Diagnostic imaging (SA08) Flashcards
(110 cards)
1
Q
What are the dangers associated with radiography?
A
- X rays are invisible
- They are painless
- Effects are ‘latent’ (not seen immediately, may only be seen years later
- Effects are cumulative; repeated low exposures are as hazardous as a single large exposure
1
Q
What are the principles of radiation protection?
A
- X rays must only be taken if definite clinical justification
- Exposure of personnel kept to minimum
- Time - reduce need for repeat exposures
- Distance - Stand 2 meters away
- Shielding - Wear PPE, stand behind lead screen
- No dose limit should be exceeded
2
Q
What is the electromagnetic spectrum?
A
- Radiations with similar properties
- Low to high energy
- Radio waves, Microwaves, Infared radiation, Visible light, Ultraviolet, X-rays, Gamma-rays
3
Q
What do all the waves of the electromagnetic spectrum have in common?
A
- Travel in waves
- Travel at same velocity
- Need no medium to travel, can pass through vacuum
- Travel in straight lines
- Interact with matter through absorption or scatter
4
Q
What is the difference between radiowaves and x-rays?
A
RADIOWAVES
- Low energy radiation
- Low frequency
- Long wavelengths
X-RAYS
- High energy radiation
- High frequency
- Short wavelengths
5
Q
What are the properties of X-rays
A
- Penetrate matter visible light can’t as high energy
- Interact with photographic film, produce latent image
- Interact with phosphor in intensifying screen to produce visible light (fluorescence)
- Interact with living tissues, produce bio changes
- Energy can be captured and converted to produce electronic images
6
Q
What are the 3 types of x-ray machines?
A
- Portable
- Mobile
- Fixed
7
Q
What are portable x-ray machines?
A
- Wall mounted or on portable stand
- Not very powerful
- Old machines only produce 20mA
- Newer machines can produce around 60mA
- kV and mA are usually linked, a given kV delivers a set mA
- Dental and equine
8
Q
What are mobile x-ray machines?
A
- Large transformer box and trolly
- More powerful than portable machines
- Produce up to 300mA
- mA and kV can be set independently
- Machines in practice (often x-hospital)
9
Q
What are fixed x-ray machines?
A
- Built in the room on overhead gantry/rails
- Needs special electricity supply
- Very powerful but more costly
- Often linked to floating tables
- Used in NHS
10
Q
What is the x-ray beam made up of?
A
- Photons (packets of energy)
- Created when electrons are slowed down/stopped
- Electrons are present in atoms of all elements
11
Q
What does the structure of an atom consist of?
A
- Protons (positively charged)
- Neutrons (no electrical charge)
- Electrons (negatively charged)
12
Q
What does it mean for an atom to be electrically neutral?
A
- Equal number of protons and electrons
13
Q
Where in an atom are the different elements?
A
- Protons + neutrons (centre of nucleus)
- Electrons orbit nucleus in shells
14
Q
How are the charges of atoms changed?
A
- Changes to amount of electrons
- More protons than electrons, positively charged, Cation
- More electrons than protons, negatively charged, Anion
- Atomic numbers are number of protons in nucleus
- Important with how x-rays interact with different types of tissue and are seen on radiographs
15
Q
What is needed for the on/off switch of a radiography machine?
A
- Must have warning light when machine on
- Now a ‘controlled area’, only radiography personnel allowed
- Often directly linked to lights outside room
- Should be isolator to turn off machine outside room in emergencies
16
Q
What is a line voltage compensator?
A
- Ensures incoming voltage is consistent
- Produced by an autotransformer
- Built in part of modern machines
- Older machines may have indicator light
17
Q
What are kilivolts (kV)?
A
- High power electrical charge
- Applied to target during exposure
- Draws electrons across
- Produced by a set up transformer
- ‘Penetrating power’
18
Q
What are Milliamps (mA)?
A
- Low power electrical charge
- Heats filament
- Releases electrons during ‘prepping’ stage
- Produced by a step down transformer
- Number of electrons (quality)
19
Q
What are seconds (S)?
A
- Timer for exposure time
- Some machines as low as 0.01 seconds
- Most exposures made at 0.05-0.5 seconds
20
Q
What are the differences in old and new machines with inputting settings?
A
- Some modern machines automatically input settings from species, area and depth of patient
21
Q
What are the 3 exposure factors?
A
kV
- Controls energy of photons
- Quality/penetrating power of primary beam
- Affects contrast and density of image
mA
- Controls number of photons
- Quantity/intensity of primary beam
- Affects density of image
s
- Controls number of photons
- Quantity/intensity of primary beam
22
Q
What is mAs?
A
- mA x s
- Control number of photons per exposure
- mA = number of electrons emitted
- s = how long emission lasts for
23
Q
What will happens if mAs or kV is too high?
A
- Black, over exposed image
- Few shades of grey
- Everything dark grey
- Flat, lacking contrast
24
What happens if mAs or kV is too low?
- White, underexposed image
- x-rays not strong enough or not enough to penetrate tissues
- Tissue pale on black background
- Soot and whitewash film
25
What does MRI stand for?
Magnetic Resonance Imaging
26
What is an MRI machine?
- Typically long thin tubed shaped
- Powerful magnet running front to back
- Body part must be in exact centre of magnetic field (isocentre)
- Can take 2-D or 3-D map of body tissues
- Magnet 30,000 x stronger than earth magnetic field
- Can draw all metal objects within several yards
27
How is an MRI image created?
- Magnet causes nuclei of hydrogen atoms to line up in parallel formation
- Body hydrogen atoms normally point in different directions
- Radiofrequency wave produced by RF coil
- H atoms move orthogonally (Resonance)
- When turned off, move back to align with magnet
- Another RF wave is produced
- Signals produced are detected by RF coil and converted to form and image
- Speed of H atom movement creates image
28
What is ultrasound?
- Sound energy at higher frequency than can be heard
- Frequency determines how far waves travel through body
- Higher frequency gives better pictures but can't travel far
- Different frequency transducer heads are available
29
What does ultrasound equipment consist of?
- Transducers
- TV monitor
- Control panel
30
How can ultrasound images be stored?
- On patient records
- Printed
- Uploaded to PACS
31
What are the types of ultrasound transducers?
SECTOR ARRAY
- More suitable for SA as small contact area
LINEAR ARRAY
- More suitable for large animal
32
How are ultrasound images produced?
- Crystals in transducer alter shape when current is applied; piezoelectric effect
- When applied to skin, waves pass through and 'reflect' off tissues, back to transducer
- Returning sound waves cause vibration of crystals and converted back to electric impulses to create images
33
What are ultrasound transducers?
Probes
34
What is echogenicity?
- Ability of tissue to reflect ultrasound wave
35
What is anechoic?
- Without echoes
- No sound waves return
- Appear black
- Fluid
36
What is the piezoelectric effect?
- Crystals in ultrasound transducer change shape when electrical current is applied
37
What is hypoechoic?
- Not many echoes
- Not many sound waves returned
- Appear dark grey
- Dense tissue
38
What is hyperechoic?
- Lots of echoes
- Many waves returned
- Appear bright white
- Bones/gas
39
What is acoustic resistance?
- When sound waves bounce back off of tissues
40
What does homogenous mean?
- Of uniform composition
- Smooth appearance
41
What does heterogenous mean?
- Not of uniform composition
- Mottled appearance
42
How does different tissue appear on a ultrasound?
- Fluid is black - Anechoic
- Tissues shades of grey
- Bone/gas white - Hyperechoic
43
What is the brightness or B mode in ultrasounds?
- Most commonly used mode
- Image of slice though organ/tissue
44
What is the time-motion or M mode in ultrasound?
- Vertical section through tissue
- Constantly updated
- Appears as rolling horizontal image
- Heart scans
45
What is the doppler mode in ultrasound?
- Used to detect movement
- Often used to detect blood flow
- Colour doppler assigns colour according to speed and direction of flow
46
What is contrast ultrasonography?
- Small quantities of microbubbles of sulphur hexafluoride gas
- Injected into blood stream in phospholipid capsules
- Microbubbles reflect waves
- Increased echogenicity in proportion to vascularity
- Looks at direction of blood
47
What other uses does ultrasonography have?
- Allows for accurate sampling
- FNA, biopsies
-Tru-cut biopsy (larger sample)
- Tru-cut requires heavy sedation or GA
- Cystocentesis easier, especially if bladder small
48
Why may starvation be needed for an ultrasound?
- Full stomach causes increased echogenicity
- Avoid regurge in sedated animal
- Most animals won't require sedation but stress and pain must be managed
49
What is the purpose of contrast studies?
- Visualise structures not normally seen on plain films
- Due to surrounding tissue similar radio-opacity
- Provides information re size, shape, position and structure
- Information re function of organ
50
What structures can be visualised using contrast media?
- Oesophagus
- Stomach
- Stomach & SI
- Large intestines
- Bladder
- Kidneys & Ureters
- Vagina & Urethra
- Spinal cord
- Blood vessels & heart chambers
- Internal structures of joints
51
What must contrast agent have the ability to do?
- Absorb a different amount of x-rays than the surrounding tissue
52
What are positive contrast agents?
- High atomic numbers
- Barium AN = 56
- Iodine AN = 53
- More radio-opaque than tissue
53
What are negative contrast agents?
- Low atomic numbers
- Air AN = 8
- More radiolucent than tissues
- Carbon dioxide sometimes used
54
An ideal contrast agent should:
- Show area of interest well
- Non-irritant
- Non-toxic
- Persist in area of interest
- Be totally eliminated from the body
55
What is Barium?
- For GI studies
- Suspension, paste, powder
- BIPS = Barium impregnated polyethylene spheres
56
Powder and suspension Barium?
- For stomach, small and large intestine
- Care when administering orally
- Aspiration causes granulomas
- Fatal aspiration pneumonia
- Contraindicated if perforation of oesophagus or bowels
- Leakage into thoracic or abdominal cavity causes granulomas
- Will persist indefinitely in those cavities.
57
What are the 3 types of adverse affects caused by radiation?
- Somatic
- Carcinogenic
- Genetic
58
What somatic effects can be seen from radiation?
- Occurs soon after exposure
- Red skin, cracking, hair loss, cataracts, GI upset
- Foetus particularly sensitive
- See in nuclear accidents
- Tumour cells more sensitive
- How radiation treats cancer
59
What carcinogenic effects can be seen from radiation?
- Cancer causing
- Leukaemia
- Latent
- May be 20 - 30 years later
60
What genetic effects can be seen from radiation?
- Mutations in chromosomes of germ cells
- Inherited mutations in offspring
- Occurs when ovaries and testes exposed
61
What are the two sources of radiation?
PRIMARY BEAM
- Direct from tubehead window
- Straight lines but does diverge
- Very high energy, biggest hazard
- Lead clothing will not shield from primary beam
SCATTER/SECONDARY
- All directions when beam hits object, but in straight lines
- Lower energy than beam
- Absorbed by PPE
- Energy falls rapidly further it travels
62
What is the light beam diaphragm?
- Legal requirement
- Movable, adjustable metal plates
- Indicated by visible light
- Collimation should be as small as possible
- Accuracy checked using coins along margin
63
How should radiograph exposures be recorded?
- Every exposure recorded in day book
- Date, patient ID and description, exposure factors, quality and restraint
- HSE can do spot checks
64
What legistlation must be followed when performing x-rays?
- Ionising Radiation Regulations 2017
- Developed with HSE
- BVA produced simplified version
65
What is the Radiation Protection Adviser (RPA)?
- External person
- Usually medical physicist with certificate of competence
- Give advice on protection, controlled area, local rules and safe working
66
What is the Radiation Protection Supervisor?
- Person within practice
- Ususally RVN or VS
- Ensure rules followed and procedures are safe
- Don't need to be present for every exposure
67
What are the local rules and written arrangements for radiography?
- Set of instructions written by the RPA
- Details of equipment, procedures and controlled area for specific practices
- Includes action to be taken for each exposure
68
Who is not allowed in the controlled area?
- Persons under 16 years old
- Clients
- Anyone untrained with no personal dosemeter
69
Manual restraint in radiography
- Only in exceptional circumstances when threat to life
- Must wear full PPE and record in day book
- Rotate staff
- Large animal requires handlers but minimal present
70
What is the maximum possible dose of x-rays?
- 20 mSv
- 6 mSv for under 18s
71
What can affect dosemeters?
- Heat
- Sunlight
- Washing
- Microwaves
72
Where should a dosemeter be worn?
- On trunk under lead gown
- Wear whenever dealing with radiation
- Personal badges
- Checked every 1 - 3 months
73
What are the different types of dosemeter badges?
FILM BADGES
- Contain film
- Usually blue
- No longer common
THERMOLUMINESCENT
- Contain lithium fluoride crystals
- Store energy from interaction with photons
- Give off light during processing
74
What PPE is available for radiography?
APRONS
- Down to mid thigh
- Minimum thickness 0.25mmLE
- Must be used if not behind screen
GLOVES
- Open palm mitts or hand shields
- Must be used if restraining
- Lead sleeves available
- Minimum thickness 0.35mmLE
- Never in primary beam
THYROID PROTECTORS
75
How should radiography PPE be stored and checked before use?
- Never fold
- Aprons on hanger
- Check for cracking
- Can x-ray to check
76
What can help reduce repeat exposures?
- Exposure chart
- For particular machine
- Various views and patient sizes
77
Who does the practice need to register to when using ionising radiation?
HSE
Heath and Safety Executive
78
What is the film focal distance?
- Distance between focal spot and cassette
- Usually 75 - 100 cm
79
What are the 2 stages to the exposure button in radiography?
HALF PRESS
- Prepping stage heats filament and rotates anode
FULL PRESS
- Charge applied to draw across electrons and take exposure
80
What is the tubehead made of and what is it inside of?
Glass inside a vacuum
81
Why is the tubehead surrounded by oil?
Absorb vast amounts of heat produced during exposure
82
Why is the tube head and oil surrounded by lead?
Absorbs all x-rays except the primary beam
83
Why is the x-ray window made of aluminium?
- Filters out low energy x-rays
- Would be of no diagnostic use but increase irradiation of patient
84
What is inside the tubehead?
CATHODE
- Tungsten filament
- Surrounded by molybdenum focusing cup
ANODE
- Tungsten target
- On copper stem
85
Why is copper and tungsten used in the tubehead?
COPPER
- Conducts excess heat to cooling fins in the oil
TUNGSTEN
- High melting point
- High atomic number = many electrons
86
How is an x-ray produced?
- mA applied across cathode
- Tungsten filament heats up
- Tungsten electrons gain energy and move away from nucleus
- Released in cloud around filament = thermionic emission
- kV applied across tube
- Makes anode +ve and cathode -ve
- Cathode electrons attracted to +ve anode
- Move at high speed
- Crash into tungsten target/anode focal spot
- Energy released; most heat, rest x-rays
- X-rays travel in waves
- Packets of x-rays are photons
87
What happens when mA is increased?
- Increases filament current in cathode
- More electrons released
- More x-rays produced
- Increases intensity of primary beam
88
What happens when kV is increased?
- Increases voltage across tube
- Increases speed of electrons hitting tungsten target in anode
- Produces x-rays of greater energy
- Increases energy/penetrating power of primary beam
89
What are the types of anode in x-ray machines?
STATIONARY
- On portable machines
- Only cope with low mA
- Higer mA would cause heat damage to anode
ROTATING
- Larger focal spot
- Moving all the time to reduce build up of heat in one area
- Molybdenum stem is poor heat conductor so protects rotating motor
90
What is the angle of the tungsten target and why?
- Angle of 20
- Deflect x-rays out of tubehead
- Not straight back to cathode
- Provide a small, effective focal spot
- Actual focal spot is size of target due to heat
- Angle allows x-rays to emerge from effectively smaller source
91
What is the idea focal spot size and why is this not practical?
- Pin point
- Target would burn out with heat
- Larger focal spots allow higher settings but produce shadowing effect
92
What is the x-ray shadowing effect?
- Penumbra effect
- Unsharp halo around image
- Occurs because x-rays arise from all over the focal spot in all directions
93
When can a small focal spot be used in radiography and when should a larger one be used?
SMALL
- Low exposure
- Detailed work
- Fine focus
LARGE
- High exposure work
- Course focus
94
What happens when x-rays encounter tissue?
- Pass straight through
- Photoelectric absorption
- Compton scatter
95
What is the absorption of x-rays within tissues of the body dependent on?
- Atomic number of tissue
- Specific gravity (density) of tissue
- Thickness of tissue
- Higher atomic #, density and thickness allows less photons to reach plate
- These areas will appear more while
96
Where do different materials sit on the scale of x-ray absorption?
- Metal absorbs all the photons (white)
- Bone
- Soft tissue
- Fat
- Gas does not absorb photons
97
How are x-rays absorbed in tissue?
- Incoming photon collides with and displaces electron
- Photon energy transferred to electron = photoelectron
- Complicated stuff **
98
How does absorption and kV affect the radiograph?
- Absorption only at low kV
- Photoelectric absorption decreases as kV increases
- More x-rays get through bone
- Appears more grey, lower contrast
- Absorption minimal above 65kV
- Absorption more likely in tissue with high atomic #, density and thickness
99
Where can scatter go?
- Primary beam
- Absorbed by patient
- Safety hazard
- Film fog
100
How can scatter be reduced?
- Collimate
- Low kV
- Lead lined table/rubber sheet
- Intensifying screens (film)
- Compression band
- Grids
101
When should grids be used?
- Tissue > 10cm
- Thorax > 15cm
102
How does radiation scatter affect image quality?
- Scatter contacts detector
- Causes fogging
- Leads to reduced contrast and definition
103
What makes radiation scatter a hazard to human health?
- Can travel in all directions
- Not predictable
- May deflect back off table, floors, walls
104
How can a lower kV be used?
- Higer mA
- Longer exposure time (s)
105
What is a grid factor?
- Dictates how exposures must be increased to compensate for the grid
- Dependent on grid ratio, lines per cm and thickness of lead strips
- kV not increased for this
- mAs x GF = new mAs
106
Where is x-ray scatter less of a problem and what settings should be used here?
- Chests
- Filled with air
- Use high kV and low mAs
107
What affects the diagnostic quality of radiographs?
- Correct exposure factors
- Correct positioning
- No movement blur
- Good contrast
- Correct labelling
108
What is the inverse square law?
- Film Focal Distance and intensity are linked
- Doubling FFD reduces intensity over given area by 1/4
- The intensity of the primary beam is inversely proportional to the square of the distance from the source
- Further away from the source, less intensity of x-rays
- New mAs = old mAs x (new FFD^2 / old FFD^2)
109
