Safety 2 Flashcards
Filtration effect on skin and organ exposure
-reduces entrance skin exposure to pt
Filtration effect on average beam energy
- removes low energy, non diagnostic xray photons from beam
- increases the effective energy and quality of xray beam (hardening)
Operating kVp below 50
Total filtration (inherent + added)= 0.5 mm aluminum
Operating kVp 50-70
Total filtration = 1.5 mm aluminum
Operating kVp above 70
Total filtration = 2.5 mm aluminum
Voluntary motion controlled by
Patient communication
Involuntary motion uses what?
Shortest possible exposure time
Air gap technique
- alternative to grid use
- long SID and increased OID
- does NOT result in decrease in production of secondary or scattered radiation
Pt dose reduced by what exposure factors
Increased kVp decreased mAs
Fluoro time max
5 min or 300 seconds
Magnification factor
SID/SOD
Minimum source to skin distance fixed fluoro unit
15 inches (38 cm)
Minimum source to skin distance mobile fluoro unit
12 inches (30 cm)
Dose Area Product
To measure total dose to a pt site in order to reduce pt rad dose
Mobile radiographic unit
Minimum 6 ft/ 72 inches/ 180 cm/ 2 meters
Medical imaging’s principle of radiation protection is based on what
The non threshold, linear dose response relationship
Leakage radiation
- emitted from xray tube
- limited to 100 mR/hr at 1 meter (1 mGy/hr at 1 meter)
Natural sources of rad
Radon, cosmic, terrestrial
Greatest source of artificial radiation
- Medical imaging
- other sources can be nuclear fallout, consumer products
What is the most effective method of personnel protection
Distance
Inverse square law example
By increasing distance from rad source from 4 ft to 8 ft, rad exposure will decrease by factor of 22, or 4 times
Half value layer
Thickness of an absorbing material required to reduce the intensity of rad to one half of its original value
Lead apron lead equivalent
0.5 mm Pb
Lead apron lead equivalent on port
0.25 mm Pb
Gloves lead equivalent
0.25 mm Pb
Thyroid shield lead equivalent
0.5 mm Pb
Glasses lead equivalent
0.35 mm Pb
Bucky slot cover lead equivalent
0.25 mm Pb
Spot film device protective curtain lead equivalent
0.25 mm Pb
Clear lead-plastic overhead protective barrier
0.5 mm Pb
Primary protective barrier
- the surfaces that can be struck by primary beam
- located perpendicular to primary beam
Primary protective barrier Pb equivalent
- 1/16 inch (0.16 cm or 1.6 mm)
- if primary barrier is a wall, lead must extend 7 ft (210 cm or 2.3 meters) from floor
Secondary protective barrier
Surfaces struck with leakage and scatter radiation, located parallel to primary beam
Secondary protective barrier Pb equivalent
- 1/32 inch (0.08 cm or 0.8 mm)
- 1/2 inch (1.25 cm) of secondary barrier must overlap primary barrier where they meet
6 ft to meters
1.8 or 2 meters
Typical conventional (non digital) fluoroscopy units operate within what range
2 to 5 mA
Automatic brightness control
Designed to maintain a predetermined level of light intensity exiting the image intensification tube
Fluoroscopic exposure switch should be what type
Dead man
Film badge
- relies on ability of ionizing radiation to effect a density change on the film emulsion
- amount of dose received by badge is a function of the degree of film blackening that happens on the surface of the film emulsion that lie under various forms of attenuating filters like tin or copper
Film badge benefits
- good for monitoring over long period of time
- inexpensive and reliable
- provides permanent or archival record
functional component Of Thermoluminescent dosimeter (TLD)
lithium fluoride
How are reading from TLD made
By heating lithium fluoride chip to a point of combustion
Thermoluminescent dosimeter (TLD)
- the light spectrum the chip yield will change with changing levels of energy absorbed by the chip
- once chip is heated it is destroyed
- no archival record other than a written record of findings
Pocket dosimeter
-relies on ability of ionizing radiation to ionize a gas within a sealed chamber resulting in a change of charged electrode, discharging the electron
Pros of Pocket dosimeter
- good for short term monitoring or testing (immediate readout)
- may be recharged and reused
Cons of Pocket dosimeter
- prone to inaccurate readings with rough handling
- does not offer permanent record of dosage
Detector for Optically stimulated luminescent dosimeter (OSLD)
Aluminum oxide
Optically stimulated luminescent dosimeter (OSLD)
- laser light reads the sensing material which causes the material to become luminescent in proportion to the exposure that the sensing material received
- filters made of aluminum, tin, and copper allow for determination of the energy levels striking the badge
Greatest to least sensitive dosimeters
1) greatest sensitivity: pocket dosimeter
2) OSLD
3) TLD
4) least sensitivity: film badge
Annual whole body exposure (occupational)
5 rem (50 mSv)
Lens of the eye (occupational)
15 rem (150 mSv)
Red bone marrow, breast, lung, gonads, skin, and extremities (occupational dose)
50 rem (500 mSv)
Cumulative effective limit (occupational)
1 rem x age in years
10 mSv x age in years
Annual effective dose equivalent limit (public)
0.5 rem (5 mSv)
Dose equivalent limits for the lens of the eye, skin, and extremities (public)
5 rem (50 mSv)
Embryo/fetus exposure
0.5 rem (5 mSv) for the entire gestational period and max 0.05 rem (0.5 mSv) per month during gestational period
Dose equivalent limits (DEL)
The max dose of radiation that in light of present knowledge would not be expected to yield any significant radiation effects
Inherent filtration includes what
Xray tube window, oil in the xray tube housing, and housing port
Added filtration includes
Aluminum plate and the collimator mirror
Order in which primary xray beam passes through filters in their path
1) xray tube window
2) oil surrounding xray tube
3) xray tube housing port
4) aluminum plate
5) collimator mirror
DAP (dose area product)
Xray exposure in air based on a specific area
