minimizing exposure to the patient Flashcards
what 2 things does EfD incorporate?
effect of the type of radiation (EqD)
variability in radiosensitivity of the organ or part irradiated
define risk (general term)
the probability of injury, ailment, or death resulting from an activity
defin risk (medically, ref to radsci)
the possibility of inducing a radiogenic cancer or genetic defect after irradaition
what is a willingness to accept risk
the perception that the potential benefit if greater than the risk involved
with whom does the responsibility for ordering a radiologic exam lie with?
the ordering or referring physician
what are 2 reasons for which a patient would elect to assume risk
essential diagnostic information of illness or injury
health screening purposes
name 4 benefits of effective communication
- reduces anxiety and emotional distress
- enhances professional image, as caring
- increases the likelihood for cooperation
- reduces repeats due to poor communication
when is communication between radt and pt effective? (3)
- verbal and nonverbal are understood as intended
- demonstration of respect for dignity and individuality
- clear, concise instructions
what are the two types of pt motion
voluntary and involuntary
how can pt exposure be reduced in regards to motion
use proper body part immobilization, or motion reduction techniques
what accuracy must be obtained with distance and centering
distance - 2%
centering - 1%
to reduce dose, the SOD must be ____
as large as possible
what is the minimum SSD
30cm or 12 inches
what is SSD
source to skin distance
what is the general distance used for mobile radiography
100 cm
sometimes 120cm
what is the dose advantage of imaging PA?
reduction of dose to gonads, breast tissue, thyroid
why would you maybe not use a PA position
if AP is needed for demonstration
for comfort
pt might not be able to move/perform PA
name 4 x-ray beam limitation devices
light-localizing variable-aperture rectangular collimator
aperture diaphragms
cones
cylinders
what are the 2 major advantages to beam limitation
- significant reduction in pt dose (scatter is reduced)
- improves image quality
every ____, _____ checks collimation and ___ ____ _____
year, SC35, light beam congruency
what is the purpose of radiographic beam filtration
to filter out (absorb) the low energy photons, which are the most harmful
what are the 2 types of filtration
inherent and added
what is the most common material used for filtration?
aluminum
what is a HVL?
half-value layer is the thickness of an absorber required to dec the ea, by 50% of it’s initial value
in what units is HVL expressed in
mm of aluminum (generally)
how often is HVL measured?
yearly
what are the 2 most common filter materials for mammographic equipment
molybdenum and rhodium
what do compensating filters do
partially attenuate x-rays directed towards thinner/less dense areas
what are 3 types of compensating filters
wedge filter
through/bilateral wedge filter
boomerang
what is the function of a radiographic grid
to absorb scatter
what grid ratio is used for <90 kVp
8:1 is satisfactory
what grid ratio must be used for >90kVp
more than 8:1
what 4 grid mistakes can create grid cutoff
off-level
off-centre
off-focus
upside-down
how often is grid performance checked
yearly
what lead equivalent is required for gonadal shielding
0.25mm
what protects patients and staff from radiation leakage
lead-lined metal diagnostic protective tube housing
what is the threshold for the leakage limit
at 1mm from source, leakage does not exceed 1mGya/hr aka 100mR/hr
when tube at highest voltage & current
how can IR sensitivity reduce dose?
higher sensitivity required less ra<dilation, and thus creating less dose
what is the minimum SSD for mobile fluoroscopy units
30 cm, 12 inches
what is the minimum SSD for stationary fluoroscopy units
38 cm, 15 inches
in fluoro, smaller the imaging mode:
(more/less) magnification
(more/less) pt dose
more magnification
more dose
intermittent/pulsed fluoro (inc/dec) pt dose
decreases, especially in long procedures
what does a cumulative timing device do? (in fluoro)
sounds an alarm every 5 minutes, bringin awareness to dose
what type of switch MUST fluoro machines have
dead-man switch
what is the minimum source-to-end of collimator assembly in mobile C-arm
30 cm, 12 inches
where is the C-arm tube ideally positioned?
under the patient
with mobile C-arm, why is under the pt the best position?
scatter radiation is less intense (absorbed by table)
what does ESE stand for?
entrance skin exposure
what is ESE
a measurement of radiation output at the point of skin entry for common x-ray examinations
what is the unit ESE is measured in?
C/kg, mR, mGy
how often should ESE measurements be performed
at least semi-anually, or each time the equipment is serviced
what may need to be updated after ESE measurements are taken
the radiographic technique chart
what is the calculation for ESE
ESE = mR (or mGy) x (SCD/SOD)^2
what is SCD
source to chamber distance (dosimeter)
