Physics 2 test 4 Flashcards
ALARA stands for
As Low As Reasonably Achievable
Three cardinal principles of x-ray
STD (MAX, MIN, MAX)
Max, Shielding
Min, Time
Max, Distance
Exposure rate formula
2rad/mA/time
2)(mA)(time
How should thr fluro foot pedal be used?
In pulsating fashion to reduce exposure and anode heating
Heat unit formula
(mA)(time)(kV)
single phase
6 phase pulse
12 phase pulse
A point source or non-point source follows the inverse square law if the distance from the source is what?
7 times the source diameter
If the focal spot of the tube is 3mm, how far do you need to be before the inverse square law applies?
21 mm (7 times away, 7X3=21)
Occupational effective dose is how much of monitor report?
10%
Where do you stand in Fluoro?
Stay back Sides of table NOT ends behind other personnel wear protective apparel
The tenth value layer equals…
3.3 hvl
1 TVL= 3.3 HVL
What is my year occupational dose limit?
5 Rem a year
would look like 5000 on my report
Protective houseing must reduce leakage radiation to
Less than 100 mR/hr at 1m from housing
Control panel MUST indicate when tube is energized, kVp & mA meters by what?
Some type of audible notification
MUST be an SID indicator provided with what type of accuracy?
2%
Collimators MUST be provided witha light beam with what type of accuracy?
2%
`PBL (what does is stand for) is REQUIRED to collimate to receptor size with what type of accuracy?
Positive Beam Limitation 2%
Total filtration of at least (blank) equivalent when operated above (blank) kVp
2.5 mm Al
70 kVp
Total filtration includes…
Glass envelop
Mirrors
Tube housing port
Al filters
Reproducibility refers to
Same exposure over and over
Reproducibility exposure duplication can have what variance?
5%
Linearity refers to
Same mR/mAs using adjucment mA but get the same output
Linearity can have what variance?
10%
How far should a technologist be able to get away from a portable machine and still shot an exposure?
2.0 meters
6+ feet
Fluoro source to skin distance
Can’t be less than 38 cm
30 for mobile c-arm
Tabletop Exposure intensity not allowed to exceed:
2.1 R/min/mA at 80 kVp
Maximum tabletop intensity
What about with pulsating fluoro (optional high level control)
100 mGy/min (10R/min)
200 mGy/min (20R/min)
What is the primary barrier shielding for scatter requirement?
1/16” Pb equiv to 7 ft; 1/32” Pb equiv there to celling
What is the concrete equivelant?
4” of concrete replaces 1/16” Pb
Radiation weighting factors: how many more times exposure: X & Gamma rays? Protons? Fast Neutrons? Alpha Particles?
1
2
5
20
Personel Monitoring is with?
Film Dosimetry (photographic emulsion)
Intensity/detect contamination is measured with what?
Gas-filled radiation detector (Geiger counter)
xrays come from what source?
Cloud
Gamma rays come from what source?
Nucleous
Alpha particles-what do you know?
Huge
External not to worrysome, internal source very worrysome, can’t get out of the body
Not going to go far before stopped
Beta particles-what do you know?
Small
Going to go far before being stopped
Scintillation detection-gamma camera uses what to detect rays?
Crystals, like the crystals in our badges
The heat them up and then they give off light, based on the amount of light they give off determins the exposure
TLD-Thermoluminescence dosimetery radiation detection-how does it work
Has a poshpor when it’s heated up, gives off light.
Lithium Floride crystals, radiolucent can use the same time you’re taking an xray won’t interfere with image
This is nearly tissue-equivalent and relatively sensitive
Lithium Flouride (LIF)
An aluminum oxide detector that gives off light proportional to exposure during processing. Based on excitation of electrons during exposure
OSL-Optically Stimulated Luminescence
How are OSL’s read and how do they work
They’re read with a lazer beam they have “stair step” crystals and work sort of like a step wedge.
The readout gives you quality and strength of the photon
Why are OSL’s the most used detector?
Significantly more durable and less sensitive to water, heat and light. Can be worn for 3 months at a time.
What is the number one cause of Radiation Exposure?
Diagnostic Repeats
Patient dose/skin entrance dose is measured with what and why
TLD, radiolucent, doesn’t measure anything in diagnostic range and doesn’t interfere with image.
Describe a “Mean Marrow Dose”
A dose of radiation given to a portion of the body and then averaged out over entire bone marrow. Used to estimate risk of late effect leukemia to a population
GSD (Genetically Significant Dose)
Dose that would produce the same effect on anyone exposed if equal exposure to entire population
1000 people x 0.1 rem=
(10 people x 10 rem)+
(990 people x 0 rem)
What is the concern in Mammography exposure?
Glandular (not skin dose) accounts for 15% of dose
In Mammography when you’re using a grid how much more is the dose increased?
Double
What type of scanning is CT versus Fluro?
CT is dynamic and increases occupational exposure, fluoro is pulsating
What are the fetal exposure limits?
5 mSv or 500 mrem WHOLE durration of pregnancy
How quickly can the total exposure inutero be applied?
May not be accumulated faster than 0.5 mSv/month or 50 mrem a month
