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Transcript of Patient Interactions 1. Review Tube Interaction Heat Brems Characteristic Patient Interactions ...
Patient Interactions
1
Review Tube Interaction Heat Brems Characteristic
Patient Interactions Classic Coherent Compton Photoelectric Pair Production Photodisintegration
Why These are Important? Image Production Patient/Tech Safety
Patient Interactions
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Review of Tube Interactions: Heat Brems Characteristic
Patient Interactions
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Heat
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Brems
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Characteristic
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Review Tube Interaction Heat Brems Characteristic
Patient Interactions Classic Coherent Compton Photoelectric Pair Production Photodisintegration
Why These are Important? Image Production Patient/Tech Safety
Patient Interactions
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Interaction in the body beginInteraction in the body beginat the atomic levelat the atomic level
AtomsAtomsMoleculesMoleculesCellsCellsTissuesTissuesOrgansOrgans
Patient InteractionsPatient Interactions
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Patient InteractionsInteractions of X-rays with matter
1. No interaction: X-ray passes completely and get to image receptor
2. Complete absorption: no x-rays get to image receptor
3. Partial absorption with scatter-some x-rays get to image receptor but some get scattered
What happens to our What happens to our Primary Beam?Primary Beam?
Patient InteractionsPatient Interactions
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EM Interactions with MatterEM Interactions with Matter
General interactions with matter include:1. Scatter
– With or without partial absorption
2. Absorption– Full attenuation
Patient InteractionsPatient Interactions
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X-ray photons can change X-ray photons can change cellscells
Patient InteractionsPatient Interactions
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Some radiations are energetic enough to rearrange atoms in materials through which they pass, and can therefore he hazardous
to living tissue.
1913
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Some radiations are energetic enough to rearrange atoms in materials through which they pass, and can therefore he hazardous
to living tissue.
Hiroshima victim
Patient InteractionsPatient Interactions
I don’t want that to happen to me!!
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Patient Interactions
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Patient Interactions
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Classical (Coherent) Scattering
Classical (Coherent) Scattering
Excitation of the total complement of atomic electrons occurs as a result of interaction with the incident photon
No ionization takes place
Electrons in shells “vibrate”
Small heat is released The photon is
scattered in different directions
Energies below 10kV
Patient Interactions
Classical scattering
Patient Interactions
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Net Result of ClassicalNo energy transferPhoton changes direction with same energyOccurs with LOW ENERGY photonsNo ionizationNot diagnostic
Classical (Coherent)
Classical (Coherent)
Patient Interactions
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COMPTON SCATTERING
1. Outer shell electron in body
2. Interacts with x-ray photon from the tube
3. Moderate energy electron
Patient Interactions
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Patient Interactions
Recoil electron can Recoil electron can produce another produce another interaction if high interaction if high enough energy. enough energy. Compton scattering Compton scattering doesdoesnot provide any not provide any useful diagnostic useful diagnostic information. information.
compton scattering (effect)
Patient Interactions
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Patient Interactions
Moderate energy x-ray photon ejects an outer shell electron.
Energy is divided between scattered photon and the Compton electron (ejected e- or recoil electron)
Scattered photon has sufficient energy to exit body.
Since the scattered photon exits the body, it does not pose a radiation hazard to the patient.
Can increase film fog (reduces contrast)
Radiation hazard to personnel 24
Patient Interactions
photoelectron
Incoming photon interacts with inner shell electron. The “knocked-out” electron is called a photoelectron. The energy of the incoming photon is absorbed.
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photoelectric interaction
Patient Interactions
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27CASCADE
Patient Interactions
Patient Interactions
Moderate energy x-ray photon ejects inner shell electron (energy absorbed)
Leaves an orbital vacancy, releasing a photoelectron. (As vacancy is filled, another photon is produced-scatter radiation )
More likely to occur in absorbers of high atomic number (bone, positive contrast media)
Contributes significantly to patient dose,
As all the photon energy is absorbed by the patient , this is responsible for the production of short-scale contrast.
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Patient Interactions
positron
Electron (Negatron)
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Patient Interactions
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Very High Energy Photon…..MkV
Not used in Diagnostic X-ray
Patient Interactions
Nuclear fragment
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Patient Interactions
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Very High Energy Photon…..MkV
Not used in Diagnostic X-ray
Patient Interactions
Classical Coherent Low energy photons No diagnostic effect Contributes to scatter
Compton Effect (Scattering) Moderate energy photons No diagnostic effect Contributes to scattering Contributes to personnel dose
Photoelectric Effect Moderate energy photons Definite diagnostic effect Contributes to image contrast Atomic number dependent Contributes to patient dose
Pair Production High energy photons Not useful in diagnostic range
Photodisintegration High energy photons Not useful in diagnostic range
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What kind of interaction is What kind of interaction is this?this?
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What kind of interaction is What kind of interaction is this?this?
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What kind of interaction is What kind of interaction is this?this?
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What kind of interaction is What kind of interaction is this?this?
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What kind of interaction is What kind of interaction is this?this?
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ssssssssssssssssssss
What kind of interaction is What kind of interaction is this?this?
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What kind of interaction is What kind of interaction is this?this?
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Things to Remember About X-ray Interactions with
Matter
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Things to Remember About Diagnostic Radiation
Production
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Review Tube Interaction Heat Brems Characteristic
Patient Interactions Classic Coherent Compton Photoelectric Pair Production Photodisintegration
Why These are Important? Image Production Patient/Tech Safety
Patient Interactions
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summary of interactions
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Image production
Why Interactions are Important?
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Biggest Contributor to Personnel HazardBiggest Contributor to Personnel Hazard
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During Fluoro – the patient is the largest scattering object
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Both Compton and Classical cause scatter Both Compton and Classical cause scatter radiation. radiation. Why is one of these a concern to diagnostic Why is one of these a concern to diagnostic radiography and one is not?radiography and one is not?Why is one a concern to patient safety and Why is one a concern to patient safety and one is not?one is not? Why is one a concern to technologist safety and one is not?
Image Production
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Image Production and Patient Safety
Photoelectric absorption is what gives us our image contrast.
Photoelectric absorption is determined mostly by atomic number. The lower the kV of the photons, the more it is affected by atomic number. The higher the kV, the less atomic number factors into photon absorptions.
However, patient dose increases with photoelectric absorptions because the energy of the photon is deposited in the tissue. This affects patient dose.
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Differential Absorption
Results from the differences between x-rays being absorbed and those transmitted to the image receptor
1. Compton Scattering2. Photoelectric Effect 3. X-rays transmitted with no interaction
Image Production
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Compton and Differential Absorption
Image Production
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Photoelectric and Differential Absorption
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Beam Attenuation
Image Production
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Review Tube Interaction Heat Brems Characteristic
Patient Interactions Classic Coherent Compton Photoelectric Pair Production Photodisintegration
Why These are Important? How our image is created Patient/Tech Safety
Patient Interactions
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Patient/Tech Safety
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UNITS OF RADIATION MEASUREMENT
1.To quantify the amount of radiation
A: Received by Patient Employee Public
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Units of Measure
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Unit of Exposure
Exposure is a measure of the strength of a radiation field at some point in air. This is the measure made by a survey meter. The most commonly used unit of exposure is the roentgen (R).
RoentgenRoentgen: measures the amount of ionization in a certain amount of air after a certain measure of radiation exposure, abbreviated by “R”
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ROENTGEN (R)
I. Unit of measurement =measures ion pairs in a cubic centimeter at given conditions
II. The quantity of radiation exposure in air
III. Measures output of the x-ray tube
IV. Does not indicate the actual patient dose or absorption
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Absorbed Dose
Dose or Absorbed DoseDose or Absorbed Dose: Absorbed dose is the amount of energy that ionizing radiation imparts to a given mass of matter. In other words, the dose is the amount of radiation absorbed by and object. The abbreviation for absorbed dose is “rad”.
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Absorbed Dose
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Dose Equivalent
Dose Equivalent: The dose equivalent relates the absorbed dose to the biological effect of that dose. The absorbed dose of specific types of radiation is multiplied by a "quality factor" to arrive at the dose equivalent. Rem is an acronym for "roentgen equivalent in man."
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Dose Equivalent
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Roengten EQUIVALENT MAN(REM)
1. Different types of radiation produce different responses
2. The unit of dose equivalence, expressed as
RAD x QF = REM
3. Used for occupational (employee) exposures
4. Can be used when for dose of patient68
QUALITY FACTOR Qualifies what the damage is from different types of radiation Example: QF for X-ray is 1 QF for alpha is 20 Alpha is 20 x more damaging to
tissue
Type of Radiation Rad Q Factor RemX-Ray 1 1 1Gamma Ray 1 1 1Beta Particles 1 1 1Thermal Neutrons 1 5 5Fast Neutrons 1 10 10Alpha Particles 1 20 20
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Why did the bunny die??
BUNNY A
Received 200 rads
BUNNY B
Received 200 rads
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Why did the bunny die??
BUNNY A 200 rads x 1 for X-RAY = 200 REMS
BUNNY B200 rads x 20 for alpha
= 4000 REMS
Types of Measurement
Conventional UnitsSI Units
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Conventional vs. SI units
British units used since 1920’s
United States still uses this system
New system developed in 1948
System of Units based on Metric measurements developed by International Committee for Weights and Measures
1985- officially adopted
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Conv. Units SI Units
1. RADS
2. REMS
3. R
1. GRAYS
2. SIEVERT
3. C/KG
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Comparsion of Units
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Comparison of Units
Exposure R C/kg 1R=2.58x10-4 C/kg
Absorbed Dose
Rad Gray 1rad=.01Gray1Gray=100rad
Dose Equivalent
Rem Sievert 1rem=.01Sv1Sv=100rem
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RADS REMS
RADS
GRAYS
Patient absorbed dose
REMS
SIEVERTS
Employee(technologists) =
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R - ROENTGENS
RADS –
PATIENT DOSE
REMS
OCCUPATIONAL EXPOSURE
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A portable x-ray machine has an output intensity of 4mR/mAs at 40 inches. What will be the output intensity at 30 inches.
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22
2
1
d
d
I
I
2
2
40
30
?
4
inches
inches
mR
mR
inches
inches
mR
mR
1600
900
?
4
inchesmRinchesmR 900*?1600*4
900
6400? mR
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The exposure from an x-ray tube operated at 70kVp, 200mAs is 400mR at 36 inches. What will the exposure be at 72 inches? 100mRThe x-ray intensity at 40 inches is 450mR. What is the intensity at the edge of the control booth which is 10 feet away?......think carefully… 50mRA temporary Chest Unit is set up in an outdoor area. The technique used results in an exposure intensity of 25mR at 72 inches. The area behind the chest stand in which the exposure intensity exceeds 1 mR. How far away from the x-ray tube will this area extend?30 feet
The exposure from an x-ray tube operated at 70kVp, 200mAs is 400mR at 36 inches. What will the exposure be at 72
inches?
100mR
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22
2
1
d
d
I
I Use Inverse Square Law
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22
36
72
?
400
inches
inches
mR
mR The first exposure value is 400mR. The first distance is
36 inches. The second intensity is what we are looking for. The second distance is 72”
2
2
1296
5184
?
400
inches
inches
mR
mR Square both 72 and 36.
22 12964005184? inchesmRinchesmR Cross multiply
2
2
5184
1296400?
inches
inchesmRmR Cancel out “inches2”, multiply, divide
?mR= 100mR
The x-ray intensity at 40 inches is 450mR. What is the intensity at the edge of the control booth which
is 10 feet away?......think carefully…
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21
22
2
1
d
d
I
I Use the Inverse Square Law. The first intensity is 450mR, the
Second intensity is unknown. The first distance is 40 inches. TheSecond distance is 10 feet…..Convert feet to inches.
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40
120450
inches
inches
xmR
mR So 10 feet is equivalent to 120 inches.
2
2
1600
14400450
inches
inches
xmR
mR
2
2
1
9450
inches
inches
xmR
mR Short cut method
2
2
14400
1600450
inches
inchesmRxmR Cross multiply
Cancel units
2
2
9
1450
inches
inchmRxmR
mRxmR 50
A temporary Chest Unit is set up in an outdoor area. The technique used results in an exposure intensity of 25mR at 72 inches. The area
behind the chest stand in which the exposure intensity exceeds 1 mR. How far away from the x-ray tube will this area extend?
30 feet
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21
22
2
1
d
d
I
I
Use Inverse Square Law. The first intensity is 25mR, the secondIntensity is 1mR. The first distance is 72 inches, the second distanceUnknown.
2
2
721
25 x
mR
mR
2
22
51841
25
inches
inchesx
mR
mR
222 5184251 inchesmRinchesxmR Cross Multiply
mR
inchesmRinchesx
1
518425 222
222 129600inchesinchesx
22 129600inchesx inchesx 360
Patient/Tech Safety
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Allowable Dose LimitsAn exposure of 500 roentgens in five hours is An exposure of 500 roentgens in five hours is usually lethal for human beings.usually lethal for human beings.The typical exposure to normal background The typical exposure to normal background radiation for a human being is about 200 radiation for a human being is about 200 milliroentgens per year, or about 23 microroentgens milliroentgens per year, or about 23 microroentgens per hour.per hour.In human tissue, one Roentgen of x-ray radiation In human tissue, one Roentgen of x-ray radiation exposure results in about one rad of absorbed dose exposure results in about one rad of absorbed dose (= 0.01 Gy). (= 0.01 Gy). When measuring dose absorbed in man due to When measuring dose absorbed in man due to exposure, units of exposure, units of absorbed dose absorbed dose are used (the are used (the related related radrad or SI or SI graygray), or, with consideration of ), or, with consideration of biological effects from differing radiation types, biological effects from differing radiation types, units of units of equivalent doseequivalent dose, such as the related , such as the related remrem or or the SI the SI SievertSievert..
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PUBLIC EXPOSURE NON MEDICAL EXPOSURE
10 % of Occupational exposure0.5 rad or 500 mrad or 5mGray
Under age 18 and Students 0.1 rem
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Education and Training Exposures
Student’s must never hold patients during exposures
Effective dose limit (Annual) 0.1 rem or 1 mSv
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Permissible Occupational Dose
Annual dose : 5 Rem/year 50mSv/year 5000 mrem
Cumulative Dose 1 rem x age or 10mSv x
age
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Allowable DOSE - ANNUAL
CONVENTIONAL UNITS
5 REMS
SI UNIT
5O mSv
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OCCUPATIONAL EXPOSURES
5 REMS / YEAR
BUT NOT TO EXCEED 1.25 REM/QUARTER
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Allowable DOSE – TOTALCUMMULATIVE
CONVENTIONAL UNITS
Age x 1 rem
SI UNIT
Age x 10msv
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Declared Pregnant WorkerDeclared Pregnant Worker
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Declared Pregnant WorkerDeclared Pregnant Worker
2 badges provided 1 worn at collar (Mother’s exposure) 1 worn inside apron at waist level (baby exposure)
Under 5 rem – negligible risk Risk increases above 15 rem Recommend abortion (spontaneous) 25 rem
www.ntc.gov/NRC/RG/08/08-013.html
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Pregnancy & Embryo
1. Mother occupational worker
5 rem
2. Baby 500 mRem or .5 rem/
year .05 rem/month
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Fetus Exposure
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Fetus Exposure
Patient/Tech Safety
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Detection Devices
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Personal Radiation Monitoring
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Personnel Monitoring Devices
1. Film Badges
2. Thermoluminescent Dosimeters (TLD)
3. Pocket Dosimeters
4. Optically Stimulated Luminescence (OSL Dosimeters)
Personnel Monitoring Devices
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Personal Monitoring Devices-
Film Badges – c changed monthly
Thermoluminescent Dosimetry
(TLD)
Personnel Monitoring Devices
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Based on property that x-ray can luminescence in certain materials
Contains reusable crystal
More expensive than film badge
Pocket Dosimeter
Personnel Monitoring devices
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Pen-like deviceContains an ionization chamberVisible scale which provides estimate of gamma dose-provides immediate dose estimate
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POSL
POSL
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Looks similar to film badgesContains a piece of aluminum oxide instead of filmLaser reads the luminescence to determine exposureEasy to change out, keep track of records
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Field Survey Instruments
Geiger Muller counter
• “Cutie Pie”
Ionization Chamber
Field Survey Instruments
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Patient/Tech Safety
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Governing Bodies
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REGULATORY AGENCIES
NCRP - Reviews recommendation for radiation protection & safety. Distributes information re: radiation
awareness
National Council on Radiation Protection and MeasurementsNational Council on Radiation Protection and Measurements
Nuclear Regulatory CommissionNuclear Regulatory Commission makes laws and enforces regulations
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What is the annual allowable dose for a 32 year old Technologist?
Review
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What is the annual allowable dose for a 32 year old Technologist?
5 rem = 5000 mrem - 50 msv
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What is the cummulative allowable dose for a 32 year old Technologist?
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What is the cumulative allowable dose for a 32 year old Technologist?
32 REM or 320 mSv Or 3200 mrem