Test 3 Unit 3 - Cont'd Flashcards
Power. Responsible for penetrating anatomy, responsible for producing scatter. higher=more scatter, more penetration.
kVp
radiation interacting with matter that travels in all different directions and has experiences loss of energy. Fogs an xray, leading to decreased contrast of the image. radiographic noise.
scatter
5 xray interactions with matter
Compton’s Effect, Photoelectric Effect, Classical Scatter, Pair Production, Photodisintegration
in the diagnostic energy range (40-150kEv), clinically significant interactions with matter
Compton’s and photoelectric effects
most of the scatter produced is this. xrays interacting with matter deflect off outer shell electrons of the material, lose energy, and change direction.
Compton’s Effect
the probability that an xray photon will scatter is contingent upon the….
energy of the xray and density of the object
xrays are absorbed. xrays lose all of their energy through an ionization interaction with an inner shell electron. causes differential absorptionof xray tissues, thereby producing subject contrast. The elctron has been absorbed causing white on the film.
photoelectric effect
As kVp increases, penetration and scatter_______
increase
What do high energy xrays tend to do?
pass through matter
What low energy xrays tend to do?
become totally absorbed
What do mid to high energy xrays tend to do?
scatter
The larger the subject ___________________
the more kVp needed = the more scatter produced
Xray absorption is also contingent upon…..
xray energy and tissue density
Absorption is most likely to occur when…….
the energy of the xray is equal to or slightly greater than the binding energy of the electron it interacts with
Greater energy will cause….
the ray to scatter or penetrate straight through
Increased absorption is due to
more dense tissues
results from low energy xrays interacting with matter
classical scatter (aka Coherent, Thompson, or Rayleigh)
These xrays have insufficient energy to cause ionization, but vibrate the atom. Vibrating electrons produce a summative xray with the same wavelength as the incident xray, but in a different dierction
classical scatter
occurs with xrays in the MeV (milivolt) range. It interacts with the nucleus and the energy is converted into matter in the form of two particles, a positron and a negatron. The two oppositely charged particles annihilate each other releasing 2 .51 MeV gamma rays in opposite directions
Pair Production
occurs when a 10 MeV xray invade a nucleus. The energy is absorbed by the nucleus and nuclear fragments are emitted
photodisintegration
Conditions that contribute to scatter radiation production
high kVp, thick soft tissue (water density), large field size
Scatter control methods for contrast improvements
optimum kVp, field size control (collimation), scatter-absorbing grids, air-gap technique, recumbent radiography
affects radiographic density and contrast
scatter-absorbing grids and air-gap technique
selective lead strip filter, placed between the patient and the film, designed to absorb scatter radiation. Gustave Bucky in 1913
scatter absorbing grids
Were are grids installed?
inside the front cover of the Bucky
When is a grid used?
when the patient part measures greater than 10 cm or when using techniques above 70 kVp
how well the grid cleans scatter
grid ratio
To reduce scatter radiation, the scatter radiation enters the lead strips…
at an angle where it is absorbed and does not reach the film.
Some xray photons, having interacted with the patients body…
change direction, loose energy, and have the potential to reach the film entering from a different direction which degrades the quality of the image
the orientation of lead lines follow a ….
linear, cross hatched, or rhombic cross hatched pattern
What is the grid made of?
very thin lead lines separated by thin strips of aluminum or carbon fiber
two types of linear grid
parallel and focused
the lead lines are parallel to each other across the grid plate creating an infinity focus.
parallel grid
Because the xray beam diverges from the focal spot, parallel grids typically produce images with reduced exposure on the sides called _______.
grid cutoff
Peripheral cutoff of exposure. Grid cutoff appears as underexposure on film.
Parallel lead lines ( we don’t use)
grid specifications
grid ratio, grid frequency, grid radius, grid focal range
Grid ratio
is the measure of the height of the lead strips divided by the distance between them. h/d
the higher the grid ratio, the _________ the contrast
higher
common chiropractic grid ratios
8:1 and 10:1 and 12:1
12:1
focused grid used with a single phase generator
10:1
focused grid used with a high frequency generator
a measure of the number of lead lines per inch or centimeter the more present the less grid lines on the film but patient does increases
grid frequency
every focused grid is manufactured to a set distance
grid radius
the set distance without a significant amount of peripheral cutoff
grid focal range.
xray outside the range _________ peripheral cutoff
increases
removing scatter = _______ film density
reduced. removing gray layers which affects the overall darkness of the film.
decreased collimation = ________ density
decreased
scatter results from….
primary xray interacting with matter
smaller field size = ______ scatter
less. because less primary xrays are interacting with tissues
using smaller films and tight collimation
spot filming
if the patient part is moved a short distance away from the film, some of the scatter radiation exiting on the film side of the patient will miss the film
air-gap technique (not diagnostic)
air gap technique produces a ______ scale contrast
shorter 10” gap maximum
recumbent radiography
laying patient down decreases the diameter of the patient which allows for less kVp=less scatter. also helps stabilize a patient
not often used in chiropractic. stretched across bucky to compress abdominal tissues with the patient in an upright position
compression band
used to cover areas of film on film cassettes where multiple exposure are made on a single film
lead vinyl blockers
