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1456: Rad Tech 2 > Unit Two: Indirect and Direct Imaging > Flashcards

Unit Two: Indirect and Direct Imaging Flashcards

1
Q

Two types of Indirect Imaging

A
  1. Charged Coupling Device (CCD)
  2. Thin Film Transistor (TFT)
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2
Q

Indirect w/ CCD steps

A
  1. x-ray photons strike scintillator (CSI)
  2. Scintillator produces light
  3. light energy is transmitted to CCD through fiber optics
  4. CCD converts light to electrical signal
  5. Electrical signal is sent to the ADC
  6. ADC converts electric signal to digital signal, then sends to the computer.
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3
Q

Two types of scintillators

A

Cesium Iodide
Gadolinium Oxysulfide

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4
Q

Why is CSI used instead of gadolinium?

A

Higher resolution due to less light spread

(Higher dose, more expensive)

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5
Q

What makes up a matrix?

A

DELs (pixels)

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6
Q

Each DEL contains:

A

CSI, fiber optics, and CCD

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7
Q

Indirect w/ TFT steps

A
  1. xray strikes scintillator
  2. Scintillator produces light
  3. light gets absorbed by photodetector/photodiode (amorphous silicon)
  4. Amorphous silicon converts photons into electrons
  5. Electrons (electric charges) are captured and transmitted by TFT array to the computer
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8
Q

CCD and Amorphous Silicon job?

A

Converting light into electrical signal

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9
Q

Does indirect w/TFT use fiber optics?

A

No

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10
Q

Why is direct conversion better for SR than indirect?

A

No light step (less light spread)
Direct doesn’t use a scintillator but uses a semi-conductor and TFT array

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11
Q

Underneath each DEL is:

A

TFT and Storage Capacitor

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12
Q

Indirect capture flat panel IR:

A

3000x3000 matrix that contains 9 million DELs within a glass substrate

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13
Q

Direct Conversion steps

A
  1. exposure takes place
  2. xray absorbed by amorphous selenium
  3. AS converts photons into an electric signal
  4. Electric signal migrate to the TFT array
  5. Storage capacitor stores and amplifies signal
  6. TFT reads and releases signal to the ADC
  7. ADC converts to digital signal - sends to computer
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14
Q

Radiosensitive portion of the DEL

A

Fill Factor

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15
Q

What contains the Amorphous Selenium?

A

Fill Factor

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16
Q

SR list of 8

A

OID
SID
Filament Size
Anode Angle Size
Pt. Motion
Shape Distortion
Size Distortion
Image Processing and Display

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17
Q

Spatial Resolution influenced by (non-geometric factors)

A
  1. Size of matrix (monitor)
  2. Pixel size (monitor)
  3. Pixel pitch (monitor)
  4. FOV
  5. DEL
  6. Sampling Frequency
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18
Q

How efficiently a system converts the xray input signal into a useful output image.

A

Detective Quantum Efficiency (DQE)

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19
Q

Measurement of xray absorption efficiency within the IR

A

DQE

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20
Q

Describes how effectively an xray imaging system can produce an image from the output signal (remnant beam) with a high signal-to-noise ratio (SNR)

A

DQE

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21
Q

Noise

A

Mottle/Blur

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22
Q

Mottle

A

Underexposure

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23
Q

Hardware:

A

Storage capacitor, TFT, DEL

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24
Q

Hardware produces:

A

Noise - not signal

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25
Q

Higher SNR

A

DESIRABLE

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26
Q

Electronic noise is inherent in all systems

A
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27
Q

Each DEL contains hardware and fill factor

A
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28
Q

Larger Fill factor = ____ radiation detected

A

More

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29
Q

larger FF = ____ SNR = ___ DQE

A

larger FF = more SNR = higher DQE

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30
Q

A larger FF is ____ efficient at absorbing radiation

A

more

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31
Q

100% of the transmitted remnant beam =

A

Signal

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32
Q

Edges of the DEL produce

A

Noise

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33
Q

Every photon that creates signal (interacts with the fill factor) ____ the SNR

A

increases

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34
Q

An increase in kVp = a ____ in DQE

Why?

A

An increase in kVp = a decrease in DQE

every photon that transmits through the IR lowers SNR ratio

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35
Q

DQE is dependent on:

A

radiation exposure, spatial frequency, MTF, and detector material

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36
Q

too little exposure = mottle = ____ SNR

A

decreased

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37
Q

2 reasons why direct has a higher DQE

A

Amorphous Selenium has a higher quantum efficiency
No light step (less light spread)

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38
Q

Highest to lowest DQE

A

Direct, indirect, CR, film

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39
Q

What is SR determined by?

A

Pixel pitch

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40
Q

How is pixel pitch measured?

A

center to center

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41
Q

Small DEL = __ SR

A

Increased

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42
Q

Referred to as a pixel within the detector

A

Detector Element (DEL)

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43
Q

The detector is made up of

A

a matrix of many DELs (pixels)

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44
Q

More pixels (DELs) within a matrix = __ SR

A

better

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45
Q

larger fill factor = ___ radiation required

A

less (less hardware kinda)

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46
Q

Why does dose increase with a smaller DEL?

A

A smaller DEL has less fill factor which means that more photons are needed because they hit the hardware - which produces noise not signal

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47
Q

Dose ___ w/ large DEL = ___ SR = ___ MTF

A

Dose decreases w/ large DEL = decreased SR = increased MTF

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48
Q

Dose ___ w/small DEL = __ SR = ____ MTF

A

Dose increases w/ small DEL = increased SR = decreased MTF

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49
Q

Smaller pixel has ___ SR

A

Better

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50
Q

Smaller DEL = ___ SR = ___ MTF

A

higher SR and higher MTF

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51
Q

If FOV remains constant, matrix size increases, and pixel size and pitch decrease, then SR ____

A

Increases

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52
Q

How accurately a system converts xray input signal into a useful output image

A

(Modular Transfer Function) MTF

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53
Q

A subcategory of DQE that quantifies spatial frequency/SR capabilities of the IR

A

MTF

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54
Q

Smaller DEL = ___ MTF

A

increased

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55
Q

A measure of the ability of an imaging system to preserve signal contrast as a function of the SR

A

MTF

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56
Q

Often regarded as the ideal expression of image quality provided by a detector

A

MTF

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57
Q

Blur, mottle, and penumbra ___ MTF

A

Decrease

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58
Q

The frequency that a data sample is acquired from the exposed detector

(how many samples are we taking)

A

Sampling Frequency

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59
Q

How is sampling frequency expressed

A

Pixel Pitch and Pixels/mm

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60
Q

Determined by receptor size depending on the vendor

A

Sampling Frequency

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61
Q

KODAK 8x10 has better detail than 14x17

A
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62
Q

To get the highest sampling rate, use the

A

smallest imaging plate possible for each exam

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63
Q

The ___ the spatial frequency (smaller an object) = the harder to image with accurate resolution

A

Higher

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64
Q

Smaller DEL = more DELs on board = ___ sampling freq.

A

Higher

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65
Q

Small DEL = smaller objects can be imaged

A
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66
Q

When sampling a signal, the sampling freq, must be greater than twice the bandwidth of the input signal because half of the info will be lost in translation

A

Nyquist Theorem

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67
Q

If too few DELs are sampled = ____ of resolution

A

loss

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68
Q

there must be ____ DELs as there are pixels in the monitor matrix

A

2x

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69
Q

The highest spatial freq. (smallest object) that can be recorded by a digital detector is determined by:

A

Pixel pitch

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70
Q

The distance from the center of one pixel to the center of an adjacent pixel

A

Pixel Pitch

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71
Q

DEL/pixel density of 10 pixels/mm = Nyquist frequency of

A

5 pixels/mm

72
Q

SNR (signal-to-noise ratio)

A
73
Q

Background electronic noise

A

Always a very small electric current flowing in any circut

74
Q

Higher DQE = ___ SNR

A

higher

75
Q

Measure for assessing the ability of an imaging system to generate clinically useful image contrast

A

CNR (contrast-to-noise) ratio

76
Q

Gives objective measure of useful contrast

A

CNR

77
Q

Why is a bigger pixel size better?

A

More signal than noise

78
Q

Why is a smaller pixel worse?

A

Smaller pixel = less signal = more noise

79
Q

Lines of the matrix produce

A

Noise

80
Q

Useful image info

A

Signal

81
Q

Accumulation of quantum noise and electronic interference

A

Noise

82
Q

Decreased pixel size = ____ signal capture = ___ SNR

A

Decreased
Decreased

83
Q

Must balance the pixel size and SNR to provide optimal SR

A
84
Q

Pixel size is known by the system so that the software can measure image structures based on

A

pixel size

85
Q

Can give an angle measurement between 2 structures, and is commonly used when reading spine studies

A

Angle Measurement

86
Q

Gross overexposure of the IR

A

Saturation Effect

87
Q

When does saturation effect happen?

A

When you expose past the allowed 200% of overexposure

88
Q

Saturation effect cannot be corrected through

A

Rescaling

Have to retake it

89
Q

Underexpose 50% or overexpose 200%

A

dynamic range

90
Q

Photoconductive material/layer

A

Fill factor

91
Q

Where an electrical charge/signal is created in proportion to xrays received

A

Photoconductive Layer

92
Q

Processing methods used to:

A
  1. Reduce image noise
  2. Increase visibility of detail
  3. Adjust and optimize the image contrast characteristics.
93
Q

Performed to plot the raw data

A

Histogram Analysis

94
Q

Used to form the histogram are compared with a “normal” histogram of the same body part by the computer.

A

Raw data

95
Q

Histogram Y axis

A

how many pixels in the image represent that gray level

96
Q

VOI

A

Values of interest

97
Q

Each pixel has a luminance value

A
98
Q

Amount of light coming off a monitor

A

Luminance

99
Q

The acquired histogram containing the VOI is compared to a default histogram =

A

Rescaled image produced

100
Q

A set of anatomic specific algorithms that determine the appropriate amount of contrast and brightness for a displayed image.

A

Look Up Table (LUT)

101
Q

Window level is for

A

Brightness

102
Q

Window Width for

A

Contrast

103
Q

adjusts pixel display for the area of interest, regardless of the amount of exposure unless the exposure is too low or too high. In those cases, quantum mottle or contrast loss occurs.

A

Automatic rescaling

103
Q

anatomic region specific and remains fairly constant from patient to patient.

A

histogram

104
Q

determined by the number of bits used to define each pixel

A

bit depth

105
Q

A grayscale image is composed of pixels represented by multiple bits of information, typically ranging from _ to _ bits or more

A

2 to 8

106
Q

The greater the bit depth, the ____ the number of tones (grayscale or color) that can be represented.

A

greater

107
Q

Determines the number of grays

A

bit depth

108
Q

LUT has a box of crayons: how many crayons in box is controlled by bit depth (because bd controls number of grays)

A
109
Q

Controlling factor of image contrast

A

LUT

110
Q

1 bit (2^1)= 2 tones
2 bits (2^2) = 4 tones
3 bits = 8 tones

A
111
Q

the amount of error that still results in a quality image at an appropriate dose.

A

exposure latitude

112
Q

The total range of exposures that can be captured by the detector.

A

dynamic range

113
Q

Histograms show a wide range of exposure because of

A

automatic rescaling of the pixels

114
Q

What has the highest dynamic range

A

DR

115
Q

smallest amount of radiation that can be detected

A

dynamic range

116
Q

Sharpness control is referred to as

A

spatial/frequency resolution

117
Q

Factors such as FSS,OID, SID , matrix size, pixel pitch, processing speed class, light spread during image acquisition, processing, and computer algorithms will ALL affect

A

SR

118
Q

SR measured in

A

lp/mm

118
Q

used to adjust where on the scale the window is set (brightness of the image).

A

window level

119
Q

used to adjust the contrast of an image

A

Window width

120
Q

allows text to be added to an image.

A

annotation

121
Q

allows for flipping of an image for proper interpretation.

A

image flip

122
Q

allows for the changing of the image from negative (bone is white) to positive (bone is dark)

A

image inversion

123
Q

used to better view smaller objects in an image

A

magnification

124
Q

Increases the contrast along the edge of a structure through a software function.

A

edge enhancement

125
Q

A function to suppress noise that results from averaging of the frequency of each pixel with surrounding pixel values to remove high-frequency noise. Results in a reduction of noise and contrast

A

Smoothing

126
Q

software function that allows underexposed areas (light areas) to be made darker and overexposed areas (dark areas) to be make lighter

A

equalization

127
Q

A quantitative function of digital imaging that allows for the pixel value of a selected area of interest to be calculated. This value can help characterize disease

A

region of interest

128
Q

Protocol is defined as how a set of images will be displayed on the monitor

A

hanging protocol

129
Q

Removal of the white unexposed borders results in an overall smaller number of pixels.
Reduces the amount of info to be stored.

A

Masking

130
Q

Tool is used to orient the image in the correct anatomic hanging position.
Tool is usually a left-to-right flip and a 90-degree clockwise and counterclockwise icon.

A

Flip and Rotate

131
Q

Digital R and L may not be upheld in court during a legal case because of the ability to mark anywhere on the image and flip and rotate the image into any layout on the screen.

A
132
Q

used for anatomy or areas of interest too large to fit on one image receptor.

A

image stitching

133
Q

Sometimes, special cassette holders are used and positioned vertically, corresponding to foot to hip or entire spine radiography, scoliosis, or long bone measurement (orthoroentgenography).

A

Image Stitching

134
Q

Annotations used to:

A

indicate prone or supine, 30 minutes, upright or flat.

135
Q

Allows for the changing of the image from negative (bone is white) to positive (bone is dark). Some pathologic conditions are better identified in this way.

A

image inversion

136
Q

Annotations are NOT to be used to label left or right to indicate the patient’s side. Will NOT hold up in court!!!

A
137
Q

Most common measurement function on PACS

A

distance measurement

138
Q

light coming from the monitor.

A

luminance

139
Q

light coming from sources other than monitor.

A

ambient

140
Q

matrix and pixel size will contribute to the sharpness of structural edges recorded in the image.

A

SR

141
Q

Exposure to DEL (IR) will determine

A

brightness

142
Q

overall lightness or darkness in the radiographic image due to level of exposure to the IR

A

brightness

143
Q

Replaced the term “density“, when the transition was made from film to digital.

A

image brightness

143
Q

unit of measurement for luminance

A

candela/sq. meter

144
Q

brighter image = ____ image

A

darker

145
Q

An underexposed image receptor will produce a

A

mottled image

146
Q

An overexposed image will produce

A

darker image

147
Q

Increasing window/level will increase brightness and create an overall

A

darker image

148
Q

Decreasing window/level will decrease brightness and create a

A

lighter image

149
Q

Why do digital systems havesignificantly greater latitude?

A

Area receiving little radiation can be enhanced by the computer
Higher exposure levels can be separated and brought down to the visible brightness ranges

(more room for error- dynamic range)

150
Q

Describes the ability of an imaging system to distinguish between similar objects that attenuate the x-ray beam similarly in digital imaging.

A

contrast resolution

151
Q

is the smallest exposure change or signal difference that can be detected by the IR.

A

contrast resolution

152
Q

which is the range of exposures that can be captured by a detector.

A

dynamic range

153
Q

a product of the bit depth of each pixel.

A

dynamic range

154
Q

pixel pitch depth

A

2^2 = 4 shades of gray
2^8 = 256 shades of gray

155
Q

Appearance of more detail is due to the

A

wider dynamic range/contrast resolution

156
Q

Because so many more brightness levels are recorded in DR (wide dynamic range), images appear to have greater

A

SR

157
Q

a basic picture element on a display.
A pixel is “any of the small discrete elements that together constitute an image.”

A

pixel

158
Q

the process or capability of distinguishing between individual parts of an image that are adjacent.

A

resolution

159
Q

The smallest area represented in a digital image.

A

pixel

160
Q

A term that describes the number of pixels/mm in an image. Pixel density is determined by the pixel pitch.

A

pixel density

161
Q

smaller pitch = ___ density

A

smaller

162
Q

The typical number of pixels in a matrix range from about 512 × 512 to 1024 × 1024 and can be as large as 2500 × 2500

A
163
Q

larger matrix = ___ pixels = ____ resolution

A

more
better

164
Q

Direct conversion converts xrays into

A

Electrons

165
Q

Direct uses TFT, which functions to

A

Collect electrical charges

166
Q

Which devices collect and convert light into an electronic signal?

A

Photodetector and CCD

167
Q

Direct capture DR means no

A

Light step to form the latent image

168
Q

The measure of the ability of an imaging system to preserve contrast as a function of SR

A

MTF

169
Q

The purpose of the photodetector in indirect

A

Absorb light

170
Q

Can prevent a repeat if a mistake in technique is made

A

Rescaling

171
Q

Individual components comprising the matrix of a digital detector

A

DEL

172
Q
    1. the smallest structures that may be seen in an image measured in LP/mm.
    1. the ability to image adjacent objects as being separate.
    1. refers to the distinctness or sharpness of structural lines that represent an image.
A

SR

173
Q

the amount of error that still results in a quality image at an appropriate dose.

A

exposure latitude

174
Q

Adjusts the pixel values to fit the normal histogram of the body part and adjust for small exposure errors.

A

rescaling

1456: Rad Tech 2 (4 decks)

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