War Machine RR Flashcards
Bremsstrahlung
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
Characteristic Xrays
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
X-Ray Production Device
Glass Enclosure / Envelope
- Maintain a Vacuum
* Allow the amount and speed of the electrons to be controlled independently.
X-Ray Production Device
Cathode
• The Filament
• The place in the device where the
electrons enter
X-Ray Production Device
Focusing Cup
Help the electron beam strike the target in an acceptable size
X-Ray Production Device
Target of tungsten
Increased Target Atomic Number (Z)
Increases Quality and Quantity
Increased kVp
Increases Quality and Quantity
Increased mAs
Increased Quantity
Increased Voltage Ripple
Decrease in Quantity and Quality
Added Filtration
Increased Quality,
Decreased Quantity
H e e l E ffe c t
Smaller Angles
Worsening Heal Effect
(steeper angle = more abmpt intensity
change)
H e e l E ffe c t
Cathode Side
Strong Side
more intense side of the beam
H e e l E ffe c t
Larger Focus to Film Distance (FFD)
Less Heel Effect
H e e l E ffe c t
Smaller Film (field of view)
Less Heel Effect
Assuming same FFD
H e e l E ffe c t
Mammo - Cathode Side on the …
Chest Wall
Target (Anode) overview
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)
Filament (Cathode) Overview
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)
Area of Interest Cathode Side
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)
Loss of Characteristic X-Rays
If you drop the kVp below the
threshold for k shell electrons you are going to lose those characteristic peaks
X-Ray In te ra c tio n s
Compton
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
X-Ray In te ra c tio n s
Photoelectric
Major Contributor to Image Contrast
Involves the INNER Shell Electron
“All or Nothing”
Depends on Z3
Dominates below 30 keV
G eometric Relationship
Magnification Increases With
- Greater Object to Detector Distance
2. Less Source to Object Distance
G eometric Relationship
Less Blur
- Small Focal Spot
2. Closer the object is to the detector
G eometric Relationship
More Blur
- Closer the source is to the image
2. More Magnification
DQE =
Measurement of efficiency
• High DQE = Low Dose
• Low DQE = High Dose
DQE is directly proportional to
MTF
MTF describes the relationship between
sharpness and resolution.
DQE is inversely proportional to
Signal to Noise Ratio
DQE is better at
Low spatial resolution
Approximate DQE:
DR = 0.45
Plain Film = 0.25
mAs Controls the
Radiographic Density
how black the image is
kVp Controls the
Radiographic Contrast
• Low kVp = High Contrast
• High kVp = Low Contrast
To achieve a noticeable difference in “density”
Increase mAs by 30%
To maintain density after decreasing mA by
50% you would
Increase kVp by 15%
4 cms o f tissue requires
Double the mA
Grids typically are NOT used with
Babies and Extremities
Cons to using a Grid
Increased Dose
Ways to Reduce Scatter (Improve Contrast)
1 - Collimate
2 - Compress the Part
3 - Lower kVp
4 - Grid / Air Gap
Pros of Collimation
1 - Increase Contrast
2 - Decrease Scatter
3 - Decrease KAP
Cons o f Collimation
1 - Smaller FOV
Scatter is Most Severe With
- High kVp Technique
- Large Field o f View
- Thick Parts (or People)
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.
The primary factor influencing image contrast
in film systems
kvp
The primary factor influencing image contrast (in digital systems)
LUT
kVp still influences contrast, but digital
systems have a much wider dynamic
range.
Digital response curve
- Digital has a linear response curve,
* Film has a curvilinear response curve.
Major determinant of spatial resolution with
digital images is
Pixel Size and Spacing (pixel pitch)
Digital
Decreased Pixel Pitch
Better Spatial Resolution
Digital
Increased Pixel Density
Better Spatial Resolution
Digital
Direct vs Indirect
Indirect (scintillators)
Xrays ==> Light = > Charge
Direct (photoconductors) =
X rays ==> Charge
Digital
Indict uses
Thallium doped Cesium Iodide (Csl)
“Scintillator”
Digital
Direct uses
Amorphous Selenium
Specific Factors Affecting the Spatial Resolution of CR
Laser Spot Size:
smaller is better
Specific Factors Affecting the Spatial Resolution of CR
Phosphor Pate Density / Thickness
More Thick = More Light Spreading = Less Resolution
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.
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.
Specific Factors Affecting the Spatial Resolution of CR
Increasing x-rays will NOT improve
Maximum spatial resolution
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.
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)
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)
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
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
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)
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)
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.
Mammo Target Trivia
“Intermediate” density breasts
Mo anode with Rhodium filter
Mammo Target Trivia
“Thin” breasts
Mo anode with Mo filter
Mammo Target Trivia
What Combination would you
“never” use?
Rh Target (21 kev) with a Mo Filter (20 Kev K edge)
PPV1
Abnormal Screener “Call Back”
3-8%
4.4%
PPV2
Recommended Biopsy (4 or 5)
15-40% (25*50% if palpable)
25.4%
PPV3
Biopsy Done
- Actual Cancer
20-45% (30-55% if palpable)
31.0%
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
Appropriate Target Range
for Medical Audit
Recall Rate 5-7%
Cancers/ 1000 Screened 3-8
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
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
General Radiology vs fluoro
general rads
mA 200-800
kVp 50 -120
Very short exposure times
Focal Tube Spot 1.0 -1.2mm
General Radiology vs fluoro
fluoro
mA 0-5
kVp 50 -120
Longer exposure times
Focal Spot 0.3-0.6mm
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
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
Digital Spot
Digital Equivialant to Spot
Film - minus the cassette
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
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
Fluoro Trivia
Best Position of the I.I. and X-ray Tube ?
X- Ray tube far away, with the I.I. close.
Fluoro Trivia
Where is the ideal place to stand ?
On the same side of the patient as the
imaging intensifier
Fluoro Trivia
Double the distance from the tube does what to dose ?
Decreases it by a factor of 4 (inverse
square law).
Fluoro Trivia
Normal Air Kerma Limit ?
87 mGy/min (10 Roentgens per min)
Fluoro Trivia
High Level Control (Really Fat Level Control) ?
176 mGy/min (20 Roentgens per min)
Fluoro Trivia
In “high level mode”, you must have ?
Audible or visual alarms (in addition to the
normal time alarm used in normal
fluoroscopy.)
Pulsed Fluoro
Conventional fluoro
long very low continuous mA.
• Pulse fluoro is pulsed (NOT continuous mA but instead pulse of higher mA).
Pulsed Fluoro
Pulse Fluoro is good for moving patients (Wiggling Babies)
Gives you sharper
images with less motion blur
Pulsed Fluoro
Pulsed Fluoro can reduce dose
when the frame rate is below 30 frame /second
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.
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.
Fluoro in IR Trivia
Best kVp to use with IV contrast is ?
Between 60-80 kVp (average beams
hit that k-edge nicely)
Fluoro in IR Trivia
IR uses relatively Small Focal Spots, and
Small Anode Angle Because ?
The need for maximum spatial resolution
Fluoro in IR Trivia
Grids ?
Usually
■ but Not with Peds and
■ Not with Extremities
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)
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
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.
Fluoro in IR Trivia
Magification will … ?
increase Air Kerma, but NOT KAP
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
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
CT Trivia
What kind of x-rays are used with CT?
Highly filtered, High kV
average energy 75 keV
CT Trivia
Bow Tie Filters do what ?
- Compensate for uneven filtration,
- Reduce Scatter,
- Reduce Dose
CT Trivia
“Septa” is the CT term for ?
A Grid
CT Trivia
Minimal slice thickness is determined by ?
Detector element aperture width in a modem CT
CT Trivia
Pixel size =
Field of View / Matrix Size
CT Trivia
How do you improve spatial resolution ?
You need to make the pixels smaller (matrix larger).
Remember that Pixel Size = FOV/ Matrix
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)
Pitch
o f “ l ” ?
There is no overlap
between slices.
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
Pitch
“Less than 1 ” ?
This means the table
moved slow, and your
slices overlapped.
Spatial Resolution
Improved
Dose Increased
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.
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
A narrow (decreased) window width
Increases Contrast.
A wider (increased) window width
Decreases Contrast.
WL - “Brain” ?
W 80, L +40
WL - “Stroke” ?
W 3 0 , L +30
WL - “Lung’
W 1500, L - 400
WL - “Abdomen” ?
W 400, L + 50
WL - “Bone” ?
W 1600, L +500
Cardiac CT
Prospective:
“Step and Shoot”
- R-R interval
pro
There is reduced
radiation b/c the
scanner isn’t on the
whole time
Cardiac CT
Prospective:
“Step and Shoot”
- R-R interval
con
No functional
imaging.
Susceptible to
motion artifact.
Cardiac CT
Prospective:
“Step and Shoot”
- R-R interval
trivia
Always axial, not
helical.
You need a slow heart
rate (50-65 bpm)
Cardiac CT
Retrospective:
Scans the whole
time, then back
calculates
pro
Can do functional
imaging (evaluate
contraction and wall
motion)
Cardiac CT
Retrospective:
Scans the whole
time, then back
calculates
con
Higher radiation
(use of low pitch -
increases dose)
Cardiac CT
Retrospective:
Scans the whole
time, then back
calculates
trivia
none lol
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
Beta Blockers
CI
• SBP < 100 • Decompensated Cardiac Failure • Asthma on beta-aeonist inhalers (albuterol) • Active bronchospasm • Severe COPD • 2nd or 3rd-degree AV block
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.
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.
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
Spatial Resolution
Holding matrix size
constant and
decreasing FOV
This will decrease pixel size.
Spatial Resolution is Improved
Spatial Resolution
Holding matrix size
constant and
increasing FOV
This will increase pixel size.
Spatial Resolution is Degraded
Spatial Resolution
Optimal Reconstruction
Filter
Bone “sharp ” algorithm gives
a higher spatial resolution
Contrast Resolution
Holding matrix size
constant and
decreasing FOV
This will decrease pixel size.
Contrast Resolution is Degraded
(less photons per box)
Contrast Resolution
Holding matrix size
constant and
increasing FOV
This will increase pixel size.
Contrast Resolution is Improved.
Contrast Resolution
Optimal Reconstruction
Filter
“Soft tissue ” or “smooth ”
improves contrast resolution -
relative to bone
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.
Spatial Resolution Trivia
A “?” Focal Spot will
improve spatial
resolution
Smaller Spot = Better
Determines Spatial Resolution in the X-YPlane… sided to side.
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)
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.
Spatial Resolution Trivia
Consequences of
decreasing the pitch ?
More Dose
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).
CT Dose Related Trivia
Larger Pitch ?
Decreased Dose
50% increase in pitch = 50% dose decrease
CT Dose Related Trivia
```
Reconstruction Method
Iterative > Filtered Back
~~~
Iterative algorithms handle noise better — allows for a lower
dose technique to be used.
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.
CT Dose Related Trivia
Increased Rotational Time ?
Less Dose (Faster rotation = less dose.) Dose is proportional to both scan time and rotation time.
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.
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)
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
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
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.
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.
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.
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.
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”
U ltra so u n d R e la te d T riv ia
High Frequency Probes:
- Scatter ?
- Attenuation ?
- More Scatter.
* More Attenuation
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
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.
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
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.
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)
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.
U ltra so u n d R e la te d T riv ia
Focal Zone Maximizes “?”
lateral resolution
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.
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”
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)
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)
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
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
R e s o lu tio n T riv ia US
Axial Resolution
depends on ?
Spatial Pulse Length
R e s o lu tio n T riv ia US
Lateral Resolution
depends on ?
Transducer Element Width
R e s o lu tio n T riv ia US
Elevation Resolution
depends on ?
Transducer Element Height
R e s o lu tio n T riv ia US
Axial Resolution is
independent of ?
Depth
* Lateral Resolution changes with depth.
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
R e s o lu tio n T riv ia US
Harmonics improves ?
Lateral Resolution
Harmonics works by ?
Transmitting at one frequency and
receiving at another
Compound Imaging works by ?
Using electronic steering of the ultrasound
beams from the transducer to image an
object in multiple different directions
Harmonics are NOT produced in the ?
Near Field
they haven’t traveled fa r enough
Harmonics can result in reduced ?
1 - Reverberation Artifact
2- Depth Penetration
(remember higher frequency attenuates -
so the beam is attenuated-faster).
Compound Imaging can result in reduced ?
Posterior shadowing
Compound Imaging will “?” the edges
Sharpen them
Artifact
comet tail
harmonics - more visible
compounding - less visible
Artifact
ring down
harmonics - n/a
compounding - reduced
Artifact
reverberation
harmonics - reduced/eliminated
compounding - n/a
Artifact
increased through transmission
harmonics - increased
compounding - n/a
Artifact
acoustic shadowing
harmonics - increased
compounding - decreased
Artifact
speckle noide
harmonics - reduced
compounding - reduced
Artifact
harmonics -
compounding -
Artifact
side lobe/grating
harmonics - reduced
compounding - n/a
Thermal Index (T.I.) ?
Heating: this is the maximum temperature rise
in tissue secondary to energy absorption.
Mechanical Index (M.I.) ?
Cavitation (Mechanical Damage):
this is how likely it is that cavitation will occur
considering peak rarefaction pressure and
frequency.
What should be avoided with neonatal
imaging ?
Pulsed Spectral Doppler
What should be used instead ?
M-Mode US (to document fetal HR)
The T.I. should be ?
Under 1.0 (some sources say 0.7)
Ideal Doppler Angle ?
The angle should be between 30- 60.
Theoretically the best angle is zero.
Doppler Angle of 90 Degrees will ?
Look like no flow
If you are looking for slow flow, you
should ?
- Use a low pulse repetition frequency (PRF)
* Use Power Doppler
Power Doppler does Not depend on ?
The Doppler Angle
Power Doppler does Not provide
information on ?
The Direction of Flow
Power Doppler will Not demonstrate
this artifact ?
Aliasing (both color and spectral can).
Aliasing Artifact occurs when ?
the doppler shift is greater than a threshold called the
“Nyquist frequency”
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)
Artifacts from Multiple Echoes
Reverberation
Two parallel highly reflective surfaces - Multiple equidistantly spaced
linear reflections.
Artifacts from Multiple Echoes
Comet Tail
Two parallel highly reflective surfaces - closer together (< 1/2 SPL) Triangle (comet) shaped
Artifacts from Multiple Echoes
Ring Down Artifact
Fluid trapped between a tetrahedron of
air bubbles
Parallel band extending
posterior to a collection of gas
Artifacts from Multiple Echoes
Mirror Image
Trapped behind a strong reflector This is almost always shown
with the liver on lung.
IsotoPe
Same Number of Protons.
IsotoNe
Same Number of Neutrons
IsoBAR
Same MASS Number.
*Lift the barbell to put on some mass
IsoMer
Same Number of Protons and Neutrons. But the energy
level is different — classic example is isoMeric Tc99M to
Tc99.
H a lf Life
Physical
How long it takes to decay to 1/2 activity. You’ll need to memorize these.
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
H a lf Life
Effective
Takes both Physical and Biologic into account (it’s always less)
1/Effective = 1/Physical + 1/Biologic
Tc - 99m
Analog:
Energy:“Low” - 140
Physical half life: 6 hours
Iodine-123
Analog:Iodine
Energy: “Low” - 159
Physical half life: 13 hours
Xenon -133
Analog:
Energy: “Low” - 81
Physical half life: 125 hours
(biologic tl/2 30 seconds)
Thallium - 201
Analog: Potassium
Energy: “Low” - 135(2%) - 167(8%) use 71 201 Hg daughter x-rays
Physical half life: 73 hours
Indium -111
Analog:
Energy: “Medium”
- 173 (89%),
- 247(94%)
Physical half life: 67 hours
Gallium - 67
Analog: Iron
Energy: Multiple:
- 93 (40%),
- 184(20%),
- 300(20%),
- 393 (5%)
Physical half life: 78 hours
Iodine -131
Analog: Iodine
Energy: “High” - 365
Physical half life: 8 days
Fluorine -18
Analog: Sugar
Energy: “High” -511
Physical half life: 110 mins
Cobalt -57
Analog: Used for Extrinsic
Field Uniformity
QA (Flood)
Energy: “Low”
- 122
- 136
Physical half life: 270.9 days
Germanium 68/
Gallium 68
Analog: Used for PET QA
Energy: “High” - 511 (via Ga)
Physical half life: 270 days - Ge
68 minutes - Ga
Treatment Radionuclides
Half Life
Strontium 89
50.5 DAYS
14 days in bone
Treatment Radionuclides
Half Life
Samarium 153
46 Hours
Treatment Radionuclides
Half Life
Radium 223
11 Days
Treatment Radionuclides
Half Life
Yttrium 90
64 Hours
Cardiac Radionuclides
Half Life
Rubidium 82
75 seconds
Cardiac Radionuclides
Half Life
Nitrogen 13
10 mins
Beta Minus
Lots of Neutrons Not Enough Protons Generate a Beta Particle (Electron) ISO BA R IC transition
Beta Plus
Lots of Protons
Not Enough Neutrons
Generate a Positron
has 1.02 MeV
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
Alpha
Heavy Unstable Atoms Omits a heavy Helium nuclei (2 protons, 2 neutrons)
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).
Collimator Type
Parallel Hole Image size and used for
Imase Size =
- 1:1 - Equal to Patient
“The work horse ”
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.
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).
Collimator Type
Converging
Distance Sensitive - amount of
magnification increases as object
gets farther from the collimator.
The FOV decreases with distance.
Collimator Type
Converging Image size and used for
Image Size = - Magnifies without inverting Usedfor: - Multiple choice questions. - Sometimes small body parts
Collimator Type
Diverging
Distance Sensitive - amount of
minification increases as object gets
farther from the collimator
The FOV increases with distance.
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)
Parallel Hole Factor
Septa Length
Long Septa: - Low Sensitivity (Noisy) - High Spatial Resolution Short Septa: - High Sensitivity - Low Spatial Resolution
Parallel Hole Factor
Hole Diameter
Wider Hole: - High Sensitivity - Low Resolution Narrow Hole: - Low Sensitivity - High Resolution
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)
Q/A on the Dose Calibrator (Ionizing Chamber
Consistency
Daily
Should be within 5% of
computed activity
Checked with reference
sources
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.
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)
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)
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”)
Ionizing chamber
For measuring dose rate.
Used with higher rates.
Lower Sensitivity
Stable across a wide voltage range - Excellent
for accurate estimates (or exposure).
“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.
“Solid State Dosimeter ”
Accumulated dose or rate can be read real
time with LCD display.
“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…
“Optically Stimulated Dosimeter”
the film badge. Chips /
Strips are placed under a filter.
Survey Meters
G-M and Ionization Detectors - discussed on prior page
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.
Dose Calibration
& Automated Dose
Injection Systems
Used to measure radiopharmaceuticals.
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.
Intra-operative
Probes
Used for lymphoscintigraphy
10CFR part 19
Nwootrik,c eerss,. instmctions, and reports to workers
…i nspecti. ons „
10 CFRpart 20
Standards for protection against radiation,
“radiation protection”
10CFR part 35
Medical use of by-product material.
“human use of
radioisotopes”
Regulations
Major Spill
Tc-99m
Greater than 100 mCi
Regulations
Major Spill
Tl-201
Greater than 100 mCi
Regulations
Major Spill
In-111
Greater than 10 mCi
Regulations
Major Spill
1-123
Greater than 10 mCi
Regulations
Major Spill
Ga-67
Greater than 10 mCi
Regulations
Major Spill
1-131
Greater than 1 mCi
Regulations
Major Spill
steps
- Clear area.
- Cover spill with absorbent paper.
Do NOT clean it up. - Clearly indicate boundaries of spill
Limit movement of contaminated
pet sons - Shield source if possible
- Notify the Radiation Safety Officer
immediately - Decontaminate persons
Regulations - General Public
Annual Dose limit
100 mrem
Regulations - General Public
“Unrestricted area”
Not greater than 2 mrem per hour
Regulations - General Public
“Restricted Area”
Defined as:
“Any place that receives a dose greater than 2 mrem/h”
Radiation Area
Any place you could get 0.005 rem (0.05mSv) in 1 hour at 30cm
High Radiation Area
Any place you could get O.lrem (lmSv) in 1 hour at 30cm
Very High Radiation Area:
Any place you could get 500 rads (5 gray) in 1 hour at 1 meter
Regulations - NRC Occupational Exposure Dose Limits
Total Body Dose per Year
5 rem (50 mSv)
Regulations - NRC Occupational Exposure Dose Limits
Dose to the Ocular Lens per year
15 rem (150 mSv)
Regulations - NRC Occupational Exposure Dose Limits
Total equivalent organ dose
50 rem (500 mSv)
Regulations - NRC Occupational Exposure Dose Limits
Total equivalent extremity dose per year
50 rem (500 mSv)
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.
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
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)
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
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
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.
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
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
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
Multiple Packages
Those shipped together
Sum should NOT exceed
50 mR.
Radionuclide
Purity
What is it?
How much Mo
in the Tc ?
“Moly
Breakthrough ’’
Radionuclide
Purity
Tested?
Tested in a dose calibrator with lead shields; Looking for 700 keV photons of Moly (remember Tc is only like 140)
Radionuclide
Purity
Limit?
0.15 microcuries of Mo per
1 millicurie of Tc
Chemical
Purity
What is it?
How much A1
in the Tc ?
“Aluminum
Breakthrough
Chemical
Purity
Tested?
Tested with pH
paper (Color
Indicator Paper, or
Paper Strip Test)
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
Radiochemical
Purity
What is it?
How much Free
Tc?
Radiochemical
Purity
Tested?
Tested with Thin
Layer
Chromotography
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
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)
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
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
Attenuation Correction pet
ligth skin and light lungs
Uncorrected pet
hot skin andhot lungs
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.
Dose units pet
Exposure
C/kg
Charge (C) in the air created divided by the mass (kg) of that
air.
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.
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.
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”
Deterministic Effects
Deterministic Effects
Severity is dose related
Does Not include Cancer Risk
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)
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.
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.
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.
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.
Dose Units - CT
“Weighted
CTDI”
mGy
This is 1/3 the central CTDI + 2/3
the Peripheral CTDI (expressed in
mGy)
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)
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.
Dose Units - CT
“Effective
Dose” fo r CT
mSv
Effective Dose = k x DLP.
Remember that “k” is a body
part constant.
This vs That: Direct vs Indirect Radiation
Direct Radiation
minority
Acts on DNA
Most likely for High
LET Radiation
(unusual in x-ray
imaging)
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
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.
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
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)
WB Dose (Gy)
< 1
No vomiting No skin redness
Surveillance for 5
weeks
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
WB Dose (Gy)
2-4
Vomiting 1 -2 hours after exposure Skin redness (8-15 hours after exposure)
Hospitalize - Bum
Center
WB Dose (Gy)
> 4
Vomiting < 1 hour after exposure Skin redness (1-6 hours after exposure)
Hospitalize -
Specialized Radiation
Center
Skin Problem
Dose (Gy) Onset
Early Transient Erythema
2 Gy skin dose hours
Skin Problem
Dose (Gy) Onset
Severe “Robust” Erythema
6 Gy skin dose 1 Week
Skin Problem
Dose (Gy) Onset
Telangiectasia
10 Gy skin dose 52 Weeks
Skin Problem
Dose (Gy) Onset
Dry Desquamation
13 Gy skin dose 4 Weeks
Skin Problem
Dose (Gy) Onset
Moist Desquamation / Ulceration
18 Gy skin dose 4 Weeks
Skin Problem
Dose (Gy) Onset
Secondary Ulceration
24 Gy skin dose > 6 weeks
Hair Problem
Dose (Gy) Onset
Temporary Epilation
3 Gy 21 Days
Hair Problem
Dose (Gy) Onset
Permanent Epilation
7 Gy 21 Days
Cell Sensitivity - Trivia
Order of Sensitivity M > G2 > Gl > S.
Most radiosensitive part of the GI tract ?
Small Bowel
MOST sensitive blood cells in the body ?
Lymphocytes. A dose of 0.25 Gy is enough to
depress the amount circulating in the blood.
< 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)
> 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)
100-500 mGy fetus
Consider aborting - based on individual risk factors, and various superstitious beliefs
T 1 (Longitudinal) is determined by ?
Interaction with the Spin - Lattice
77 = has grown to 63% o f magnetization
T2 (Transverse) is determined by ?
Spin-Spin Interactions dephase magnetization
12 = has decayed to 37% o f original value
T2* (Free Induction Decay) is determined by ?
Spin-Spine Interactions PLUS the Non-
Uniformity of the Magnetic Field
T1 “Shortening” is ?
Bright
T2 “Shortening” is ?
Dark
T1
Short TR
Short TE
T2
Long TR
Long TE
Proton Density
Long TR
Short TE
Spin Echo
Short TR 250-700 ms
Long TR >2000 ms
Short TE 10-25 ms
Long TE >60 ms
GRadient Echo
Short TR < 50 ms
Long TR >100 ms
Short TE 1-5 ms
Long TE >10 ms
MRI - Table Time
Standard Sequence ?
TR x Phase Matrix x NEX
MRI - Table Time
3D Sequence ?
TR x Phase Matrix x NEX x # Slices
MRI - Table Time
Fast Spin Echo ?
Acquisition time is approximately proportional to 1/Echo Train Length
MRI - Slice Thickness
Thinner Slice
Steep (“Increased”)
Slice Selection Gradient
Decreased Transmit
Bandwidth
MRI - Slice Thickness
Thicker Slice
Shallow (“Decreased”)
Slice Selection Gradient
Increased Transmit
Bandwidth
MRI Modification
Thicker Slices
Signal to noise:Increased
Spatial resolution:Decreased
Duration of Exam:No Effect
MRI Modification
Larger Field of View
Signal to noise:Increased
Spatial resolution:Decreased
Duration of Exam:No Effect
MRI Modification
Larger Matrix
Signal to noise:Decreased
Spatial resolution:Increased
Duration of Exam:Increased
MRI Modification
Greater Field
Strength
Signal to noise:Increased
Spatial resolution:No Effect
Duration of Exam:No Effect
MRI Modification
Greater Receiver
Bandwidth
Signal to noise:Decreased
Spatial resolution:No Effect
Duration of Exam: decreased
MRI Modification
Greater Transmit
Bandwidth
Signal to noise:Increased
Spatial resolution:Decreased
Duration of Exam:No Effect
MRI Modification
More Excitations
per Slice
“More Averages ”
Signal to noise:Increased
Spatial resolution:No Effect
Duration of Exam:Increased
MRI Modification
Utilizing Partial K
Space Sampling
Signal to noise:Decreased
Spatial resolution:No Effect
Duration of Exam:Decreased
MRI - Receive vs Transmit
Large Receiver
Bandwidth
Decrease SNR
MRI - Receive vs Transmit
Large Transmit
Bandwidth
Increased SNR
Large Slice
MRI - Receive vs Transmit
Small Receiver
Bandwidth
Increased SNR
MRI - Receive vs Transmit
Small Transmit
Bandwidth
Decrease SNR
Thin Slice
MRI - “Tradeoffs”
Thicker Slices
Improves SNR Degrades Spatial
Resolution
MRI - “Tradeoffs”
Thinner Slices
More Noise Improves Spatial
Resolution
MRI - “Tradeoffs”
Stronger Magnet
Better SNR *more signal Worsening Chemical Shift (Type 1) and Susceptibility “Metal” Artifacts
MRI - “Tradeoffs”
Thinner receiver
bandwidth
Improves SNR Worsening Chemical Shift (Type 1) and Susceptibility “Metal” Artifacts
MRI - “Tradeoffs”
Increasing NEX
(Number o f
Excitations)
Improves SNR Increased Table Time
MRI - “Tradeoffs”
Longer TR
Improves SNR Increased Table Time
MRI - “Tradeoffs”
Shorter TE
Improves SNR Can screw up you tissue contrast (reduced T2 effect) - should only be done with Tl.
Best Sequence for SNR ?
Proton Density
Long TR, Short TE
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
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
fMRI depends on ?
T2* effects
uses Blood Oxygen Level Dependent
(BOLD) imaging
Cardiac Sequence “Bright Blood” ?
Gradient
Cardiac Sequence “Black Blood” ?
Double Inversion Spin Echo
Cardiac Sequence to Null Myocardium ?
Inversion Recovery (TJ. selected to match patient’s myocardium)
Magnevist
Gadopentetate (Gd-DTPA) Linear Ionic Oldest PDA Approved Agent Probably has the highest NSP Risk
Multihance
Gadobenate
(Gd-BOPTA) | Linear Ionic 5% Hepatocyte Uptake
Eovist
Gadoxetate
(Gd-EOB-DTPA) Linear Ionic 50% Hepatocyte Uptake
Gadavist
Gadobutrol
(Gd-BT-D03A) Macrocylic Non-Ionic High Viscosity
Low (none?) Risk of NSP
Fat Saturation Sequences Post Gad ?
NOT STIR - Inversion time is too similar
Gad Works By?
Increasing Spin-Lattice interactions
“Shortens” T1
NSF is a risk when ?
Renal Failure (GFR < 30) Pro-Inflammatory States (Acute Illness)
NSF highest association ?
“Omniscan” (Gadodiamide)
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
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
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.
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
Artifact
Partial Volume
Direction:
Better: •Decrease Pixel Size
(increase PE Steps,
Decrease FOV)
Worse: Thicker Slices
Trivia:
Artifact
Motion Artifact
Direction: Phase
Encoding
Better: •Saturation pulses •Respiratory gating •Faster sequences (BLADE, PROPELLER)
Worse:
Trivia:
Artifact
Cross Talk
Direction:
Better: •Increase slice gap
•Interleave slices
Worse:
Trivia:Caused by overlap of
slices
Artifact
Zipper
Direction: Phase
Encoding
Better:
Worse:
Trivia:Caused by poor shielding
Artifact
Field Inhomogeneity
Direction:
Better: •Shimming
Worse: GRE Sequences
Trivia: Caused by geometric
distortion
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
Artifact
Eddy Current
Direction:
Better: •Optimize sequence of
gradient pulses
Worse: DWI - large gradient
changes
Trivia: Caused by geometric
distortion or nonuniformity
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
Artifact
Magic Angle
Direction:
Better: •T2
Worse: Tl, PD
Trivia: Occurs at 55 Degrees
MR - Safety Related Trivia
Zone I
No Restriction This is basically outside the building
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.
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.
MR - Safety Related Trivia
Zone IV
Restricted Room This is the actual MRI scanner room (the
same room as the magnet)
MR - Safety Related Trivia
Quenching - Only if ?
There is a fire or trapped patients or staff member trapped
MR - Safety Related Trivia
Prior to the quench …
Get the fuck out of the room (zone 4)
MR - Safety Related Trivia
Quench if code ?
A code is NOT a reason to quench
MR - Safety Related Trivia
Who should push the Quench
button
Medical Student, Tech, Non-English Speaking Observer….
Anyone but you
MR - Safety Related Trivia
5 G Line ?
.It is an implanted device safety thing, not a pulling
(translational force) thing
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
MR - Safety Related Trivia
Neurostimulation ?
High-bandwidth readouts and rapid gradient switching
(echo-planar imaging) are the usual culprits
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).
MR - Safety Related Trivia
SAR Limit ?
4W/kg
MR - Safety Related Trivia
Doubling the TR will do what
to the Duty Cycle?
Double the TR - will half the Dutv Cycle
Fat Saturation Sequences Post Gad ?
NOT STIR - Inversion time is too similar
Gad Works By?
Increasing Spin-Lattice interactions
“Shortens” TI
NSF is a risk when ?
Renal Failure (GFR < 30) Pro-Inflammatory States (Acute Illness)
NSF highest association ?
Omniscan” (Gadodiamide)
Lactation ?
Current guidelines: No need to stop
breastfeeding after contrast administration.
This goes for both CT Contrast (iodine) and MR
Contrast (Gadolinium)
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
Precision
This is the immunity to variation
Accuracy Definition
This is the immunity to systematic error or bias
Type 1 Error
The is a false positive.
The fire alarm has gone off, but there is no fire.
Type 2 Error:
This is a false negative.
The house is on fire, but the alarm does NOT go off.
Incidence Rate
New Cases of Disease/
Total Number of People are Risk
Prevalence Rate
Number of Cases of Disease/
Total Number of People at Risk
Sensitivity
True Positive/
True Positive + False Negatives.
Specificity
True Negative/
True Negative + False Positives
*Specific Exams Rule IN Disease
Accuracy
True Positive + True Negative/
TP + FP + TN + FN
Positive Predictive Value
True Positive/
True Positive + False Positives
Negative Predictive Value
True Negative/
True Negative + False Negative
Absolute Risk
Same as Incidence Rate
New Cases of Disease/
Total Number of People are Risk
Relative Risk
Incidence of disease among persons exposed to risk factor/
Incidence of disease among people who did NOT get exposed to risk factor.
Odds Radio
Cases WITH Exposure x Controls WITHOUT Exposure/
Controls WITH Exposure x Cases WITHOUT Exposure