Radiography Flashcards
1
Q
What is scatter radiation?
A
The movement of radiation in different directions after it’s had contact with matter (i.e. not the primary beam!)
2
Q
What can increase scatter?
A
High kV or high exposure factor
3
Q
What are sources of high scatter radiation?
A
The patient’s thickness is too large
Collimator not used effectively
Too high a voltage
4
Q
How can scatter be controlled?
A
Using a grid! (85-95% scatter reduction)
Decreasing the thickness of the patient (e.g. compression bands)
Reducing the voltage
5
Q
What is the basic structure of a grid?
A
Alternating lead strips with radiolucent material gaps to allow the primary beam to pass through (made from aluminium or carbon plastic fibres)
6
Q
What is a grid ratio?
A
The ratio of the height of each lead strip to the distance between the strips.
7
Q
What is a grid ratio used for?
A
To calculate the grid factor. This is then used to calculate the correct exposure factor (mAs) (correct exposure factor with grid = exposure factor x grid factor)
8
Q
Where must the centre of the X ray be focussed on a grid?
A
On the grid focal point
9
Q
What is the Grid Focus?
A
The distance between the tube head and the grid
10
Q
What is Grid Cut off?
A
An unwanted absorption of x-rays via an x-ray grid,
11
Q
What does Grid Cut-off cause?
A
Lighter image and white lines over the unexposed areas of film.
12
Q
What causes Grid cut-off?
A
Improper centring of X ray tube head over the grid
Titling tube laterally
Tilting the grid
Focussed grid upside down
13
Q
Where can grids be placed?
A
On top of a cassette
Within a cassette (built in)
Under the X ray table
14
Q
Name the common grid types
A
Parallel
Potter Bucky
Linear
15
Q
What is a parallel grid?
A
Lead strips run parallel to each other
Cheapest, most common
Stationary grid
Gives a good result
16
Q
What is a Potter Bucky grid?
A
Mobile grid - moves rapidly from side to side
A parallel grid that is integrated into the table
Eliminates fine lines usually visible with a stationary grid
17
Q
Why does care need to be taken when handling grids?
A
Delicate and expensive
If dropped on its side, can damage inside permanently - lead stalks may become bent or warped
18
Q
How is an X ray actually recorded? Using what?
A
Radiographic Film
- sensitive to both light and X rays
The X rays are converted to a latent image
Processing of the film allows the image to be visible
19
Q
What are the 2 types of X ray film?
A
Duplitised and Single
20
Q
What is the better type of film and why?
A
Duplitised
- layers are duplicated on either side of the polyester base (emulsion/active layer)
- increases its efficiency - more effective at producing an image than single
- results in a lower radiation dose to the patient
(the single just has one active side and a counterbalanced side to prevent curling)
21
Q
How should X ray film be stored?
A
Within expiry Rotated stock Vertical! - prevents black lines/crescents Handle from corners with clean hands Handle in paper Keep away from chemicals On dry side of room Away form radiation and light
22
Q
What does film contain?
A
Silver halide crystals - specifically silver bromide
these are sensitive to x rays and light
23
Q
How is an image produced on the film?
A
There is a sensitivity speck on the film. During exposure, the silver bromide migrates to the sensitivity speck and the bromide is released.
The more silver that move, the more bromide is released and the darker the film becomes
24
Q
What determines the film speed?
A
The size of the grain that’s within the film - the larger the grain, the faster the film
The type of film used (either screen or non-screen)
25
How does film speed affect image?
The faster the film speed the poorer the image generally
26
What are the 2 types of film?
Screen and Non-screen
27
Describe a screen film?
Intensifying screen used
Cheaper than non screen films
Speed is characterised by the grain size
Film speed increases with grain size but loses definition
Shorter developing time and shorter exposure time than non-screen films
28
Describe Non-screen film?
Light-tight envelopes
Used for high definition in areas where thick cassettes cannot be used e.g. dental x rays
Greater developing time and greater exposure time than screen films.
Greater definition than screen films
29
Can you use any screen with the screen films?
No- it has to be able to detect the light given off by the screen!
30
What are the 2 types of Film Screens?
Calcium Tungstate and Rare Earth
31
Describe the calcium tungstate screen
Emits blue light
| Film used with it must be 'blue-light sensitive' or 'monochromatic'
32
Describe the Rare earth screen?
Emits green light and sometimes blue
| Film used with this has to be sensitive to blue and green lights or Orthochromatic
33
What affects the intensifying screen speed?
The size of the phosphor grain
Thickness of the intensifying screen layer
Presence or absence of the reflective layer
34
What is important to get a good sharp image?
Contact with the film screen
35
How would you clean a film screen or cassette?
Cleaned on a regular basis dependant on workload. Any dirt on it with show up as bright white specks
- brush with a soft brush to remove any debris
- Use a preparatory cleaner with a lint-free swab
- Use a circular motion from inside to out
- stand the film/ cassette vertically to dry in a dust free area
- label and date
36
What are the 2 types of digital radiography?
Computed Radiography and Direct Radiography
37
What are the main differences between digital radiography and analogue radiography
No film solution used
Quicker
Less equipment
38
What equipment is needed for a CR?
Imaging plate
39
Describe an imaging plate?
Phosphor plate
Looks like an intensifying screen
Has a large layer of crystals that can store X ray energy
Placed inside the cassette
40
What is the process of CR ? Simple!
After the X ray has been taken, the cassette is placed into a reader
The reader scans the plate with a red laser, causing the electrons to fluoresce and produce light. The light is converted to a digital signal and an image is sent to the computer
The image is then erased form the plate
41
What are the advantages of digital imaging (CR) to analogue imaging?
- More sensitive to radiation so can use lower dose
- Shorter exposure times
- Easier to use
- Less time consuming
- More forgiving than film giving better image
- Fewer need for repeat exposures
- can get objects of different thicknesses onto 1 image
- quicker processing time - no chemical development
- no chemicals or associated hazards, environmental impacts, costs of disposal
- reduced GA/sedation time
- No dark room needed - less equipment
- Immediate review/analysis of image
- Can be sent to specialist - email, burned to disc
- Editing possible
- Can store electronically - saves space
42
How does DR differ from CR?
Requires a special DR plate
- converts light into a digital signal directly without requiring a reader
- much more expensive!
43
What is a good DR plate?
Coated with amorphous silicone
44
What are the benefits of DR over CR?
- real time image
- highest quality digital image
- zoom facility
- maximum resolution to identify small anomalies
- can use for many helpful things .e.g. comparing 2 pictures side by side, measuring pins for orthopaedics whilst someone is X raying, calculating angles for TPLO from theatre
- Moral of staff increased as less admin
- no need for films allows for improved positioning
- data can be stored within the image
45
What are the limitations of DR?
```
Expensive!!!!!!!
CPD needed for staff
Staffing for the day
Space?
Certification programmes needed
```
46
When should radiography be used to check for in a debilitated patient?
To check for any invisible trauma e.g. diaphragmatic trauma, bladder rupture, internal bleeding etc.
A fracture also, but this can wait as its not life-threatening!
47
What must we consider before X raying a debilitated patient?
Is it worth it? Do the potential benefits of the scan outweigh the risk to the patient?
48
What must be done before an emergency patient is X rayed?
Stabilise!
o2 therapy, IVFT
Have to consider if vital signs are stable enough for GA/sedation - if not, vet may have to hold as an exceptional circumstance.
Need to ensure that the positioning and manipulation of the patient isn't contraindicated
49
When should radiography be delayed?
If animal's condition may be aggravated by radiographic procedures
The benefits do not outweigh the risks
If wont have an effect on the treatment plan
50
What is very important in preparing a debilitated patient for radiography??!
Debilitated patients rarely need, and often cannot tolerate, fasting and/or enemas in relation to abdominal radiology
51
What are the main point to remember in radiography of exotics?
Lower kV generally due to smaller size
(chelonia may require high kV due to shell)
Grids rarely used as patients rarely >10cm
Non screen films better to show finer details
Need rapid exposure of 0.008-0.016s as high respiratory rates can cause blurry images
Need chemical restraint usually
52
What is PACS?
Picture Archiving and Communication Systems
Makes storage and retrieval of images easy. Can store data with the image (e.g. patient details, consultation numbers etc)
Can store previous X-rays together, allowing continuity of patient care and assessment
53
What is kV?
Kilovoltage = energy across the tube. It determines the penetrating power of the xrays and therefore affects the contrast and density of the film.
54
The higher the kV, the higher the ____?
Penetrating power
55
What should the aim be when setting kV for an image?
Should be as low as possible sufficient enough to penetrate the part of interest
56
What will too high a kV result in?
Increased scatter
| Lack of contrast
57
Which would need a higher kV, a small dog or a large dog?
A large dog as its thicker so needs more penetrative power
58
What is the mA?
The milliamperage i.e. the current supplied to heat the filament in the tube head. It determines the quantity of Xrays produced, and therefore affects the density of the film (i.e. the blackening effect the X-rays have on the radiograph).
59
What temperature can the Tungsten filament withstand?
3360 degrees C
60
What does mA not affect?
The penetrating power and therefore the contrast
61
What will happen if the mA is too high or too low?
mA too high will produce a film that is too dark (too many particles)
mA too low will produce a film that is too light (not enough particles)
62
What kind of image will be produced is the mA is too high and the kV is too high?
A dark image with no contrast
63
What does the time of an Xray control?
The time that the animal is exposed to the x ray and the amount of x rays that reach the film.
64
What is mAs?
Milliampere seconds
= the exposure factor
indicates the amount of xrays that are being used for that image
65
What can be done with mA and s to produce the saem exposure factors
Can alter either as long as they still multiply to make the same mAs! So if movement is an issue, you'd want a shorter exposure time and therefore you would need a higher mA/current
66
What is the focal film distance?
The FFD is the distance from the focal spot of the x ray tube head to the x ray film
67
What happens to the quality and intensity as the FFD increases?
The quality remains the same, but the intensity decreases
68
Should the FFD be changed? What is the usual FFD value?
Not ideally. 75cm
69
What will happen to the mAs if the FFD is increased?
They will have to be increased. The amount by which they are increased is proportional to the square of the difference
70
What happens to the mAs is the FFD is doubled? Why?
If the FFD is doubled, the mAs has to be x4
| because the intensity is reduced by 1/4
71
What is the inverse square law?
new mAs = old mAs x (new FFD^2 / old FFD^2)
72
What factors of the Xray beam affect the image?
```
kV (the penetrating power)
mA (the quantity of Xrays)
Seconds (the time and therefore amount of X rays)
Collimation of the beam
FFD
```
73
What can affect the image in terms of the patient?
Movement - should sedate or GA
Positioning - should use cradles, wedges, sandbags
Preparation of area - compression band, contrast
74
What can affect the X ray in terms of film?
Intensifying screen or non-screen
75
What do radio-opaque and radio-lucent mean?
```
Radio-opaque = not allowing the x rays to pass
Radio-lucent = permits passage of X rays
```
76
What 2 things does the degree of absorption of X rays depend on?
What effect do they have on the colour?
Atomic number of tissues
Specific gravity of tissues
(bone has higher both than soft tissue)
Thickness of tissues
Combination of Atomic number and specific gravity cause colour variations:
77
What is line voltage compensation?
The normal mains alternating current (ac) fluctuates and can result in poor quality x rays. Large machines have an auto-transformer whereas smaller machines have a volt-meter dial.
78
What is the formula to calculate mAs initally?
mAs = mA x s
79
What happens to the mAs if kV is
a) increased by 10
b) decreased by 10
a) mAs are halved
| b) mAs are doubled
80
What is the formula to calculate the new mAs if the FFD is altered?
new mAs = old mAs x (newFFD^2 / old FFD^2)
81
What happens to the mAs if the FFD is doubled?
x4
82
What is Santes Rule?
kVp = (2 x thickness in cm) +40
It is a method of measuring the peak kV in relation to area thickness
83
What does kVp mean?
The peak kV i.e. the maximum energy available at that kV setting.
84
What are films stored in?
A filing system, film hoppers or PACS (for digital)
85
What are the 2 types of safe light? What is a safe light?
Direct safe light
= shine directly over the working area
Indirect safe light
= produce light upwards which is then reflected from the ceiling
A safe light is a light that can be used in the dark room and the light produced will not affect the film. It has a small wattage (15-) and a filter that removes light from the blue and green spectrum
86
What are the 2 most common light filters?
Brown filter for blue light sensitive film
| Dark red filter for green and blue light sensitive film
87
How can screens be cleaned?
Gently in circular motion with cotton wool and mild soap. Placed vertically to dry naturally
88
What info is required when labelling a radiograph?
Name and address of the hospital or vets
Date the x ray was taken
patient ID (name, owner name, patient sex and breed)
89
What can be used to mark a radiograph?
Lead pencil or lead impregnated tape
90
What is a good quality radiograph a result of?
Good positioning of structures
Quality of contact
No artefacts
91
Where should the part to be x rayed be? (in terms of the film)
As close to the film as possible!
92
Imaging what can make scatter worse? What does it to the image?
Imaging a thick area.
| Results in random darkening of the film leading to loss of contrast and definition
93
What causes scatter radiation?
Scatter is produced when the primary beam interacts with objects in its path e.g. patient, table top etc. The amount of scatter depends on the intensity of the beam, the composition of examined tissues, the kV and the thickness of the patient.
Scatter usually travels in an upward path
94
What can be used to reduce scatter?
Tight collimation of LBD and use of grids
95
What is fog?
the darkening of the film unrelated to the image
96
What causes fog?
Scatter
Accidental exposure of image to white light or radiation
Unsuitable safe light filter for film and screen used
Prolonged storage
Overdevelopment
Poor contact between the screen and the cassette (e.g. due to cassette damage)
97
What effect does phosphor crystal size have in the definition?
Larger grain sizes gives faster film speed.
| The faster the film speed the worse the definition
98
What would you use if great clarity is required e.g. for a dental?
A non-screen film - takes longer though!
99
What is focal spot size?
The focal spot is where the electrons collide. The size of this spot is important in forming the image
100
What effect does a small or large FSS have on the image?
A small focal spot produced an image with great clarity, but produces a LOT of heat and therefore exposure factors are limited.
A larger Focal spot, the images becomes less sharp and more shadowed, but higher exposure factors can be used
101
What is the Penumbra effect? When does it happen?
The penumbra effect occurs when the focal spot size is bigger than a pin.
Penumbra means 'partial shadow' which is blurring of the margins related to the geometry of the beam.
102
Why is a large focal spot ever chosen if it produces less sharp images?
Because imaging over a wider area is beneficial for thicker tissues as it allows the use of higher exposure factors
103
What types of anode can use each focal spot size?
A stationary anode is limited to a large focal spot size because it cannot accommodate the higher temperatures of a small FS. A rotating anode can use a small focal spot as the rotating motor allows dissipation of heat
104
What is the magnification/object film distance? What is the ideal value?
The distance between the patient and the cassette. Ideally, the patient should be as close to the cassette as possible and the area being x rayed too (i.e. don't have the limb being x rayed on the top!)
105
What is the aim of positioning in terms of distances?
To keep the object film distance as small as possible and the focal film distance as large as possible
106
What is an artefact?
Something that shouldn't be in the image. It can be artificial and due to errors in equipment, software, human error, tilted grid etc.
e.g. lead collars, hands, blur, fog, chemicals, static
107
What do we do to prevent motion artefacts?
Lower the exposure time and increase the mA
108
Why is contrast media used?
To visualise soft tissues
109
What are the 2 types of contrast media?
Positive contrast media and negative contrast media
110
What is a positive contrast media?
Contains elements of a high atomic number that are radio-opaque (i.e. appear white on X ray film - whiter than bone)
111
Name the 2 main types of contrast media?
Barium compounds and water-soluble iodine compounds.
| Both have higher atomic numbers and densities than soft tissues.
112
What is a negative contrast?
Gases which because of their low density are radiolucent and appear black on an Xray..
The low SG
113
Give examples of negative contrast
Room air, o2, co2 and n2o
114
Describe what double contrast is? Give examples of when this would be used?
Use of a positive and a negative contrast media. Gastrogram - use barium to line the organ and use air to distend it.
Cystogram - use iodine to line the bladder and then distend with air.
115
What care needs to be taken when using barium and why?
- cannot use if any suspicions of perforations!
| - If it leaks out, it will not move out of the area causing FB signs, granulomas and peritonitis.
116
What should you use for a gastrogram with suspected perforation ? Why wouldn't you just this all the time if it's safer?
Water-soluble iodine.
Because its water soluble, it dilutes as it moves down the GI tract (because it draws extracellular fluid in)and it doesn't give as clear an image.
117
Give an example of a barium product
Micropaque.
| in a powder or paste or solution.
118
What are the advantages and disadvantages of using barium
Advantages - inert (doesn't move) and insoluble.
Disadvantages - may cause a FB reaction. Messy and need to ensure that cassette is clear before taking image to avoid artefact,
119
When should barium be used?
Should give an enema at least 24hours before. Preferable one 3 hrs before and 1 hr before a barium meal is given.
120
What two types can water-soluble iodine be?
Ionic or non-ionic
121
What are the features of water-soluble iodine?
When they are placed in the bloodstream, fluid from extravascular space is drawn into the bloodstream.
They are soluble so dissolve quickly.
Is excreted via the kidneys.
122
What warnings are there with ionic salt preparations?
All have local irritant effect and should be administered IV.
They are contraindicated in myelography.
123
What types of contrast is used for myelography?
Low osmolarity non-ionic solution.
| It doesn't draw fluid into vascular space and therefore is safe for use in myelography of the spinal cord.
124
What is myelography?
Use to identify cord compression. Indicates lesions that are not detectable on ordinary X rays
125
What are the 2 injection sites for myelography
Cisternal puncture - into the cisterna magna (in base of skull)
Lumbar puncture - needle into the caudal equina
126
What should be done to contrast media before being injected into the subarachnoid space?
Warmed to body temperature to reduce viscosity and ease injection
127
How can a patient be prepared for myelography?
```
- have IV access - have patient well-hydrated and on fluids.
Has be to anaesthetised.
Clip relevant area and surgical scrub
Use spinal needle (20-22G)
Warm contrast media
Check dose variations
Syringe and sample bottle for CSF
Aid to elevate the head (90 degrees to spine)
Elevate table to about 10 degrees.
Sterile gloves
```
128
What drug is contraindicated for myelography? What should be used instead?
ACP is contraindicated because it has a risk of causing seizures (or has a 'low seizure threshold')
129
What is the most common study using contrast media?
Gastrointestinal study - can be upper or lower. Used to evaluate the stomach or intestines. Used to investigate vomiting, abnormal bowel, suspected fb, weight loss etc.
130
When would stomach tube be used for contrast media study?
When only the stomach is being looked at. In this case double contrast can be used.
131
What is the contrast media usually used for gastrogram?
Barium sulphate
132
What equipment is needed for a gastrogram?
Syringe
Stomach tube (if only stomach being looked at)
Water soluble iodine or barium
Lubricant!
133
Would you give a GA for a gastrogram?
No because need them to swallow it
134
How would you prepare a patient for a gastrogram?
Fast for 12-24 hours
Cleansing enema 24 hours before procedure and 3hrs and 1 hr before procedure.
Sedate patient if necessary
Should take a radiograph before CM also.
135
What is the suggested sedative for a patient receiving a gastrogram?
Suggested sedative is ACP.
| Shouldn't use GA as slows gut and shouldn't use atropine as slows gut.
136
Describe the procedure of a gastrogram
Administer barium or water-soluble iodine (if suspect perforation).
Place the CM into the patients mouth using a syringe. Allow patient to swallow or use oro-gastric tube, Infuse a small amount of water to check correct placement.
Cough will suggest its in the lungs.
Should take survey (or sequential) pictures.
137
When should radiographs be taken?
Immediately after CM administered. Take radiographs at 15.30.60 and 90minute intervals.
138
What is used for a pneumocystography?
Contrast media is air or gas (such as co2). Negative CM
139
What should you do when administering air into the bladder?
Palpate the bladder whilst administering air to prevent air or over-distension of the bladder.
140
What equipment is needed for cystogram?
```
Urinary catheter
3 way tap
Syringes
Sterile lubricant
Sterile spray
Gauze
GA if possible
Sterile gloves
Otoscope speculum
Kidney dish
```
141
How does CM interfere with cytogram investigations
If need a urine sample should take before CM inserted as it can increase the SG and give a false reading
