War Machine RR Flashcards
1
Q
Bremsstrahlung
A
Variable Distances of Interactions
Average Brems energy is equal to one third of the kVp selected
Continuous Spectrum of Energy
Majority of the Photons in X-Ray Beam
2
Q
Characteristic Xrays
A
Incident Electron Eject an INNER SHELL
electron from the Target.
Energy of the characteristic photon is
specific to the shell and the target
Classic -69.5 K shell Tungsten
Small Minority of the Photons in the X-Ray Beam
3
Q
X-Ray Production Device
Glass Enclosure / Envelope
A
- Maintain a Vacuum
* Allow the amount and speed of the electrons to be controlled independently.
4
Q
X-Ray Production Device
Cathode
A
• The Filament
• The place in the device where the
electrons enter
5
Q
X-Ray Production Device
Focusing Cup
A
Help the electron beam strike the target in an acceptable size
6
Q
X-Ray Production Device
A
Target of tungsten
7
Q
Increased Target Atomic Number (Z)
A
Increases Quality and Quantity
8
Q
Increased kVp
A
Increases Quality and Quantity
9
Q
Increased mAs
A
Increased Quantity
10
Q
Increased Voltage Ripple
A
Decrease in Quantity and Quality
11
Q
Added Filtration
A
Increased Quality,
Decreased Quantity
12
Q
H e e l E ffe c t
Smaller Angles
A
Worsening Heal Effect
(steeper angle = more abmpt intensity
change)
13
Q
H e e l E ffe c t
Cathode Side
A
Strong Side
more intense side of the beam
14
Q
H e e l E ffe c t
Larger Focus to Film Distance (FFD)
A
Less Heel Effect
15
Q
H e e l E ffe c t
Smaller Film (field of view)
A
Less Heel Effect
Assuming same FFD
16
Q
H e e l E ffe c t
Mammo - Cathode Side on the …
A
Chest Wall
17
Q
Target (Anode) overview
A
Negative Charge - Repels Electrons
Made of Tungsten
Tungsten is Used Because: Has a hiqh atomic number (A 184, Z 74) - this allows for more efficient bremsstrahlunq production
It wont’t melt (hiqh
melting temperature
(3422°c)
Rhenium is often added to tungsten: To prevent cracking at
high temperatures
Rotating Anodes will use a molybdenum stem: Molybdenum will not transmit heat to the thing that spins the target disc (rotor and bearing)
18
Q
Filament (Cathode) Overview
A
Positive Charge - Attracts Electrons
Made of thin (0.2 mm) Tungsten wire
Tungsten is Used Because:
Has a hiqh atomic
number (A 184, Z 74)
Is a good thermionic
emitter (poops out lots
of electrons)
It wont’t melt (hiqh
melting temperature
(3422°c)
19
Q
Area of Interest Cathode Side
A
Breast Chest Wall
CXR (AP) Abdomen (belly is denser than lungs)
Thoracic Spine (AP) Abdomen (belly is denser than lungs)
Femur (AP and lateral) Head (upper thigh is thicker)
Femur (AP and lateral) ** PEDS Knee (reduce dose to gonads)
Tibia / Fibula (AP and lateral) Knee (upper calf is thicker)
Humerus (AP and lateral) Shoulder (upper arm is thicker)
Forearm (AP and lateral) Elbow (upper forearm is thicker)
20
Q
Loss of Characteristic X-Rays
A
If you drop the kVp below the
threshold for k shell electrons you are going to lose those characteristic peaks
21
Q
X-Ray In te ra c tio n s
Compton
A
Major Contributor to Scatter / Fog
Involves the OUTER Shell Electron
Variable Energy Transfer
Does NOT Care About Z
Depends on Density
Dominates above 30 keV
22
Q
X-Ray In te ra c tio n s
Photoelectric
A
Major Contributor to Image Contrast
Involves the INNER Shell Electron
“All or Nothing”
Depends on Z3
Dominates below 30 keV
23
Q
G eometric Relationship
Magnification Increases With
A
- Greater Object to Detector Distance
2. Less Source to Object Distance
24
Q
G eometric Relationship
Less Blur
A
- Small Focal Spot
2. Closer the object is to the detector
25
G eometric Relationship
More Blur
1. Closer the source is to the image
| 2. More Magnification
26
DQE =
Measurement of efficiency
• High DQE = Low Dose
• Low DQE = High Dose
27
DQE is directly proportional to
MTF
MTF describes the relationship between
sharpness and resolution.
28
DQE is inversely proportional to
Signal to Noise Ratio
29
DQE is better at
Low spatial resolution
30
Approximate DQE:
DR = 0.45
| Plain Film = 0.25
31
mAs Controls the
Radiographic Density
| how black the image is
32
kVp Controls the
Radiographic Contrast
• Low kVp = High Contrast
• High kVp = Low Contrast
33
To achieve a noticeable difference in “density”
Increase mAs by 30%
34
To maintain density after decreasing mA by
| 50% you would
Increase kVp by 15%
35
4 cms o f tissue requires
Double the mA
36
Grids typically are NOT used with
Babies and Extremities
37
Cons to using a Grid
Increased Dose
38
Ways to Reduce Scatter (Improve Contrast)
1 - Collimate
2 - Compress the Part
3 - Lower kVp
4 - Grid / Air Gap
39
Pros of Collimation
1 - Increase Contrast
2 - Decrease Scatter
3 - Decrease KAP
40
Cons o f Collimation
1 - Smaller FOV
41
Scatter is Most Severe With
- High kVp Technique
- Large Field o f View
- Thick Parts (or People)
42
D ig ita l - T riv ia S um m a ry
Digital imaging provides a wider dynamic range than film screen
Spatial Resolution of film is still probably superior.
The typical standard o f care for a digital display is 3 Mega-Pixels.
43
The primary factor influencing image contrast
| in film systems
kvp
44
The primary factor influencing image contrast (in digital systems)
LUT
kVp still influences contrast, but digital
systems have a much wider dynamic
range.
45
Digital response curve
* Digital has a linear response curve,
| * Film has a curvilinear response curve.
46
Major determinant of spatial resolution with
| digital images is
Pixel Size and Spacing (pixel pitch)
47
Digital
Decreased Pixel Pitch
Better Spatial Resolution
48
Digital
Increased Pixel Density
Better Spatial Resolution
49
Digital
Direct vs Indirect
Indirect (scintillators)
Xrays ==> Light = > Charge
Direct (photoconductors) =
X rays ==> Charge
50
Digital
Indict uses
Thallium doped Cesium Iodide (Csl)
| “Scintillator”
51
Digital
Direct uses
Amorphous Selenium
52
Specific Factors Affecting the Spatial Resolution of CR
Laser Spot Size:
smaller is better
53
Specific Factors Affecting the Spatial Resolution of CR
Phosphor Pate Density / Thickness
More Thick = More Light Spreading = Less Resolution
54
Specific Factors Affecting the Spatial Resolution of CR
Sampling Frequency (Rate of Light Sampling):
Increasing the sampling frequency
| results in a smaller pixel pitch with improves the spatial resolution.
55
Specific Factors Affecting the Spatial Resolution of CR
Imaging Plate:
You are supposed to use the SMALLEST plate size reasonable for the anatomic
area of interest. The reason is that for fixed matrix size CR systems using a smaller plate for a
given field of view improves your spatial resolution.
56
Specific Factors Affecting the Spatial Resolution of CR
Increasing x-rays will NOT improve
Maximum spatial resolution
57
Specific Factors Affecting the Spatial Resolution of DR
* Spatial Resolution for DR is Superior to CR because the pixel detector is built into the DR flat panel -
* Direct systems that avoid lateral dispersion of light have better spatial resolution
* Spatial Resolution for Flat Panel Detectors is limited to the DEL (detector element); smaller detector elements = better spatial resolution.
58
Direct Conversion
Directly converts x-rays to electrical signal
Detector material is amorphous selenium
Signal does not “laterally disperse”, as the applied voltage separates the electrons and holes made by x-rays
Fill Factor is high (near 100%)
Fligher Detector Quantum Efficiency (DQE)
59
In d ire c t Conversion
X-Ray -> Light -> Electrical Signal
Phospor material is usually thallium doped cesium iodine
Light can scatter (worse with thicker crystal),
better if columnar structure is used.
Moderate fill factor (depends on size of pixel)
Moderate Detector Quantum Efficiency (DQE)
60
Mammo vs General Radiology
mammo
Low Energy 25-35 kVp
Most Common Anode is Moly
Low Tube Current 100mA
Long Exposure Times: 1000 ms
High Receptor Air Kerma lOO(micro)Gy
Beryllium Window
Small Focal Spot
Lower Grid Ratio: 5-1
High Optic Density
Brighter View boxes - 3000cd/m2
Longer Processing Times
61
Mammo vs General Radiology
general radiology
High Energy: 50-120 kVp
Most Common Anode is Tungsten
High Tube Current 500mA
Fast Exposure Times: 50 ms
Low Receptor Air Kerma 5 pGy
Pyrex Glass Window
Larger Focal Spot
Higher Grid Ratio 10-1
Low Optic Density
Darker View boxes - 1500cd/m2
Shorter Processing Times
62
Contact Mode - The Normal Mammogram
Breast is in direct contact with the bucky
The Grid is on
Larger Focal Spot - 0.3mm
Regular Paddle
Regular mA — around 100
Normal Exposure Time (around 1 second)
63
Magnifications - 1.5x - 2x (mammo)
Air Gap between Boob and Detector
No Grid - A ir Gap used to reduce scatter
Small Focal Spot 0.1mm
- need better spatial resolution
Smaller Paddle
Less mA - around 25
Increased exposure time (around 3
seconds)
64
Mammo Target Trivia
Larger or denser breasts
R h /R h
Mo anode can also be combined with an aluminum
filter, fo r a harder beam to penetrate denser breasts.
65
Mammo Target Trivia
“Intermediate” density breasts
Mo anode with Rhodium filter
66
Mammo Target Trivia
“Thin” breasts
Mo anode with Mo filter
67
Mammo Target Trivia
What Combination would you
“never” use?
Rh Target (21 kev) with a Mo Filter (20 Kev K edge)
68
PPV1
Abnormal Screener “Call Back”
3-8%
4.4%
69
PPV2
Recommended Biopsy (4 or 5)
15-40% (25*50% if palpable)
25.4%
70
PPV3
Biopsy Done
- Actual Cancer
20-45% (30-55% if palpable)
31.0%
71
Specific QA Tasks
```
Processor QC Daily
Darkroom Cleanliness Daily
Viewbox Conditions Weekly
Phantom Evaluation Weekly
Repeat Analysis Quarterly
Compression Test Semi-Annually
Darkroom Fog Semi-Annually
Screen-Film Contrast Semi-Annually
Evil Overlord behind MQSA? FDA
```
72
Appropriate Target Range
| for Medical Audit
Recall Rate 5-7%
| Cancers/ 1000 Screened 3-8
73
The Privilege to Read a Mammogram
```
During the last two years of
training you have to read
240
Formal Training Requirement 3 months
Documented Hours of Education 60
```
74
Brea st Phantom Trivia
```
Breast Phantom is ?
• “The Average Breast”
• 50% Fat
• 4.2 cm Compressed
Phantom Dose
Should Be?
300 millirads (3 mGy)
Phantom Dose is
Performed?
WITH a Grid
```
75
General Radiology vs fluoro
general rads
mA 200-800
kVp 50 -120
Very short exposure times
Focal Tube Spot 1.0 -1.2mm
76
General Radiology vs fluoro
fluoro
mA 0-5
kVp 50 -120
Longer exposure times
Focal Spot 0.3-0.6mm
77
Last Image
| Hold
The last frame of the
fluoroscopic loop is “held”
Low Dose
More Quantum
Mottle (less photons)
Spatial Resolution
around 2 Line Pairs
per mm
78
Spot Film
Cassette is placed in front of the detector - like a conventional X-Ray
Higher Dose
Less Quantum Mottle (increased mA, with
optimized kVp)
Spatial Resolution
around 3 Line Pairs
per mm
79
Digital Spot
Digital Equivialant to Spot
| Film - minus the cassette
80
Geometric
| Mag
To magnify something, you generally bring it closer to the x-ray source.
Mag = SID/SOD
Closer to the tube you get more radiation— and it doesn’t double, it squares (inverse square law in reverse).
Operator Dose also increases (scatter is not blocked as efficiently)
Causes Focal Spot Blurring (decreased resolution)
Creates an Air Gap - which reduces scatter
81
Electronic
| Mag (Zoom)
Magnification that occurs from projecting a small field of view onto the matrix of detectors (change in minification gain).
With FPD - the image is enlarged digitally.
There is an increase in dose - driven by the automatic brightness control (typically 1.4x-2.0x per setting).
Increases Air Kerma
Does NOT Increase KAP
Does NOT Cause Focal Spot Blurring (resolution is improved)
Allows for Increased: Collimation
82
Fluoro Trivia
Best Position of the I.I. and X-ray Tube ?
X- Ray tube far away, with the I.I. close.
83
Fluoro Trivia
Where is the ideal place to stand ?
On the same side of the patient as the
| imaging intensifier
84
Fluoro Trivia
Double the distance from the tube does what to dose ?
Decreases it by a factor of 4 (inverse
| square law).
85
Fluoro Trivia
Normal Air Kerma Limit ?
87 mGy/min (10 Roentgens per min)
86
Fluoro Trivia
High Level Control (Really Fat Level Control) ?
176 mGy/min (20 Roentgens per min)
87
Fluoro Trivia
In “high level mode”, you must have ?
Audible or visual alarms (in addition to the
normal time alarm used in normal
fluoroscopy.)
88
Pulsed Fluoro
Conventional fluoro
long very low continuous mA.
| • Pulse fluoro is pulsed (NOT continuous mA but instead pulse of higher mA).
89
Pulsed Fluoro
Pulse Fluoro is good for moving patients (Wiggling Babies)
Gives you sharper
| images with less motion blur
90
Pulsed Fluoro
Pulsed Fluoro can reduce dose
when the frame rate is below 30 frame /second
91
Pulsed Fluoro
People always use a drop o f 30 to 15 frames per second as an example
because
that equals a dose reduction o f 30%. Math to get there isn’t important, just
understand it’s not a direct 1:1 thing. 50% reduction in pulse rate = 30 %
reduction in dose.
92
Pulsed Fluoro
Be careful how the question is worded
because a lower frame rate will have more
mA per individual pulse - but the overall mAs will be decreased relative to regular
fluoro below 30 frames per second.
93
Fluoro in IR Trivia
Best kVp to use with IV contrast is ?
Between 60-80 kVp (average beams
| hit that k-edge nicely)
94
Fluoro in IR Trivia
IR uses relatively Small Focal Spots, and
Small Anode Angle Because ?
The need for maximum spatial resolution
95
Fluoro in IR Trivia
Grids ?
Usually
■ but Not with Peds and
■ Not with Extremities
96
Fluoro in IR Trivia
50% of the dose is delivered ?
in the superficial 3-5 cm of skin/fat
The depth o f this 50% depends on the kVp
andfiltration (higher kVp + Copper
Filtration = more penetration)
97
Fluoro in IR Trivia
“Dose Spreading”
The idea here is to change the angle of the
gantry (especially in a long case) in order
to spread the skin dose over a broader area
- decreasing the skin dose to any specific
location
98
Fluoro in IR Trivia
“Best Place to Stand”
```
You should try and stand / work on the
image receptor side of the patient.
You are trying to avoid the large amount
of Compton scatter radiation produced
where the beam enters the patient.
```
99
Fluoro in IR Trivia
Magification will ... ?
increase Air Kerma, but NOT KAP
100
Fluoro in IR Trivia
```
The dose (outside lead) standing 1 meter from
the patient is about “?” of the dose received by
the patient.
```
1/1000
101
General Radiology vs CT
mA 200-800 mA HIGH up to 1000
kVp 50-120 kVp 80-120
Focal Tube Spot 1.0 -1.2 mm Focal Spot 0.6-1.2 mm
102
CT Trivia
What kind of x-rays are used with CT?
Highly filtered, High kV
| average energy 75 keV
103
CT Trivia
Bow Tie Filters do what ?
* Compensate for uneven filtration,
* Reduce Scatter,
* Reduce Dose
104
CT Trivia
“Septa” is the CT term for ?
A Grid
105
CT Trivia
Minimal slice thickness is determined by ?
Detector element aperture width in a modem CT
106
CT Trivia
Pixel size =
Field of View / Matrix Size
107
CT Trivia
How do you improve spatial resolution ?
You need to make the pixels smaller (matrix larger).
| Remember that Pixel Size = FOV/ Matrix
108
CT Trivia
Decreasing kV from 140 to 80 will do
what to the HU of a contrast enhanced
vessel?
It will increase.
*Increase is only seen with high “Z ” substances
such as Iodine. The benefit is not really there
with water, soft tissue, Calcium etc...
*It s a k-edge thing (Iodine k-edge 32, mean
photon energy o f 80 kVp is 44)
109
Pitch
| o f “ l ” ?
There is no overlap
| between slices.
110
Pitch
| “Greater than 1” ?
This means the table
moved faster than the
beam, and you have gaps
betw’een your slices.
Spatial Resolution
Decreased
Dose Decreased
111
Pitch
| “Less than 1 ” ?
This means the table
moved slow, and your
slices overlapped.
Spatial Resolution
Improved
Dose Increased
112
Window Level (or Center)
Thing you change for “Brightness”
This is the midpoint of the gray scale
display (the “center”). You want your
level at the attenuation of the thing you are interested in.
For example, if you are interested in bone
- you want a high level.
113
Widows Width
Thing you change for Contrast
```
This is selected based on what you are
comparing. If you are comparing things
with very different densities you want a
wide width. If you are comparing things
with very similar densities (example white
and gray matter), you want a very narrow
window width.
```
Above the upper limit of the width
everything will look white. Below the
lower limit of the width everything will
look black
114
A narrow (decreased) window width
Increases Contrast.
115
A wider (increased) window width
Decreases Contrast.
116
WL - “Brain” ?
W 80, L +40
117
WL - “Stroke” ?
W 3 0 , L +30
118
WL - “Lung’
W 1500, L - 400
119
WL - “Abdomen” ?
W 400, L + 50
120
WL - “Bone” ?
W 1600, L +500
121
Cardiac CT
Prospective:
“Step and Shoot”
- R-R interval
pro
There is reduced
radiation b/c the
scanner isn’t on the
whole time
122
Cardiac CT
Prospective:
“Step and Shoot”
- R-R interval
con
No functional
imaging.
Susceptible to
motion artifact.
123
Cardiac CT
Prospective:
“Step and Shoot”
- R-R interval
trivia
Always axial, not
helical.
You need a slow heart
rate (50-65 bpm)
124
Cardiac CT
Retrospective:
Scans the whole
time, then back
calculates
pro
Can do functional
imaging (evaluate
contraction and wall
motion)
125
Cardiac CT
Retrospective:
Scans the whole
time, then back
calculates
con
Higher radiation
(use of low pitch -
increases dose)
126
Cardiac CT
Retrospective:
Scans the whole
time, then back
calculates
trivia
none lol
127
Beta Blockers
Metoprolol Tartrate
(Lopressor) 2.5-5.0 mg IV
Regulate / lower heart rate
to less than 65 bpm for
prospective ECG-triggered
coronary CT
128
Beta Blockers
CI
```
• SBP < 100
• Decompensated Cardiac
Failure
• Asthma on beta-aeonist
inhalers (albuterol)
• Active bronchospasm
• Severe COPD
• 2nd or 3rd-degree AV block
```
129
Nitroglycerine
0.8-1.2 mg glycerol trinitrate
• 5 mg isosorbide dinitrate
Dilates coronary arteries.
Improves visualization /
sensitivity etc... etc.. so on
and so forth.
130
Nitroglycerine
CI
```
• Aortic stenosis (severe)
• Hypertrophic
cardiomyopathy
• Phosphodiesterase-5
(PDE-5) inhibitor — i.e.
boner pills: Viaura
(sildena///) and the others
“fils” like tadalafil etc...
for 48 hours prior to the
exam. Keep that dirtv dick
in your pants 48 hours prior
to exam.
```
131
Beta Blockers
reversal
```
Antidotes / Treatment:
(1) Fluids — careful in CHF
(2) Atropine 0.5 mg IV - can
be repeated up to 3 mg.
(3) Glucagon - 50
micrograms/kg iv loading
dose, followed by a
continuous infusion of
1-15 mg/h
```
132
Spatial Resolution
Holding matrix size
constant and
decreasing FOV
This will decrease pixel size.
| Spatial Resolution is Improved
133
Spatial Resolution
Holding matrix size
constant and
increasing FOV
This will increase pixel size.
| Spatial Resolution is Degraded
134
Spatial Resolution
Optimal Reconstruction
Filter
Bone “sharp ” algorithm gives
| a higher spatial resolution
135
Contrast Resolution
Holding matrix size
constant and
decreasing FOV
This will decrease pixel size.
Contrast Resolution is Degraded
(less photons per box)
136
Contrast Resolution
Holding matrix size
constant and
increasing FOV
This will increase pixel size.
| Contrast Resolution is Improved.
137
Contrast Resolution
Optimal Reconstruction
Filter
“Soft tissue ” or “smooth ”
improves contrast resolution -
relative to bone
138
Contrast Resolution Trivia
What changes to kVp
and mA will maximize
contrast resolution ?
```
Increased mA (less mottle, more signal).
Decreased kVp (less scatter, less noise). **especially in “small”
patients (kids), and contrasted exams.
```
139
Spatial Resolution Trivia
A “?” Focal Spot will
improve spatial
resolution
Smaller Spot = Better
| Determines Spatial Resolution in the X-YPlane... sided to side.
140
Spatial Resolution Trivia
A “?” Detector Width
will improve spatial
resolution
Smaller Detector = Better
Determines Spatial Resolution in the Z Plane (the long axis or
Cranial Caudal direction)
141
Spatial Resolution Trivia
A “?” Pitch will
improve spatial
resolution
• Pitch < 1 improves spatial resolution,
• Pitch > 1 shitty spatial resolution
Pitch > 1 “increases slice sensitivity profde (SSP) ”. As the SSP
widens the slice thickness increases.
142
Spatial Resolution Trivia
Consequences of
decreasing the pitch ?
More Dose
143
CT Dose Related Trivia
Decrease kVp or
Decreased mA
Decreasing mA will decrease the dose
50% decrease in mA = 50% dose decrease
Decreasing kVp will decrease the dose
Quadratic relationship between kVp and radiation dose
Remember this is different than plain film because the skin
dose is spread via the rotating gantry
Decreasing kVp with compensatory increase in mA will
probably decrease the dose (although this is complicated -
a lotta ins, a lotta outs, a lotta what-have-yous).
144
CT Dose Related Trivia
Larger Pitch ?
Decreased Dose
| 50% increase in pitch = 50% dose decrease
145
CT Dose Related Trivia
| ```
Reconstruction Method
Iterative > Filtered Back
```
Iterative algorithms handle noise better — allows for a lower
dose technique to be used.
146
CT Dose Related Trivia
Acquired slice thickness?
*Z-Axis Resolution
Short Answer: Thinner = Maybe* Increase in Dose
Long Answer:
• Part A: Thinner slicer will have more noise. To compensate
for noise you may* be tempted to increase mA which would
increase dose.
• Part B: If you are increasing beam collimation to acquire a
thinner slice, this may* result in higher dose.
*In general CTDI is independent o f collimation, but this
can change at higher / narrow beam collimation settings.
147
CT Dose Related Trivia
Increased Rotational Time ?
```
Less Dose (Faster rotation = less dose.)
Dose is proportional to both scan time and rotation time.
```
148
CT A r tifa c t R e la te d T riv ia
Ring
Call the manufacturer / “Scanner Mechanic”
| The detector needs fix ed / replaced.
149
CT A r tifa c t R e la te d T riv ia
Partial Volume
Acquire thinner slices (decrease beam width , increase beam
| collimation)
150
CT A r tifa c t R e la te d T riv ia
Stair Step
Acquire thinner slices (decrease beam width , increase beam collimation)
Reconstruction with overlapping intervals
151
CT A r tifa c t R e la te d T riv ia
Beam Hardening
Reposition the patient (arms up - etc...)
| Increase the kVp
152
CT A r tifa c t R e la te d T riv ia
Metal
* Increase the kVp (sometimes works).
* Use thinner slices.
* Certain interpolation software can help.
153
CT A r tifa c t R e la te d T riv ia
Photon
Starvation
• Automatic tube current modulation (increase mA). If you
increase the dose through the area of greater attenuation you can add enough photons to overcome this effect.
• Adaptive filtration can be performed to correct the
attenuation profile “smooth the data” in the high attenuation
portions.
154
CT A r tifa c t R e la te d T riv ia
Motion
• Tie the crazy patients down.
• Use a modem (fast) scanner ~ decrease scan acquisition time.
• “Over scanning” an extra 10% on the 360 rotation, with the
repeated portion averaged.
• Gating / Beta Blockers - cardiac.
155
U ltra so u n d R e la te d T riv ia
Reflection
Ultrasound energy gets reflected at a boundary between two tissues because of the differences in the acoustic
impedances of the two tissues.
156
U ltra so u n d R e la te d T riv ia
Refraction - Influenced by:
(1) Speed Change - which is based on tissue compression,
| (2) the Angle of Incidence. “Snells Law”
157
U ltra so u n d R e la te d T riv ia
High Frequency Probes:
- Scatter ?
- Attenuation ?
* More Scatter.
| * More Attenuation
158
U ltra so u n d R e la te d T riv ia
Piezoelectric Materials
(PZT) are ?
• Functional part of the probe
• “The Crystal”
• Determines the frequency of the probe:
■ Lower frequency is seen with thicker crystals
■ Higher frequency is seen with thinner crystals
159
U ltra so u n d R e la te d T riv ia
High Q Dampening Block
* Low Damping (high Q)
* Narrow Bandwidth
* For Doppler, to preserve velocity information.
160
U ltra so u n d R e la te d T riv ia
Low Q Dampening Block
• Heavy Damping (low Q)
• Broad Bandwidth
• Gives you high spatial (axial) resolution *fewer
interference effects and therefore more uniformity
161
U ltra so u n d R e la te d T riv ia
Matching Layer Function ?
Minimizes the acoustic impedance differences between
| the transducer and the patient.
162
U ltra so u n d R e la te d T riv ia
French / Latin Sounding words
for:
• Near Zone:
• Far Zone:
* The Near Field (Fresnel Zone)
| * The Far Field (Fraunhofer Zone)
163
U ltra so u n d R e la te d T riv ia
Higher Transducer Frequency
does what to the near field ?
Higher Transducer Frequency = Longer Near Field.
164
U ltra so u n d R e la te d T riv ia
Focal Zone Maximizes “?”
lateral resolution
165
U ltra so u n d R e la te d T riv ia
How do you improve tissue
penetration (depth) ?
Use a lower frequency probe.
166
U ltra so u n d R e la te d T riv ia
How do you brighten up deep
structures ?
Start fucking around with the “TGC”
- Time Gain Compensation
Buzzword “Uniform brightness”
167
Im p ro v in g A x ia l
| R e so lu tio n US
Shorter Pulses
(Smaller Spatial Pulse
Length)
Greater Damping “Low Q ”
(shorter pulses)
Higher Frequency Probe
(shorter wavelength)
168
Im p ro v in g L a te ra l
| R e s o lu tio n US
Put the thing you want to
look at in the focal zone.
Phased array with multiple
focal zones
Increasing the “line density”
or lines per cm.
Higher Frequency Probe
(less beam spreading)
169
Im p ro v in g E le v a tio n
| R e s o lu tio n US
Use a fixed focal length
across the entire surface of
the array (downside is
partial volume effects)
Use a Thinner Crystal
Minimize slice thickness -
done by phase excitation of
the outer to inner arrays
170
R e s o lu tio n T riv ia US
The stand off pad serves
what function?
* Helps place superficial things in the focal zone
| * This improves the lateral resolution
171
R e s o lu tio n T riv ia US
Axial Resolution
depends on ?
Spatial Pulse Length
172
R e s o lu tio n T riv ia US
Lateral Resolution
depends on ?
Transducer Element Width
173
R e s o lu tio n T riv ia US
Elevation Resolution
depends on ?
Transducer Element Height
174
R e s o lu tio n T riv ia US
Axial Resolution is
independent of ?
Depth
| * Lateral Resolution changes with depth.
175
R e s o lu tio n T riv ia US
High Frequency Probes
improve ?
Axial Resolution
* Small wavelength allows for smaller spatial pulse length
Lateral Resolution
*Less beam spreading
176
R e s o lu tio n T riv ia US
Harmonics improves ?
Lateral Resolution
177
Harmonics works by ?
Transmitting at one frequency and
| receiving at another
178
Compound Imaging works by ?
Using electronic steering of the ultrasound
beams from the transducer to image an
object in multiple different directions
179
Harmonics are NOT produced in the ?
Near Field
| they haven’t traveled fa r enough
180
Harmonics can result in reduced ?
1 - Reverberation Artifact
2- Depth Penetration
(remember higher frequency attenuates -
so the beam is attenuated-faster).
181
Compound Imaging can result in reduced ?
Posterior shadowing
182
Compound Imaging will “?” the edges
Sharpen them
183
Artifact
comet tail
harmonics - more visible
compounding - less visible
184
Artifact
ring down
harmonics - n/a
compounding - reduced
185
Artifact
reverberation
harmonics - reduced/eliminated
compounding - n/a
186
Artifact
increased through transmission
harmonics - increased
compounding - n/a
187
Artifact
acoustic shadowing
harmonics - increased
compounding - decreased
188
Artifact
speckle noide
harmonics - reduced
compounding - reduced
189
Artifact
harmonics -
compounding -
190
Artifact
side lobe/grating
harmonics - reduced
compounding - n/a
191
Thermal Index (T.I.) ?
Heating: this is the maximum temperature rise
| in tissue secondary to energy absorption.
192
Mechanical Index (M.I.) ?
Cavitation (Mechanical Damage):
this is how likely it is that cavitation will occur
considering peak rarefaction pressure and
frequency.
193
What should be avoided with neonatal
| imaging ?
Pulsed Spectral Doppler
194
What should be used instead ?
M-Mode US (to document fetal HR)
195
The T.I. should be ?
Under 1.0 (some sources say 0.7)
196
Ideal Doppler Angle ?
The angle should be between 30- 60.
| Theoretically the best angle is zero.
197
Doppler Angle of 90 Degrees will ?
Look like no flow
198
If you are looking for slow flow, you
| should ?
* Use a low pulse repetition frequency (PRF)
| * Use Power Doppler
199
Power Doppler does Not depend on ?
The Doppler Angle
200
Power Doppler does Not provide
| information on ?
The Direction of Flow
201
Power Doppler will Not demonstrate
| this artifact ?
Aliasing (both color and spectral can).
202
Aliasing Artifact occurs when ?
the doppler shift is greater than a threshold called the
| “Nyquist frequency”
203
Aliasing Artifact Can be reduced by ?
• Increasing the scale
• Increasing the Pulse Repetition Frequency
(which will increase your Nyquist)
• using a lower frequency transducer or using a
doppler angle closer to 90 (increasing the angle)
(which will reduce the doppler shift)
204
Artifacts from Multiple Echoes
Reverberation
Two parallel highly reflective surfaces - Multiple equidistantly spaced
linear reflections.
205
Artifacts from Multiple Echoes
Comet Tail
```
Two parallel highly reflective surfaces -
closer together (< 1/2 SPL) Triangle (comet) shaped
```
206
Artifacts from Multiple Echoes
Ring Down Artifact
Fluid trapped between a tetrahedron of
air bubbles
Parallel band extending
posterior to a collection of gas
207
Artifacts from Multiple Echoes
Mirror Image
Trapped behind a strong reflector This is almost always shown
with the liver on lung.
208
IsotoPe
Same Number of Protons.
209
IsotoNe
Same Number of Neutrons
210
IsoBAR
Same MASS Number.
| *Lift the barbell to put on some mass
211
IsoMer
Same Number of Protons and Neutrons. But the energy
level is different — classic example is isoMeric Tc99M to
Tc99.
212
H a lf Life
Physical
How long it takes to decay to 1/2 activity. You’ll need to memorize these.
213
H a lf Life
Biologic
How long it takes your body to shit, piss, cry, sweat out the tracer. They have
to provide you with this number
214
H a lf Life
Effective
Takes both Physical and Biologic into account (it’s always less)
1/Effective = 1/Physical + 1/Biologic
215
Tc - 99m
Analog:
Energy:“Low” - 140
Physical half life: 6 hours
216
Iodine-123
Analog:Iodine
Energy: “Low” - 159
Physical half life: 13 hours
217
Xenon -133
Analog:
Energy: “Low” - 81
Physical half life: 125 hours
(biologic tl/2 30 seconds)
218
Thallium - 201
Analog: Potassium
```
Energy: “Low”
- 135(2%)
- 167(8%)
use 71 201 Hg
daughter x-rays
```
Physical half life: 73 hours
219
Indium -111
Analog:
Energy: “Medium”
- 173 (89%),
- 247(94%)
Physical half life: 67 hours
220
Gallium - 67
Analog: Iron
Energy: Multiple:
- 93 (40%),
- 184(20%),
- 300(20%),
- 393 (5%)
Physical half life: 78 hours
221
Iodine -131
Analog: Iodine
Energy: “High” - 365
Physical half life: 8 days
222
Fluorine -18
Analog: Sugar
Energy: “High” -511
Physical half life: 110 mins
223
Cobalt -57
Analog: Used for Extrinsic
Field Uniformity
QA (Flood)
Energy: “Low”
- 122
- 136
Physical half life: 270.9 days
224
Germanium 68/
| Gallium 68
Analog: Used for PET QA
Energy: “High” - 511 (via Ga)
Physical half life: 270 days - Ge
68 minutes - Ga
225
Treatment Radionuclides
Half Life
Strontium 89
50.5 DAYS
| 14 days in bone
226
Treatment Radionuclides
Half Life
Samarium 153
46 Hours
227
Treatment Radionuclides
Half Life
Radium 223
11 Days
228
Treatment Radionuclides
Half Life
Yttrium 90
64 Hours
229
Cardiac Radionuclides
Half Life
Rubidium 82
75 seconds
230
Cardiac Radionuclides
Half Life
Nitrogen 13
10 mins
231
Beta Minus
```
Lots of Neutrons
Not Enough Protons
Generate a Beta Particle
(Electron)
ISO BA R IC transition
```
232
Beta Plus
Lots of Protons
Not Enough Neutrons
Generate a Positron
has 1.02 MeV
233
Electron
| Capture
Lots of Protons
Not Enough Neutrons
Does NOT require
1.02MeV
```
Captured “sheath”
electron and proton
merge to form a neutron.
Can produce gamma
photons when coupled
with an isomeric
transition
```
234
Alpha
```
Heavy Unstable
Atoms
Omits a heavy Helium
nuclei (2 protons, 2
neutrons)
```
235
Collimator Type
Parallel Hole
```
Size of image is NOT affected by
distance. The FOV is constant with
distance.
You want the collimator and
detector as close as possible to the
patient for the best spatial
resolution (this is affected by
distance).
```
236
Collimator Type
Parallel Hole Image size and used for
Imase Size =
- 1:1 - Equal to Patient
“The work horse ”
237
Collimator Type
Pinhole
```
Distance Sensitive - amount of
magnification decreases as object
gets farther from the collimator. If
the object is as far from the pinhole
as the pinhole is the camera crystal
there will be zero magnification.
The FOV increases with distance.
```
238
Collimator Type
Pinhole Image size and used for
```
mage Size =
- Magnifies and Inverts
Usedfor:
- Thyroids and other small parts
(hip joint, peds, etc...)
- Large objects get distorted (front
is magnified more than back).
```
239
Collimator Type
Converging
Distance Sensitive - amount of
magnification increases as object
gets farther from the collimator.
The FOV decreases with distance.
240
Collimator Type
Converging Image size and used for
```
Image Size =
- Magnifies without inverting
Usedfor:
- Multiple choice questions.
- Sometimes small body parts
```
241
Collimator Type
Diverging
Distance Sensitive - amount of
minification increases as object gets
farther from the collimator
The FOV increases with distance.
242
Collimator Type
Diverging Image size and used for
```
Image Size =
- “Minifies” , Takes a large object
and makes it small.
Usedfor:
- Large Body Parts (lung scan with
mobile gamma camera in the ICU)
```
243
Parallel Hole Factor
Septa Length
```
Long Septa:
- Low Sensitivity (Noisy)
- High Spatial Resolution
Short Septa:
- High Sensitivity
- Low Spatial Resolution
```
244
Parallel Hole Factor
Hole Diameter
```
Wider Hole:
- High Sensitivity
- Low Resolution
Narrow Hole:
- Low Sensitivity
- High Resolution
```
245
Parallel Hole Factor
Septa Thickness
```
Thick Septa:
- Less Penetration
- Less Available space for
holes (Less Sensitivity)
Thin Septa
- More Penetration (Blur)
- More Available space for
holes (More sensitivity)
```
246
Q/A on the Dose Calibrator (Ionizing Chamber
Consistency
Daily
Should be within 5% of
computed activity
Checked with reference
sources
247
Q/A on the Dose Calibrator (Ionizing Chamber
Linearity
Quarterly
Accurate readout for
activities over the whole
range of potentially
encountered activities
```
Checked with a large
activity of Tc (around
200mCi) and decaying it
down to less than the
smallest activity you
would measure for use.
```
248
Q/A on the Dose Calibrator (Ionizing Chamber
Accuracy
Annually
Standard measurements
of radiotracers measured
and compared to what the
activity should be
Standard Energy Sources:
• Low (Co-57)
. Medium (Cs-137)
. High (Co-60)
249
Q/A on the Dose Calibrator (Ionizing Chamber
Geometry
Installation and any
time you move the
device
Correction for different
positioning and size
Different volumes of
liquid (Tc-99m)
250
G e ig e r - M u lle r C o u n te r
Detects Ionizing Radiation (alpha, beta, gamma)
Detects Ionizing Radiation (alpha, beta, gamma)
Great for Low-Level Radioactive Survey
Terrible for Very High Radiation Fields
(“Dead Time”)
251
Ionizing chamber
For measuring dose rate.
Used with higher rates.
Lower Sensitivity
Stable across a wide voltage range - Excellent
for accurate estimates (or exposure).
252
“Pocket Ionization Detector”
uses a miniature ionization chamber.
They give you real-time estimated dose, but must be charged and zero’d
prior to use. These are not used anymore - which makes them high yield.
253
“Solid State Dosimeter ”
Accumulated dose or rate can be read real
| time with LCD display.
254
“Film Badge ”
Uses a thin metallic filter with a radiosensitive film.
The degree of darkening (relative optic density) corresponds with dose.
They can be damaged by temperature, humidity, etc...
255
“Optically Stimulated Dosimeter”
the film badge. Chips /
| Strips are placed under a filter.
256
Survey Meters
G-M and Ionization Detectors - discussed on prior page
257
Well Counter
Basically a small gamma camera, with one PMT. Susceptible to “dead
time” at counts over 5000 per second. Good for urine and blood
samples. Good for “wipe test” samples.
258
Dose Calibration
& Automated Dose
Injection Systems
Used to measure radiopharmaceuticals.
259
Thyroid Uptake
| Probe
Compares counts from region over the thyroid to a calibrated capsule of
the same radionuclide. The probe is a cylindrical scintillator detector
attached to a PMT. A positioning guide keeps the distance constant. A
Chi-Squared test can be used to evaluate the reliability of consistent
operation.
260
Intra-operative
| Probes
Used for lymphoscintigraphy
261
10CFR part 19
Nwootrik,c eerss,. instmctions, and reports to workers
...i nspecti. ons „
262
10 CFRpart 20
Standards for protection against radiation,
"radiation protection”
263
10CFR part 35
Medical use of by-product material.
“human use of
radioisotopes"
264
Regulations
Major Spill
Tc-99m
Greater than 100 mCi
265
Regulations
Major Spill
Tl-201
Greater than 100 mCi
266
Regulations
Major Spill
In-111
Greater than 10 mCi
267
Regulations
Major Spill
1-123
Greater than 10 mCi
268
Regulations
Major Spill
Ga-67
Greater than 10 mCi
269
Regulations
Major Spill
1-131
Greater than 1 mCi
270
Regulations
Major Spill
steps
1. Clear area.
2. Cover spill with absorbent paper.
Do NOT clean it up.
3. Clearly indicate boundaries of spill
Limit movement of contaminated
pet sons
4. Shield source if possible
5. Notify the Radiation Safety Officer
immediately
6. Decontaminate persons
271
Regulations - General Public
Annual Dose limit
100 mrem
272
Regulations - General Public
“Unrestricted area”
Not greater than 2 mrem per hour
273
Regulations - General Public
“Restricted Area”
Defined as:
| “Any place that receives a dose greater than 2 mrem/h”
274
Radiation Area
Any place you could get 0.005 rem (0.05mSv) in 1 hour at 30cm
275
High Radiation Area
Any place you could get O.lrem (lmSv) in 1 hour at 30cm
276
Very High Radiation Area:
Any place you could get 500 rads (5 gray) in 1 hour at 1 meter
277
Regulations - NRC Occupational Exposure Dose Limits
Total Body Dose per Year
5 rem (50 mSv)
278
Regulations - NRC Occupational Exposure Dose Limits
Dose to the Ocular Lens per year
15 rem (150 mSv)
279
Regulations - NRC Occupational Exposure Dose Limits
Total equivalent organ dose
50 rem (500 mSv)
280
Regulations - NRC Occupational Exposure Dose Limits
Total equivalent extremity dose per year
50 rem (500 mSv)
281
Regulations - NRC Occupational Exposure Dose Limits
Total Dose to Embryo/fetus over entire 9 months
```
0.5 rem (5 mSv)
I f the fetus has already got 5 mSv at
the time o f declaration - the NRC
states you can get 0.5 mSv more fo r
the remainder o f the pregnancy.
```
282
Regulations - NRC Occupational Exposure Dose Limits
units
1 rad = 1 rem, 1 rad = 0.01 Gy
1 mSv =100 mrem = 0.1 rem
1 rad = 1 rem
1 rad = 0.01 Gy
1 mSv =100 mrem = 0.1 rem
283
Reportable vs Recordable
(wrong drug, wrong dose
- by 20%, wrong pt, etc...
Whole Body Dose > or < 5 rem
Single Organ Dose > or <50 rem
greater
RePORTabie Event
```
Call NRC within 24 hrs
Write NR C Letter within
15 days
Present your testicles to
the NR C for castration
(within 30 days)
Notify Referring Doctor
within 24 hours
Notify the Patient (or let
referring do it)
```
284
Reportable vs Recordable
(wrong drug, wrong dose
- by 20%, wrong pt, etc...
Whole Body Dose > or < 5 rem
Single Organ Dose > or <50 rem
lesser
ReCORDable Event
Record Locally
Institutional Review
285
Receiving, Storing, and Disposing of Radioactive Material
Within 3 hours of receipt (3 working hours) you (the tech) has to survey packages when they
arrive. This process involves a GM counter test at the surface and 1 meter from the package, as
well as wipes of all surfaces of the package (>6600 dpm/300 cm2 is not allowed).
Next Step => Contact both the shipper and the NRC if beyond allowable limits
286
Package labe: white 1
no special handling
Surface dose rate <0.5 mrem/hr, 1 meter 0 mrem/hr
There is no T.I.
(Transportation Index)
because the rate at 1 meter
will be so low.
287
Package
| Label: yellow 1
special handling required
Surface dose rate <50 mrem/hr,
1 meter < 1 mrem/hr
T.I. < 1.0 mR per hour
288
Package label yellow 2
special handling rquired
Surface dose rate < 200 mrem/hr,
1 meter < 10 mrem/hr
T.I. >1.0 mR per hour
289
Common Carriers
A truck that carries regular packages
and radioactive material
T.I. should not exceed
10 mR / per hour.
Surface rate should not be
more than 200 mR
290
Multiple Packages
Those shipped together
Sum should NOT exceed
50 mR.
291
Radionuclide
Purity
What is it?
How much Mo
in the Tc ?
“Moly
Breakthrough ’’
292
Radionuclide
Purity
Tested?
```
Tested in a dose
calibrator with lead
shields;
Looking for 700
keV photons of
Moly (remember Tc
is only like 140)
```
293
Radionuclide
Purity
Limit?
0.15 microcuries of Mo per
| 1 millicurie of Tc
294
Chemical
Purity
What is it?
How much A1
in the Tc ?
“Aluminum
Breakthrough
295
Chemical
Purity
Tested?
Tested with pH
paper (Color
Indicator Paper, or
Paper Strip Test)
296
Chemical
Purity
Limit?
```
<10 micrograms A1 per 1ml
Aluminum Contamination
Can Be Shown Two Ways:
1. Liver Spleen Scan + Luna =
Aluminum Contamination
2. Tc scan + Liver Activity =
Aluminum Contamination
```
297
Radiochemical
Purity
What is it?
How much Free
| Tc?
298
Radiochemical
Purity
Tested?
Tested with Thin
Layer
Chromotography
299
Radiochemical
Purity
Limit?
```
. 95% Na99mTc04
• 92% for 99mTc sulfur colloid
(MAA)
• 91% for all other Tc
radiopharmaceuticals
Free Tc Classically Shown as:
- Gastric uptake
- Salivary Glands uptake
- Thyroid uptake
```
300
Tc - Moly Generator operates with “Transient Equilibrium ”
which occurs at 4 daughter
| half lives — Remember the t 1/2 of Tc is 6 hours. (4 x 6 = 24 hours)
301
2D PET vs 3D PET
| 2d
Septa collimator (reject scatter)
Less Sensitivity
Fewer True, Scattered and Random
Coincidences
Smaller FOC for true coincidences
More Tracer
302
2D PET vs 3D PET
3d
NO Septa Collimator
(fast coincidence detector)
More Sensitivity
More True, Scattered and Random
Coincidences
Larger FOV for true coincidences
Less Tracer
303
Attenuation Correction pet
ligth skin and light lungs
304
Uncorrected pet
hot skin andhot lungs
305
SUV Trivia
Monstrously Obese Fatties SUVs are overestimated
Delayed Scan Timing
In other words, if you did “delays” you would get higher FDG values.
High Blood Glucose SUVs are Lower
Smaller Tumor (or object of interest)
Smaller than 1 cm = Lower SUV.
IV Dose Extravasation Dose Extravasation = Lower SUV
Iterative reconstruction More iterations the higher the SUV.
306
Dose units pet
| Exposure
C/kg
Charge (C) in the air created divided by the mass (kg) of that
air.
307
Dose units pet
| Absorbed Dose
Gy
1 Gy = 100 rads
Energy deposited per kilogram of material (J/kg = Gy),
Organ Dose =
Total energy to that organ / Total mass of the organ.
308
Dose units pet
| Equivalent Dose
Sv
Absorbed dose of different types of radiation creates
different levels of biologic damage (thus measured in
Sv). A weighting factor is used to adjust the value. For
example, an alpha particle can do more damage than an
electron.
EqD = Dose x Weight Factor
Weight Factor = for x-rays and gamma rays this is 1,
Weight Factor = for alpha particles it’s 20.
309
Dose units pet
| Effective Dose
Sv
Closest measure of cancer risk,
since it considers both
radiation and tissue type.
This takes into account whether radiation has been
absorbed by the specific tissue. In other words, you are
taking into account the type of radiation and the
variable sensitivity of the organ / body part.
Bone Marrow and Bowel are Radiosensitive (higher
wT). The Brain is relatively insensitive (lower wT).
If all the dose is absorbed then 1 Gy = 1 Sv. If you are
dealing with organs or specific body parts you have to
use a “tissue weighting” conversion factor.
EfD = Equivalent Dose x Tissue Factor “wT”
310
Deterministic Effects
Deterministic Effects
Severity is dose related
Does Not include Cancer Risk
311
Stochastic Effects (“Random”)
Has NO threshold
Probability of effect increases with dose
Severity is NOT dose related
Includes heritable effects and carcinogenesis
(NOT cell killing)
312
Dose Units - Fluoro
| Air Kerma
AK
(Gy/min)
```
Measures the intensity of the
x-ray beam.
Absorbed dose in Air
Energy transfer from the primary
interaction of photons on tissue
atoms. NOT the secondary
production of scatter electrons
which also contribute to the
overall dose.
Relates to Deterministic Risk
Decreases with distance from the
x-ray source — inverse square.
```
313
Dose Units - Fluoro
| Kerma-Area
Product (KAP
Gy-cm2)
```
Accounts for both exposure
and area exposed - best thought
of as “the whole beam.”
KAP = Dose “AK” x Cross Sectional Area
Relates to Stochastic Risk
Independent of the source
distance. You can measure it
at any point along its path and
it will be the same.
Collimation will DECREASE
the KAP.
```
314
Dose Units - Fluoro
| Cumulative Air
Kerma (CAK
Gy)
Total of all the AK values for
individual exposures,
```
Described at a specific
interventional reference point:
15 cm toward the x-ray tube
measured from the isocenter of
the fluoroscopy machine.
```
315
Dose Units - CT
CTDI
“CT Dose
Index”
mGy
This is the radiation dose,
normalized to beam width
```
CTDI numbers are based on
phantoms. The body phantom
is 32 cm in diameter.
If the patient is larger (a big fat
pig) than the phantom, then
dose is over estimated.
If the patient is smaller (peds)
than the phantom, then dose is
under estimated.
```
316
Dose Units - CT
“Weighted
CTDI”
mGy
This is 1/3 the central CTDI + 2/3
the Peripheral CTDI (expressed in
mGy)
317
Dose Units - CT
“Volume
CTDI”
mGy
```
This is obtained by dividing
weighted CTDI by the Pitch.
2/3 CDTIp + 1/3 CTDIc / pitch
“Reference Dose ”
set by the ACR at 75 percentile
CTDI vol:
• 75mGy for Head,
• 25 mGy for Adult Abd,
• 20 mGy for Peds Abd (5 year old)
```
318
Dose Units - CT
DLP
“Dose Length
Product”
mGy - cm
CTDI - Vol x the length of the
scan in cm.
It is appropriate to add DLP from
series to series.
319
Dose Units - CT
“Effective
Dose” fo r CT
mSv
Effective Dose = k x DLP.
Remember that “k” is a body
part constant.
320
This vs That: Direct vs Indirect Radiation
| Direct Radiation
minority
Acts on DNA
Most likely for High
LET Radiation
(unusual in x-ray
imaging)
321
This vs That: Direct vs Indirect Radiation
| Indirect Radiation
majority
```
Acts on water in the
cytoplasm, creating
free radicals - which
in turn damage the
DNA
```
More likely for Low
LET Radiation
This process is
promoted by the
presence of oxygen
322
Acute
Radiation
Syndrome
Bone Marrow
Dose Needed - > 2 Gy
Dose Needed
“Rounded For
Memory” - 5 Gy
Latent Period -1 -6 Weeks
```
Outcome -You do worse
with higher
doses. It’s
possible to
survive.
```
323
Acute
Radiation
Syndrome
GI
Dose Needed - > 8 Gy
Dose Needed
“Rounded For
Memory” - 10 Gy
Latent Period -5-7 Days
Outcome -Death within 2
weeks
324
Acute
Radiation
Syndrome
CNS
Dose Needed - > 20-50 Gy
Dose Needed
“Rounded For
Memory” - 100 Gy
Latent Period -4-6 Hours
Outcome -Death within 3
days (unless you
get to Elysium)
325
WB Dose (Gy)
< 1
No vomiting No skin redness
Surveillance for 5
weeks
326
WB Dose (Gy)
1-2
```
Vomiting 2-3 hours
after exposure
Skin redness
(12-24 hours after
exposure)
```
Surveillance for 3
weeks, Consider
General Hospital
327
WB Dose (Gy)
2-4
```
Vomiting 1 -2 hours
after exposure
Skin redness
(8-15 hours after
exposure)
```
Hospitalize - Bum
Center
328
WB Dose (Gy)
> 4
```
Vomiting < 1 hour
after exposure
Skin redness
(1-6 hours after
exposure)
```
Hospitalize -
Specialized Radiation
Center
329
Skin Problem
Dose (Gy) Onset
Early Transient Erythema
2 Gy skin dose hours
330
Skin Problem
Dose (Gy) Onset
Severe “Robust” Erythema
6 Gy skin dose 1 Week
331
Skin Problem
Dose (Gy) Onset
Telangiectasia
10 Gy skin dose 52 Weeks
332
Skin Problem
Dose (Gy) Onset
Dry Desquamation
13 Gy skin dose 4 Weeks
333
Skin Problem
Dose (Gy) Onset
Moist Desquamation / Ulceration
18 Gy skin dose 4 Weeks
334
Skin Problem
Dose (Gy) Onset
Secondary Ulceration
24 Gy skin dose > 6 weeks
335
Hair Problem
Dose (Gy) Onset
Temporary Epilation
3 Gy 21 Days
336
Hair Problem
Dose (Gy) Onset
Permanent Epilation
7 Gy 21 Days
337
Cell Sensitivity - Trivia
Order of Sensitivity M > G2 > Gl > S.
338
Most radiosensitive part of the GI tract ?
Small Bowel
339
MOST sensitive blood cells in the body ?
Lymphocytes. A dose of 0.25 Gy is enough to
| depress the amount circulating in the blood.
340
< 50 mGy fetus
0-2 Weeks: “All or Nothing” - Spontaneous Abortion or Not
- but probably OK at these low doses
> 2 Weeks: Dose isn’t enough to matter (probably)
341
> 50-100 mGy fetus
0-2 Weeks:"All or Nothing" - Spontaneous Abortion or Not
- risk o f fetal loss is more legit above 100 mGy
8-15 Weeks:Neuronal Development - might cause a retard (Borat’s Brother Billo).
Most sources call this period the greatest risk of teratogenesis
> 25 Weeks: No teratogenic effects at diagnostic doses (those less than 100 mGy)
342
100-500 mGy fetus
Consider aborting - based on individual risk factors, and various superstitious beliefs
343
T 1 (Longitudinal) is determined by ?
Interaction with the Spin - Lattice
| 77 = has grown to 63% o f magnetization
344
T2 (Transverse) is determined by ?
Spin-Spin Interactions dephase magnetization
| 12 = has decayed to 37% o f original value
345
T2* (Free Induction Decay) is determined by ?
Spin-Spine Interactions PLUS the Non-
| Uniformity of the Magnetic Field
346
T1 “Shortening” is ?
Bright
347
T2 “Shortening” is ?
Dark
348
T1
Short TR
| Short TE
349
T2
Long TR
| Long TE
350
Proton Density
Long TR
| Short TE
351
Spin Echo
Short TR 250-700 ms
Long TR >2000 ms
Short TE 10-25 ms
Long TE >60 ms
352
GRadient Echo
Short TR < 50 ms
Long TR >100 ms
Short TE 1-5 ms
Long TE >10 ms
353
MRI - Table Time
Standard Sequence ?
TR x Phase Matrix x NEX
354
MRI - Table Time
3D Sequence ?
TR x Phase Matrix x NEX x # Slices
355
MRI - Table Time
Fast Spin Echo ?
Acquisition time is approximately proportional to 1/Echo Train Length
356
MRI - Slice Thickness
Thinner Slice
Steep (“Increased”)
Slice Selection Gradient
Decreased Transmit
Bandwidth
357
MRI - Slice Thickness
Thicker Slice
Shallow (“Decreased”)
Slice Selection Gradient
Increased Transmit
Bandwidth
358
MRI Modification
Thicker Slices
Signal to noise:Increased
Spatial resolution:Decreased
Duration of Exam:No Effect
359
MRI Modification
Larger Field of View
Signal to noise:Increased
Spatial resolution:Decreased
Duration of Exam:No Effect
360
MRI Modification
Larger Matrix
Signal to noise:Decreased
Spatial resolution:Increased
Duration of Exam:Increased
361
MRI Modification
Greater Field
Strength
Signal to noise:Increased
Spatial resolution:No Effect
Duration of Exam:No Effect
362
MRI Modification
Greater Receiver
Bandwidth
Signal to noise:Decreased
Spatial resolution:No Effect
Duration of Exam: decreased
363
MRI Modification
Greater Transmit
Bandwidth
Signal to noise:Increased
Spatial resolution:Decreased
Duration of Exam:No Effect
364
MRI Modification
More Excitations
per Slice
“More Averages ”
Signal to noise:Increased
Spatial resolution:No Effect
Duration of Exam:Increased
365
MRI Modification
Utilizing Partial K
Space Sampling
Signal to noise:Decreased
Spatial resolution:No Effect
Duration of Exam:Decreased
366
MRI - Receive vs Transmit
Large Receiver
Bandwidth
Decrease SNR
367
MRI - Receive vs Transmit
Large Transmit
Bandwidth
Increased SNR
Large Slice
368
MRI - Receive vs Transmit
Small Receiver
Bandwidth
Increased SNR
369
MRI - Receive vs Transmit
Small Transmit
Bandwidth
Decrease SNR
Thin Slice
370
MRI - “Tradeoffs”
Thicker Slices
Improves SNR Degrades Spatial
| Resolution
371
MRI - “Tradeoffs”
Thinner Slices
More Noise Improves Spatial
| Resolution
372
MRI - “Tradeoffs”
Stronger Magnet
```
Better SNR
*more signal
Worsening
Chemical Shift (Type 1)
and Susceptibility
“Metal” Artifacts
```
373
MRI - “Tradeoffs”
Thinner receiver
bandwidth
```
Improves SNR
Worsening
Chemical Shift (Type 1)
and Susceptibility
“Metal” Artifacts
```
374
MRI - “Tradeoffs”
Increasing NEX
(Number o f
Excitations)
Improves SNR Increased Table Time
375
MRI - “Tradeoffs”
Longer TR
Improves SNR Increased Table Time
376
MRI - “Tradeoffs”
Shorter TE
```
Improves SNR
Can screw up you
tissue contrast (reduced
T2 effect) - should only
be done with Tl.
```
377
Best Sequence for SNR ?
Proton Density
| Long TR, Short TE
378
1.5 T: Out of Phase, In Phase Times ?
Out of Phase 2.2 msec, In Phase 4.4 msec,
| Out of Phase 6.6 msec, In Phase 8.8 msec
379
3.0 T: Out of Phase, In Phase Times ?
Out of Phase 1.1 msec, In Phase 2.2 msec,
| Out of Phase 3.3 msec, In Phase 4.4 msec
380
fMRI depends on ?
T2* effects
uses Blood Oxygen Level Dependent
(BOLD) imaging
381
Cardiac Sequence “Bright Blood” ?
Gradient
382
Cardiac Sequence “Black Blood” ?
Double Inversion Spin Echo
383
Cardiac Sequence to Null Myocardium ?
```
Inversion Recovery
(TJ. selected to match patient’s myocardium)
```
384
Magnevist
```
Gadopentetate
(Gd-DTPA) Linear Ionic
Oldest PDA Approved Agent
Probably has the highest NSP
Risk
```
385
Multihance
Gadobenate
| (Gd-BOPTA) | Linear Ionic 5% Hepatocyte Uptake
386
Eovist
Gadoxetate
| (Gd-EOB-DTPA) Linear Ionic 50% Hepatocyte Uptake
387
Gadavist
Gadobutrol
(Gd-BT-D03A) Macrocylic Non-Ionic High Viscosity
Low (none?) Risk of NSP
388
Fat Saturation Sequences Post Gad ?
NOT STIR - Inversion time is too similar
389
Gad Works By?
Increasing Spin-Lattice interactions
| “Shortens” T1
390
NSF is a risk when ?
```
Renal Failure (GFR < 30)
Pro-Inflammatory States (Acute Illness)
```
391
NSF highest association ?
“Omniscan” (Gadodiamide)
392
Artifact
Aliasing
Direction: Phase
Encoding
Better: •Increase the field of
view
•Change the phase
encoding direction
Worse: Smaller FOVs
Trivia:Caused by a small FOV
393
Artifact
Chemical Shift
Type 1
Direction: Frequency
Encoding
Better: •Bigger Pixels
•Fat Suppression
•Increase Receiver
Bandwidth
Worse: •Stronger Magnetic
Field
•Lower Receiver
Bandwidth
Trivia:Caused by differences in
resonance frequencies
394
Artifact
Chemical Shift
Type 2
“India Ink”
Direction: Both phase
and
frequency
```
Better: •Adjust the TE
• Perfonn Spin Echo
Sequence (remember
this only occurs with
GRE)
```
Worse:
Trivia:Caused by differences in
resonance frequencies -
oppose each other at
specific TE intervals.
395
Artifact
Gibbs /
Truncation
Direction: Both phase
and
frequency
```
Better: • Bigger Matrix
•Decrease Bandwidth
•Decrease Pixel Size
(increase PE Steps,
Decrease FOV)
```
Worse:
Trivia:•Caused by limited
sample of FID
•Classically seen in the
spinal cord
396
Artifact
Partial Volume
Direction:
Better: •Decrease Pixel Size
(increase PE Steps,
Decrease FOV)
Worse: Thicker Slices
Trivia:
397
Artifact
Motion Artifact
Direction: Phase
Encoding
```
Better: •Saturation pulses
•Respiratory gating
•Faster sequences
(BLADE,
PROPELLER)
```
Worse:
Trivia:
398
Artifact
Cross Talk
Direction:
Better: •Increase slice gap
•Interleave slices
Worse:
Trivia:Caused by overlap of
slices
399
Artifact
Zipper
Direction: Phase
Encoding
Better:
Worse:
Trivia:Caused by poor shielding
400
Artifact
Field Inhomogeneity
Direction:
Better: •Shimming
Worse: GRE Sequences
Trivia: Caused by geometric
distortion
401
Artifact
Susceptibility
“Metal”
Direction:
```
Better: • Spin Echo
• Less Field Strength
•High receiver
bandwidth
•Short echo spacing
•Thin Slices
```
Worse: GRE Sequences
Bigger Field
Strength
Trivia: •Caused by augmentation
of magnetic field
•Very bad in EPI
402
Artifact
Eddy Current
Direction:
Better: •Optimize sequence of
gradient pulses
Worse: DWI - large gradient
changes
Trivia: Caused by geometric
distortion or nonuniformity
403
Artifact
Dielectric
Effects
Direction:
Better: •Parallel Transmit
•Use 1.5 T
Worse: 3 T
Trivia: • Standing waves created
as radiowave approaches
length of body part
404
Artifact
Magic Angle
Direction:
Better: •T2
Worse: Tl, PD
Trivia: Occurs at 55 Degrees
405
MR - Safety Related Trivia
Zone I
No Restriction This is basically outside the building
406
MR - Safety Related Trivia
Zone II
No Restriction
This is the waiting room and the dressing
room. This is where you can screen patients
and control access to Zone 3 and 4.
407
MR - Safety Related Trivia
Zone III
Restricted Room
This is typically the control room, where the
MRI tech does his/her thing. There should be
some kind of a lock on the door between
zone 2 and 3.
408
MR - Safety Related Trivia
Zone IV
Restricted Room This is the actual MRI scanner room (the
| same room as the magnet)
409
MR - Safety Related Trivia
Quenching - Only if ?
There is a fire or trapped patients or staff member trapped
410
MR - Safety Related Trivia
Prior to the quench ...
Get the fuck out of the room (zone 4)
411
MR - Safety Related Trivia
Quench if code ?
A code is NOT a reason to quench
412
MR - Safety Related Trivia
Who should push the Quench
button
Medical Student, Tech, Non-English Speaking Observer....
| Anyone but you
413
MR - Safety Related Trivia
5 G Line ?
.It is an implanted device safety thing, not a pulling
| (translational force) thing
414
MR - Safety Related Trivia
Hearing Damage Trivia:
• Noise - from the gradient set.
• Worse with Echo Planar
• Damage to the fetal ossicles is part of the
theoretical (complete bullshit) reason fetal
415
MR - Safety Related Trivia
Neurostimulation ?
High-bandwidth readouts and rapid gradient switching
| (echo-planar imaging) are the usual culprits
416
MR - Safety Related Trivia
SAR Formula ?
Bo2 x Alpha2 x Duty Cycle
(B = magnet strength, Alpha = Flip angle, Duty Cycle —
how short your TR is).
417
MR - Safety Related Trivia
SAR Limit ?
4W/kg
418
MR - Safety Related Trivia
Doubling the TR will do what
to the Duty Cycle?
Double the TR - will half the Dutv Cycle
419
Fat Saturation Sequences Post Gad ?
NOT STIR - Inversion time is too similar
420
Gad Works By?
Increasing Spin-Lattice interactions
| “Shortens” TI
421
NSF is a risk when ?
```
Renal Failure (GFR < 30)
Pro-Inflammatory States (Acute Illness)
```
422
NSF highest association ?
Omniscan” (Gadodiamide)
423
Lactation ?
Current guidelines: No need to stop
breastfeeding after contrast administration.
This goes for both CT Contrast (iodine) and MR
Contrast (Gadolinium)
424
What agents are NOT
safe with Lactation ?
What are the
recommendations ?
I131 No more breast feeding
Gallium67 No more breast feeding
Tc"m You can resume breast feeding in 12-24 hours
I123 You can resume breast feeding in 2-3 days
425
Precision
This is the immunity to variation
426
Accuracy Definition
This is the immunity to systematic error or bias
427
Type 1 Error
The is a false positive.
| The fire alarm has gone off, but there is no fire.
428
Type 2 Error:
This is a false negative.
| The house is on fire, but the alarm does NOT go off.
429
Incidence Rate
New Cases of Disease/
| Total Number of People are Risk
430
Prevalence Rate
Number of Cases of Disease/
| Total Number of People at Risk
431
Sensitivity
True Positive/
| True Positive + False Negatives.
432
Specificity
True Negative/
True Negative + False Positives
*Specific Exams Rule IN Disease
433
Accuracy
True Positive + True Negative/
| TP + FP + TN + FN
434
Positive Predictive Value
True Positive/
| True Positive + False Positives
435
Negative Predictive Value
True Negative/
| True Negative + False Negative
436
Absolute Risk
Same as Incidence Rate
New Cases of Disease/
Total Number of People are Risk
437
Relative Risk
Incidence of disease among persons exposed to risk factor/
| Incidence of disease among people who did NOT get exposed to risk factor.
438
Odds Radio
Cases WITH Exposure x Controls WITHOUT Exposure/
| Controls WITH Exposure x Cases WITHOUT Exposure
