Diagnostic-Typed protective Tube Housing
This is required for both the radiographer and patient from off focus or leakage radiation by restricting the emission of x-rays to the area of the useful or primary beam.
Diagnostic-Typed protective Tube Housing leakage has to be:
Reduce the leakage to less than 100 mR/hr at 1 m from the protective housing.
Bucky slot cover: how thick and what is it made of?
0.25mmPb
Protect curtain: how thick and what is it made of?
0.25mmPb
what factors Affecting Barrier Thickness?
distance, occupancy, controlled area vs uncontrolled area, workload, use factor, kvp
What are primary barriers?
lead and concrete
What are secondary barriers
leakage radiation, scatter radiation: steel, glass, gypsum, wood
The x-ray beam and light beam must coincide to within ____ of the SID.
2%
Positive Beam Limitation (PBL) – automatic light localizer must be within __ of the SID
2%
Source-to-image distance indicator – SID indicator must be provided, and must be accurate within ___.
2%
filtration
Reduces exposure to the patient’s skin and superficial tissue by absorbing most of the lower energy photons.
change in beam quality due to filtration is referred to as:
“hardening” of the beam.
Two types of Filtration available:
Inherent filtration and Added filtration
Added filtration:
Usually consists of sheets of aluminum (or its equivalent) of appropriate thickness.
Where is added filtration located:
outside the glass window of the tube housing above the collimator shutters
Readily accessible to service personnel
Total filtration should be at least:
2.5mm Al.
Mobile diagnostic units and fluoroscopic equipment also require________________ total permanent filtration when the tube is operating over 70 kvp
2.5-mm aluminum equivalent
What is the most widely selected as filter material because it effectively removes low energy?
aluminum
positive stuff about aluminum
lightweight, relatively inexpensive and readily available
Compliance with the Radiation Control for Health and Safety Act of 1968 states
diagnostic x-ray beam must always be adequately filtered.
Total filtration equals:
Inherent filtration plus added filtration
ability of x-ray units to duplicate certain radiation exposure for any given combination of kilovolts at peak value (KVP).
Reproducibility
ability of the output radiation intensity at a select Ma value should remain constant (mAs)
Linearity
The variation in x-ray intensity should not exceed ___. (reproductivity)
5%
linearity should not exceed ____ change in intensity from one mA station to the adjacent.
10%
Provide radiation shielding for both imaging department personnel and the general public.
protective barrier
three Categories of radiation sources can be generated in an x-ray room
Primary radiation, secondary radiation, and leakage radiation
Two categories of secondary radiation:
scatter and leakage radiation
_____ sheets of appropriate thickness placed in the walls are generally used.
Lead
Two types of barriers:
Primary and secondary
to prevent primary radiation from reaching personnel or members of the general public.
primary barrier
how thick should the primary barrier be:
2mm Pb equivalent
Primary barrier consist of ______________ and extend _____ upward from the floor.
1/16 inch lead; 1/16 7 feet
Any wall to which the useful beam can be directed is designated:
a primary protective barrier.
What is most often used as a primary protective barrier?
any wall to which the useful beam can be directed
what may be used instead of lead?
Concrete, concrete block, or brick
Factors that affect barrier thickness
distance, occupancy factor , control or uncontrolled area
Distance (Factors that affect barrier thickness)
The distance between the source of radiation and the barrier.
Occupancy factor (T) (Factors that affect barrier thickness)
Radiation barriers are installed to protect personnel and general public from radiation.
To calculate this, one must account for the workweek activities in that room
If a region adjacent to a wall of an x-ray room is used only by occupationally exposed personnel, that location is designated as a _______.
controlled area
an area such as a nearby hall or corridor that is frequented by the general public is termed ________
uncontrolled areas
consists of radiation that has been deflected from the primary beam.
secondary barrier
Secondary barrier
- scatter radiation and leakage radiation
- lead is not required
- Gypsum board, glass or lead acrylic is adequate.
- control booth barrier for the protection of the radiographer
- Intercepts leakage and scattered radiation only.
In a typical installation the secondary barrier consists of _______. This barrier must extend______ upward from the floor.
1/32 inch lead; 7 feet (2.1 m)
Three types of gas-filled radiation survey instruments
- The ionization chamber-type survey meter (fig. 10-11)
- The proportional counter and
- The Geiger-Muller (GM) detector
Ionization Chamber-Type Survey Meter also known as
cutie pie
Ionization Chamber-Type Survey Meter
- Used for area surveys
- Measures x-radiation and gamma radiation.
- Used to monitor diagnostic x-ray installations exposure times
- Exposure rates of patients containing therapeutic doses of radioactive materials.
- Exposure rates in radioisotope storage facilities.
Proportional Counter:
- serves no useful purpose in diagnostic imaging.
- It is generally used in a laboratory setting to detect alpha and beta radiation and small amounts of other types of low-level radioactive contamination.
area monitoring devices that detect and measure radiation
Radiation survey instruments
indicates the presence or absence of radiation
detection system
measures only cumulative radiation intensity
dosimeter system
3 personal monitors used
Film
Optically stimulated dosimetry
Thermoluminescent dosimetry
2 area monitors used
Ion chamber
Geiger counter
Radionuclide assay measurement device
Proportional counter
Nuclear medicine/ ct imaging measurement device
scintillation detectors
What is the active ingredient in film? (monitoring radiation)
photographic emulsion
What is the active ingredient in optically stimulated dosimetry? (OSL)
aluminum oxide (Al2O3)
What is the active ingredient in thermoluminescent dosimetry? (TLD)
Lithium Fluoride (LiF)
The SSD (source to skin distance) must be not less than ___ on the stationary fluoro and not less than ____ on mobile fluoro
38cm; 30cm
primary radiation is the _______ beam
useful
The intensity of scatter radiation ____ from the patient is approximately ____ of the intensity of the useful beam at the patient,
1m; 0.1%
Rad tech receive most of their occupational radiation exposure during _________
fluoroscopy
Design limits for a controlled area are based on the annual recommended occupational dose limit of _____.
50 mSv/yr
geiger- muller counter
limited to 1 mGy/hr portable- survey for low radiation levels and radioactive contamination
The use factor for a secondary barrier is always ___
1
The ionization of gas is the basis for _______________.
gas filled radiation detector
high sensitivity means:
that an instrument can detect very low radiation intensities
photocathode
a device that emits electron when illuminated
dynode gain
the ratio of secondary electron to incident electron
the size of the electron pulse is ____ to the energy absorbed by the crystal from incident photon.
proportional
TLD is:
emission of light by a thermally stimulated crystal following irradiation.
Lithium fluoride is:
nearly tissue-equivalent radiation dosimeter