Section 1
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Things to do when you xray a baby
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Section 1
(50 cards)
Things to do when you xray a baby
Lower the kVP (you don't need as much to penetrate), keep mAs similar or slightly lower Dont use a grid
Focal spot
Part of the anode where bombardment/xray production takes place
What does the II do when you mag?
Simply not "minifying" as much. But it still needs the same amount of light at the end so it uses more mA. Double mag = double skin dose. (but kerma area dose stays the same bc smaller area)
Change in unsharpness with increase in focal spot size
Bigger focal spot = less sharp. Small focal spot = more sharp
Flat panel detector components
CsI input phosphor (convert photons to light) Photodiode (convert light to charge) Readout elements - read out charge directly (vs II which needs to convert back to light and then use TV display)
Compton scatter
Predominates at higher energies relative to coherent and photoelectric. Ionizes an outer shell electron and redirection of the xray (which still has energy) to somewhere random. This is the worst!
Heel effect
Xrays that are closer to the anode side had to travel through more attenuating material and are less intense. Remember "cathode to chest wall"
Which focal spot determines the blur?
The apparent focal spot (on the patient), not the actual focal spot on the anode
Steeper (smaller) anode angle
Makes a smaller apparent focal spot, but the actual focal spot is also smaller so heat dissipation can be a problem
Average energy relative to kVP
Approximately 50% (prob slightly less) of the kVP
Types of mammo target/filter combos
Moly/moly, moly/rho, rho/rho. No such thing as rho/moly
Double the mA
Double the intensity of the energy spectrum
Which causes more dose increase, geometric mag or electronic mag?
Geometric (Physical distance) mag (squared vs doubled)
Relationship between Z and amount of Bremsstrahlung
Directly proportional
Auger electron
Inner shell electron gets ionized, another drops down, emits energy but this energy ionizes another (outer shell) electron. No x-rays produced
Material for mammo exit window
Beryllium (vs pyrex glass for standard radiography) bc you dont want to attenuate these low energy xrays
Max energy of the xray that is created at the anode
Can't be higher than the energy of the electron that created it (which maxes at the voltage between the cathode and anode in kV)
Heel "cutoff"
Smaller (steeper) anode angle results in worse heel effect
Focal spot in mammo
Has to be really small! ~0.3mm. This does not tolerate heat as well. You have to lower the mA or you'll melt the anode. Also means longer exposure time
Best energy of the beam to visualized iodinated contrast
Just above the K-edge of iodine, so approx 34-35 keV
K-shell binding energy proportional to...
Z^2
Soft tissue half value layer
~3cm
K edge of Iodine
33.2 keV
Linear attenuation coefficient
The portion of photons that gets attenuated per unit thickness. Ex: LAC of 0.1/cm would mean that 10% of the beam gets attenuated per cm of material. Kind of inverse to half value layer.
When do you never use a grid?
Anything less than 10cm basically (either a baby or an extremity)
Why is rhenium mixed with tungsten in a filament?
Prevent cracking with repeated heating/cooling
Actual focal spot vs apparent focal spot
Actual focal spot is on the target. Apparent focal spot is on the patient
Average energy of the xrays is based on the...
kVP, unrelated to mA
Dose change when you bring patient closer to the source
Inverse Squared!
How to improve heel effect
Smaller film size, larger source to image distance, larger (less steep) anode angle
Where do you want to stand as the operator?
On the side of the receptor. This avoids the majority of the scatter
Direct DR system (Selenium)
No light involved (hence direct). Photon hits detector and gets turned into charge by amorphous selenium
How does Z affect Compton scatter?
Doesnt matter. Compton scatter directly proportional to tissue DENSITY
Which new target/filter setup is for denser breasts?
Rho/Al, or even Tungsten/Rho or Tungsten/Silver
Smaller focal spot
Better spatial resolution, worse heat dissipation
Components of fluoro image intensifier (II)
Input phosphor (Cs) turns xrays into light Photo-cathode turns light into charge Charge accelerated, hits output phosphor Output phosphor is smaller (concentrates) and turns back into light (minification gain)
Fluoro focal spot vs general radiograph
Fluoro focal spot is smaller (want less blurring)
K edge of barium
37.4 keV
K shell binding energy of tungsten
69.5 keV
Breast tissue half value layer
~1cm
What elements tend to make Auger electrons?
Lower Z. This is also why you pick high Z for anodes
Which classic mammo target/filter setup is for denser breasts?
Rho/rho
How does Z affect photoelectric effect?
Probability is directly associated with Z^3. So much more photoelectric effect at high Z
What is classical/coherent (Rayleigh) scatter?
Occurs in low energy situations (think mammo) usually <10keV. No ionization occurs. Can result in some loss of image contrast.
"Blooming" of the focal spot
Happens when you have high mA, low kVP. Imagine crowded low energy electrons that are bumping each other when theyre going from cathode to anode.
Breast mag views
No grid, use air gap. Even smaller focal spot (0.1mm) Even lower mA / longer exposure Smaller paddle
Minimum energy (in eV) needed to be ionizing
15eV
Why compress the breast?
Decrease scatter (improved contrast), lower kvP, less mA needed, less motion.
Increase kVP by 15%
Double intensity of energy spectrum
Type of shielding to use when blocking beta emitters (like a syringe full of Y90)
Low Z shield (like plastic) because high Z shield will create tons of Bremsstrahlung xrays
Section 2
(50 cards)
What increases axial resolution?
Higher frequency probe
Dose limit for an IR fellow
50mSv per year. In reality you get about 5mSv
Bowtie filter
Filter attenuates less in the center than in the edges so that you get a more homogeneous beam.
Absorbed dose vs equivalent dose
Equivalent dose takes into account the type of radiation (Ex: alpha particles are a **ton worse than xrays)
When to use a narrow window
When the things you're trying to tell apart are close in density (like stroke windows for white/gray matter)
Compound imaging
"Peeking around the corner" Cleaner edges Lose posterior shadowing
What is the reconstruction kernel?
Post-processing, tradeoff between spatial resolution and noise. Sharp kernel has high spatial resolution and tons of noise (think bone). Soft kernal has low spatial resolution and low noise. Dose is the SAME b/c its post-processing
What is weighted CTDI?
1/3 the central CTDI + 2/3 the peripheral CTDI
What is DLP?
Dose length product (DLP) = Volume CTDI * Scan length
Dark streak artifact
Look for arms down, streaks in the mediastinum. This is a kind of beam hardening artifact. Easiest fix is to tilt the gantry or position the patient with arms up.
Frequency vs spatial pulse length
The higher the frequency the smaller the spatial pulse length, the better your axial resolution
Pitch > 1
There's a gap between slices. Less dose. More spatial resolution
Output power vs gain
Output power = how big the wave is that you're sending out. Receiver gain is how much you tune up the strength of the pulse you get back.
CT minimum slice thickness determined by
Detector element aperture width (smaller is thinner)
Pitch < 1
There is overlap. More dose. Improved spatial resolution.
Absorbed dose units
In Gy (1 Joules/kg)
Which has better SNR, the smooth kernel or the sharp kernel?
The smooth kernel has better SNR, poorer spatial resolution.
When to use wider window
When the things you're trying to tell apart are wide apart in HU (like looking at a cancer in lung window)
Ring artifact
Defective detector element
Output power vs lateral resolution
Lower output power = better lateral resolution
Iterative reconstruction
Basically you can lower the dose and allegedly maintain imaging quality with advanced reconstruction
How to increase SNR
Thicker slices (fatter transmit bandwidth), larger FOV, smaller matrix, stronger magnet, narrower readout badwidth, biger voxel
Effective dose units
In Sieverts
What is the effective dose?
You need the DLP times a constant which depends on the body part
What is axial resolution in US?
Resolution in the direction of the probe (depth)
What is a projection?
All the rays in a given angle of the tube. Ray is a single beam to a single detector.
Harmonics
Transmit at one frequency and receive in another. Improves LATERAL resolution. Needs to travel a certain distance before you get this.
Locations of collimation in CT
Pre-patient (reduces dose on the source side) Post-patient (gets rid of scatter from patient on the detector side)
What is volume CTDI?
Weighted CTDI / pitch
Relationship between HU and xray attenuation
Increase HU by 10 = increase xray attenuation by 1%
Pixel/voxel size relative to FOV and matrix
Pixel size = Field of view / Matrix
Is KAP related to source distance?
No, independent. Entrance air kerma goes down with distance, but the area hit goes up.
What is CTDI?
Radiation dose that is normalized to the width of the beam. Based on a phantom
Increased beam width effect on dose
Does NOT change. mAs unchanged. Lower scan time but bigger chunk of tissue exposed
Equivalent dose units
In Sieverts
Stair step artifact
Reconstructions with slices that are too thick (non overlapping intervals)
Where is lateral resolution the best?
At the focal zone
Kerma area product / dose area product
Entrance air kerma * area of entrance - measured in Gy-cm^2
Matrix size in CT
512 x 512
Equivalent dose vs effective dose
Effective dose takes into account tissue weighting factor (how sensitive an organ is to radiation)
CT mA compared to xray
CT mA is higher (up to 1000) compared to 100-800mA for radiograph
What is power doppler
Just detection of presence of doppler shift and how much. Doesnt give directional information.
Pitch
Pitch = table movement per tube / beam width
Doubling the xrays does what to the signal? What to the noise?
Doubling xrays doubles the signal, increases noise by sqrt(2). So overall SNR improves by 1.4x
Cupping artifact
Center of the image looking darker, didnt get enough juice relative to the outside
Incomplete projection artifact
Guy is too fat, tissue hanging out outside of field of view causing computer to spaz. Reposition patient if possible
Best angle for doppler
Theoretically, 0 is best and 90 is worst (cosine) but you MUST have <60.
Color vs power doppler
Power is more sensitive No aliasing in power Power not affected by doppler angle Both can get FLASH artifact
What is mechanical index in US?
Indication of US beam's ability to cause cavitation/micromechanical damage
Will mag increase the KAP?
No. The entrance air kerma will be bigger but the area will be smaller
Section 3
(50 cards)
What are stochastic effects?
No threshold. As dose increases, probability of occurrence increases but the severity does not. Think about cancer risk with radiation
Effects of acute radiation syndromes are seen above what cutoff?
1Gy
Dose limit for a fetus of an occupational worker
500 mrem (5mGy) through the term of the pregnancy
Dose calibrator mnemonic
CLAG for daily, quarterly, annually, whenever moved
CDTIvol phantoms
Estimated on 16cm or 32cm phantom. If the patient is smaller than the phantom, dose is underestimated. If patient is larger, dose is overestimated.
What is the max whole body annual dose allowable?
50mSv / 5rem / 5000mrem
Flow related enhancement is most commonly seen on..
T1 weighted sequences at the end (entry) slice
Threshold for permanent hair loss
7Gy
Units of exposure
Roentgen (Coulomb/kg)
FDA limits of mechanical index
1.0 for baby ~2.0 for adult
Threshold for main erythema reaction
Main erythema rxn occurs ~10 days post exposure (after transient) and threshold is ~5Gy
Threshold for skin exposure at which additional care and followup is instituted
15Gy to single exposure field
What does NRC regulation 10 CFR Part 35 deal with?
Medical use of by-product radioactive material
Annual dose limit to the public
1mSv / 100mrem
Max whole body annual dose for a pregnant worker
5mSv / 500mrem
Purpose of normalization scan in PET QA/QC
Correct for nonuniformity of detector elements to a uniform source (varying efficiency along different lines of response)
Thermal index and OB
Avoid using color doppler on a fetus bc this requires higher power and increases thermal index
Beta plus decay
Occurs in proton rich environments. Proton turns into a neutron, emits a positron. Atomic number decreases
Allowed difference from prescribed nucs dose by licensee
Up to 20%
Who defined the thresholds for deterministic effects?
International Commission on Radiological Protection (ICRP)
Ring down artifact
Gas bubbles with water inside that resonates and keeps generating more return waves
Who needs to wear radiation badges
People who have the possibility of getting more than 10% annual dose limit (so more than 5mGy or 500mrem)
Threshold for late erythema reaction
~15Gy. This happens 8-10 weeks after exposure and can appear bluish 2/2 ischemia.
Mirror image artifact
Type of reverberation artifact with an angled reflector
What is most adjusted by automatic exposure control?
Exposure time to achieve appropriate exposure of the detector (ends up changing mAs)
Thermal index in ultrasound
Ability to cause heat. Thermal index of 1 raises the temperature of tissue 1 degree celcius. This is tissue specific
Threshold of I-131 that needs written AU directive
>30uCi (1.11Mbq). Or any therapeutic dosage of unsealed byproduct
Anisotropy artifact
Tendon looks hyperechoic when perpendicular and hypoechoic when at an angle (can simulate tear). Fix = keep probe steady at perpendicular
Refraction artifact
Happens related to interfaces.
Threshold for permanent sterility in males from acute exposure
6Gy
Maximum MQSA glandular dose from single view
3mGy per image on the phantom. No specific limits on an actual breast.
What improves susceptibility artifact?
Lower field strength, increasing receive/transmit bandwidth, spin echo (as opposed to GRE or EPI)
Interval for dose calibrator accuracy test
Annually
What does 10 CFR 20 deal with?
Dose exposure limits for workers
Relative biological effectiveness
Ratio of doses from diff types of radiation (xrays, alpha, beta) to cause a given effect.
What is MQSA?
Mammo Quality Standards Act Regulations
Minimum distance needed for axial resolution in US
Half of an SPL (spatial pulse length)
Color bleed artifact
Will look like color extending beyond vessel wall. Improve by turning down color gain
Interval for dose calibrator linearity test
Quarterly
Twinkle artifact
Looks like theres movement/flow when there isnt. bc rough surface causes split into complex wave pattern. Also could be related to "phase jitter"
Acute dose threshold for permanent sterility
6Gy in men, 3Gy in women.
Threshold for cataracts from acute exposure
0.5Gy. Cataracts will develop >20 years after acute exposure
Threshold for temp hair loss
2-5Gy
Threshold for transient erythema
2Gy / 200 rads
Cancer incidence increase for radiation according to BEIR VII
8% per 1Gy (0.08% per rad)
What is multiple scan average dose (MSAD)?
Avg dose to a slice in the central portion of a scan taking into account scatter from adjacent slices (compton)
Max dose limitation for public from release of patients injected with radioactive materials
5mSv / 500mrem
Probe frequency vs mechanical index
High frequency has low MI Low frequency has high MI
Interval for dose calibrator constancy test
Daily
Aliasing ultrasound artifact
Point where you screw up and lose data unless you increase sampling speed = Nyquist frequency. Appears as wrap-around Nyquist limit = 1/2 pulse repetition frequency
Section 4
(50 cards)
Type of artifact seen with colloid inspisations
Comet tail
Things that cause comet tail artifact
Cholesterol and colloid
Dose threshold for risk of organ malformation to fetus
100 mGy
Dynamic range of digital vs plain film
Digital has wider dynamic range
In an II, what is flux gain?
Acceleration of electrons towards the output phospor, increasing their energy
Window width and contrast
Wide window - decreased contrast Narrow window - increased contrast
Annual MR QC
Done by medical physicist, includes RF coil check, slice thickness and slice position accuracy
Max dose to public accessible areas in 1 hour
2mrem/hr (0.02mSv/hr)
CR vs DR decentralized
CR is centralized (C for centralized) DR is decentralized (D for decentralized)
Diamagnetic materials
Water and calcium, induced field opposes the external field
Bucky factor
mA required with grid / mA required without grid. Most common Bucky factor is 2-3
Probability of photoelectric effect relative to photon energy
INVERSELY proportional to the energy CUBED
Resonance frequency per 1T
~42 MHz
Dynamic range curves for film vs digital
Linear and wide for digital, curvilinear and narrow for film
What changes to make to kVP / mAs in a kid
Lower kVP (need less penetrating photons) and keep the mA same to slightly lower
Comet tail artifact
Looks kinda like ring down but quickly tapers off (ring down extends to deep image). It is a type of reverb artifact
What is grid cut off?
The grid blocks so many photons that you cause quantum mottle
What is minification gain?
Electrons from a large surface, concentrated on a smaller surface
Linear vs mass attenuation
Linear attenuation differs for water, vapor, and ice bc they take up different amounts of space Mass attenuation is the same regardless of phase because it's measured per unit mass
Type of change to lower dose for a stone study
Lower the mA and keep the kVP the same. You get more noise but this is ok bc youre looking for a super high contrast finding
Pair production
At super high keV and super high Z target (Colossus from xmen) the photon hits straight into the nucleus and emits a pair (1 electron and 1 positron). Positron then annihilates and you can image like PET
Pixel pitch
Spacing between pixels. The lower the pixel pitch the better the spatial resolution.
Fluoro mA, exposure time, and focal spot relative to regular dx
Fluoro has longer exposure times, lower mA (so you dont melt the anode) and a smaller focal spot
Spatial resolution of DR vs CR
DR is better, with direct better than indirect (no lateral dispersion)
Threshold at which PE vs compton dominates
PE dominates <30keV, compton dominates >30keV. Note that both types decrease with increasing energy, its just that there's more compton at those energies relatively
Ideal energy for mammo
Between 16-23keV, so you have to use a voltage of 25-30kVp (vs ~120 for chest radiograph)
Tenth value layer (TVL)
Thickness needed to attenuate 90% of the beam. Ends up being 3.xx HVLs
When does an II need to be replaced?
Conversion gain falls below 50%
Indirect DR system
Xrays hit CsI scintillator -> light -> converted to charge by photodiode -> readout by TFT (thin film transistor) array
How long must calibration records of dose calibrators be kept?
NRC says 3 years.
Highest energy anode/filter pairs in mammo
Tungsten/rho and Tungsten/silver
Material in a CR cassette
Barium fluorohalides
Things that cause ring down artifact
Trapped air bubbles in fluid
Probability of photoelectric effect
Directly proportional to Z^3 Inversely proportional to photon energy ^3
Weekly MR QC
Done by tech. Includes high/low contrast resolution, table positioning, center frequency
Storage phosphor (CR) radiography
Type of indirect, casette based system. Xray -> light -> charge
Is there lateral dispersion in direct DR?
No, no scintillator intermediate so no opportunity for light dispersion.
SI unit for magnetism
Tesla. 1T = 10,000 gauss. Earth field = 0.5 Gauss
What does isobaric mean?
The mass number didnt change. Beta +, beta -, and electron capture are all examples of isobaric transitions
What happens to beam width, spatial resolution, and beam intensity at the focal zone
At focal zone on US, beam width is narrowest, beam intensity highest, and spatial resolution highest
Half life equation
Half life = ln(2)/decay constant
Spatial resolution values
Screen film mammo: 15lp/mm Digital mammo: 7 lp/mm Digital radiopgraph: 3lp/mm CT: 0.7lp/mm MR: 0.3 lp/mm
How does the dose of an II change as it gets older?
Older II = more dose! Worse efficiency / conversion gain
Filter pair thats never used in mammo
Rho anode with a moly filter
Paramagnetic materials
Gado and deoxyhemoglobin, induced field enhances external field.
Appearance of normal fetal lungs on US
As echogenic as liver. If they look like fluid its effusions.
Artifact associated with prospective cardiac gating
Flash artifact
Housing vs enclosure
Housing surrounds everything, made of lead Enclosure is glass and surrounds the x-ray tube, maintaining a vacuum.
Annual extremity (or any other organ but the eye) dose limit
500mSV / 0.5Sv / 50 rem
How many spot films per equivalent dose of 1minute fluoro?
5-10
Section 5
(50 cards)
Instrument used for measuring high doses
Dose calibrator/ion chamber
Things that increase spatial resolution of gamma camera collimator
Thicker, longer septae. Narrow hole diameter
NRC CFR part 19
Notices, instructions, reports to workers
Dose limit to the public per hour in unrestricted area
No greater than 2mrem/hour in an unrestricted area
What happens to image from diverging collimator
Minifies a large object onto a smaller crystal
Range for medium energy collimator
200-400keV
Criteria for "high radiation area"
More than 1msV in 1 hour at 30cm
Things that increase sensitivity of gamma camera collimator
Thinner, shorter septae. Larger hole diameter
How often does energy window need to be tested?
Daily / before each different test using a different tracer.
What happens to image from pinhole collimator
Inverted and magnified
Major spill of I131
1mCi
How often is intrinsic flood done?
Weekly
Where should a ring badge be worn?
On the dominant hand, index finger, label facing inward toward source, under a glove
Geiger counter dead time
If you over load it (>100mR/h) it stops working until it dissipates.
Number of disintegrations per Curie
3.7 x 10^10
Effective half life
1 / effective = 1/physical + 1/biological
How often is dose calibrator consistency checked?
Daily
Recommended counts for extrinsic and intrinsic flood
5-10 million
How often is extrinsic flood done?
Once daily. This tests the collimators and the crystals
Sensitivity/resolution of thick crystal
Better sensitivity (chance of catching the gamma particle), worse spatial resolution (light produced moves before getting to PMT
Problem with sodium iodine well counter
Easily overwhelmed (if exceeds 5k counts/sec). Good for in vitro samples and wipe tests
What is an isometric transition?
Process of rearranging of electrons coupled to electron capture that causes gamma emission, good for imaging
How often is dose calibrator accuracy checked?
Annually
Range for high energy collimator
>400keV
NRC CFR part 35
Medical use of by-product material (human use of radioisotopes)
Workhorse nucs collimator
Parallel hole collimator
Star artifact
Caused by septal penetration of hexagonally oriented collimator holes by very high energy focal source (think post-therapy I131)
Extrinsic flood
WITH a collimator
How long do you keep radioactive material?
10 half lives
Amount of nonuniformity that is allowable
2-5% (1% in SPECT)
Intrinsic flood
WITHOUT a collimator
How is sensitivity affected by distance for parallel hole collimator?
NO change! Even though farther distance reduces counts by inverse square, it allows for greater field of view so no net change in counts.
Relationship between sensitivity and spatial resolution of gamma camera collimator
Inversely related
What happens to image from converging hole collimator
Magnifies WITHOUT inverting
Nucs QC stuff that has to be done daily
Extrinsic flood and energy window
Mechanism of isotope production that is "carrier free"
Cyclotron bombardment with charged particles -> transmutation
Annual dose limit to the general public
100mrem / 1mSv
Impact of matrix size in gamma camera on acquisition time
Larger matrix = longer acquisition time and reduced counts per pixel (worse SNR)
Function of pulse height analyzer
To discard background stuff that has energy too high/low to correspond to desired tracer
How often does center of linearity need to be tested?
Weekly
How is gamma camera linearity and spatial resolution tested?
By placing a lead bar phantom with parallel lines between a cobalt source and the gamma camera. Linearity is bad if the bars look wavy. Resolution is defined by ability to differentiate distinct bars
How often does gamma camera image linearity and spatial resolution need to be tested?
Weekly
How often is dose calibrator linearity checked?
Quarterly
Nucs QC stuff that has to be done weekly
Intrinsic flood, linearity and resolution, and center of rotation
Major spill of In-111, Ga-67
>10mCi
How often is dose calibrator geometry checked
Installation and anytime it's moved
Major spill of Tc, Tl
>100mCi
Range for "low energy" collimator
1-200keV
NRC CFR part 20
Radiation protection
What does flood test for?
Uniformity
Section 6
(50 cards)
Thick dampening block (low q)
"Thud" - more dampening, higher bandwidth, low Q, short spatial pulse length for better axial resolution
Annual occupational lens dose limit
20mSv / 2rem
Situation in which there is a ton of reflection
High impedance difference between adjacent tissues
Total dose to embryo allowed in 9 month pregnancy
5mSv / 500mrem
Beam width artifact
Signal from far zone falsely localizing into area of interest. Classically shown in bladder
How soon do you have to report a "medical event"
Call the doctor, patient, and NRC within 24 hours. Write them a letter within 15 days
Side lobe artifact
Artifact that happens when stuff from side lobes gets registered like it came from the main beam. Classic example = "pseudosludge" in the gallbladder or bladder
Echogenicity vs scatter amplitude
Hyperechoic = high scatter amplitude Hypoechoic = lower scatter amplitude
Reverberation artifact
Due to reflections between two parallel highly reflective surfaces. Looks like multiple equidistantly spaced linear reflections
How often do you do a "blank scan" for PET?
Daily. This is the PET equivalent of uniformity
Loss of how many dB corresponds with 50% loss in signal intensity?
-3dB = 50% loss in signal intensity
Rarefaction
The relaxed (low pressure) part of the sound wave (vs compression)
Type of crystal used in PET
BGO, LSO, or LYSO
How to tell uncorrected from attenuation correction
1. Skin is hot on uncorrected 2. Lung is hot on uncorrected
Type of crystal used in planar imaging
NaI
Truncation artifact in PET
When a fat dude cant fit in a CT and part of him gets left out of the image, but he can fit in the PET, and the attenuation correction is all jacked up as a result
Radiochemical purity
Testing for free Tc. Use thin layer chromatography.
Fasting duration prior to PET
At least 4 hours, longer to minimize cardiac activity
Absorption in ultrasound
Sound energy gets turned into heat. This increases with frequency.
Thickness of crystal ~ frequency
Thick crystal - low frequency Thin crystal - high frequency
Definition of "half value thickness" in ultrasound
Thickness of tissue that causes a reduction of ultrasound intensity by 3dB
Criteria for "very high radiation area"
More than 5 gray in 1 hour at 1m
Distance an F18 positron travels in tissue
~1mm
Criteria for a "medical event"
Wrong dose, wrong patient, wrong site (has to be off by over 20%) AND has to cause harm to the patient (whoe body dose >5rem /50mSv or single organ dose >50rem)
What is impedance?
Degree of "stiffness" of a tissue. Product of the velocity of sound in the medium and the density of the medium
Narrow receive bandwidth results in...
Better SNR, worse type 1 chemical shift, worse spatial resolution
Unit of impedance
Rayl
Limit of how much the dose can be off from what you order
20% via the NRC, 10% in some agreement states
Steeper (bigger) receive bandwidth results in...
Poorer SNR, better spatial resolution, better suppression of type 1 chemical shift
Type of transducer that gets more side lobe artifact
Linear array transducers
Half life of Mo-99
67 hours
Minimum distance between objects in order to be resolved on axial resolution
1/2 the spatial pulse length. This is smaller (better axial res) on low q / heavy damping
When testing radionuclide purity, what do you assay for first?
Mo first, to prevent issues with residual charge
SUV estimation in fat people
You'll overestimate SUV
Thin damping (high Q)
"Ding" - less dampening, narrow bandwidth, long spatial pulse length. good for doppler
Chemical purity
Testing for Al breakthrough. Test is with pH paper. Allowed amount is <10 microgram Al per 1mL
Speed that US machine assumes sound travels at
1540m/s
What changes when ultrasound goes through different mediums? Wavelength or frequency?
Speed of sound diff in diff media. As speed changes, frequency stays the same so wavelength has to change.
Bucket setup imbalance
Dark block rotating on sinogram
How does frequency relate to scatter?
Higher frequency = smaller wavelength = surfaces less smooth = more scatter
Elevation resolution
Resolution in the plane orthogonal to lateral resolution. Dependent on transducer element height
Annual occupational total equivalent organ dose
500mSv / 50rem. Same as extremity (hand) dose
How often do you do a normalization scan for PET?
Monthly. You scan a point source in the FOV
Distribution of free Tc
Salivary, thyroid, stomach
What does a change of +/- 10dB have on the power
+10dB = 10x power, -10db = 1/10th power
Causes of free Tc
Not enough tin, air in the syringe
Radionuclide purity
Testing for Mo breakthrough. You want less than 0.15MICROCi Mo per 1milCi of Tc - at the time of ADMINISTRATION
Annual occupational whole body dose limit
50mSv / 5rem
Relationship between transducer frequency and near field length
Higher frequency, longer near field
How does axial resolution change with depth?
It doesnt. Only lateral resolution does
Section 7
(14 cards)