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when we speak density that refers to film or CR
when we speak IR exposure is that for film or CR
density relates to film
IR exposure deals with CR and DR
density is defined as the overall ______ (2 reasons)
degree of blackness from the metallic silver deposited in the film emulsion
and the amount of radiation that has exposed the IR
In the digital environment (DR) DENSITY can be expressed as ______
image receptor exposure
How is a CR/DR similar to an intensifying screen on a film
what is the difference
they both absorb xray photons and then produce light
the difference is that there is a delay between the xray exposure and the production of the light
how does CR work (general steps)
Take an xray on a cassette with only stimualible phosphor screen and now becomes an invisible latent image
next the cassette is run though a processing unit
it is scanned by a very small laser beam
when the beams strikes a spot it causes light to be produced
the result is the light that is produced is proportional to the xray exposure specific spot
Are brightness and desnity interchangeable
no
what is brightness
a monitor control function that can change the lgihtness and darkness of an image on a display monitor but it is not related to IR exposure
what is window level
describes the digital post processing that produces changes in brightness so it is also appropriate to use when controlling the display of an image
deals with darkness of the image
what is window width
contrast
does mas effect recorded detail
no
what is one of the photographic properties that comprise visibility of detail
density
what two properties allow us to view an image as visible
because of density and contrast
when dealing with film what is the best decision to make when justifying between excess and insufficient density
always choice the factors produce the darker image
if the density of your film is way to dark what must you adjust
cut mas in half to much mas was used
what causes quantum mottle
low mas and high kv
what are controlling factors
factors that affect radiographic density and IR exposure
what is the controlling factor of radiographic density(film)
mAs (millapere-seconds)
what happens to xray exposure as you increase mAs
xray exposure increases proportionally and radiographic density increases as well
Reciprocity law states what about film density
if density is unchanged on film as long as mas stays the same
if i took a knee xray at 60 kv @ 3.2 mas (80 ma .04s) what other ma stations could I use to get the same image
160 ma and .02s
or 60 kv @ 3.4 mAs
what percentage change in mas is necessary to cause a visible shift in density when using film and DR
25-35 percent of mas
what is the general rule of the thumb when changing mas
cutting mas in half or doubling it
when using DR what must we check to make sure we are exposing our patient properly
the s value number b/c DR systems like when you over expose the image the computer will rescale the image and make it appear acceptable to the human eye
what is the main influencing factor of radiographic density
kVp
what three things does kvp alter or change
contrast, the intensity(strength) of the beam and some scatter is produced
if your image is underexposed or too light what could you do to fix it
you could increase kvp or double the mas
what could you do to your image if it was exposed too much
decrease kvp
how does quantum mottle occur in CR and DR
underpenetration or underexposed
a visible change in density is usually detected with what percent change at low kv (30-50kv), 50-90kv 90-120kv
4-5percent
8-9%
10-12%
what is the 15% rule to compensate and maintain density
a 15% increase in kv causes a doubling of exposure to film
a 15% decrease in kv causes a halving of exposure to film
why do we need to use the 15% rule
to get a different scale of contrast (kv)
a increase in kvp will _______ contrast and an a decrease in kv will _______ contrast
decrease
increase
if you were using a single phase 2 pulse configuration would you need double the radiation or half of the radiation
double because the single phase is less efficient and needs more energy photons to create the same image
the closer the OID the _____ the IR exposure
the further the OID the _____ the IR exposure
more
less
when we decide to use large mA stations what happens to the focal spot
Does FSS deal with density
focal spot increases because the electrons are not easily contained (focused) in the focusing cup
No it deals with detail
when is the anode heel effect most noticeable
at short SID and Large IR size
(ex humerus on a wall bucky)
how do we take advantage of the anode heel effect
the thicker body part should be placed under the cathode end of the tube
whats SID aka
FFD focal film distance
can SID alter the intensity of the beam
yes
the density maintenance formula is based on what?
direct square law
if you double your SID from 40 to 80 using 10 mAs what is you new mas to maintain density
is patient dose increase or decreased
40 mAs
the distance is doubled so you increase Mas 4x
patient dose decreases
if you decrease the SID from 72 to 36 at 10 mAs what is your new mAs to maintain density
2.5mas
since the distance is cut in half you decrease mas by 4x
what would do to your mas once you increase your SID from 40-56-72
decreasing SID
double mAs from 40in SID to 56in and then double again if you are going up to 72inches
halve mAs
what is OID and does it affect IR exposure
object to image distance and yes
an increase in OID can _______ radiographic density and why?
decrease b/c the air gap between the object and IR is more so less photons will hit the IR reducing density
when using and SID ____ _____ radiation gets to the film and therefore causes a density difference when radiographing large patients
less scatter
can filtration(added coherent total compensating) affect radiographic density
yes b/c when you use a filter it gets rid of xray photons unwanted photons low energy there reducing IR exposure
what does beam restriction do (2 things)
reduces the total numbers of photons available and reduces the amount of tissue irradiated.
this reduces the amount of scatter produced and reduces overall density of the image
when restricting the beam to a 4x4 with no grid what is required to maintain image density
mAs compensation (double it) because collimating will underexpose the image
As tissue thickness increases what also increases and decreases
tissue density increases and radiographic density decreases b/c due to the thickness of the tissue less photons will hit the IR thus reducing IR exposure/density
what does radiolucent contrast due to density and why?
increase density because xray beams will penetrate right through since the contrast is radiolucent
what does radiopaque contrast do to density and why?
this contrast will decrease radiographic density because the contrast is absorbing the majority of the photons so less are hitting the IR reducing density
does additive pathology increase or decrease tissue density
does destructive pathology increase or decrease tissue density
decrease
increase
what happens to body part thickness once the tube is angled
if the angle is more than 15 degrees the tissue thickness increases therefor reduces density /IR exposure
what is used to calculate necessary changes in Mas when using grids
maintaining density formula with grid conversion factors
(must use 4x more mas)
what is the function of grids
do grids add density to the film
it improves contrast by absorbing scatter
yes and the more efficient the grid the less radiographic density
in film processing what three variables will increase density
developer solution temperature increases, immersion time increases or replenishment rates increase, concentration
what condition of the tissue require an increase of kvp
additive conditions because it makes the body part thicker denser which requires more penetration
what are some diseases that cause attenuation or additive conditions
pagets disease ostepetrosis acromegaly
hydro thorax
some cancers
empyema
what are decreased attenuation (destructive) conditions