final Flashcards
what controls x ray energy?
KVP
what are INTENSIFYING screens used for?
to reduce patient exposure
difference between voltage ripple and x-ray energy?
inverse - as voltage ripple increases x ray energy decreases
lead screen on the back of the casette does what?
reduces compton scatter
for a compensating filter in a lateral lumbar spine radiograph?
filter up
xray production is slowed down due to an electromagnetic force field called
bremsstrahlung
at what point are xrays produced in the tube?
when electrons strike the anode (focal spot, target)
electron transition in tungsten that produces the highest energy xray?
P to K - characteristic 69.5 kEv
in lateral spine thoracic radiograph where is the anode?
down
what exposure factor controls the QUANTITY of xrays in the beam?
mAs
what factor is selected to select filament size (large vs small)
mA
which side of the radiograph exhibits the most blur?
cathode side
which has the greatest specific ionization alpha or beta?
alpha
define isotropic
360 degree emission
which is most likely to occur in human tissue direct or indirect effect?
indirect effect
what is the only similarity between particulate radiation and xray?
they can ionize
define the term ionize
when an electron is totally removed from an atom
xray tubes target is made of what?
tungsten
if a tube overload occurs what must be done to fix it?
decrease mA and increase time
how often must lead walls be replaced
NEVER
what does a rectifier do?
converts AC to DC current
what does an electromagnetic induction motor do
spins the rotor/anode target
what type of radiation can be stopped by a piece of paper
alpha
what is the charge on the focusing cup?
very negative
what is the difference between x ray and gamma ray
the origin gamma comes from nucleus - otherwise it is identical
where should anode for an AP thoracic spine film be
UP
primary parts of cathode
filaments large and small and focusing cup
ALARA
as low as reasonably achievable
which rectifier will provide the least radiation exposure to patient
high frequency (30% less)
compare the mass of an xray to an alpha particle
an xray has no mass - alpha particles have 4 AMU of mass
compare wavelengths of xrays to radio waves
xrays have shorter wavelengths
electrons travel from where to where
cathode to anode to make xrays
to double radiographic density you must
also double mAs
to double radiographic density using kVP
increase kVp by 15%
what is the controlling factor of radiographic density?
mAs
define linearity
the ability to manipulate mA and time and get the same mAs
define reproducibility
doing the exact same exposure over and over and getting the exact same results
relationship between frequency and wavelength
inverse
formula for heat units
kVP x mAs
what produces the majority of xrays in the xray beam
bremsstrahlung
optimum kvp for extremities under 10 cm
50-60
optimum kvp for spine imaging
70-90
two akas for SID
FFD and TFD
wave equation
speed of light = wavelength x freq
define LD 50/30
means lethal dose where 50% of exposed pop dies within 30 days
does a nonstochastic effect have a threshold?
YES (stochastic means random)
stochastic effect
does NOT have a threshold
males receiving radiation for ankylosing spondylitis experience increases in
leukemia
2 devices used to reduce compton scatter
collimation
bucky and compression band
lead lining in back of casette
hormesis
the notion that some radiation may actually be good for you
mutation that is unique to radiation exposure
none
relationship between SID and magnification
inversely related
two radiation induced malignancies
leukemia
thryoid, skin, bone, lung cancers
interaction with matter that results in inner shell ionization
photoelectric absorption
differential absorption of xrays by tissues results in this photographic property
contrast on xray film
one disadvantage to use of radiographic grids
increases patient exposure dramatically
improper or wrong SID used on focus grid, pattern of grid cutoff looks like
both sides are cutoff so the film is underexposed on both lateral edges
personnel dosimeter should be worn
on the collar or outside apron
annual whole body MPD for occupational exposure is
5 REM
MPD for pregnant occupational worker
0.5 REM over the gestation period
how are kvp and compton scatter related
directly, as kvp goes up compton scatter goes up
the shortest latent period of all cancers is
leukemia
dust on an intensifying screen results in
little white specks on the processed film
color safe light required to be used with rare earth film screen combos
RED
a red safe light is considered universal - state the name of the safelight
GBX
degree and direction of central ray angle used with a crosshatch grid
none
5 mAs required at 40 SID what is necessary at 80 SID to maintain density
20 mAs (distance doubled so multiply by 4x)
radiation that comes from the tube housing in areas other than the port
leakage radiation
level of fetal exposure below which no abortion is recommended
10 RAD (bushong 10-25 rule)
what is film latitude?
range of error
a long latitude film will respond to a wide range of useful _____
density
relationship of film contrast to film latitude
inverse
the writing on the safelight filter is placed where
away from bulb so it wont melt - 4 ft
what is film base made of
mylar
what is the film emulsion made of
silver halide crystals in gelatin
what are intensifying screens made of
rare earth crystals
minimum speed for spine imaging
400
film speed for detailed extremities
100
safelight bulbs should be this watts
15 or less
black tree branch artifact caused by
static
humidity to store films
40-60%
latent image
invisible image on the film before processing
manifest image
the visible image on film after processing
an occupationally exposed person’s own personal exposure if included in REM unit T/F
False
which is most likely to cause fog in an image
use of high kvp - creates longer range higher kvp goes further into range of compton scatter
grid that is designed so that strips coincide with the divergence of the xray beam
focused
image density can be DOUBLED by
inc kvp 15% and inc mAs by 100%
short scale of contrast wanted (high contrast)
decr kvp and incr mAs 2x
when OID is long it is more what kind of xrays produce image
divergent xrays produced
stochastic effect
requires no threshold of radiation exposure for effect to occur
linear non threshold
dose response relationship
non stoachastic threshold
requires a threshold to reach first
maximum permissible dose
max radiation dose would not be expected to produce significant radiation effect
what is the annual whole body MPD for occupationally exposed persons
5 REM
cumulative MPD old formula
5(n-18) n = age
new formula MPD
1X Age = 55 REM/year
on dosimeter report what does m mean
exposure received was so minimal it did not record
cardinal principles of radiation protection
time
distance
shielding
what allows a greater amount of weekly radiation exposure
controlled area - entire x ray room
max exposure rate of controlled area
less than 100 mR per week
max exposure rate of uncontrolled area
less than 10 mR per week
protective tube housing
must reduce leakage radiation to less than 100 mR/hour at one meter
SID indicator
must be accurate withing 2% of indicated SID
filtration
total 2.5 mm Al equivalent
PBL positive beam limitation
automatic collimation - must be accurate to within 2%
how often must film badges be sent in for processing
once every month
non-stochastic effects
erythema, cataracts, sterility
what factors influence the amount of effect produced by radiation
dose rate and area of body exposed
cells most sensitive to radiation
lymphocytes
law of bergonie and tribondeau
cells that are undifferentiated and rapidly dividing are more likely to be effected by xrays
major cell types at risk
embryonic
lymphocytes
erthyrocytes
sperm
women are more x ray resistant than men are T/F
true
acute radiation syndrome is relevant in diagnostic xray T/F
false
hematopoietic syndrome
200-1000 RAD whole body
GI syndrome
1000-5000 RAD whole body
CNS syndrome
over 5000 RAD
there is no UNIQUE radiation induced disease T/F
true
long term effects DO NOT occur in most irradiated individuals T/F
true
some ways to reduce exposure to patients
- aim beam at a primary wall that is not facing a waiting room
- collimate well each time
- gonadal shields
- set up patient correctly - high mA short time
- use high freq rectifier for xray
- use a high speed system
- only use the bucky when appropriate (>10 cm or >60 kvp)
- use compensating filters to assist
- long SID
- maintain equipment
- proper record keeping
as speed increase detail/sharpness
decreases
slow speed has little ___ and is more
divergence and blurrier bigger
black crescent moon shapes artifact are from
bending film
what is not a cardinal principle of radiation protection
kvp
radiation does not add up T/F
true - damage does
