Radio Principles Theory 1-6 Flashcards
What are the 16 indications in which imaging should be considered?
- Age more than 50
- Had a significant trauma
- Neuromuscular defecits
- Unexplained weight loss
- Suspision of AS or an inflammatory arthritis
- History of cancer
- History of corticosteroid use
- Drug and alcohol abuse
- Patient has scoliosis
- Patient failing to improve with treatment
- Temp above 37.8 deg
- Patient seeking compensation
- Inconsistent biomechanical spinal examination findings
- Complex postural or biomechanical disorders
- History of surgery in area.
- Limited examination due to pain
Conditions and when to X-ray:
- DJD
- Rheumatological Disease
- Traumatic considerations
- Congenital and Structural Conditions
DJD:
- when theres osseus, foraminal encrochement
- xrays neccessary to see progression every couple of years
- RD:
- Films neccessary to evaluate extent - Traumatic considerations:
- Not all trauma needs imaging
- significant (fractures)
- Repetative activities (stress fx)
- Epiphyseal unjuries in children
- Follow up (eg fx healing)
4. Not all pts need imaging to rule out congenital abnormalities -Abn only occur in small % of pop -only small % of those are significant -need to way up risk/ benefit
Physical findings may lead to consideration of imaging:
- altered mechanics
- abnormal palpation findings
- significant pain
- Neurological findings
Curvatures:
- structural and congenital can be imaged
- progression films are justified
- DO NOT DO LATERAL FULL SPINE
Pathological considerations:
- ROS will help guide imaging decision (mody area/ modality)
- Diseases (osteoporosis, malignancy, hyper[arathyroidism etc)
- Infectious processes (imaging for confirmation and extent)
List teh differences between Hard X-rays and soft X-rays
- Hard X-rays
- high frequency
- high energy
- short wavelength
- highly penetrating
- give low contrast images (HARD to see the difference in colours?) - Soft X-rays
- not as high frequency
- not as high energy
- not as highly penetrating
- longer wavelength
- give high contrast images
Tell me the properties of X-rays
- no mass
- electrically and magnetically neutral
- invisible
- travel at light speed
- highly penetrating
- travel in straight lines in a divergent beam
- diagnostic range of energy 15- 150 keV
- can ionise matter
- produce minimal amounts of heat while passing through matter.
X-ray tube
Vacuum tube
Cathode
Anode:
Produced in a vacume tube to prevent oxidation that would burn out filament and allows electrons to maintains speed with no air molecules to slow them down.
Cathode
- negatively charged side of the X-ray tube which has 2 main parts
a) Filaments (coil of wire made of tungsten- high melting point) - when current flows through filaments it heats up and e- ate emitted (thermionic emission)
- there are 2 types of filaments to produce different focal spot sizes
i) Small focal spot (50-100ma)
ii) Large (>100mA)
b) Focusing cup - negatively charged cup that focuses the e-beam- without it, e- would scatter around inside of tube.
ANODE:
- positively charged side of the tube were xrays are produced
- tungsten target rotates to increase heat capacity
- TARGET is the area of the anode struck by e- from the cathode
- interactions of the e- and atoms on the target create the X-rays to be emitted (photons).
Anode Target: have the focal spot which is an area hit by e-beam and dispersed and determined by the anode angle and the focusing cup size..
The effective focal spot is the area projected onto the pt (ie the e- that get through the tube window). The smaller this area is the better the image detail.
-by changing angle of the anode target the EFS can be inc. or decreased.
-most angles are at 12 deg.
-size of the ffective focal spot is determined by the size of the e- beam.
Tell me about the Penumbra and Image detail:
How do you decrease Penumbra and optimise image detail
Its the lighter hazier area at the edge of the image. Caused by rays passing tangentially to edge of an object.
decrease penumbra and optimise image detail by:
- increasing SID
- decreasing focal spot size
- object as close to film as possible. .
Tell me about the Anode Heel effect:
- X-ray photons travel out in all directions, and some a partially re-absorbed meaning that x-ray beam will vary across the beam.
- more intense beams at the cathode enod of the beam.
- magnitude of the variation depends on the anode angle (smaller angle = greater effect)
- anode angle is fixed so this effect can be controlled by using longer SID and placing smaller area towards the anode end of the beam.
What is the purpose of the Lead Tube Housing?
serves 3 primary functions:
1) to house and protect the glass tube
2) to absorb the non-ueseful portion of the primary X-ray beam
3) To help with heat dissipation via industrial grade oil stored within the housing.
What are the prblems you come across with X-ray generators? and how do you fix them?
Voltage
Variable power supply
Current.
What is the sequence of events in the Tube? Lec 3
a
How are photons actually produced? lec 3
bremsstrahlung photons
characteristic photons
a
Once the photons have been produced what will happen to them
- Leakage
• Spills out of tube housing - Primary radiation
• Exits through port in housing and directed at pt - Secondary radiation
• Originates in the pt, travels in all directions - Remnant radiation
• Emerges from pt towards film cassette and produces the image
• Mixture of scattered and unscattered radiation
Current Wave
describe each of them, how they differ and when each would be used?
AC current wave
Single phase 1/2 wave
single phase full wave
Triple Phase wave
High frequency wave
s
Describe secondary radiation and the Photoelectric effect?
pg 10 notes
What are the different kinds of Scatter? Describe them
pg 11
- Classical (Coherent, Rayleigh, Thompson, unmodified)
• Absorption of low energy photons (
What are grids? what is their purpose?
what are the Different types of grids?
pg 12
Types 1. Linear • Lead strips run in one direction only 2. Crossed • Cross-hatched lead strips • This will clear scatter from all directions but can’t angle tube and need a very high dose to pt 3. Parallel • Lead strips all point in one direction • May be linear or crossed 4. Focused • Lead strips point towards a central point • May be linear or crossed 5. Stationary • Not moving 6. Moving • Moving (Causes blurring of grid to reduce artefact on image)
What are the common ratios used?
what is the ratio firstly?
• Height of lead strips: Space between them
• Common ratios are
- 8:1
- 10:1
- 12:1
• High ratio grids have a higher absorption ability, but have more lead, so require more exposure to the pt (as they also absorb more of the remnant beam)
Tell me about the grid frequency and how it affects the imageand radiation?
- # of lead strips per inch or cm
- Typically range from 60-103 inch (24-40 cm)
- The higher the # the more efficient the grid is at cleaning up scatter
- The higher the frequency the thinner the strips, and the less visible on image
- The higher the # the more remnant beam absorbed
- The higher the frequency the higher the exposure must be to maintain image density
Grid Rdaius/ Grid Focus
13
• Grid Cut-off
- Poor grid alignment causes loss of remnant radiation and reduces the image density in the area of cut-off
• Grid radius/ focus is the SID for which a grid will operate
- Can be set in a specific range
• If SID is outside of set range for the grid, cut-off will result
• Linear (most) grids- the distance of the beam (SID) and the horizontal centring to the grid that matters-
- T4 angling the tube will not result in cut-off
• Parallel grids- longer SID or small cassette size is required to capture the most parallel portion of the beam
SEE PHOTOS be able to draw them.
Air gap technique
- Much of the scatter simply misses film
- No additional radiation dose needed
- Increased magnification and distortion
X-ray films must be stored properly b/c they are sensitive to:
• Heat • Light • X-rays • Moisture • Aging - Rotate frequently • Physical pressure
Composition of film
15
- Film Base
- Made from polyester
- Tinted blue
- Flexible so can be rolled through processor
- Does not form the image but is the support - Emulsion
- Where the image is created and stored
- Gelatinous matrix (silver halide crystals and gelatin (for even distribution) - Super Coating
- Protective coat but not strong and easily damaged
Tell me about a direct exposure film
15
- Film that is only exposed to x-rays (no screen)
- Excellent detail
- Very high dose and longer exposure times b/c not as sensitive to x-rays
- Dental imaging and industrial radiography
Tell me about a screen film
16
• M.C types in medical imaging
• Film exposure id=s via phosphorescent light
- Screen converts x-rays to visible light
• Film sensitivity (e.g. blue) must match screen colour emission (e.g. blue)
• 2 types of screen films
1. Single emulsion
- Emulsion on only one side of base
- Better detail than dual emulsion but higher dose
- Better for extremity and mammography
2. Double emulsion
- On both sides of base
- Faster so reduce pt dose
- Reduced image detail
- Used for central body regions (axial) an/or large pts
Duplicating Types films
tell me about them
16
• This is used for copying images and printing digital images
• Single emulsion
• Sensitive to different types of light
- Slower than normal film
- Produces “Positive” image
• To lighten up- increase mAs
• NB. X-ray films to lighten up need to decrease mAs
Film characteristics:
Film speed.
What is it?
What is it determined by?
• Inherent sensitivity of film
• Amount of optical density (darkness) produced by a given amount of exposure
- If film A is faster than film B, film A will become darker than film B if they are given the same amount of exposure
Speed determined by:
A. Fixed characteristics:
-thickness of emulsion layers
-size of silver halide crystals
B. Variable characteristics
-processing temp
See graph on pg 17 notes
Film characteristics:
Contrast
- Response of the film to recording differences in optical densities
- In a graph the steeper the curve the higher the film contrast
- High contrast means that small changes in exposure will lead to large changes in shades of grey visible
See graph on page 18
Film characteristics:
Latitude
• Range over which the film will react to the exposure (i.e. change density)
• Wide latitude= long greyscale (lots of different shades of grey) = low contrast images
- Less likely to produce a sub optimal image (too/ not enough darkness/ density. i.e. over/under exposed)
For any two optical densities achieved, the film with the largest difference in exposure values has the greatest latitude.
See graphs on pg 18 notes
Film characteristics::
Film Cassette:
18
• Air tight container that protects the film from unwanted light
• Front made of low absorptive radiolucent material
• Intensifying screens
- Contain a phosphor/crystals that converts x-ray photons to visible light
- Greatly decrease the number of x-rays needed to expose film (b/c x-ray film is much more sensitive to visible light than x-ray photons
- Decreased exposure times= dec. motion blur
- Smaller focal spot can be used= inc. image quality
- DISADVANTAGE= Image resolution drops due to light diffusion within crystal layer)
- Available in a variety of speeds/sensitivities
Film characteristics:
Intensifying screen.
What are the different layers of the construction?
- Base
• Provides support - Reflective or absorptive layer (undercoat)
• Reflect light back towards film (increase speed of the system)
• Absorb backscatter light (maximises image detail) - Phosphor layer
• Contains phosphorescent crystals which emit visible light photons distributed in a polymer matrix
• What determines the speed and latitude of the screen?
- Are the crystals small or large
- Is the layer think or thin - Protective Coating
• Prevents damage to phosphor layer
See pics on pg 19
Image quality with screens.
What different aspect affect the screens
pg 20
- Phosphor crystal size
• Larger= dec. resolution from inc. light diffusion - Thickness of phosphor crystal layer
• Thicker= dec. resolution from inc. light diffusion - Presence of reflecting layers
• Dec. resolution from increased light diffusion - Presence of light absorbing dyes
• Inc. resolution from dec. light diffusion - Film screen contact
• Must be very tight or image quality dec.
Latent Image Processing
Describe the Gurney-Mott Theory of latent image production
• The change within the emulsion (AgH crystals) change in rxn to light from screens
• This change is invisible to the naked eye so needs to be amplified to visualise
• How do the crystals change?
- Within the crystal lattice, free e- and free Ag ions are able to migrate
- A built in defect (Sensitivity speck) on the crystals will attract free e-
1. Film exposed to light
2. Halide to release e- into lattice
3. E- drawn to sensitivity speck
4. This creates –ve charged region in crystal which attracts +ve charged Ag ions
5. Once there the Ag ions are reduced to atomic silver
6. This atomic silver creates the dark regions on the film
7. Developing process amplifies latent image through chemical processing
Chemical processing and developing the image:
Is controlled by?
- Concentration of developing agents
- Temperature
- Time the film is exposed to the chemicals
- Inc. conc/temp/time = reduction of Ag+ = Too dark = low contrast
- Dec conc/temp/time = insufficient reduction of Ag+ = white film too light = dec. contrast
What are the 3 stages of image processing and what kind of happens in them?
- Developing
• Reducing agents
- Reduce remaining Ag + to atomic silver
- Hydroquinone
o Produces blackest densities
- Phenidone
o Produces shades of grey in areas of low exposure
• Activator
- Allows reducing agent to reach crystals by increasing permeability
• Restrainer (anti-fogging agent)
- Stops the reducing agents from developing unexposed Ag+
• Hardener
- Maintains uniform thickness to prevent damage during automatic processing
• Preservative
- Minimises developer oxidation (when exposed to air) to increase life of developing agents
• Water
- Provides proper dilution and delivery of substrate - Fixer
- Stops development and removes underdeveloped silver halide crystals
- Shrinks and hardens the emulsion
• Acidifier
• Clearing agent
• Hardeners
• Preservative
• Water - Washer
- Clears off developer and fixer
- Failure to wash will result in: - Powdery-white costing
- Will collect fingerprints and other artefacts permanently
- Chemical smell
- Discoloration of film over time (brownish or yellow)
- Water should be running and changed daily to prevent algae formation - Drying
• Must be hung to dry or pass through heater
• Failure to do so will result in a kissing artefact
What power are safe lights?
40 watts or less
What can cause chemical fog on an image?
Chemical fog can be caused by development of unexposed silver halide crystals
