Exposure Limits
What are occupational exposure limits measured in?
rem (Roentgen equivalent man)
The occupational exposure limits are given in rem because rem refers to the effective dose, which takes into account the type of radiation and the radio-sensitivity of the tissue being exposed.
What are the three cardinal rules of radiation protection?
Shielding, distance, and time
Shielding- A dense barrier that protects body against radiation
Time- The duration of the exposure is directly related to the dose of radiation being received
Distance- As the distance between the source and an individual increases, the radiation exposure decreases.
When is a worker required to wear a personnel dosimeter?
When the worker may exceed 10% of the occupational limit
How thick is the lead curtain used during fluoroscopy?
.25mm pb
This curtain offers no protection to the patient, but is used to protect the technologist and radiologist from scatter radiation coming from the patient. It is assumed that lead aprons are being worn, which is why the lead curtains are only required to have a thickness of .25 mm Pb.
How does filtration minimize patient exposure?
By removing low-energy long-wavelength photons.
This protects the patient's skin and superficial tissues. Photons with long wavelengths are easily absorbed by the body but do not contribute to the x-ray image, making the patient receive an unnecessary dose.
What is the annual limit for radiation workers?
5 Rem
Limits can vary depending upon the affected part of the body, but the annual total effective dose equivalent for the whole body is 5 rem.
What is the required thickness of lead for the primary barrier of an examination room?
1/16 inch
The primary barrier of an examination room should be no less than 1/16 inch Pb. This is because it is in the path of the primary beam.
Where should a personal monitoring device be worn while performing a procedure?
At collar level outside the apron
A personnel monitoring device is worn at collar level outside the lead apron so an estimate of the radiation dose to the eye lens , any unprotected skin, and/or the thyroid can be obtained.
What is the purpose of utilizing the “pulsed” feature?
lower patient exposure
generator produces a pulsed x-ray beam.Most fluoroscopy procedures do not require continuous fluoroscopy and can be accurately performed using pulsed fluoroscopy as low as 7.5 pulses per second
Methods of reducing radiation exposure to patients and/or personnel include
A) beam restriction.
B) shielding.
C) high-kV, low-mAs factor
D) All the above
D)All the above.
Beam restriction keeps the total amt of tissue irradiation to a minimum, shielding provides a dense barrier that protects body against radiation, and using a high kvp/low mAs factor reduces the number of photons that a person could get exposed to.
What is the exposure limit for a fetus?
.5 rem
The exposure limit for a fetus can not exceed more than .5 rem for the entire gestation period. The low limit is due to the increased risk of cancer during the early stages of pregnancy when the fetus is rapidly developing (2-15 weeks).
What is the recommended thickness of lead aprons used by radiographers for personal radiation protection during exam?
50 mm Pb
Though the NCRP requires lead aprons to have a minimum thickness of .25 mm Pb, .50 mm of Pb is recommended because it can better absorb radiation.
What must a personal dosimetry dose report include?
dose to the whole body, lens of the eye, and extremities.
These doses are reported for the quarter, for the year-to-date, and the lifetime total
Gonad dose does not have to be included
Entrance dose rate for the patient should not exceed?
10 rads per minute
Which is not a beam restricting device?
A) Cones
B) Collimators
C) AEC
D) Aperture Diaphram
C)Aec
Automatic exposure control (aec) is used as an X-ray exposure termination device, not used for beam restriction. It terminates the exposure when a predetermined amount of radiation is reached.
What is the annual dose limit for members of the public?
0.1 rem
The limit is so low because this group refers to those who do not work directly with ionizing radiation.
What is the required thickness of lead for the secondary barrier of an examination room?
1/32 mm Pb
The required thickness of lead for the secondary barrier of an examination room is less than the primary because it is only intended to protect from scatter radiation and not the primary beam.
Which type of personal monitor device uses aluminum oxide to trap excited electrons after being exposed to radiation?
OSL
Optically stimulable luminescent dosimeter uses aluminum oxide to trap excited electrons after being exposed to radiation.
During C-arm fluoroscopic procedures, the patient-image intensifier distance should be:
As short as possible.
This reduces patient entrance dose. The closer the image intensifier gets to the patient, the further away the tube (source of exposure) will be.
What are dose area product (dap) meters?
It is a meter used for the assessment of patient dose.
This is done utilizing an ionization chamber mounted on the collimator of the x-ray tube. The amount of ionization produced within the chamber is proportional to the dose and the area of the beam.
What is the annual dose limit for extremities?
50 rem
Extremities can withstand a much larger dose than the whole body because they do not hold any major blood producing organs.
What material has the best radiation shielding capabilities
Lead
Lead is the most desirable material for shielding and protection due to its high atomic number.
What type of personal monitoring device utilizes lithium or calcium fluoride?
TLD
TLD’s containing calcium fluoride are used to record gamma exposure and those containing lithium fluoride are used to record neutron exposure.
Source to Object Distance (SOD) in fluoroscopy
The SOD cannot be less than 15 inches or 38 cm
When using a c-arm the SOD cannot be less than 12 inches or 30 cm
Filters used in x-ray tubes are usually composed of?
Aluminum.
Aluminum is used because it has the greatest effect on low energy photons, which is what filtration is protecting the patient from.