study this Flashcards
2 examples of inherent filtration
glass envelope
tube window
metal housing
immersion oil
what occurs when you have a low kV
high gray scale
(high kV/voltage= low contrast= more shades of gray)
(low kV/voltage= high contrast= less shades of gray
inverse square law, if distances is doubled from 8 to 16, what is the new intensity
1/4
by using adjustment tools such as edge enhancer, you can stimulate illnesses and abnormalities to show that are actually not there
yes
too much info on computer can cause
not function properly
which of the following has most biological affect
direct or indirect
indirect 2/3
direct 1/3
XR photons absorbed by H2O-> free radicals-> biological damage
indirect
outcomes: repair, mutation, death
directly ionizes biological macromolecules
direct
- lethal dna damage
- cell death
- ex: xerostomia, acute radiation syndrome, erythema, fetal development
HAS threshold
severity is proportional to dose
deterministic (dose based)
- sublethal dna damage
- gene mutation
- replication of mutated cells
- examples: leukemia, thryoid cancer
- NO threshold
- severity of effects DOES NOT depend on dose
stochastic (frequency)
genetic mutations cause malignancy to what cells
somatic cells
genetic mutations cause heritable effects to what cells
germ cells
what factors modify effects of xradiation
- decrease age (pediatric pts at risk)
- increase dose rate
- increase total dose
- increase oxygen
- cell type and function
what stage of acute radiation syndrome is non lethal
prodromal period
<2 Gy
what is the most lethal stage of acute radiation syndrome
CNS/CVS
>100 Gy
what stage of acute radiation syndrome is lethal 2-8Gy?
what is supralethal >8Gy?
lethal: hemiatopietic
supralethal: Gastrointestinal
what is the effect of radiation on
mucosa
teeth
salivary gland
bone
muscle
mucosa: mucositis, 2 degree infection
teeth: radiation caries and underdeveloped teeth
salivary gland: xerostomia
bone: osteoradionecrosis
muscle: fibrosis
what kind of radiation causes radiation caries
indirect
what are
occupational limits
non-occupation limits
pregnant limits
occupational limits: 5 rem or 50mSv
non-occupation limits: 0.5 rem or 5mSv
pregnant limits: 0.5 rem or 5 mSv (9 months)
.1rem or 1mSv (1 month)
what kind of xrays do you take on pregnant patients
only take xrays during emergency circumstances
examples of background radiation
radon
cosmic
terrestrial
internal
what cancers have the highest risk for dental radiograph exposure
thryoid and leukemia
where should you stand when taking xrays
6 feet away, behind barrier, 90-135 degree from beam
primary reason for taking water’s skull xr
see the maxillary sinus
(chin is up)
SLOB rule, move tube mesial and object also moves mesial
lingual
what comprises the inverted Y
nasal cavity floor and maxillary sinus
which of the following provides the best protection against radiation
thyroid collar
when tooth is not parallel to receptor, and beam is directed perpendicular to receptor
foreshortening
when tooth is not parallel to receptor and beam is perpendicular to tooth
elongation
if you shorten source to receptor what happens
a. increases sharpness
b. decreases magnification
c. decreases sharpness
d. increases magnification
c and d
what ionization has the most effect
compton scattering
photoelectric
coherent
compton- most common
57-62%
-can ionize multiple
-interacts with outer shell electron
-xr photons continue in diff directions with less energy creating scatter until all energy lost
compton scatter ionization
-only ionizes
-absorbed by inner shell electron
-collides and loses energy
photoelectric
-excites but does not ionize
-xr photon of low energy interact with outer orbital electron and change direction but no photoelectric produced
coherent
lady has colon cancer and thus had radiation. however, her 2 kids are at increased risk. this affected
germ cells
what is the most lethal part of hematopoetic syndrome
sepsis
the effect only seen in the person effected, NOT future generation generations
somatic
by federal law, a signal and light are required on every xray unit
true
how many Gy needed for treatment of
solid tumors
lymphomas
intraoral cancer
solid tumors 60-80 Gy
lymphomas 20-40 Gy
intraoral cancer 50 Gy
operating kV listed below, what size of filtration do you need
<50=
50 to 70=
>70=
<50= 0.5mm
50 to 70= 1.5mm
>70= 2.5mm
full time xray operator needs to have what on their person at all times
dosimeter
personal monitor device
in x-radiation, absorbed dose is ______to equivalent dose
equal
equivalent dose Ht= QF of 1 x absorbed dose Dt
in x-radiation, absorbed dose is _____ to the effective dose
less
effective dose E= sum of absorbed dose Dt X Wt (tissue weighing factor)
what happens when you increase mA
increase density (and increase # of photons)
alpha particles have _____charge and a _____ LET than a proton
larger
larger
aplha +2 (high LET)
beta +1
beta -1
neutron 0
electron -1
proton +1
xray NO CHARGE (low LET)
this reduces the amount of scatter radiation exposing film (and improves contrast)
grid
(image inhancer)
radiograph sensor sizes
0= pediatric
1= anterior PA, pediatric BW
2= adult PA, adult BW, pedi occlusal
3= not used, longer BW
4= adult occlusal
what does rectifier do
converts AC to DC
(convert alternative current to direct current)
AND
moves from cathode to anode
multiple line ruler picture that shows
quantitative image analysis
if you increase tube voltage, it will _____the x-ray quantity and _____the quality
increase
increase
otto walkhoff
first dental radiograph
what occurs if images are compressed on computer and there is no space
decrease in storage
what does atomic number measure
protons
alpha particles have a ____LET, which means it has a ____mass and a ____velocity
higher LET
higher mass
lower velocity
what does tungsten target do
transform the kinetic energy of the colliding electrons into x-ray photons
what do you do to increase magnification
BAD, dont want this
decrease source to object length
or
increase object to receptor length
what would increasing the sensor to object distance and decreasing the object to receptor distance do?
minimize magnification
what is the probability of occurence
stochastic (frequency)
what is the interaction of xray with matter called___radiation
ionizing
what is the indirect x-ray photons absorbed by to create free radicals
water
what are examples of threshold effects?
this is deterministic
xerostomia
erythema
cataracts
fetal development
as the oxygen content ____, it ____in the sensitivity
increases
increases
what two things are important factors in radiosensitivity
younger age and increase of oxygen content
increase total dose
increase doe rate
cell
area exposed
cell type and function
what is the max radiation dose of a pregnant dental hygienist
5mSv
what is it called when you do whatever you can to reduce the radiation dose
ALARA
ALADA- as low as dx possible
if operating kV is equal to 70 and the aluminum filtration is 1.5mm, what needs to occur?
nothing needs to occur because kv of 50-70 is adequate with aluminum filtration size of 1.5mm
kV <50 .5mm
50-70 1.5mm
>70 2.5mm
what is the most effective way to reduce the dose
recessed x-ray tube
a. xray tube head (mandated)
b. filtration (aluminum filter)
c. collimation (lead)
another question about effective way to reduce something
speed of sensor (want quicker)
where do you want to place the bacscatter shield at
at the end of the PID(closest to patient)
what do you do with new patient that has a lot of things done to them. what dental radiographs do you use?
full mouth series
what occlusal radiographs do we use
PSPP
cross sectional has ____ posterior coverage and ___angle
more coverage
less angle
what occlusal radiographs do we use
film and PSPP
secondary photons resulting in image degradation when doing extraoral imaging
what is the point of waters radiograph
see the maxillary sinus
