Repeat protocols:
1. Kept to a minimum
2. Repeat analysis performed
3. Reasons for repeats should be documented
4. In-service training for frequent repeat exams
Repeats result in ____________ the radiation to the patient and the technologist.
twice
Repeats range from about _______ % of exams performed
5%-15%
What is the purpose of immobilizing a patient?
to reduce patient motion and motion unsharpness
When is scattered radiation produced?
During compton interaction
What happens during compton interaction?
photon interacts with outer shell and electron and changes direction
Scattered beam intensity is about ________th the intensity of the primary beam at a _______ degree angle at a distance of ____ meter from the patient.
1/1000th
90 degree angle
1 meter
Types of Beam Limiting Devices:
1. Diaphragms
2. Cones
3. Collimators
What is the most commonly used collimator?
variable-aperture collimator
Accuracy within ____% of the SID is required with automatic collimation.
2%
Inherent filtration
limits x-ray beam by use of glass window in the tube
Added filtration
limits x-ray beam by use of piece of aluminum outside glass window of tube housing
Total filtration
maximum amount of x-ray beam through the use of added and inherent filtration
which type of filtration can be changed by a radiographer?
wedge filter
What is the minimum total filtration for mobile diagnostic and/or fluoroscopy units?
2.5 mm Al equivalent
Half-Value Layer (HVL)
thickness of material that will reduce x-ray intensity to half of its original value
For lead aprons, if there is overlap on the front how much does protection increase?
1.0 mm
What is the gonadal shielding requirements?
shield reproductive organs when they are in or near 5 cm of a properly collimated beam
Gonadal shielding should be used:
reproductive age
children
pregnant patients front and back
Types of Gonadal shielding
Flat Contact Shields
Shadow Shields
Shaped Contact Shields
Shaped contact shields are worn by ________- and reduce exposure by ____%.
Males
90%
Flat Contact Shields absorb how much of the primary beam?
95%-99%
Lead equivalent for flat contact shields
1mm Pb
Flat contact shields are used by ______ and reduce exposure by _____%.
Females
75%
Where are shadow shields attached?
To collimator and is placed between x-ray tube and patient
When is exposure latitude wide?
Computed Radiography
Digital Radiography
Air Gap
reduced need for grid and will decrease exposure as much as 5 times
What are causes of repeat radiographs?
Dirty screens
Artifact
Incorrect projections
Positioning errors
Grid errors
Poor communication skills
ASRT supports gonadal and fetal shielding when shielding:
is safe and appropriate
reduces excess radiation exposure
increases patient comfort and confidence
Why have shielding recommendations changed?
risks of genetic effects are lower
shielding can interfere with AEC
it is difficult to shield gonads during certain exams
gonadal shielding may obscure important findings
improvements in technology have reduced absorbed dose to pelvic organs
a significant portion of dose to the ovaries is delivered by internally scattered x-rays that can't be blocked by shielding
NCRP No. 13 reevaluates
the effectiveness of gonadal shielding considering technical advancements in medical imaging and current scientific evidence and provides updated recommendations regarding gonadal shielding for the medical imaging community
aperature diaphragm
piece of flat lead with a hole in the center that attaches to the x-ray tube to confine the area of the beam
cones
circular metal structure attached to the x-ray tube housing to restrict the x-ray beam to a predetermined size
source-tabletop distance for fixed fluoroscopes
15 inches (38 cm)
source-table top mobile fluoroscope
12 inches (30 cm)