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51 Cards in this Set
- Front
- Back
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how is the radiographic image formed
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by differential absorption of xrays
As a beam of x-rays penetrates the body, portions of the beam are absorbed by the patient while some of the x-ray beam passes through the body and strike the film thereby exposing it. The bony structures absorb more radiation than the soft tissue structures therefore less radiation interacts with the film beneath the bone. The areas of the film below the bone are exposed less and appear whiter than the film below the soft tissues which receive a higher radiation dose. |
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______ is the basis of the radiographic image.
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The differential absorption of the radiation by the body
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Areas of film exposed to more xrays are ________
(darker/ lighter) |
darker
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list the 5 basic radiographic densities in order of their density or what percentage of the x-rays will be absorbed by each (most radiodense to least radiodense)
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metal
mineral/ bone water / soft tissue fat air |
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the most critical part of film radiography is _______
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developing
- time & temp |
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what is the purpose of an intensifying screen
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1) decreases the number of xrays needed to expose a film (no sunburns)
2) needing fewer xrays allows you to take the image quicker an emulsion of crystals with paper backing. when a crystal is hit with an xray it will produce a set # of light photons (up to 100) which exposes the film with a lower quantity. so only about 10% of the film is exposed by xrays, the rest is exposed by the light from the intensifying screen. |
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the most critical part of processing an xray film is
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the development
- very time and temp depd |
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describe the processing of the film radiograph
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developer
- causes precipitation of metallic silver around this sensitivity spot if it has been exposed - TIME AND TEMP DEPD - MOST CRITICAL PART OF PROCESS rinse bath fixer - stop development process with acetic acid - clears film of all undeveloped silver crystals rinse - removes the chemicals - can rinse for hours drying - hardens the emulsion |
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True or False
The fixer removes all unexposed crystals |
False
the fixer removes all undeveloped crystals |
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if the fixer is weak, what does the film look like?
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cloudy radiograph
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What are the interactions of xray photons with matter
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classical (coherent) scatter
compton scatter photoelectric effect pair production photodisintegration |
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what is compton scatter
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an interaction of an xray photon with matter - creates fog
occurs at higher kVp provides no useful image info, just contributes to exposure an xray photon comes down and knocks out electron on outer shell of an object and will change direction (deflect the xray). that creates an ion that will get an electron back in (no big deal). the problem is that the path of this xray changes (gets scattered). once the xray changes its direction, it loses all info that is useful to you. - we rely on xray going straight down and creating a shadow pattern (it's either absorbed or not absorbed) - once it starts bouncing around, it just creates fog |
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which xray interactions with matter are impt for diagnostic xrays
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compton scatter & photoelectric effect
they are the only ones we care about in the diagnostic xray energy range (40-150 kVp) |
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photoelectric effect
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xray interaction with matter- results in better contrast/ better image quality
occurs at lower kVp results in higher patient exposure (capable of creating ionized atom, which if it is in DNA and isn't repaired correctly could be a prob) xray comes in and interacts with inner shell electron, knocks that electron out and is absorbed. you wind up with an ionized atom (that is a problem) |
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what is kVp
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the potential you put across the anode and cathode
quality (energy of xrays) and quantity |
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why do you care about the energy of the xray?
how do you change it |
higher energy = shorter wavelength = thicker object it can penetrate
by changing the kVp |
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what is mAs
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how much current is getting though the electrode (amt of xrays per sec)
quantity of xrays higher mA = higher voltage = more xrays but also more heat |
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exposure causes brightness or darkness
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darkness
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what technique is utilized to shoot a thorax
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lower mAs and higher kVp
b/c higher subject contrast (due to air and soft tissue) |
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what is the inverse square law
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if you double the distance between you and a radiation source, you cut the exposure by 1/4th
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You had 40" and 5 mAs setting but you don't have the space. how do you calculate your new mAs
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the closer you get, you have to decrease your exposure to get a good film
calculate new mAs by original mAs/new mAs = (original distance^2) / (new dist^2) |
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components of xray tube
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cathode
anode target housing tube housing focal spot rotor window 2 separate electrical units that operate different fxns low voltage circuit to the cathode high voltage circuit to anode & cathode |
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spatial resolution
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digital isn't as good at as film
the higher the spatial resolution, the closer that 2 objects can be together and be seen as separate |
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spatial resolution is limited by
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the digital matrix
need big matrix also need good technology to record latent image |
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Film or Digital
Which has better contrast resolution contrast resolution Which has better spatial resolution |
digital
film |
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the unaided eye can resolve how many line pairs per mm
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~ 10
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what is dicom
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digital image and communication in medicine
medical imaging std |
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xray tube - cathode
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2 separate electrical circuits
- low voltage circuit - high voltage circuit contains coiled wire filament - heating of filament controled by low voltage circuits - an electron cloud develops around the filament by a process called thermionic emission the focusing cup (metal shroud) focuses electrons to a specific point on the anode usually have 2 filaments - small filament used for low output exposures (where high detail needed) - large filament used for high output exposures |
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xray tube
describe the different fxn of the 2 filaments of the cathode |
small filament used for low output exposures (where high detail needed)
large filament used for high output exposures both filaments create an electron cloud by thermionic emission |
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xray tube - anode
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high voltage circuit
- applies voltage differential from cathode to anode - this high voltage is applied during the time of exposure the neg charged electrons are accelerated towards pos charged anode the ejection interact with the tungsten atoms to produce xrays |
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xray tube - anode design
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xray tube converts the kinetic energy of the accelerated e- into xrays
the majority of the kinetic energy of e- is converted to heat (99%) advancement in xray tube design has been the focus toward heat dissipation anode is made of Cu with tungstern insert called the target the focal spot is the area of the target where the e- beam is focused and the location where the xrays are produced |
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where in the xray tube are the xrays produced
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the focal spot of the target (tungsten) of the anode
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Name 2 causes of fog
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compton scatter
weak fixer |
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what are the factors affecting xray exposure
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mAs - quantity
kVp - quality (energy of xrays) & quanitity time - quantity distance - quantity |
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how do you get better contrast on a screen film
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lower kVp and increase mAs (increase photoelectric effect)
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when will the flow of electrons occur in the xray tube
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when the anode is + and the cathode is -
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full wave rectification
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using a circuit to keep the voltage potl applied to the tube always has the anode + and the cathode -
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what does increasing the kVp do
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increase avg energy of the beam
increase the # of xrays produced increase compton scatter |
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what does doubling the mAs do?
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double the number of xrays produced
can be doubled by doubling the time or by doubling the mA |
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_____ is the biggest factor in xray machine cost
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mA
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The inverse square law can be used to adjust radiographic technique following a change in focal film dist. The loss of xray intensity at increasing FFDs is a result of
a. Absorption of xray beam b. Attenuation of xray beam c. Divergence of xray beam d. Scatter of xray beam e. loss of energy of xray beam |
c. Divergence of xray beam
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The heel effect occurs b/c of
a. A + charge applied to the focusing cup forcing the e- toward the heel of the tube b. reduction in tube current to the filament due to high kVp techniques c. Using the small focal spot for high exposure techniques d. Xray absorption in the anode target e. The line focus principle resulted in less heat deposition in the target |
d. Xray absorp in the anode target
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Xray wavelength is
a. Directly proportional to freq b. Directly proportional to velocity c. Directly proportional to energy d. Inversely proportional to energy e. 60 Hz (cycles per sec) in the US and 50 Hz in Europe |
d. Inversely proportional to energy
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Which of the following processing chemicals are responsible for clearing the unexposed silver crystals from the radiographic film
a. Hydroquinone b. Ammonia thiosulfate c. Phenidone d. KBr e. Glutaraldehyde |
b. Ammonia thiosulfate
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The right kidney overlapping the left kidney creates what effect
a. remasking opacity b. hybird opacity c. silhouetting opacity d. summation opacity e. an analog image |
d. summation opacity
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which of the following would have the best spatial resolution
a. 100 speed cassette- screen system costing $400 per cassette b. DR plate costing $1200 per plate c. Direct exposure film costing $4 per sheet of film d. CR plate costing $2300 per plate e. 800 speed screen system costing $600 per cassette |
c. direct exposure film costing $4 per sheet of film
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if a radiograph turns yellow during storage, it is mostly likely the result of which of the following
a. developer retention b. incomplete washing c. radiation fog d. light leaks e. motion unsharpness |
b. incomplete washing
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Name some reasons for loss of radiographic contrast
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improper exposure
lack of fat compton scatter improper development (esp temp/ time) using weak fixer |
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xray wavelength is
a. directly proportional to freq b. directly proportional to velocity c. inversely proportional to freq d. inversely proportional to velocity e. increased with increasing xray energy |
c. inversely proportional to frequency
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a TL rad was taken at the following technique with proper exposure. 20 mAs & 72 kVp @ 100 cm using a 200 speed cassette. The dist was changed to 150 cm. What will be the new technique?
a. 45 mAs & 72 kVp b. 80 mAs & 72 kVp c. 9 mAs & 72 kVp d. 20 mAs & 60 kVp e. 20 mAs & 100 kVp |
a. 45 mAs & 72 kVp
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which of the following could be used to improve image contrast by reducing scatter radiation (choose all that apply)
a. use of a 10:1 grid b. change from 100 speed to 300 speed screen/ cassette c. collimate xray beam to area of interest d. double the mAs e. increasing kVp by 15% |
a. use of a 10:1 grid
c. collimate xray beam to area of interest |
