XRay Physics Flashcards
When fast moving electrons collide with matter in any form, what is produced?
X-Rays
In an x-ray tube, this is done by directing a stream of electrons at a high speed against a ….
metal target
As they interact with the atoms of the target, the electrons give up most of their energy in the form of…
Heat
However, about 1% of their energy is emitted as….
X-Radiation
The x-ray tube is inside a heavily lead-lined protective housing & is located…
Within a glass envelope (Pyrex) inside the tube housing
The tube consists of 2 electrode called the…
Cathode & Anode
Which electrode consists of a large filament, a small filament, and a focusing cup.
Cathode
The filaments serve as the source of _____ in the production of x-rays, and are made of _____.
Electrons
Tungsten
What occurs when a current is applied to the filament?
Thermionic Emission
The coil of the wire becomes very hot, boiling off electrons
What controls the quantity of electrons (mA) emitted from it?
Temperature of the filament
What determines the number of x-rays created?
Number of electrons
This is part of the cathode and encases the two filaments. Place where thermionic emission occurs.
Focusing Cup / Filament Cup
The Positive Electrode in the x-ray tube
Anode
Most x-ray tubes consist of a _____ anode.
Rotating
Rotating target receives electrons as they move from cathode to anode.
What is the reason for the rotating target?
Dissipate the heat generated
Rotating Anode exposes an area of the tungsten target of the anode, which is called the _____.
Focal Spot
The focal spot will be determined by the …
Size of Filament chosen
Smaller filament = ?
Better detail
The Line Focus Priniciple has the effect of making the actual focal spot size appear _____ when viewed from the position on the film.
Smaller
The smaller the target angle = ?
The smaller the effective spot
Stream of electrons narrows down to an….
effective beam
What heats the filament causing a boiling off of electrons?
Milliamperage (mA)
Milliamperage Per Second (mAs)
More Current = ?
More Current = More electrons produced = more x-rays produced = greater radiograph density (darker)
The overall blackening on a film?
Density
Density term used to describe structures that produce more blackening on the film
Radiolucent
Density term used to describe structures that produce less blackening on the film (whiter on x-ray)
Radio-opaque
T/F: The relationship between mAs and density are directly proportional
True
What is the primary method to control the blackening on the film?
Changing the mAs
mAs increases = ?
More film exposure
What is the minimum change of mAs that it takes to see a minimum change in density on the film?
30%
If the mAs is doubled, the density is ….
Doubled
If the mAs is halved, the density is…
Halved
The force applied to accelerate the electrons from the cathode to the anode at the time of exposure is…
Kilovoltage (kVp)
T/F: The greater the force of the kVp, the greater the numbers of high energy x-ray photons will be produced.
True
T/F: Wavelength and frequency are inversely related
True
T/F:
Low kVp = low energy = weak penetration
High kVp = high energy = strong penetration
True
Higher kVp produces (longer or shorter) wavelengths with a greater ability to penetrate the body tissue
Shorter
The difference in density between two structures.
Contrast
Contrast makes detail….
visible
T/F: kVp controls contrast but they are inversely related
True
Low kVp = ____ Contrast = Short Scale
High
Low kVp film will have _____ differences in dark and light areas. (ex: Black & White film; bone = Underexposed)
Sharp
Low kVp produces ____ scatter, however, the amount of radiation absorbed by the patient is ____
Less Scatter
Increased Radiation
High kVp = ____ Contrast = Long Scale
Low
T/F: High kVp film shows very little differences between densities. (ex: more shades of grey; soft tissue)
True
High kVp produces ____ scatter, however, the amount of radiation absorbed by the patient is ____
More Scatter
Less Radiation
To lower your contrast - longer scale of contrast - more shades of grey - you must:
Increase kVp by 15% & Decrease mAs by 50%
Double Density
To raise your contrast - shorter scale of contrast - fewer shades of grey - more black & white - you must:
Decrease kVp by 15% & Increase mAs by 100%
Half Density
What is the prime method to control density?
mAs
T/F: The relationship between kVp and density is NOT proportional.
True
Explain the 15% rule?
An increase in kVp by 15% will double overall density of the film, whereas, a decrease by 15% will cut the density in half.
Denser tissue absorbs x-rays whereas less dense tissue transmits more x-rays. What are the radiographic densities as seen on an x-ray:
- Gas
- Fat
- Muscle, Water, Soft Tissue
- Bone, Metal
Gas - BLACK
Fat - BLACK
Muscle, Water, Soft Tissue - GRAY
Bone, Metal - WHITE
T/F: The rotating target is angled thus producing a varied intensity
True
The intensity of the x-ray is greater at the ____ side.
Cathode
Since intensity and density decrease on the anode side of the film, place the thinner portion of what is being x-rayed towards the anode end.
Anode-Heel Effect
Cathode or Anode?
- Less X-Ray
- Smaller effective focal spot
- More detail
- Thinner body part
Anode side
Cathode or Anode?
- More XRay
- Larger effective focal spot
- Less detail
- Thicker body part
Cathode side
This represents the length of space from the focal spot (or tube) to the recording medium (or film)
Focal Film Distance (FFD) / Source Image Distance (SID)
What happens when you increase the FFD?
Image gets smaller & clearer, which decreases magnification and distortion.
What happens when you decrease FFD?
Image gets bigger & blurrier
Intensity of radiation varies inversely with the square of the distance from the source.
Inverse Square Law
If a 40” FFD is doubled to an 80” FFD, the intensity of the radiation is ____, so the mAs must be increased _____ to maintain same amount of film blackening.
Intensity is 1/4
mAs must increase by 4x
If an 80” FFD is halved to a 40” FFD, the intensity of the radiation is _____ the intensity from the 80” if no factors are changed.
4x
Intensifying screens consist of _____ crystals.
Fluorescent
Large crystals (more light) work quickly, but yield…
Less detail
Faster screens = Higher Contrast = Short Scale = ?
Less pt exposure
Small crystals (less light) work slowly, but offer….
More detail
Slow screens = Lower Contrast = Long Scale = ?
More pt exposure
Intensifying screens increase density on the film by…
Intensifying the action of the x-rays
_____ is the picture made by the useful beam
Umbra
_____ is the blurry halo parts of the image (unsharpness)
Penumbra
What is caused by having the tube too close to the film (short FFD), having the pt too far from the film (long OFD), or having too big of a filament on the cathode making the focal spot too big.
Penumbra
Distance between the patient and the film
Object Film Distance (OFD)
As you increase the OFD, the image becomes….
bigger & blurrier (more penumbra)
As you decrease the OFD, the image becomes…
smaller & more clear (more detail)
T/F: Object should be as close to film as possible for better detail.
True
The pressure exerted by the film holder as it encloses the x-ray film. Pressure should be evenly distributed across the surface of the film.
Screen-film contact
What is the best test for screen film contact?
Wire-Mesh test
T/F: Poor screen film contact reduces the image sharpness of the image.
True
What are the two types of distortion?
Size & Magnification
Distortion can be affected by…
OFD & FFD
When x-rays strike an object one of three things can occur…
Scattered, Absorbed, or Penetrated
How can you reduce scatter radiation?
- Grids
- Air Gap Technique
- Collimators
- Filters
A device of alternating strips of lead and spacer material. This is placed between the patient and the film. The sole purpose is to improve quality of the radiograph by absorbing scatter radiation. The use of this will require an increase in exposure factors to maintain density. This increases patient dose of radiation.
Grids
What is the Grid Ratio?
Height of the lead strips to the distance b/t the strips
What is the Grid Ratio in a chiropractic office?
12:1
What is the Air Gap Technique?
6-10” between the patient and the film
This distance b/t the body part and the film causes scatter radiation to diverge away from the film, which reduces pt dose but can distort or magnify the image.
Limits the size of the beam to the size of the body part you need to capture on film.
Collimation
What is the best way to reduce scatter radiation to the patient as well as to the film?
Collimation
Preferential removal of low energy photons (those not capable to get all the way to the screen). This stops the weak photons from entering the patient’s body thus protecting them from scatter radiation.
Filtration
What are filtrations usually made from?
Aluminum
Used to identify irradiation of patients; measures the radiation energy absorbed.
Radiation Absorbed Dose (RAD)
1 RAD = ___ REM
1
This unit is typically applied to occupationally exposed persons. It identifies the biological effectiveness of the radiation absorbed. It’s measured on radiation workers by a photosensitive badge worn on the collar.
Radiation Equivalent Man (REM)
What is the safe limit of REM per year?
5 REMs (or RADs) per year
The number of REMs a person can get in a lifetime without getting radiation poisoning.
Maximum Permissible Dose (MPD)
What is the MPD in a lifetime?
MPD = 5 (age 18)
Type of radiation: majority of useful beam; interacts with the target nucleus; a high intensity electron hits an inner shell electron, which is knocked out of its position in orbit, and an outer shell electron then fills its spot.
Bremsstrahlung aka Braking Radiation
Primary form of scatter
A moderate energy x-ray knocks out an outer-shell electron, which causes a loss of energy.
Compton scatter
A low energy x-ray that changes direction with no energy loss. Contributes to film fog.
Classical Scatter aka Thompson Scatter aka Coherent Scatter
A low energy photon is absorbed by the subject creating a latent image on the film.
Photoelectric Effect
This is caused by the fluctuation of the number of photons absorbed by the intensifying screens to form the image on the film. Faster screens produce more of this. The use of high mAs, low kVp will decrease this.
Quantum Mottle aka Radiographic Noise
Solution temperatures that are too hot will _____ density.
Increase
Solution temperatures that are too low will produce radiographs with _____ density
Insufficient
Processing factor that brings out the latent image by developing the exposed silver halide crystals.
Developer
The component of the Developer that produces shades of gray and black & uses Phenidone/Hydroquinone.
Reducer/Developer
The component of the Developer that produces swelling of emulsion using Na+ Carbonate.
Accelerator/Activator
The component of the Developer that controls oxidation using Na+ Sulfite or K Sulfite
Preservative
The component of the Developer that protects unexposed crystals & uses Potassium Bromide/Iodine
Restrainer
The component of the Developer that controls swelling of emulsion & uses Glutaraldehyde.
Hardener.
Processing factor that removes the exposed silver halide crystals
Rinse
Processing factor that hardens the image, making it permanent on the film
Fixer
The component of the Fixer that neutralizes the developer aka “Stop Bath” & uses Acetic Acid.
Acidifier/Activator
The component of the Fixer that removes undeveloped Ag Halide aka “Hypo Solution” & uses Ammonium/Na+ Thiosulfate
Clearing Agent
The component of the Fixer that stiffens/shrinks the emulsion & uses Potassium Aluminum
Hardener
The component of the Fixer that maintains the pH of the fixer & uses Sodium Sulfite
Preservative
Processing factor that removes the developer & the fixer
Washing
If light leak, developer temperature too hot, overexposure
Dark Films
If developer temperature too low, chemicals need replacing
Light films
Inadequate developer
Brown films
Inadequate fixer
Milky films
Insufficient washing
Greasy films
Old film, hot developer, contaminated chemicals
Increased fog
Insufficient fixing
Soft Emulsion
How should you store the film to avoid pressure damage
Vertically
Steps up or steps down the power
Transformer
One form of energy to another
Transducer
Beam of radiation loses energy as it passes thru matter
Attenuation
What is added to the base of xray rilm to reduce glare
Green or blue tint
