing

A

customized refinements specific to radiographic procedure

237
Q

what is postprocessing also known as

A

specific anatomical procedure

238
Q

displayed image steps (2)

A

operator adjustments
application of special features

239
Q

what is segmentation? pre or post processing?

A

when 2 or more images are taken on the same PSP plate and the computer but segment/separate the images out
PREprocessing

240
Q

what is segmentation failure

A

computer’s inability to segment or separate individual exposure areas

241
Q

does segmentation failure occur on all systems?

A

No –> DR systems sent directly to computer after each exposure

242
Q

what is correcting for dexel dropout? pre or post processing?

A

computer scans for dead pixels through noise reduction software (kernel)
PREprocessing

243
Q

what are dead pixels

A

dexel areas that did not receive enough data due to electronic failure

244
Q

what is interpolation

A

noise reduction software (kernel) reads and averages pixel values surrounding dead pixel and inserts the relative number into dead spot

245
Q

correcting for mottle types? pre or post processing?

A

quantum mottle (random)
electronic mottle (periodic)
PREprocessing

246
Q

what is quantum mottle? How is it fixed?

A

occurs from xray beam being randomly distributed (Poisson distribution)
FIXED: kernel

247
Q

what is electronic mottle? How is it fixed?

A

occurs in consistent size and intervals (forms pattern)
FIX: filtering algorithms (frequency processing)

248
Q

can we avoid noise? which type of mottle is the worst?

A

no it is unavoidable
electronic mottle –> severe mottle is impossible to distinguish

249
Q

what is field uniformity? pre or post processing?

A

electronic amplification (computer software) used to compensate for areas that are outside the range of uniformity
PRE processing

250
Q

why do we need field uniformity?

A

all digital system have flaws in receptor system –> uneven distribution of background density of image

251
Q

what helps field uniformity

A

anode heel effect partially compensates

252
Q

what does histogram display? pre or post processing?

A

bar graph representing brightness value of each pixel
PREprocessing

253
Q

how do you read a histogram?

A

left to right –> light to dark
histogram shape displays each body part

254
Q

how to make a histogram

A

count is made up of all pixels sharing the same pixel value (density/brightness) in dynamic range

255
Q

what is histogram analysis? pre or post processing?

A

elimination of extreme data that skews the rescaling of image so that it is not too light or too dark –> identifies useful pixels
PREprocessing

256
Q

how does histogram analysis occur?

A

computer compares actual histogram from exposed image to expected histogram for that specific procedure

257
Q

what is exposure field recognition? what type of preprocessing is it apart of?

A

identifies field as “false” densities to not overcompensate –> keeps collimation tight
histogram analysis

258
Q

what types of histogram analysis is there? how do we choose which type to use?

A

type 1, type 2, type 3
select procedure from computer menu that auto assigns which type to be used

259
Q

what does type 1 analyze? ex?

A

analyzes two lobe histograms with tail spike in background densities
ex. chest

260
Q

what does type 2 analyze? ex?

A

analyzes single lobe histograms
ex. AB or extremities

261
Q

what does type 3 analyze? ex?

A

analyzes three lobes with some metallic metal present
ex. contrast exam

262
Q

cons in histogram analysis (5)

A

segmentation errors
fail to match histogram to actual image taken
patient with prosthetic or lead appears in collimated area
pre-fogging of IR from background radiation
LARGE amount of scatter radiation

263
Q

what is normalizing an image

A

overall brightness of image and degree of grayscale/contrast are manipulated mathematically until it has a normal appearance to a conventional radiograph

264
Q

what is a rescaled image that has undergone post processing

A

normalized image

265
Q

why do we want to have a normalized image

A

rescaling gives ideal level of brightness and balanced grayscale regardless of technique

266
Q

what is the primary goal of RAD technique

A

give enough signal to reach IR so computer can successfully process

267
Q

will digital processing always produce a diagnostic image?

A

almost always –> fails only under extreme/unusual circumstances

268
Q

what are Q-values

A

standardized labels assigned with preset pixel values that represent certain brightness levels for pixels
processed data

269
Q

how can rescaling be done?

A

electronically or with software (most common)

270
Q

what are S-values

A

data that has not been rescaled

271
Q

how does the computer rescale images

A

computer program gets S-values and reassigns them as Q-values –> places into permanent LUT

272
Q

is there anything that can affect the rescaling process? why?

A

no –> regardless of incoming pixel values –> output pixel values are always adjusted to same output Q values set by permanent LUT

273
Q

why is rescaling important? limitations?

A

align image brightness levels perfecting
Limitations: can only align overall image grayscale partially because of min/max Q values

274
Q

how is an anatomical LUT set?

A

when tech selects radiographic procedure from menu on xray console

275
Q

what are the 3 adjustments made to a histogram before displaying image?

A

histogram analysis –> selects useful pixel values of interest
rescaling to fit average histogram for body part and fixes small exposure errors
LUT –> gives image correct amount of brightness and contrast

276
Q

types of digital processing domains (3)

A

spatial location
shade (intensity)
size (frequency)

277
Q

where does an image begin and end in?

A

spatial location domain

278
Q

what are the subdivisions of spatial domain (3)

A

point processing operations
area processing operations
global operations

279
Q

what does spatial domain deal with

A

pixels acted upon depending on their location in the matrix

280
Q

what operations does spatial domain include? (5)

A

magnification
translation (flipping)
inversion (flopping)
image subtraction
all kernel operations

281
Q

what does point processing do? ex?

A

performs a specific algorithm on each individual pixel in sequence —> pixel by pixel
ex. image subtraction

282
Q

what is image subtraction? ex?

A

values in each specific pixel is subtracted from the value in the corresponding pixel from another image by comparing non-contrast and contrasted images
ex. angiography –> mask image subtracted from contrast image

283
Q

what does area processing do? ex?

A

area/local processing operations use mathematical function on subsection of image
ex. magnification

284
Q

how do you magnify an image? what occurs?

A

select portion of image and zoom
value of each single pixel spreads out across 4 hardware pixels

285
Q

what does global operations do?

A

all image reorientations across matrix –> inversion, flipping, or translating

286
Q

what is translation?

A

switches corresponding columns’ pixel values except for the middle column

287
Q

what is shade/intensity domain deal with

A

operates on pixel values –> brightness or darkness

288
Q

what does size/frequency domain deal with?

A

the number of pixels per row in matrix

289
Q

what operations are in shade/intensity domain? (3)

A

windowing
construction of original histogram
histogram analysis

290
Q

low frequency are for…? wave?

A

large objects/details
long waves

291
Q

high frequency are for…? wave?

A

small details
short waves

292
Q

does size/frequency domain alter?

A

structures or objects within images

293
Q

how does size/frequency domain occur

A

identify object –> sort and group by size into binds

294
Q

detail processing operations (4)

A

smoothing
edge-enhancement
background suppression
local contrast of only fine details

295
Q

purpose of gradation processing? pre or post processing?

A

edit final image brightness and contrast based on anatomy and predominant pathologies displayed
post-processing

296
Q

what does a gradient curve describe

A

brightness and grayscale relating to IR
curves superimpose over the histogram

297
Q

high gradient = ____ contrast = _____ curve

A

high
steep

298
Q

low gradient = ____ contrast = _____ curve

A

low
steadier incline

299
Q

body of each curve represents?

A

range of exposures

300
Q

how to read gradient curve graph

A

average brightness level –> left to right
contrast level –> curve slope

301
Q

windowing controls?

A

brightness and contrast (grayscale)

302
Q

when is gradation processing used? using?

A

on every image before displayed
uses LUT –> look up table

303
Q

window width controls?
window level controls?

A

grayscale
brightness

304
Q

when does data clipping occur

A

when either bit depth of hardware/dynamic range of the system are too limited to allow for windowing adjustments

305
Q

why is data clipping bad? fix?

A

limits radiologist’s ability to window the image = misdiagnosis
FIX: do not save before sending to PACS

306
Q

why does data clipping occur?

A

pixel values too large for dynamic range or computer system –> pixel values/data lost because values too dark for system to handle

307
Q

what is dynamic range compression (DRC)

A

removal of darkest and lightest extremes of pixel values from grayscale

308
Q

why is DRC better than data clipping?

A

allows windowing
saves computer space by eliminating unneeded data that human eye cannot identify
adjusts grayscale to be within dynamic range without removing data

309
Q

what soft tissue adjustment to technique is used? why?

A

film screen –> 20% kVp and no mAs change
lightens image
less penetration to tissue –> increased differential absorption
lightens bones

310
Q

how does the computer adjust to soft tissue techniques? (digital imaging)

A

rescales and adjust images based on LUT
uses dynamic range compression to equalize tissue/contrast and control dynamic range

311
Q

what does detail processing do

A

selects structures in images based on size and singled out for contrast enhancement or suppression

312
Q

how does detail processing affect very small details?

A

contrast increased so it can stand out more

313
Q

how does detail processing affect mid-size structures

A

image suppressed = contrast decreased
moves structure into background

314
Q

how does detail processing work? (4 steps)

A

digital algorithms fix fine details of image separately
image sorted by size of object and into own file/bin
alters contrast/brightness of each individual object
separates local contrast from global contrast so fine details are more visible but whole image has about the same amount of contrast

315
Q

pixel waveform represents?

A

alternating densities

316
Q

pixel waveform
peaks =
dips =

A

black (darkest) pixels
white (brightest) pixels

317
Q

zero point of each individual wave corresponds to?

A

transition border between each pair of pixels

318
Q

wavelength of each pulse represents?

A

pixel size

319
Q

smaller pixels = ____ frequency

A

higher

320
Q

how to read frequency on display monitor

A

left to right
number of up/down cycles = distance

321
Q

each cycle = _____
each pulse = _____

A

2 pulses
1 pixel

322
Q

given 300 cycles
how many pixels are there?

A

600 pixels

323
Q

frequency of objects correlate to?

A

number of pixels that occupy in each row

324
Q

large objects = ______ wavelengths = ____ frequency

A

large
low

325
Q

why do large objects have low frequency

A

fewer photons to fit across the screen

326
Q

small objects = ____ wavelengths = _____ frequency

A

short
high

327
Q

waveform interpretation
amplitude =
wavelength =
tall waves =
wide waves =

A

gray level/pixel value
number of pixels in object across the row (laterally)
darker object
larger object with more pixels occupying row

328
Q

tall skinny spike in wave =

A

dark and small object

329
Q

what is fourier transformer

A

mathematical process that allows frequency processing to separate structures according to size

330
Q

how does fourier transformer work?

A

it breaks up complex waveforms into component waves (long, medium and short) based on pulses with different wavelengths

331
Q

what does wavelengths represent in fourier transformation

A

different sizes of objects or structures in one row in image

332
Q

what is multiscale processing?

A

Decomposition of original image into 8+ frequency layers to perform various operations on selected individual layers and recomposing the image

333
Q

how does multiscale processing determine splitting the layers

A

repeatedly splits into high frequency component and low frequency components and so on until there are 8+ levels

334
Q

how does multiscale processing end?

A

completed image laters are put back together using inverse fourier transformation = final image

335
Q

what is filtering in multiscale processing

A

selected layer is left out when reconstructing final image

336
Q

when is band-pass filtering used

A

noise reduction –> electronic mottle

337
Q

what does low pass filtering do

A

an algorithm passes through low frequency layers

338
Q

most common filter? what does it do? con?

A

smoothing function
removes noise from image
losses some fine detail

339
Q

what does high pass filtering do? aka?

A

passes through highest frequency layers
edge enhancement

340
Q

what does background suppression do

A

eliminates very lowest frequencies

341
Q

how does image domains transition?

A

spatial –> intensity –> spatial –> frequency –> spatial = final image
or
spatial to frequency or intensity then spatial whatever is needed

342
Q

why is the intensity domain important for image transition

A

histogram analysis and gradation processing

343
Q

why does it go back to spatial domain to go to frequency domain?

A

frequency detail processing needs spatial domain in order to put reconstructed pixels back into the spatial matrix

344
Q

example of submatrix?

A

kernel

345
Q

what is a submatrix

A

a small matrix passed over a larger matrix of the whole image –> changes all of the pixel values mathematically

346
Q

how does kernel move?

A

left to right along row and moves down to repeat

347
Q

what is equivalent to frequency detail processing?

A

spatial detail processing

348
Q

what does spatial detail processing affect? (4)

A

smoothing
noise reduction
edge enhancement
background suppression

349
Q

what is a pro about spatial detail processing?

A

uses kernels to affect image –> no need to transition between domains

350
Q

What is the imaging cycle in order?

A

exposure –> histogram –> permanent LUT (rescaling) –> anatomical LUT (gradation) –> default detail processing –> displayed image

351
Q

can you alter a procedure algorithm? How?

A

yes by selecting an alternate histogram or altering window settings (brightness and contrast)

352
Q

why would we select an alternate histogram? Con?

A

gives wider grayscale
CON: histogram errors, image storage issues, record-keeping and legal liability

353
Q

when should we select an alternate histogram?

A

when approved by radiologist

354
Q

window leveling corresponds with …..?

A

brightness

355
Q

window level is also known as?

A

brightness
center
density
S number

356
Q

increase brightness = _____ window level

A

decrease

357
Q

window width corresponds with ….?

A

grayscale

358
Q

does window width alter brightness or density?

A

no

359
Q

wider window = _____ grayscale

A

longer

360
Q

increase contrast = ______ window width

A

decrease

361
Q

what does smoothing remove? con? overall effect?

A

removes highest frequency layers
CON: removes some shades of grey/fine details
Effect: edges are softened

362
Q

how does smoothing occur?

A

noise reduced by mathematical interpolation –> averages pixel values of white/black specks (corrects for dead dexels)

363
Q

what type of postprocessing feature do you use to correct for moderate amounts of mottle? Can it be used for severe mottle?

A

smoothing
no –> extreme underexposure cannot be corrected

364
Q

what is the best method to alternate procedure algorithms?

A

alter windowing settings

365
Q

what type of postprocessing feature do you use to better visualize small details? How?

A

edge enhancement –> increases contrast

366
Q

con of edge enhancement

A

increases noise and possible loss in detail

367
Q

what type of postprocessing feature do you use to better visualize specific tissues (ex. fat pads)?

A

background suppression

368
Q

how does background suppression occur?

A

Algorithms reduce contrast of larger mid-frequency and low-frequency structures

369
Q

targeted area brightness correction effect? how?

A

percentage of tissue equalization by correcting brightness of specific portions of the image

370
Q

what type of postprocessing feature do you use to allow more diagnostic area in an image

A

targeted area brightness correction

371
Q

what type of postprocessing feature do you use to visualize bones as black?

A

image reversal

372
Q

how does image reversal occur?

A

all pixel values are swapped –> high = low and low = high

373
Q

does image reversal create new information?

A

no improvement –> negative image turns to positive image

374
Q

color of bone in negative image and positive image

A

neg: white
positive: black

375
Q

what type of postprocessing feature do you use to fix vale glare?

A

dark masking

376
Q

what does dark masking do? when to use?

A

image is cropped so that the white border (from suppression error) turns into black border
WHEN: before sending image to PACS

377
Q

what type of postprocessing feature do you use to correct an upside down image? how?

A

image orientation
HOW: rotating or flipping image

378
Q

method types of magnification

A

zoom technique: magnifies entire image
Magnifying glass: magnifying box placed over anatomy

379
Q

con of magnification

A

creates pixelation

380
Q

what type of postprocessing feature do you use for elongated anatomy (ex. long bone or spinal imaging)

A

image stitching

381
Q

how does image stitching occur?

A

computer software uses grid to superimpose, crop, and combine multiple images to one image

382
Q

what type of postprocessing feature do you use to identify lesion or fracture locations

A

dual-energy subtraction

383
Q

how does dual-energy subtraction affect image

A

separates image to tissue or bone only image

384
Q

how does the dual-energy subtraction occur?

A

high energy (kVp) and low energy (kVp) obtained and computer compares images to identify xray absorption drop = soft tissue areas –> allows image reconstruction

385
Q

what type of postprocessing feature do you use to remove grid lines? when does this occur?

A

grid line suppression
WHEN: using stationary grids –> portables

386
Q

how does the computer remove grid lines

A

frequency processing identifies lines as large structures with low frequency

387
Q

collimating pros for computer system?

A

reduces failure of system to find collimation edges
reduces incorrect data collection
reduces extremes in image brightness/darkness

388
Q

pros of proper anatomy centering

A

ensure appropriate densities can be located
reduces extremes in image brightness/darkness

RAD 350 (5 decks)

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