Test 1 Flashcards
The x-ray beam can be divided into what two portions?
Primary beam and remnant beam
Radiation emitted by the x-ray tube that has not yet passed through the patient
primary beam
radiation that emerges from the body tissues behind the patient or object and strikes the IR
Remnant
What part of the beam is the image-forming radiation
Remnant
radiation that moves in random directions
scatter radiation
Primary x-rays diverge _______, that is they fan out evenly as they travel toward the object being radiographed
isotropically
what part of the x-ray beam is not divergent
central ray
The precise center of the x-ray beam which lies perpendicular to the axis of the x-ray tube above
central ray
SID
source to image distance
How is SOD measured
From focal spot to the upper surface or entrance surface of the body or object
OID
Object to image receptor plate
How is SID measured
From the focal spot to the image receptor
SOD
Source to object distance
what are the 6 radiographic variables
- technical
- geometrical
- patient status
- Image receptor systems
- image processing
- viewing conditions
what variable includes all electrical factors such as the generator kVp and mA
technical variables
what variable includes carious distances (SID, SOD, OID), the angles and alignment of the x-ray beam, part of interest, and image receptor.
Geometrical variables
What variable includes general condition of the patient and the diseases or interventional changes that further alter the quality of the final image.
patient status
what variable includes all devices which alter the condition of the remnant beam after it has passed through the patients body, such as grids, tabletop and cassette materials
image receptor systems
What variable includes chemical processors and computer software programs
image processing
what variable includes lighting, view boxes, and computer screens
viewing conditions
What 3 types of interactions do x-rays have with a patient
- photoelectric
- Compton
- cohert
the interaction where the x-ray beams are completely absorbed by the patient tissue
photoelectric effect
the photoelectric effect is primarily responsible for the production of _____ contrast
subject
When atoms lose their electrons, they are considered _____
ionized
The photoelectric effect only occurs when the energy of the incoming x-ray photon is _____ ______ than the binding energy for the inner shell electron.
slightly higher
What effect takes place when only some of the x-rays are absorbed, and the left over is re-emitted as a new x-ray photon which scatters in random directions.
Compton
What are two other names for Compton effect
- modified scattering
2. incoherent scattering
The scatter radiation caused by the Compton effect are considered ____ photons
new
the rejected electron in a Compton effect is known as a
recoil electron
True or false: scattered x-rays can be emitted backwards, directly toward the incident beam
true
Radiation emitted from the patient that comes back toward the incident beam
backscatter
Scattered radiation carries the _____ from the original x-ray
energy
what does scatter radiation do to a radiograph, and what does it destroy
degrades the image, destroys subject contrast
what percent of scatter radiation is from the Compton Effect
97%
what percent of scatter radiation comes from the Coherent Effect
3%
When the incoming x-rays is less than the binding energy of the electron what effect will take place?
Coherent Scattering
are the atoms ionized in coherent effect
no
what two interactions can occur during the coherent effect
Rayleigh, and Thompson
what interaction is taking place when an entire atom is raised to a state of excitation for a brief moment
Rayleigh
The partial absorption of the x-ray beam
Attenuation
What three factors affect attenuation in a patient
- thickness
- density
- atomic number
The subtle differences in attenuation between all the carious tissues and parts of the human body
differential absorption
All of the different attenuation have a collective effects upon the remnant x-ray beam called _________ _______
subject contrast
The greater the x-ray attenuation of a tissue with relation to adjacent tissue, the _____ the subject contrast
greater
_____ _____ in the primary beam causes magnification and distortion of structures within the image
isotropic divergence
what effect is considered the “all-or-nothing” absorption of x-rays
photoelectric effect
_____ is responsible for subject contrast in the _______ image. and scattered radiation tends to destroy subject contrast in the ____ ______
photoelectric, radiographic, remnant beam
Compton effect occurs when the x-rays are much ____ than the energy of the electrons
higher
The latent image or signal is carried to the receptor by the ____ x-ray beam
remnant
The only nondiverging ray in the primary x-ray beam is the
Central ray
Positioning of the patient actually falls under what category of radiographic variables
geometrical
Even after the radiographic image is processed and stored, what other type of variables still can alter its quality
viewing conditions
microscopic white spots are produced in the image by which interaction
photoelectric
The ideal conditions for the photoelectric effect to take place are created when the average kV of incident x-ray photon is _____ _____ than the inner shell binding energies of tissue atoms
slightly higher
which of the two major interactions can occur in a series within the patient from a single x-ray photon
compton
in terms of the quantity of radiation scattered in each direction from the CR, where is the worst place for a radiographer to be standing
At a reverse oblique angle from the direction of the CR
within the remnant x-ray beam, scatter radiation forms a type of image ____ which is always destructive
noise
Thompson and Rayleigh scatter photons have the same ____ but a different ______ from the original x-ray photon
energy, direction
why doesn’t characteristic radiation produced withing the patient affect the image signal at the receptor plate
It has too low of energy to escape the patients baby
adjust radiographic technique by a factor of 2 for every ____ change in body part thickness
4cm
what other two aspects of body tissues, besides thickness affect x-ray attenuation
density, atomic number
when x-ray beam penetration is matched properly to the differential absorption of the tissues, every radiographic image detail should be depicted as a ______
shade of grey
______ of x-ray beams in tissueshelps create subject contrast
attenuation
the ratio of x-ray attenuation between two adjacent tissues
subject contrast
For ____ tissues x-ray attenuation increases
thicker
x-ray attenuation ______ in direct proportion to the physical density of tissue
increases
The subject contrast of the image is carried by the ____ x-ray beam and is reduced by _______ radiation
remnant, scatter
high levels of kVp cause less ______ effects to occur and more ______ effect
photoelectric, compton
______ densities are lost when ____ is too high
light, kVp
the greatest subject contrast is achieved when high atomic number tissue is combined with ___ kVp
low
Define subject contrast as it pertains to the remnant x-ray beam reaching the image receptor
Subject contrast is the difference in x-ray intensity between different portions of the remnant beam, (which constitute a latent image or signal).
of the three types of x-ray interactions that occur within the patient, which ones contribute to subject contrast in the image carried by the remnant beam
all three of them
of the three aspects of a tissue, which one has a proportional relationship to x-ray attenuation
density
of the three aspects of a tissue, which one must be altered most dramatically to cause a substantive change in subject contrast
density
atoms with high atomic number are more likely to absorb x-rays because of their high ____ density
electron
scatter radiation reduces subject contrast because it adds an _____ amount of exposure to all local area of the image
equal
As kVp is increased, which way and by how much does the occurrence of the Compton effect change
Occurrence of Compton interactions decreases, but only slightly
ultimately, the subject contract in the image carried by the remnant beam is dependent not upon the raw number of the different x-ray interactions, but on their _____ in contributing to the image
Proportions
Changes in the energy of the x-ray beam is controlled by?
kVp
as kVp is increased _____ penetration is achieved
more
Is Compton interaction affected by kVp
slightly
What interaction become more prevalent at higher kVp
Compton
Penetrating x-rays produce the ____ and ____ areas in the image
black, darker
what produces the whites and lighter areas in the image
photoelectric interactions
what produces the black and darker areas in the image
penetrating x-rays
what lays down a blanket of fog at the image receptor
Compton scatter
when higher contrast is wanted _____ kVp is used
lower
What 4 components of an image may affect its visibility
brightness, intensity, contrast, and noise
Most radiographic images are inherently _____ images
negative
the divided ratio between the brightness of two adjacent details
radiographic contrast
the range of brightnesses
gray scale
what is considered to be the opposite to contrast
gray scale
what should be adjusted first contrast or brightness
contrast
anything that obscures the visibility of an image
noise
what are the 5 noise factors
material, quantum mottle, off-focus radiation, electronic and algorithmic deviations, exposure artifacts
what are the three visibility components of any image
brightness (density), Contrast (gray scale), noise
the best amount of brightness or contrast to have in any image is an _____ amount
intermediate
what is the radiographic opposite of image contrast
gray scale
List three examples of different types of noise in an image
Any three of the following: Quantum mottle, receptor mottle, fog, exposure artifacts, patient artifacts, receptor artifacts, processing artifacts, electronic noise (snow), etc.
To ensure that every image detail within the anatomy of interest is depicted as a shade of grey, producing sufficient gray scale in the image, x-ray beam ____ must be sufficient
penetration
noise is broadly defined as anything that obscures the ____ of an image
visibility
a short gray scale indicates ____ contrast
high
the use of grids to reduce scatter radiation is an example of changing what portion of the SNR
noise
increasing the kVp at the console is an example of changing what portion of the SNR
signal
in the digital age, ____ has exceeded scatter radiation as the most common form of noise appearing in the final displayed image
mottle
measures the rate of electricity flowing through the x-ray tube, and controls the rate of x-rays emitted from it
mA
when the filament is heated to the point that a cloud of electrons is formed
thermionic emissions
the product of exposure time and mA
mAs
what controls the total amount of x-rays delivered from the x-ray tube during the exposure
mAs
mA and exposure time are _____ related to each other
inversely
what is the preferred controlling factor for total exposure
mAs
a ____ focal spot should be used to maximize image sharpness
small
which can result from insufficient mAs
quantum mottle
True or false: the mAs does not affect the average energy or penetration characteristics of the x-ray beam
true
Is mAs considered a factor in controlling subject contrast
no
What exposure factor would you change if the patient keeps moving
shorter exposure time
strictly speaking, mA is a unit which measures
The flow rate of electricity
give two reasons why mAs should be considered as the prime factor in controlling x-ray exposure
1) It is directly proportional to exposure
2) It affects only the exposure level
The mAs does not alter subject contrast in the remnant beam because it does not change the ____ or different types of interactions occurring within the patient
Proportion (percentage)
for what type of radiographic procedure would a low mA and long exposure time be needed
Tomography including autotomography (breathing or wagging-jaw techniques)
insufficient mAs can cause the appearance of _____in the image
quantum mottle
generally short exposure times are desirable to minimize the probability of ____
motion
x-rays are _____ (not all the same)
heterogeneous
x-rays give off ____ when they go through matter
heat
short gray scale = ____ contrast
high
quantity of x-rays
mAs
quality of x-rays
kVp
the amount of radiation that strikes the image receptor
receptor exposure
You use 10 mA and 0.5s for your first exposure. For the 2nd exposure you want to use 0.1s. What would your mA be?
10mA(.5) = 5mAs
xmA (.1) = 5mAs
XmA = 5/.1 = 50 mA
what is the purpose of the 15% rule
to reduce patient dose while keeping the final image factors the same
what is quantum mottle caused from
not having enough x-rays (low mAs)
What charge does the cathode have
negative
what charge does the anode have
positive
what 3 things do you need to have to make an x-ray
a source of e-, a way to accelerate e- and a way to decelerate e-
what are filaments made out of
Tungsten
What is the purpose of the focusing cup and what charge does it have on it.
the focusing has a negative charge. The negative charges of the e- repel each other, they then repel away from the focusing cup which refocuses them
what are the three main function of the anode
electrical conductor, thermal dissipater, target
Calculating cool down
If you did an exposure with the factors of 90kVp, 200 mA, and .25s and you took three exposures how do you calculate the heat
1.4(kVp)(mA)(s)(# of exposures)
1.4(90)(200)(.25)(3) = 18900
You would then use the graph to find the minutes and subtract the minutes on the graph from the largest amount of minutes
kVp increase both the ______ and the _____ of the x-rays
quantity, energy
kVp should be set so that there is _____ penetration through all tissue
partial
No amount of ____ can ever compensate for insufficient kVp
mAs
subject contrast in the remnant x-ray beam depends on the level of _____
kVp
for the 15% Rule of thumb when you increase your kVp by 15%, what will happen to mAs
it will be halved
kVp has no direct impact on what three geometrical aspects of the image
sharpness, magnification and distortion
The most important function of kVp is to produce sufficient ____ of the x-ray beam
penetration
what electronic device is controlled by the kVp setting at the x-ray machine console
The autotransformer
why is higher kVp, rather than higher mAs, particullarly recommended when changing from the AP projection of the lumbar spine to the lateral L5-S1 spot view
There is a greater bone-to-soft tissue ratio in the lateral pelvis
does scatter radiation cause blurring of the image
no
Suppose you reduce the kVp by 3 steps of 15 percent each. Even though you doubled the mAs three times, the radiograph may still turn out underexposed because of
Insufficient penetration through the anatomy
radiation that is produced when electrons are deflected to other pars of the x-ray tube outside the focal spot
off-focus
what is responsible for ghost images at the edges of a collimated field
off-focus radiation
true or false: off-focus and scatter radiation are the same thing
false
to allow for inaccuracies in field light alignment, always allow ___ cm of field light beyond each edge of the anatomy of interest
1cm
excessive field size reduces ______ ______ in the remnant beam
subject contrast
what are the two purposes of reducing field size
1) Improve subject contrast in the remnant beam signal, 2) reduce patient dose
how does collimation affect the concentration or intensity of the primary beam
It has no effect on it
why is a secondary set of shutters or second aperture in a collimating device desirable
To absorb off-focus radiation
where is off-focus radiation produced
In the x-ray tube, but outside the focal spot
what does PBL stand for
“Positive-beam limitation”
it is acceptable to override an automatic collimator in order to
Collimate the field size smaller than the image receptor plate size
if anatomy of interest is clipped from a view due to overzealous collimation, how much is patient exposure increased for that view upon repeating it
100% or double
the anode disc is spun at high speeds to do what
disperse the heat
why must an x-ray tube be vacuumed of all gas
Air molecules impeded some of the projectile electrons from reaching the anode.
what is the approximate efficiency of x-ray production by an x-ray tube
0.5%
what type of x-ray tube uses a wire mesh to hold back space charge
A grid-controlled tube
name 3 things that happen during bucky radiography when the rotor switch is depressed
1) The filament is brought up to full temperature, 2) the rotor spines the anode disc,3) the bucky grid mechanism is engaged
name the process that provides a source of free electrons in the x-ray tube
Thermionic emission
what is the focusing cup usually made of
Molybdenum or nickel
what element is added to the tungsten filament to extend its life
Thorium
what element is added to the tungsten focal track to help balance the spin of the anode disc
Rhenium
The copper anode cylinder in the tube and the stator windings outside the tube, together form a
Induction motor
why are high mA stations not accessible when the small focal spot is engaged
Focusing a large amount of electrons on a very small focal spot would overheat the
anode focal track.
as an x-ray tube ages, the effective mA produced at the filament ____
increases
what is the cause of pits or melts on the anode surface
Failure of the rotor motor or ball bearings to spin the anode
why does focal spot blooming occur at high mA stations
An increased number of electrons in the space charge cloud results in them repelling each other farther away.
