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98 Cards in this Set

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Who discovered X-rays?
Wilhelm Conrad Rontgen
In 1895
What is the difference b/w an X-ray and a gamma ray?
X-rays are produced outside the body and gamma rays are created from atoms within the body
*How are x-rays produced?
When high speed electrons strike a metal target.
*What are the 3 key requirements for x-ray production?
1) Cathode electron source
2) Method to accelerate electrons
3) Anode target
*How are electrons produced at the cathode?
Electricity passes through a Tungsten filament and the filament becomes hot and releases electrons in a surrounding cloud
*What tightens the electron cloud produced at the cathode?
The focusing cup tightens the cloud, it's negatively charged therefore repelling the electron cloud=tightens cloud
What determines if there is a large or small focal spot when taking an x-ray?
Whether using a large or small Tungsten filament in the cathode
What is the mA control on an x-ray machine?
Milliamps- the strength of the current that passes through the Tungsten filament
What happens to the size of the electron cloud when the mA is increased?
Stronger the current the larger the electron cloud
True or false. The Tungsten filament is an important part of the anode.
False, the filament is part of the cathode
*What method is used to accelerate the electrons produced by the filament?
The voltage difference b/w the cathode and anode
Cloud of electrons at cathode is attracted to the anode (positively charged Tungsten target)
*What regulates the voltage difference b/w the cathode and anode in an X-ray machine?
kVp
How does the energy difference b/w the anode and cathode affect the energy of the x-ray?
Higher difference=higher energy
Higher energy=higher velocity e-
Higher velocity e-=higher energy X-rays
Why does the anode rotate?
To dissipate the heat produced from the electrons hitting the anode
*What are the 2 major types of electron interactions that occur with the tungsten at the anode?
1) Characteristic X-ray generation
5% of x-rays of diagnostic imaging
2) Bremsstrahlung radiation
95% of X-rays in diagnostic imaging
True or false. The Bremsstrahlung radiation is responsible for 85% of the X-rays used in diagnostic imaging.
False, 95%
When are X-rays actually generated?
Once the electrons hit the Tungsten-get the characteristic X-ray generation and Bremsstrahlung radiation
What produces characteristic X-rays?
The electron produced at the cathode of the x-ray tube ejects an orbital electron from the K shell. The outer shell electron of a higher energy fills the void of the inner shell and the difference in energy levels is emitted as an x-ray photon.
* True or false. Characteristic x-rays result in a broad, continuous range of x-ray energies.
False, x-rays of specific energy are released
*What does the energy of a characteristic x-ray depend on?
The material-the differences o binding energies b/w the orbital electrons.
*What produces Bremsstrahlung radiation?
Fast electrons approach the nucleus of the Tungstenand slow as it loses energy, this energy is emitted as x-rays
(e- close to nucleus=very slow=higher energy x-ray
*True or false.Bremmstrahlung radiation results in a broad, continuous range of X-ray energies.
True
What does the energy of Bremsstrahlung radiation depend on?
How close the electron gets to the nucleus
The maximum energy of the Bremsstrahlung radiation continuum is equal to what?
kVp
At what energy do you see the Characteristic radiation peaks on a graph of number of x-rays vs energy? why?
2 at about 60-this is the energy released by the k & L shell of tungsten
*What are the 3 results of increasing the kVp?
*1) Higher energy x-rays
2) More electrons from cathode accelerated to anode
*3) More X-rays
*What are the 4 interactions of x-rays with matter?
1) Coherent scatter
2) Photoelectric effect
3) Compton scatter
4) None (goes straight through)
True or false. Coherent scatter degrades image quality.
True
What is coherent scattering?
A photon interacts with an object and changes direction
-No absorption of photon
-No ionization
-X-ray looses no energy
Which x-rays undergo coherent scatter?
Very low energy x-rays
True or false. Coherent scatter is the source for most occupational radiation.
False, Compton scatter is the source of most occupational radiation
True or false. The amount of x-rays that undergo Coherent scatter is only 5%.
True
*What is the biggest contributor to radiographic contrast?
Photoelectric effect
*What is the photoelectric effect?
X-ray energy is completely absorbed (by the patient)
*The probability of a photoelectric interaction is directly proportional to what?
Z^3
Z=atomic number
How does the photoelectric effect result in contrast?
Small differences in atomic composition of neighboring tissues lead to big differences in the number of x-rays absorbed=radiographic contrast
What is the photoelectric effect inversely proportional to?
The cube of x-ray energy (kVp)
1/E^3
True or false. The photoelectric effect is more likely with low energy x-rays.
True, inversely proportional to x-ray energy (kVp) so less likely with high energy x-rays
What produces Compton scatter?
X-ray interacts with outer shell electron in atom of patient's tissues and ejects outer-shell electron resulting in ionization of the target atom and a change in x-ray direction=scatter
*True or false. Compton scatter does not change the direction of the x-ray.
False, it does change the x-ray direction=scatter
(Coherent scatter changes direction only slightly)
True or false. Compton scatter doesn't change the x-ray energy.
False, it reduces x-ray energy. Coherent scatter doesn't decrease energy of x-ray
What is the probability of Compton scatter directly proportional to?
The total number of electrons in the patient
-physical density (g/cm^3)
-e-/g
True or false. Most matter contains the same e-/g.
True, this results in poor tissue contrast
The probability of Compton scatter is inversely proportional to what?
X-ray energy
1/E
What are the 2 types of radiographs?
Conventional radiographs
Digital radiographs
What are conventional radiographs?
Films viewed using a light box
What are the 2 main systems of digital radiography?
1) Computed radiography
2) Direct Digital radiography
What are digital radiographs?
Where radiograph exists as DICOM file and displayed on a monitor.
What comprises a radiographic x-ray film?
Silver halide crystals bound to a polyester base.
Relatively speaking, do more x-rays hit a film when it is black or white?
Black-means lots of x-rays went straight through
Do films usually have singe or double layers of emulsion?
Double
*What happens to the silver halide crystals in a film after exposure to light/x-rays and development?
Converts to metallic silver
**Are x-ray films more sensitive to light or x-rays?
LIGHT
How does developed and exposed silver in a film appear?
black
*What 5 things determines the 'blackness' of an x-ray film?
1) The number of x-rays hitting the film
2) Energy of the x-rays
3) Distance from the x-ray tube to the film
4) Film and screen speeds
5) Film development conditions
*What determines the number of x-rays that hit a film?
1) mAs
2) Patient attenuation
*What determines the energy of x-rays?
kVp
What determines the distance from the x-ray tube to the film?
Focal spot to film distance
What are 3 film development conditions that affect the blackness of the film?
Temperature, time and concentration of chemicals.
*Intensifying screens for x-ray cassettes contain a _______ layer.
Fluorescent
*What is the function of intensifying screens on x-ray cassettes?
Converts x-ray energy to light
Color of light emitted is matched to color sensitivity of film
Where are intensifying screens located?
Inside cassette, adjacent to film
Why do we want the film and intensifying screen in contact?
To ensure optimal light transfer by minimizing light diffusion from phosphor (fluorescent layer) in screen to film
What are the 3 steps in 'developing' a film?
1) Develop (exposed silver)
2) Fix
3) Wash (unexposed silver)
What is the purpose of film development?
Amplifies the latent image by 10^8
What does the developer do to the film?
Turns exposed silver crystals black
How is film development accomplished?
Chemical process
-Time & temperature sensitive
-Multiple chemicals in solution
What happens during the fixing of a film?
Stabilizes developed silver & solubilizes unexposed silver halide crystals
You develop a film but it comes out milky or cloudy looking, what went wrong?
Inadequate fixing
What is washing a film?
washes fixer from radiograph
What happens if a film is not washed thoroughly enough?
Unremoved fixer reacts w/ silver in the film, forming silver sulfide= smells like rotten eggs
*You take an x-ray but your film comes out and smells like rotten eggs, what happened?
The film was not properly washed
Film will also turn brown w/ age
What does digital radiography use instead of film?
Digital x-ray sensors
*Compare contrast resolution and spatial resolution in digital and conventional radiographs.
Contrast resolution=digital is better
Spatial resolution=film is better
Are conventional or digital radiographs more forgiving to over/underexposure?
Digital
True or false. Digital radiography takes more technique to produce a similar image to conventional radiographs.
False, digital radiography requires less technique
What is technique?
mAs & kVp
What are the 2 advantages to digital radiography?
1) Allows immediate image viewing
2) Ability to digitally transfer image
-Teleradiology
-Consultation
What is used instead of a film with computed radiography?
Imaging plate
The imaging plate used for computed radiography is coated with what?
Photostimulable phosphors
What happen when x-rays strike the imaging plate?
Energizes/traps the electrons in a higher energy state=latent image
How is the latent image on the imaging plate converted to an actual image?
The plate reader extracts the imaging plate from a cassette and scans it with a red laser to release the image.
How are imaging plates cleared?
White light
(Red light releases image)
What limits the resolution of computed radiography?
The size of the laser in the ADC which converts the latent image into the digital image, can't make laser smaller so can't get better spatial resolution
*What comprises the imaging plate used for digital radiography?
Is an array of detector elements
-Built into table or portable
-Has to be connected to computer
What are the 2 types of direct digital radiography?
Direct: converts x-ray energy directly into an electrical signal
Indirect: converts x-ray energy into light, light is converted into an electrical signal
*What are the 3 fates of x-rays after leaving the tube?
1) Absorbed in patient
2) Scattered by patient
3) Pass through unchanged
*True or false. X-rays must pass through the patient to reach the film.
True
*True or false. Differential scattering of x-rays in patients is what leads to differential darkening of film.
False, differential absorption!
*The amount of x-ray absorption depends on what 4 factors?
1) Density of tissue- e-/g (Compton)
2) Atomic number of elements in tissue (photoelectric)
3) X-ray energy
4) Thickness of tissue
**What are the 5 opacities (differential x-ray absorption)?
1) Air
2) Fat
3) Soft tissue/fluid
4) Bone/mineral
5) Metal
Why does mineral appear different from fat on an x-ray?
Because mineral has a higher atomic number so has a greater photoelectric effect
Where is air normally found in x-rays?
Lungs & intestines
Where is fat normally visible on radiographs?
B/w abdominal organs
The 'soft tissue' opacity includes what 3 things?
1) Parenchymal organs
2) Muscle
3) fluids e.g. blood, bile, urine
How does contrast material appear on radiographs?
Metal opaque
Does an overexposed film appear white or black?
Black -too many x-rays hit film
On radiographs, what can be mistaken for thin bone?
Very thick soft tissues can look the same as thin bones.