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MRT > DI FINAL EXAM > Flashcards

DI FINAL EXAM Flashcards

1
Q

Define mA

A

amount of current flowing across tube during exposure

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2
Q

What does mA influence?

A

amount of radiation

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3
Q

What does time (s) control?

A

duration of exposure

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4
Q

Define secondary radiation

A

radiation coming from another source (ex. wall, floor)

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5
Q

Define primary radiation

A

radiation between tube and patient - has full E

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6
Q

Define remnant radiation

A

radiation between patient and IR - “exit” radiation has lower E

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7
Q

Define scatter radiation

A

primary radiation that has changed direction

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8
Q

What is attenuation

A

decrease in beam intensity / radiation intensity

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9
Q

Causes of attenuation

A

absorption & scatter

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10
Q

What does an attenuated beam mean?

A

a beam that has decreased in intensity

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11
Q

Define SID

A

source to image receptor distance

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12
Q

Define OID

A

object to image receptor distance

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13
Q

Define SOD

A

source to object distance

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14
Q

Factors affecting absorption

A

thickness, atomic number, density

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15
Q

Increase density =

A

increase absorption

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16
Q

High contrast vs low contrast

A

High C has black & white values with more detail, low C has more grey values with less detail

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17
Q

Cathode to anode process

A

Cathode (negative) expels electrons to anode, anode (positive) produces xrays

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18
Q

Higher kvp = _________ penetration

A

Increased penetration

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19
Q

Higher kvp = _________ energy

A

higher energy produced / beam energy

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20
Q

Higher kvp = _______ absorption

A

decreased absorption (higher penetration occuring)

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21
Q

Explain kvp

A

Max voltage difference between the cathode and the anode (quality)

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22
Q

What does kvp control?

A

penetration and quality of x-ray beam / radiation

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23
Q

Explain mAs

A

Current + time: number of electrons flowing through tube during exposure - total quantity

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24
Q

What does an increase in mAs mean for the xray tube?

A

an increase in number of xray photons

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25
Q

What does increase in mAs mean for patient?

A

increased dose

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26
Q

Explain mA

A

amount of current passing through tube during exposure (higher mA = more electrons) QUANTITY of xrays travelling

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27
Q

What does increasing mA cause

A

an increase in radiation exposure

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28
Q

Dosimeter purpose

A

measures intensity

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29
Q

Intensity measured in

A

mR

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30
Q

What do EI/DI values prove?

A

amount of radiation that reached the IR

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31
Q

Double mA results in what?

A

double rad to IR and double PT dose

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32
Q

Define reciprocity

A

techniques that are different, but will produce similar images (they all have the same mAs - so same rad exposure)

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33
Q

Advantages of reciprocity

A

control motion, breathing techniques, focal spot size

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34
Q

Smaller focal spot has better what compared to large focal spot?

A

SR and detail

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35
Q

Focal spot is limited by what technique?

A

mA

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36
Q

Which has less intensity: 100 cm or 180cm

A

180 cm (beam divergence / intensity decreases with distance)

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37
Q

Inverse square law formula

A

I 1 / 1 2 = (d2/d1) ^ 2

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38
Q

explain inverse square law

A

States that intensity reaching IR is affected by SID (distance: closer to the source = more intensity)

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39
Q

What would you change, technique wise, to get same intensity to IR at 180cm vs 100cm

A

mAs

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40
Q

The square law formula

A

mAs / mAs = (SID / SID) ^2

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41
Q

Define subject contrast

A

determined by absorption of radiation / anatomy (DETERMINES the differences in attenuation of anatomy shown)

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42
Q

Define image contrast

A

brightness values determined by subject contrast, can be high or low - SHOWS the representation of the differences in attenuation of anatomy

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43
Q

Image contrast depends on

A

scatter, subject contrast (wont have image without), post processing (windowing), algorithm (puts brightness and contrast values where they should be for proj)

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44
Q

Subject contrast depends on

A

density, thickness, atomic number, kvp, absorption

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45
Q

Which technique affects contrast?

A

kvp (penetration - how much or little it penetrates will show on image)

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46
Q

Which kvp produces a better contrast, high or low?

A

low kvp (less penetration so allows differences to show better)

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47
Q

What happens if you have a low kvp?

A

increased absorption (so, better contrast and detail), increased subj C, decreased energy

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48
Q

What happens if you have high kvp?

A

increased penetration (less absorption), decreased subj C, increased energy

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49
Q

Which technique is the potential difference?

A

kvp

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50
Q

Define potential difference

A

amount of energy required to move an electric charge from one point to another (kvp - moves electrons cathode to anode)

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51
Q

Define differential absorption

A

difference in how materials absorb xrays produced

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52
Q

What does differential absorption produce image wise?

A

contrast/details of image

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53
Q

Absorption: higher Z / thickness / density =

A

more absorption - less to IR

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54
Q

Absorption: lower Z / thickness / density =

A

less absorption - more to IR

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55
Q

Does mAs affect absorption?

A

no, mAs is just the number of xray photons travelling, kvp affects absorption

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56
Q

How do you control motion issues with chest x-rays?

A

shorter exposure, or use longer exposure if you need to blur out ribs

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57
Q

kvp & intensity formula

A

I 1 / I 2 = (kvp / kvp) ^2

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58
Q

what does kvp and intensity formula measure

A

the primary beam/radiation intensity (tube to pt)

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59
Q

kvp & IR exposure formula

A

I 1 / I 2 = (kvp/kvp) ^5

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60
Q

What does kvp and IR exposure measure

A

remnant beam/radiation

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61
Q

Explain 15% rule of thumb

A

increase in kvp by 15% approximately doubles intensity

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62
Q

a high kvp lowers patient dose when you _______ mAs

A

decrease

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63
Q

Cons of scatter

A

degrades image, makes grey shades blend together, low E

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64
Q

How to control scatter

A

grids, collimation, kvp, thickness

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65
Q

How do grids work to control scatter?

A

made of radiopaque strips that absorb the radiation, radiolucent material lets through radiation needed for the image

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66
Q

Higher the kvp, ________ the grid ratio used

A

higher

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67
Q

Increase kvp = _______ E for scatter

A

increased energy for scatter

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68
Q

Factors affecting scatter

A

kvp, field size (want small), thickness, material

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69
Q

Thicker = _______ scatter

A

more (more matter = more scatter)

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70
Q

Higher the grid ratio = _______ scatter

A

decrease in scatter (16:1 - less scatter than 8:1)

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71
Q

Define grid frequency

A

number of strips per cm

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72
Q

Higher grid frequency = _________ strips

A

more

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73
Q

Con of grids / high grid ratio

A

can get rid of useful radiation (absorb)

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74
Q

List grid types:

A

linear parallel, linear focused, crossed

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75
Q

Define grid cut off

A

unnecessary absorption of primary radiation by grid - “cut off” from reaching IR - partial or complete

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76
Q

Grid cut off is caused by what?

A

incorrect centring / position of grid, wrong SID used, tube angled against the grid lines

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77
Q

How does grid cut off affect the image?

A

poor penetration - resolution loss / grainy / grey spots

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78
Q

Linear focused grid vs parallel

A

Linear focused - grid lines are angled, Linear parallel - grid lines run straight side by side

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79
Q

Increased grid cut off with what grid ratio?

A

higher grid ratio

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80
Q

Con of focused grid?

A

need to be accurate with centring, SID must be accurate, can cause improper absorption if upside down

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81
Q

As grid ratio increases = ________ pt dose & why

A

patient dose (because you have to use a higher technique / mAs with a higher grid ratio)

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82
Q

What grid type gets rid of the most scatter?

A

crossed grids

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83
Q

List and explain grid errors (4) that lead to grid cut off

A

off center (CR not in center of grid), off level (tube and grid not perpendicular), off focus (incorrect SID), upside down (tube side not facing towards the tube)

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84
Q

Explain air gap technique

A

alternative to using grid to reduce scatter reaching IR by increasing distance between patient and IR (OID), helps reduce patient dose

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85
Q

Magnification factor formula

A

Mag factor = SID / SOD (convert: SID - OID = SOD)

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86
Q

What causes magnification (distortion)

A

increased OID, decreased SOD / SID

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87
Q

foreshortening vs elongation

A

Foreshortening - from angled object with a CR thats perpendicular to IR and elongation is from object being parallel to IR with a CR that’s angled (or other way around)

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88
Q

What controls spatial resolution?

A

pixel size / acquisition pixel size (the more pixels = the better the SR)

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89
Q

What affects spatial resolution?

A

focal spot size, movement, OID and SID

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90
Q

Define spatial resolution

A

ability to see difference between two objects close together

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91
Q

What is analog used for?

A

analog xray images are processed - converts analog signal to digital image

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92
Q

More line pairs =

A

better detail (lp/mm)

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93
Q

Small focal spot vs large focal spot

A

small has increase sharpness and spatial resolution and large has decreased sharpness and decreased spatial resolution

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94
Q

Explain anode heel effect

A

angle on tube, photons on anode side have to go through thick target material - decreased intensity on anode side. Place thinner anatomy on anode side

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95
Q

Do the size and shape of the physical AEC detectors change sizes?

A

No, only the outlines do

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96
Q

With AEC, what happens if spine isn’t over detector?

A

AEC detector will see more rad – shorter exposure time – lower mAs (over ST instead of bone) – lower DI value

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97
Q

Explain AEC

A

terminates exposure once ionization chambers receive proper amount of radiation

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98
Q

Explain falling load generators

A

start at HIGH mA and gradually decreases during exposure (kvp remains constant) - purpose is to get the lowest time possible

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99
Q

What do you pick with falling load generator?

A

kvp

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100
Q

What do you pick with AEC?

A

kvp and mA (NOT time)

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101
Q

Backup mAs/time rule?

A

1.5-2x the anticipated mAs (50%-100%)

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102
Q

Explain backup mAs with AEC and why have it

A

max mAs exposure can have incase of system failure or error by technologist - avoids overexposure to patient

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103
Q

Explain min response time

A

shortest possible exposure time (only with AEC)

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104
Q

2 types of windowing

A

brightness and contrast

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105
Q

Explain window level

A

brightness values (higher WL = brighter image)

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106
Q

Explain window width

A

contrast values (Increase WW = decrease constrat)

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107
Q

List post process examples

A

adding text, windowing, magnification, flipping/rotation, inversion

108
Q

Advantages of digital radiography

A

lower patient dose, fewer repeats (have automatic rescaling), post processing, higher contrast resolution

109
Q

Explain detective quantum efficiency (DQE)

A

How well the detector is at converting x-ray energy into an image

110
Q

The higher the DQE =

A

less mAs / rad required = less patient dose

111
Q

Disadvantages of digital radiography

A

lower spatial resolution, dose creep (because of post processing / fixing over exposures - may end up using higher mAs value than required)

112
Q

Subject contrast affected by

A

scatter rad

113
Q

How much subject contrast is required for an exposure in film vs digital radiography

A

film: 10% and digital %1 (so, less needed now with DR to see differences in structures)

114
Q

DDR acquisition types

A

indirect and direct

115
Q

Explain indirect acquisition + example

A

2 step process - offers high DQE - converts xray photons to light - CR cassettes

116
Q

Explain direct acquisition + example

A

1 step - better SR - flat panel detectors

117
Q

When comparing DQE between different detectors / systems, must be compared with same what?

A

kvp (so beam has same penetration)

118
Q

Explain quantum mottle (noise)

A

image has a grainy look - determined by number of photons hitting IR to create signal (pronounced QM - means you can SEE it) - can distract you from the image

119
Q

low kvp and mAs regarding QM

A

few photons hit IR, low signal, more noise (patchy)

120
Q

high kvp and mAs regarding QM

A

many photons hit IR, high signal, less noise = better image

121
Q

Define signal

A

determined by number of photons / information reaching IR (known as image forming xrays - or remnant radiation)

122
Q

What does high signal mean for the image?

A

more radiation hitting the IR = less noise = better image (want a high SNR)

123
Q

What can cause QM

A

larger patient, SID, grid, too low of technique, scatter, lack of information

124
Q

Signal is caused by

A

attenuation, technique(increase mAs-more photons to IR), x-ray photons (more = better chance of converting into something)

125
Q

How to get higher signal to noise ratio

A

increase mAs

126
Q

What percent of the original latent image is retained by PSP and for how long after exposure?

A

75% and up to 8 hours

127
Q

Exposure indictors predict what?

A

If IR received enough radiation and if you have a good SNR

128
Q

More lp/mm =

A

better spatial frequency

129
Q

What can affect the EI value?

A

collimation, technique

130
Q

Explain target index?

A

programmed into system - changed to match procedure. TI is what the IR SHOULD see (How DI is detected)

131
Q

Explain DI value

A

compres measured value (EI) and ideal value (TI) - how much it “deviated” from TI

132
Q

DI formula

A

DI = log (EI/TI) x 10

133
Q

List DI value terms

A

optimal range, acceptable range, out of desired range

134
Q

Explain dynamic range

A

identified by bit depth (# of brightness values each pixel can have)

135
Q

Explain pixel pitch

A

PP - distance from centre of one pixel to the centre of the one next to it (smaller PP = better SR)

136
Q

Explain pixel density

A

The higher the # of pixels, the greater pixel density within a space / FOV (better SR)

137
Q

Explain digital

A

matrix of pixels represented by numerical values

138
Q

Explain CR - computed radiography

A

Taken to a reader to be processed, considered indirect digital (more than one step) - excite electrons to a higher E level

139
Q

Explain photostimulable storage phosphor (PSP)

A

Stores energy inside a CR cassette, laser beam interacts, is exposed and converted into a digital image - stores and releases E

140
Q

Indirect acquisition process CDC

A

Scintillator converts x-ray photons to light, photodetector (CDC) converts light into electronic signal - ADC converts image and produces

141
Q

Direct acquisition process

A

Directly converts x-ray photons to an electronic signal (amorphous selenium)

142
Q

How is digital image formed?

A

matrix of pixels - displayed on a monitor

143
Q

Define pixel

A

represented by numerical value, contains series of bits / bit depth that determine the brightness/details

144
Q

Define image matrix

A

electronic image that is laid out in rows and columns

145
Q

How many different values does 2^4 have

A

16 different values

146
Q

The more bit depth =

A

the more brightness values within an image - the more CR

147
Q

Explain contrast resolution

A

ability to distinguish many shades of grey from black and white (higher the CR = the more shades) - determined by the bits

148
Q

Does a larger matrix increase CR or SR?

A

SR

149
Q

CR plates produce what?

A

the latent image

150
Q

What captures the latent image?

A

PSP - stores the latent image until processing

151
Q

What does noise (QM) limit regarding resolution?

A

contrast

152
Q

Increase pixels = increase _______

A

SR

153
Q

Increase bit depth = increase _______

A

CR

154
Q

What resolution does indirect acquisition have?

A

CR

155
Q

What colour is laser hitting photons?

A

red

156
Q

Laser colour that clears cassette signals

A

white

157
Q

What acquisition has higher DQE

A

indirect (due to scintillation layer)

158
Q

What does a higher signal to noise ratio mean?

A

IR saw more photons (want this) has clearer image

159
Q

What does signal to noise ratio mean?

A

compares level of signal (wanted) to noise (unwanted). Decreased signal = more noise

160
Q

What affects EI value?

A

technique, collimation, algorithm, scatter, SID

161
Q

Increase EI = ______ patient dose

A

increase

162
Q

Fuji Optimal number

A

S# - 200-400

163
Q

Carestream optimal number

A

EI - 800-2200

164
Q

Explain fuji mAs process

A

cut mAs in half = double s#, double mAs = half s#

165
Q

Under 200 with fuji means? and over 400 means?

A

under 200 overexposure, over 400 underexposure

166
Q

What does doubling/halving exposure do with carestream EI?

A

changes EI by 300

167
Q

What is DI optimal number? colour?

A

-3 to 2, green

168
Q

Indirect acquisition CCD process

A

x-ray photons converted to light with the scintillation layer (cesium iodide), CCD converts light to electronic signal, ADC produces image (scintillation, CDC, ADC)

169
Q

Indirect acquisition TFT process

A

x-ray photons converted to light through scintillation layer (cesium iodide), photodiode layer converts light to electronic signal, TFT holds charge briefly, sends signal to ADC to produce image (scintillation - photodiode - TFT - ADC)

170
Q

Direct acquisition process

A

One step (directly converts photons) X-ray photons interact with photoconductor (amorphous selenium) which creates electronic charge, storage capacitors in the DELs collect the charge briefly, released to ADC, digital image produced (Photoconductor - DEL - ADC)

171
Q

Explain PSL (Photostimulable Luminescence) process

A

Phosphor stimulated, Emits light when exposed to a light source (infared), light given off is collected and converted into a digital image

172
Q

Algorithm process

A

selected prior to processing - puts brightness/contrast values in proper range

173
Q

What happens if you under/over expose?

A

Automatic rescaling

174
Q

What is below -5 or above 4 with DI? colour?

A

out of desired range, orange

175
Q

Factors that affect S# or EI value?

A

size of plate, technique, collimation, centring, scatter, beam (should match plate size), algorithm

176
Q

Explain the read process

A

PMT converts light to electrical signal, electrical signal is amplified, A/D converter produces binary number

177
Q

What acquisition has better SR?

A

direct, because no light divergence

178
Q

What is ADC? what does it produce?

A

analog-to-digital-converter (raw data) produces image and binary number

179
Q

What acquisition is general radiography?

A

indirect CCD and TFT

180
Q

Purpose of cesium iodide indirect acquisition

A

Helps focus the light and improve SR

181
Q

difference between an underexposed vs overexposed image appearance

A

dark, bright

182
Q

What is bit depth dependent on?

A

amount of radiation reaching each pixel (will determine shade of pixel)

183
Q

Write 155 binary number

A

done on paper

184
Q

Increase thickness = ________ absorption

A

increase (so, less rad to IR)

185
Q

Order of absorption rates for the body (more - least)

A

bone, soft tissue, air

186
Q

Other name for focal spot blur

A

pneumbra, geometric unsharpness

187
Q

What is focal spot blur

A

whole image is affected and image has a blur to it - loss of sharpness - more noticeable on cathode side

188
Q

Causes of focal spot blur

A

increased OID, larger focal spot

189
Q

How to avoid/fix focal spot blur

A

increase SID, when smaller focal spot when possible

190
Q

What causes QM?

A

not enough photons hitting IR (less signal)

191
Q

For same body part, every 4cm thickness change, do what with the mAs?

A

double it

192
Q

kvp should never be ______ than optimum for that body part

A

less than (should be HIGHER than usual)

193
Q

need to have at least _____ subject contrast

A

1%

194
Q

Why does a nongrid chest have a lower kvp than with a grid?

A

because grids absorb good radiation - so have to compensate for this with grid chest

195
Q

List group 2 that have the same techniques

A

AP/PA knee (if no grid), lateral skull, C-spine, AP shoulder

196
Q

List group 1 that have the same techniques

A

AP abdomen, AP pelvis, AP lumbar spine, AP hip, townes skull

197
Q

Some generators produce more ________

A

output

198
Q

What is Anatomically Programmed Radiography (APR)

A

Used to select procedure / body part (selects correct mAs, kvp, SID, grid, time, FSS) - “fixed technique”

199
Q

AEC vs APR

A

AEC you don’t select time, you select kvp and mA, have to select detectors, back up mAs.

200
Q

What do you select with falling load generator?

A

kvp

201
Q

kvp for: PA wrist

A

65-70

202
Q

kvp for: AP/PA knee

A

70-85

203
Q

kvp for: AP abdomen

A

70-80

204
Q

kvp for: PA chest with grid

A

110-125

205
Q

kvp for: chest non gird

A

80-90

206
Q

kvp for: AP chest

A

120

207
Q

Why is it important to know anticipated mAs with AEC?

A

want them to be the same - tells us if we overexposed pt

208
Q

anticipated 10 mAs, actual was 20, what could have caused this?

A

Improper centring (under more or less density), grid ratio, too much filtration

209
Q

why is it important to Know the appropriate EI/DI ranges for each exposure with AEC

A

image quality

209
Q

What are Single Variable Technique Charts, what do they provide?

A

standardized techniques for procedures that are programmed into system (provides consistency and fewer repeats/errors)

210
Q

What ISN’T standardized in Single Variable Technique Charts

A

thickness (changed based on patient)

211
Q

x-ray image should have:

A

proper penetration (more rad to IR), contrast, controlled scatter, high SNR, and translucency between structures

212
Q

What does translucency mean for image?

A

means you can see overlying structures (ribs, heart shadow, can see spine detail THROUGH the heart tissue)

213
Q

Signs of improper penetration

A

can’t make out detail (blurry)

214
Q

Whats included in Single Variable Technique Charts

A

exposure factors (mAs,kvp), projections, IR (bucky or table), processing (brightness/contrast values), FS size, AEC, density selectors, grid

215
Q

What do density selectors allow control of?

A

density within the image/ radiation reaching IR - can reduce scatter hitting IR in high scatter situations

216
Q

Optimum kvp penetrates a range of ________

A

thicknesses

217
Q

For optimum mA, need to know the following:

A

Focal spot size (to use small FS, has to be within range) and exposure time (short exp time - higher mA)

218
Q

higher or lower mA for PA chest

A

Higher, higher mA allows for a shorter exposure time (so, pt doesnt have to hold breath long)

219
Q

As patient size changes:

A

time and mAs changes (adjust mAs based on thickness)

220
Q

Can use similar technique for:

A

AP lumbar spine, AP abdomen, AP pelvis, townes skull

221
Q

15% rule explain

A

cut mAs in half = increase kvp by 15%, double mAs = decrease kvp by 15%

222
Q

AP knee = _____ AP ankle

A

x 2 the technique (times knee technique by 2 to get the technique for ankle)

223
Q

Purpose of bucky factors

A

Also called grid factors, ratio that determines the extra rad exposure a patient will receive when using a grid (need to compensate for changes)

224
Q

What can cause lateral decentering?

A

Being out of D-tent lock

225
Q

Will DI change with AEC with change in SID for PA chest? what about mAs?

A

no, Di will remain the same, but mAs will be lower

226
Q

What will happen with off center AEC detector with spine, regarding technique?

A

lower mAs than anticipated, lower DI = underexposed image

227
Q

AEC detectors: single knee vs bilateral

A

centre detector with single knee, two laterals with bilateral

228
Q

If you need to repeat an image taken with AEC, what do you do?

A

switch to fixed technique unless you know reason

229
Q

If tube is off centre with AEC, but anatomy is overtop of AEC, what happens?

A

grid cut off (not centred to grid), DI remains the same (IR always sees same rad with AEC), longer exposure time, higher mAs, more rad reaching patient = more dose, amount reaching IR stays the same

230
Q

From the lab, what can you use to prove intensity changes with SID change?

A

use dosimeter (dosimeters measure intensity) for two images and compare

231
Q

From lab, how would you prove that going from a table top exposure for an AP shoulder to a table bucky exposure for the same shoulder would require an increase in technique

A

take 2 exposures (1 table, 1 bucky) using same technique for AP shoulder and compare results

232
Q

What could cause new unit set up with the same techniques, to start showing DI values as underexposures?

A

System could have different DQE, different filtration, generator performance (direct, indirect, etc)

233
Q

What can lateral decentring cause?

A

grid cut off, lower DI / higher mAs if using fixed technique

234
Q

Does AEC affect lateral decentring?

A

no

235
Q

With AEC, which will have a higher mAs 100 cm or 180cm

A

180 cm (takes longer for IR to receive proper rad)

236
Q

With AEC, which will have a higher mAs 6:1 or 12:1

A

12:1 (takes longer for IR to receive proper rad)

237
Q

with AEC, will thinner or thicker patient see more rad exposure?

A

thicker (more pt dose)

238
Q

Whats the exception when pt would see less dose with a higher mAs?

A

adding additional filtration (filter out low E photons)

239
Q

How can you tell if its a fixed technique or AEC?

A

mAs is given if its a fixed technique, back up is given if its AEC

240
Q

How to know if you can use small FS?

A

mA, if its within the correct range

241
Q

Why do you lose radiation going from 100 cm to 180 cm? if thats all you’re doing?

A

inverse square law - loss of intensity reaching IR - beam divergence (will miss IR)

242
Q

the grid 100-180 range has a what grid ratio? high or low? why?

A

Low, allow for SID range

243
Q

Increase kvp = _______ scatter

A

increase

244
Q

will direct or indirect show better SR

A

direct acquisition

245
Q

will direct or indirect show better CR

A

indirect

246
Q

Higher contrast resolution shows higher or lower DQE?

A

higher (can use lower mAs values)

247
Q

Does changing the collimator turn the AEC detectors?

A

No, they remain the same direction

248
Q

With AEC, what happens if you’re supposed to be over ST but you’re centred over bone?

A

longer exposure time, higher mAs, DI increases higher than anticipated

249
Q

With AEC, what happens if you’re supposed to be over bone but you’re centred over ST?

A

shorter exposure (premature), and lower mAs

250
Q

AEC won’t compensate for what?

A

improper centring, wrong detectors, +/- density selectors left on

251
Q

What happens if you have 100 cm selected for PA chest that should be at 180cm? with mAs and DI value

A

mAs lower than anticipated (closer to IR - 3x less), DI value stays the same

252
Q

Why doesn’t DI change if you use the wrong SID?

A

because you’re still properly centred, using correct detectors, and penetrating proper tissue - so same rad will hit AEC

253
Q

can you use AEC if someone has hardware?

A

no, use fixed (would lead to high mAs and DI value - because very dense)

254
Q

Grid errors can cause what?

A

grid cut off

255
Q

underexposure or overexposure if youre laterally decentered with fixed technique?

A

underexposure

256
Q

What to remember about MRT with AEC?

A

you can’t go lower than the MRT

257
Q

Risk when imaging metal / radiopaque material

A

overexposure

258
Q

With falling load, when having issues with motion, change what?

A

80% to 100% setting

259
Q

what does the 100% setting on falling load gen affect?

A

just the length of the exposure (shorter exposure time - doesnt affect mA)

260
Q

Does AEC compensate for lateral decentring of grid? will this affect DI value?

A

yes , DI value not affected

261
Q

What will change DI value with AEC?

A

density selector left on

262
Q

Does changing mA affect patient dose?

A

no, doesnt affect penetration

263
Q

More matter (bigger field size) = ______ mAs and exposure

A

lower and shorter

264
Q

If anatomy is off centre with AEC detectors, what happens?

A

MRT (12 decks)

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