Diagnostic Imaging Flashcards
(219 cards)
1
Q
State properties of x-rays
A
Part of electromagnetic spectrum (travels at same speed in straight line but varied wavelengths/frequencies)
High energy wave due to short wavelength and high frequency
2
Q
How is velocity of an x-ray calculated?
A
Wavelength x frequency
3
Q
Define wavelength
A
Distance between two consecutive peaks
4
Q
Define frequency
A
Number of times peak passes a fixed point per second
5
Q
How are wavelength, energy of the wave and frequency related?
A
Frequency is proportional to energy of the wave and inversely proportional to wavelength
6
Q
What are gamma rays used for?
A
Scintigraphy
7
Q
What are the different types of x-ray machines available and their features?
A
Portable- small and compact, easy to move, linked exposure, low output as use mains voltage
Mobile- uncommon, larger, higher output than portable
Fixed- permanently installed, tube on gantry, higher output due to specialised electrical supply
8
Q
What are features on x-ray control pannels?
A
On off button Mains voltage compressor (usually automatic unless old machine, adjusts incoming voltage, varies 215-240V to keep kV constant) kV control mA control Timer
9
Q
What is the main legislation for use of x-rays and what is its main priciples?
A
Ionising radiations regulations 2017
Only radiograph for clinical reasons, exposure to personnel to minimum, dont exceed dose limits
10
Q
Why is radiation dangerous and what effects can it have on the body?
A
Invisible, can’t feel, can penetrate, cumulative effects
Carcinogenic, somatic (changes to tissues shortly after exposure particularly rapidly dividing cells), genetic mutations
11
Q
What are sources of radiation hazard?
A
Tube head
Primary beam
Scatter
12
Q
What are ways of reducing effect of scatter?
A
Collimation
Keep area of interest close to plate
Lead protection worn
Grid used
13
Q
What safety measures need to be in place for all practices using x-rays?
A
General- HSE notified of using x-rays, practice has RPS and RPA (radiation protection supervisor and advisor)
Local rules- no manual restraint, protection used in controlled areas, guidelines if pregnant, warning signs for exposure
System of work- legal requirement displayed, details RPA/RPS, description and access to restricted areas, how to respond to incidences, working practices
14
Q
What is meant by a controlled area and what are features of it?
A
Where x-rays are taken and dose exceeds 7.5mSv/h
Specific room with lead lined or thick walls to prevent penetration
Large enough for 2 people to be 2m from primary beam
Warning signs and indicators of exposure
Restricted to classified personnel
15
Q
How are staff protected from x-rays?
A
Minimal exposure- rotate staff, minimal time taking x-rays
Distance- at least 2m from primary beam, leave room where possible, never manually restrain
Barriers- PPE, lead glass, lead-plywood doors
Dosimetry- follow dose limits, wear dosimeter
16
Q
What are types of dosimeters available in practice?
A
Film badges- film blackens in proportion to exposure
Thermoiluminescent detectors- crystal absorbs radiation, heating causes light emission proportional to radiation dose
17
Q
What are the protocols in place for dosimeter monitoring?
A
Worn for 4, 8 or 13 weeks then returned to NRPB for reading, reports kept for 2 years
Need individual badges worn at waist level, cant wear outside practice
18
Q
State the two methods of x ray formation
A
General emission- major
Characteristic emission- minor
19
Q
Describe how general emission x-ray formation works
A
Electrons rapidly decelerate when hit tungsten target as the pass through tungsten atoms and interact with electrons in atoms, energy lost from deceleration released as x-rays
20
Q
Describe how characteristic x-ray formation works
A
Incoming electrons knock out electrons from tungsten orbits and electron drops from outer to inner shell releasing energy as x-rays
21
Q
Describe the x-ray tube
A
Cathode and tungsten anode in vacuum, immersed in oil to help heat conduction and insulation, surrounded by lead except window for x-ray beam
22
Q
Describe how x-ray tube generates x-rays
A
Small current passed through cathode filament heating it up producing cloud of free electrons known as thermionic emission
Focusing cup keeps cloud of electrons together preventing cathode repelling
Potential difference applied across tube causes electrons to hit tungsten target and x-rays are produced
23
Q
Why is heat a problem in x-ray generation?
A
Interaction between electrons and tungsten is 99% heat and 1% x-ray generation
Electrons get focused on focal spot so heat dissipation is issue
24
Q
What are the two types of anodes used to aid heat dissipation of x-ray generation?
A
Stationary- tungsten in block of copper so conducts heat from target, portable machines
Rotating- anode on disk with angled edge, tungsten track around edge to heat gets evenly distributed and is lost by radiation and convection from disk, on larger machines
25
What is meant by kV control?
Controls potential difference across tube between anode and cathode
26
What does mA control do?
Varies small current heating the cathode
27
How does the timer on x-ray control panel work?
Closing activates kV/high tension and mA/filament circuits
28
Describe how kV control works
Step up transformer supplies high voltage across tube with higher kV the higher potential difference across the tube, faster electrons will travel so have more kinetic energy and produce higher energy x-rays
29
Why is higher kV needed, what is typical kV ranges and how does increasing by 10kV effect exposure?
To produce higher quality images and to penetrate thicker tissues
40-120kV
10kV increase doubles exposure
30
How does mA control effect the amount of x-rays produced
Allows electrons to be emitted from the cathode, higher the mA the hotter the cathode gets and more electrons are accelerated across the tube, producing more x-rays
31
What are the typical ranges for mA?
Portable- 20-60mA
| Fixed- 1000mA
32
How is time of exposure linked with x-rays production?
Increasing time increases number of x-rays produced
33
What is known as mAs?
mA and time
34
What effect does doubling mAs have on exposure?
Doubles exposure
35
How is mAs affected for thicker tissues?
Needs to be higher
36
What parameters are considered for exposure charts?
```
kV
mA
s
Distance from x-ray tube, animal and plate
Use of grid
Body part
```
37
Describe how an exposure chart is created
Note exposure factors used on good images to build up a bank of them for different situations
Take exposure and increase kV when tissues are thicker
Repeat bad images until you get a good image to record
38
What must be the same to use exposure charts?
Machine
Film focal distance
Digital detector
Use of grid
39
What is seen for over and under exposure?
Overexposed- areas of blackness
| Underexposed- grainy and lacking contrast
40
What is the relationship between intensity of x-ray and distance from x-ray tube?
Intensity is inversely proportional to square of distance from x-ray tube
Doubling distance from tube quarters intensity of radiation
41
Define film focal distance/FFD
Distance from x-ray tube to image receptor
42
What need changing if FFD is changed and how is it calculated?
mAs
| New mAs = old mAs x (new distance squared/old distance squared)
43
Define object film distance
Distance between object radiographed and x ray detector
44
What is the effect of increasing object film distance on the image produced?
Gets magnified
| Reduces sharpness due to penumbra
45
How is distortion of images prevented?
Keep area parallel to cassette and perpendicular to x-ray beam
46
What is the focal spot in x-ray machines?
Area of anode hit by electrons
47
What are advantages and disadvantages of keeping focal spot small as possible?
Advantages- image produced best if there's a point source of x-rays, limits penumbra
Disadvantages- causes issues for heat dissipation
48
When is fine focus used in x-ray machines?
Smaller and thinner areas of anatomy
49
Define penumbra
Margin of blurring around edge of a structure due to beam diverging
50
What is the difference between actual and effective focal spots?
Target on anode is angled so electrons hit actual focal spot then beam is produced from smaller effective focal spot
51
Why is filtration of x-rays needed?
X-ray beam contains spectrum of energies
| Low energy x-rays have insufficient energy to penetrate to produce an image so thin sheet of aluminium filters them out
52
What is meant by collimation?
Using light beam diaphragm to reduce aperture therefore primary beam size produced on the patient
53
What are the benefits of collimation?
Reduce unnecessary exposure to the patient
Reduce scatter produced
Improves image quality
Reduce exposure into controlled area
54
State the ways x-rays can interact with matter
X-ray photons pass through unchanged
X-ray photons are absorbed
X-ray photons are scattered
55
How can x-ray photons pass through matter unchanged and what effect does this have on the image produced?
Travel in straight line without losing energy
| Forms useful x-ray image
56
Define radiolucent
Permeable to x-rays
57
Define radiopaque
Blocks x-rays
58
Describe how x-rays can be absorbed as they pass through matter
Depending on if material is radiolucent or radiopaque depends on proportion absorbed, depends on atomic number of tissues atoms
59
How does absorption of x-rays differ between tissues? (general, bone, gas, soft tissue)
General- higher atomic number, higher density and thicker tissue increase absorption due to more interactions
Bone- high atomic number, good absorption
Gas- low density, poor absorber
Soft tissue- intermediate atomic number and density, varied absorption
60
What colours are seen on x-rays when passing radiolucent and radiopaque tissues?
Radiolucent- black
Radiopaque- white
Between- grey
61
Describe what causes x-ray photons to scatter when interacting with matter and the impact this has
Deflected in random directions, some losing energy
| Reduces image quality and not useful as dont reflect anatomy, increase exposure risk
62
When and why are grids used?
At high exposures to reduce the large amounts of scatter than will be produced, improving image quality
63
What is an x-ray grid?
Flat plates with series of thin lead strips to absorb scatter alternating thin radiolucent strips to allow primary beam through cassette
64
Why does use of a grid increase exposure factors needed?
Some of primary beam gets absorbed by the lead and some scatter passes through spacing material
65
What is a grid ratio?
Height of strips/width of spacing
66
What are typical grid ratios and what affect does a higher ratio have?
6:1-12:1
| More efficient at removing scatter but removes more primary beam so need higher exposure
67
What effect does increasing lines per cm on a grid have?
Removes more scatter but absorbs more primary beam so need higher exposure
68
Define grid factor
Number mAs is multiplied by when using grid
69
What is a parallel grid and what are its advantages and disadvantages?
Parallel equal height lead strips
Advantages- cheap, easy to use, can use either way up, at any FFD or centring point
Disadvantages- beam divergence means increased primary beam absorption at edges
70
What is a focused grid and what are its advantages and disadvantages?
Lead strips slope progressively towards grid periphery
Advantages- no image cut off as mimic divergence
Disadvantages- needs correct orientation and centring, correct FFD needed to match divergence, expensive and complex
71
What is a pseudo-focused grid and what are its advantages and disadvantages?
Parallel lead strips with height reducing to periphery
Advantages- reduction of grid ratio to periphery compensates cut off in parallel grids
Disadvantages- needs correct orientation, more expensive
72
What is a cross-hatched grid and what are its advantages and disadvantages?
Lead strips at right angles to each other
Advantages- efficient at removing scatter
Disadvantages- need high exposures, accurate centring, expensive
73
What is a moving grid and what are its advantages and disadvantages?
Parallel grid permanently under radiolucent x-ray table, oscillates during exposure
Advantages- fine lines as in stationary grids blurred so not seen
Disadvantages- expensive, always used
74
What is meant by digital imaging in radiography?
X-ray machine and table are unchanged and images are produced on various image receptors
75
What are the advantages of digital imaging?
Low running costs
Higher quality images
Adjustments can be made reducing time and exposure
Easy to store, communicate and retrieve images
76
What are the disadvantages of digital imaging?
Viewing limited to availability of computer
May have artefacts
Need backing up
77
Describe how computed radiography works
Uses storage phosphor cassette
Energy from interactions with x-ray beam is stored in phosphor, later released as light when excited by laser beam in plate reader
Light is captured and quantified by photomultiplier tubes which converts to electrical signal as image on screen
78
How is phosphor plate for CR erased for re use?
Bright light removes residual energy, takes 1-2 minutes
79
Describe how direct radiography works
Patient information is entered into system
Flat panel detector produces instant image on connected monitor
Processing algorithms and formula reconstructs image depending on anatomical region being viewed
Can manipulate filters, contrast, size, orientation, measurements
80
How are digital images stored?
Computer files in ditcom format
Regularly backed up, can print at extra cost
Long term storage on PACS for identification, manipulation, back up and retrieval of images
81
What is meant by PACS and ditcom?
PACS- picture archiving and communication system
| Ditcom- digital imaging and communications in medicine
82
What is meant by a satisfactory radiograph?
A radiograph that can be diagnostic
83
List factors assessed when looking at image quality
```
Opacity
Contrast
Sharpness
Technique faults
Artefacts
```
84
How does opacity affect image quality and what effects opacity?
How black or white overall
| Depends on tissue type, thickness, exposure factors, processing of image
85
How does contrast affect image quality and what effects it?
Difference in tone between areas either long or short scale contrast
Depends on part being x-rayed, atomic number, density, algorithm applied, scatter
86
How does sharpness effect image quality and when affects it?
How clearly defined the image is
| Depends on movement, scatter, object film distance
87
State some technique faults that effect image quality of radiographs
```
Poor positioning
Not enough projections taken
Not using L/R markers
No date or patient information
Movement blur
Incorrect grid use
Poor centring and collimation
```
88
List some artefacts that can affect quality of radiograph image
Double exposure- only on CR
Digital exposure error
Uberschwinger artefact- radiolucent zone around areas with high density difference caused by excess edge enhancement by computer
Ghost artefact- residual image from previous radiograph
Moire artefact- bands across image on CR due to interference between frequency of laser reader and lines/cm on grid
Dirt on light guide
89
What is contrast media?
Agents more or less opaque than surrounding tissue
90
What is the purpose of contrast studies?
Introduce contrast between otherwise same contrast structures
See normally poorly visible structures
Gain information on soft tissues and internal anatomy of structures
91
What is the difference between the two types of contrast media?
Positive- high atomic number, white on radiograph
| Negative- low density, black on radiograph
92
What are examples of each type of contrast media?
Positive- barium, iodine
| Negative- air, carbon dioxide
93
State the use, formulation and properties of barium for contrast studies
GI tract to provide good mucosal detail
Powder or suspension, reasonably palatable
Inert, non-toxic, no osmotic effect so wont draw in water
94
What are the properties of ionic iodine for contrast studies?
```
Irritant extravascularly
Toxic in large doses
Viscous, reduced before use with warming
Water soluble preparation
Contraindicated with CV or renal insufficiency and for myelography in subarachnoid space
```
95
What are the properties of non-ionic iodine for contrast studies?
Viscous
Water soluble preparation
Cause potential side effects- anaphylaxis, nephrotoxicity, pyrexia
More expensive
96
How is iodine given to patients for contrast studies and how is it removed from the body?
IV
| Renal excretion
97
What are the positives and negatives of negative contrast media?
Positives- cheap, easy to use, minimal risk or side effects, combine with positive for double contrast study
Negatives- small risk of air embolism, poor mucosal detail, less contrast than positive due to air already in body
98
What are indications for performing contrast studies?
The study will demonstrate a lesion
Time
Cost
99
How do you prepare for contrast studies?
Take plain radiographs to ensure its needed and to check correct positioning and exposure
Ensure patient is properly restrained
100
What situations mean a contrast study isn't needed?
Plain radiography is enough
Endoscopy for GI better
Ultrasound for urinary tract in many cases
CT and MRI used instead of myelography
101
What are indications for doing barium swallow study and what are risks?
Indications- dysphagia, regurgitation, suspected oesophageal rupture
Risks- aspiration, especially if struggling to swallow, weak, respiratory distress
102
What is shown by a barium swallow test and how is it carried out?
Shows pharynx and oesophagus when swallowing, most of barium should be in stomach after swallowing
Use liquid barium or food with barium in, iodinated contrast if suspect rupture
103
What is the purpose of barium follow through and how is it carried out?
Evaluate stomach and small intestine
| Liquid barium give by mouth or stomach tube, radiographs taken immediately and at intervals until reaches colon
104
What are disadvantages to barium follow through study?
Time consuming
| Can be hard to interpret radiographs so endoscopy or ultrasound preferred
105
What is the purpose and how is barium enema carried out?
Evaluate large intestine
| Liquid barium infused into rectum post enema, can follow with air for double contrast
106
What are advantages and disadvantages of barium enema contrast study?
Advantages- minimal complications
Disadvantages- messy, hard to interpret, faeces remaining look like lesions, could have leakage or rupture if over inflate, tend to use ultrasound instead
107
What contrast media is used for the urinary tract and why?
Water soluble iodinated contrast medium as barium is irritant to bladder and cant be used IV
108
What is the purpose of excretory urography study and how is it carried out?
Assess kidney, ureters and vesicoureteral junction
Bolus of contrast given to peripheral vein, follow through with radiographs taken immediately and then every 5 minutes for 15 minutes
109
What do the radiographs taken at each time interval for excretory urography show?
Immediately- nephrogram (deliniates kidneys)
5 minutes- pyelogram (renal pelvis visible)
10 minutes- ureterogram (ureters visible)
15 minutes- ureterovesicular junction (where ureters meet bladder)
110
What does cystography show and how is contrast introduced?
Delineates bladder
| Introduced via urinary catheter
111
What are the 3 types of cyctography?
Pneumocystogram- air only, shows bladder location, any large masses or thickenings
Positive contrast cystogram- iodinated contrast used
Double contrast cystogram- uses air and iodine to deliniate wall and contents
112
What is the purpose of urethrography and how is it carried out and are there any risks?
Delineate urethra and vagina
Water soluble iodinated contrast introduced via foley catheter to distal urethra, radiographs taken at end of injection when vagina and urethra are distended by contrast. Can be combined with cystography
Small risk of urethral damage
113
What is the purpose of myelography?
Delineate subarachnoid space, localise lesions on spinal cord or surrounding structures
114
Why do you need to use non-ionic water soluble contrast medium for myelography?
Ionic can cause seizures and arachnoiditis
115
Why is CT and MRI preferred over myelography and when is CT myelography used?
Non invasive
| increases soft tissue detail
116
What are the risks of myelography and how can they be reduced?
Seizure if enters the brain, minimal neurotoxicity otherwise
| Keep head elevated on recovery to stop entering the brain, IV catheter placed with IV diazepam available
117
What are other contrast studies that can be performed?
Angiography- blood vessels
Arthrography- joints
Fistulography- sinus tracts
118
What is ultrasound and why can't it travel through a vacuum?
High frequency sound waves
| Relies on compression and relaxation of physical material
119
How does the velocity of ultrasounds differ for air, soft tissue and bone?
Air- 330m/s
Soft tissue- 1540m/s
Bone- 3200m/s
120
What are advantages of ultrasound?
```
Widely available
Safe, no ionising radiation
Quick
Non-invasive
Rarely need GA
Good soft tissue detail, including internal structures
Can distinguish between soft tissue and fluid
Guide biopsies
Functional information of heart
```
121
What are some disadvantages of ultrasound?
Relatively expensive
Easily damaged
Need to clip patient
Experience needed to interpret images, real time so cant look back
Gas, fat and bone limits vision
Biopsies usually needed for definitive diagnosis
122
How is ultrasound produced?
Piezoelectric effect- electric voltage applied to disk in transducer and disk expands and contracts with movement proportional to voltage, movement produces a sound wave
123
What is meant by pulsed production of ultrasound?
Transducer produces ultrasound by piezoelectric effect then sends out pulse of sound (3 wavelengths of 1.5mm at 1microsecond)
Transducer waits for sound to echo from tissue which distorts the disk and generates voltage proportional to pressure
Machine processes and displays as an image
124
What is the equation for acoustic impedance?
Density of tissue x speed of sound in tissue
125
How do ultrasound waves interact with the patinet?
Travels through tissues with varied acoustic impedance and when crosses boundary between tissues of different acoustic impedance some gets reflected back, with proportion reflected back dependent on difference of acoustic impedance between the tissues
126
How does reflection of ultrasound differ at different boundaries?
Weak reflection- soft tissue boundaries
| Large reflection- soft tissue bone interface
127
What is meant by long and short scale contrast?
Long scale- many shades of grey
| Short scale- black and white
128
What is the difference between specular and non-specular reflection of ultrasound?
Specular- beam hits large smooth surface
Non-specular- beam hits small structures so weak echoes get re-radiated in all directions so give texture/speckled appearance to organs
129
State the 3 display modes for ultrasound
A mode- amplitude
B mode- brightness
M mode- motion
130
What is A mode ultrasonography used for?
Opthamology
131
How does B mode ultrasonography work?
Pencil beam of ultrasound scans back and forth to build up an image, brightness on image depends on amplitude of returning signals and position on image depends on time for signal to return
Image is a slice through patient so need to scan in multiple planes
132
What is M mode ultrasonography used for and how does it work?
Mainly cardiology
Shows movement of points along a line with image displayed as position vs time
Continually produces a trace
133
Describe how an ultrasound exam is carried out
Select area of interest, ideally avoiding bone and gas if possible
Clip and clean skin, surgical spirit removes grease (can damage transducer), need good contact with skin
Apply lots of acoustic gel
Place transducer on skin
Keep patient still with restraint, sedation or GA
134
Why should you starve overnight for abdominal ultrasounds?
Improves ability to examine organs
| Allow safe sedation/GA if needed
135
How should you clip for ultrasound for abdomen, heart, left kidney and right kidney?
Abdomen- xiphisternum to pubis, follow line of costal arch to lumbar muscles including last 2-3 intercostal spaces
Heart- right side, 4th to 6th intercostal space, costochondral junction to sternum
Left kidney- lateral approach, behind last rib and below lumbar muscles
Right kidney- last 2-3 intercostal spaces and below lumbar muscles
136
What are phased and linear ultrasound transducers?
Phased- beam steered electronically
| Linear- lots of elements triggered in turn
137
Why should practice have a range of frequencies and types of ultrasound transducers?
Not one suitable for everything
| Consider type, footprint and frequency
138
What is a phased array transducer and what are the benefits of it?
Beam steered electronically
| Easy to manipulate, small contact area but wide field at depth
139
What is a linear array transducer and what are the benefits of it?
Multiple elements triggered in groups
| Large contact area, large field of view near skin so good for superficial structures
140
What is a microconvex/convex transducer and what are the benefits of it?
Elements arranged in curve triggered like linear
| Easy to manipulate, small contact area with wide field at depth
141
What frequency are high frequency transducers and what is their resolution and image at depth like?
Frequency- 7.5-18MHz
Resolution- good
Can't image at depth
142
What frequency are low frequency transducers and what is their resolution and image at depth like?
Frequency- 2.5-5MHz
Resolution- poorer
Can image at depth
143
What are high frequency ultrasounds useful for and what can they not view properly?
Good image resolution, good for superficial structures or for small animals
Can't penetrate deep
144
What are low frequency ultrasounds useful for?
Deep structures and large animals
145
Why does frequency of transducers need to vary?
Velocity is constant in soft tissues and as frequency increases wavelength decreases
146
How do you get better resolution in ultrasounds and why?
Short wavelength and pulse length because when longer reflections overlap on return so objects close are seen as one
147
How should you care for ultrasound machines?
Regular cleaning to remove gel and hair build up
Safely store leads and transducers
Service regularly
148
Define echogenic
Produces ultrasound echo
149
Define anechoic
No ultrasound echo produces
150
What is the appearance of fluid, fat and soft tissues on ultrasounds?
Fluid- black (anechoic)
Fat- white (echogenic)
Soft tissues- variable, compare to other tissue
151
What can be seen at borders of soft tissue with gas and bone in ultrasound?
Gas- totally reflects sound so cant see past the gas
| Bone- reflects or absorbs sound so cant see past but can see bone surface
152
What is meant by advanced imaging techniques?
Imaging techniques used mainly by referral centres that usually produce cross sectional images
153
What is shown by MRI and CT and scintigraphy images?
MRI and CT- slices through
| Scintigraphy- functional remodelling of bone
154
What do CT and MRI stand for?
CT- computed tomography
| MRI- magnetic resonance imaging
155
What are safety measures for CT?
Same restrictions as radiography
| Whenever on can emit radiation due to calibration etc so room stays locked
156
How does CT work?
Cross sectional imaging produced by ionising radiation
Rotating x-ray and detector take 360 degree x-ray and patient is advanced through as machine rotates
Computer reconstructs data into 3D image with tissue represented on image the same as x-ray
157
What is meant by windowing in CT?
Choice of how to display information
158
How does windowing of CT work?
Tissues get assigned Hounsfield unit depending on attenuation of beam, window level and width, choses to optimise certain tissues details
159
What are uses of CT?
Good for bony structures
| Multiple anatomical reconstructions from one scan
160
List advantages of CT
High bony detail and more soft tissue detail than x-ray
Can use contrast
Shorter scan time than MRI
Can create 3D reconstructions and models for surgical planning
Good for lung pathology and detecting metastatic disease
Avoids superimposition of joints
Cheaper than MRI
161
List disadvantages of CT
```
Limited availability
Expensive
Need to sedate
Higher radiation doses than x-ray
Limited to horses head or extremeties
```
162
How does scintigraphy work?
Radioisotope (technetium 99m) is bound to substance to determine where in body to localise then injected into the body
Binding is increased in areas with increased metabolism (tumours etc)
Radiation emitted is measured by gamma camera
163
What are used of scintigraphy?
Detect equine skeletal injury or lesions undetectable by radiography
164
What are advantages of scintigraphy?
Available in most large equine practices
| Element of functional assessment as uptake depends on metabolism and anatomy
165
What are disadvantages of scintigraphy?
Ionising radiation risk to patient and staff
Patient radioactive for 48 hours, minimise contact, correctly dispose bedding, faeces etc
Poor detail produced so hard to interpret image
Additional legislation due to excretion of radioactive isotopes
166
How does MRI work?
Cross sectional image produced using magnetic fields
Nucleus with odd number of protons and/or neutrons spins creating mini magnetic field which combine to form strong field
Protons get targeted
Patient in magnetic field causes magnetic moments of spinning nuclei to line up with magnetic field
When patient bombarded with radio waves nuclei temporarily disorientate and emit radio signals until they realign when radio waves stop
Timing depends on tissue environment and emitted signals from patient are detected giving information about tissue composition, appearance depends on timing of pulses and echoes which the computer reconstructs into an image
167
What are uses of MRI?
Neurology
Soft tissue lesions
Bone marrow oedema
168
What are advantages of MRI?
Good contrast resolution
Excellent soft tissue detail
No ionising radiation so not long term damaging
169
What are disadvantages of MRI?
```
Not widely available
Expensive
Need to be completely still under GA
Cant have metallic objects around
In horses can only use on distal limbs under standing sedation
```
170
Define positioning
Use of pads, wedges, sand bags, ties to ensure that the animal is straight and restrained
171
What should be checked before positioning animals for diagnostic imaging?
Correct animal
Projections needed
Exposure factors and use of grid
Correct positioning, collimation and centring
172
Why is it important to restrain animals for diagnostic imaging?
Produce good quality images
| Avoid manual restraint
173
State some positioning aids
Radiolucent troughs- VD or DV
Foam pads and wedges
Floppy sandbags
Tapes, ropes and ties
174
Define centring
Using light beam diaphragm to position primary beam over correct area
175
Briefly describe how to position patients for radiography
Put in comfortable position
Place markers and make sure are visible
Centre and collimate area of interest
176
What are features of a good quality radiograph?
Present identification and markers
Correct area and projection with suitable exposure factors, contrast, density and sharpness
No artefacts
Repeats done when needed
177
What information can you gain from the projection the radiography is taken?
Path of beam from x-ray tube to image receptor
Animal positioning
If lateral named after side animal is lying on
178
When can certain projections not be taken?
DV or VD shouldnt be taken after lateral as lung will have collapsed
Dont take VD if dyspnoeic take DV instead
179
Describe how to position for lateral thorax
Right lateral recumbency
Wedge under sternum to keep spine and sternum at same height
Forelegs pulled cranially
Centred at caudal border of scapula
Collimate 1/2 to 2/3 thorax including sternum and shoulder
180
Describe how to position for DV/VD thorax
Dorsal or sternal recumbency
Support legs so not over thorax
Animal straight head to toe, may need trough
Centre on midline at highest point of scapula (DV) or middle of sternum on midline (VD)
Collimate to include all of lungs and chest wall edges
181
Describe how to position for lateral abdomen
Right lateral recumbency
Wedge under sternum
Cranially positioned forelimbs
Hind limbs held parallel with pad to prevent rotation and pulled caudal to prevent superimposition
Sandbag over neck
Centre at level of last rib halfway down abdominal wall
Collimate to include cranial margin of diaphragm and pubic rim
182
Describe how to position for VD abdomen
Dorsal recumbency
Legs held by sandbags
Trough to prevent rotation and needs to be straight head to toe
Centre at umbilicus along midline
Collimate to include entire diaphragm and pubis
183
Describe how to position for PD hock and DP carpus
Animal in sternal with limb rotated and extended until straight
Centre over joint
Collimate to include soft tissues and 1/3 adjacent long bones
184
Describe how to position for mediolateral hock and carpus
Side to radiograph place on cassette, other leg pulled back and sandbagged
Centre over joint
Collimate to include proximal phalanges and distal tibia/radius
185
Describe how to position for mediolateral elbow and stifle
Joint in contact with cassette and other leg held back
Joint flexed or extended depending on whats being looked for
Centre over joint
Collimate to include distal/proximal long bones
186
What is shown on flexed and extended elbow radiographs
Flexed- anconeal process and humeral epicondyles
| Extended- cranial aspect of radial head and humeroradial joint space
187
Describe how to position for cranio-caudal elbow
Sternal with leg extended, head towards limb being examined
Centre over joint
Collimate to include 1/3 humerus and antebrachium
Can use horizontal beam, animal in lateral recumbency with examined limb most upper
188
Describe how to position for craniocaudal or caudocranial stifle
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Sternal so limb is straight
Craniocaudal- limb extended forward
Caudocranial- limb pulled back
Centre below patella
Collimate to include proximal and distal long bones
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189
Describe how to position for VD pelvis
Dorsal recumbency with legs extended and rotated so stifles are straight
Legs and tail tied
Hocks supported ad weighed down
Centre over pubis at level of greater trochanter
190
Describe how to position for mediolateral shoulder
Limb examined nearest film and drawn forwards to extend shoulder
Head and neck extended
Upper limb retracted
Centre at level of and caudal to greater tuberosity
191
Describe how to position for spinal radiographs
Need anaesthetising for good image quality as sedation keeps some muscle tone and rotation
Pads under head, neck and waist to keep spine straight
Take multiple images so beam passes directly through the joint rather than diverging at the edges
192
Describe how to position for lateral cervical spine
Lateral recumbency
Support spine to remove natural curvature
Pulled back forelimbs so shoulder doesn't superimpose
Centre at C3
Collimate to include base of skull
193
Describe how to position for VD cervical spine
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Dorsal recumbency
Forelimbs pulled down over chest
Neck straight
Centre over C3 on midline
Extubate to prevent superimposition
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194
Describe how to position for thoracic and lumbar spine
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Lateral recumbency
Support curves of spine
Pad between legs to prevent rotation
Extend limbs
Centre over region of interest
Make sure films overlap if taking multiple
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195
Describe how to position for lumbosacral junction
Lateral recumbency
Pads between hind limbs
Spine supported
Centre between iliac wing and greater trochanter
196
Describe how to position for ventrodorsal skull
Dorsal recumbency
Support with sandbags
Hard palette to table
Centre to level of interest along midline
197
Describe how to position for lateral/oblique skull
Lateral recumbency
Support nose to keep head in lateral or at desired angle
Centre over area of interest
198
Describe how to position for rostrocaudal tympanic bulla
Dorsal recumbency
Neck flexed until nose upright
Mouth held open in V with ties and gag
Centre where tongue goes down back of throat
199
Describe how to position for DV intra-oral nose
Sternal recumbency
Hard palette to table top
Centre between eyes on midline
Collimate to include nose and soft tissue around mouth
Can have imaging plate in mouth to prevent mandible superimposing
200
Describe how to position for VD mandible
Dorsal recumbency
| Plate in mouth to prevent superimposition of skull
201
Describe how to position for lateral pharynx
Lateral recumbency
Forelimbs pulled back towards chest
Pads under nose and neck to prevent rotation
Centre caudal to angle of mandible
Collimate to include nasopharynx, oropharynx and larynx
202
What are the dangers involved in equine radiography?
Radiation
| Conscious horse
203
How is physical safety maintained in equine radiography?
Sedate horse unless very sensible, compliant but not too sleepy
Procedure done quickly and quietly with no sudden movement or noise
Always prepared to move if horse kicks
204
Why is their more radiation danger associated with equine radiography?
Need lots of people in room to restrain
| High exposure as thick tissue so lots of scatter
205
What safety measures are in place for radiation for equine radiography?
Minimal personnel- one at head, one plate holder, one radiographer
Use PPE and dosimeters
Barrier behind horizontal beam
Cassette holder when possible
206
How should you prepare horses for radiography?
Brush off mud (radiopaque)
Remove shoe
Pick out feet
Pack frog with same opacity as soft tissue
207
What are the 4 standard views for equine radiography?
Dorsopalmer/plantar
Mediolateral/lateromedial
DLPMO/dorsal lateral palmer/plantermedial
DMPLO/dorsal medial palmer/plantar lateral
208
What views are radiographed for horses foot?
Lateromedial
Dorsopalmer/plantar
60 degree dorsoproximal/palmarodistal oblique
45 degree palmaroproximo/palmardistal oblique
209
What views are radiographed for horses fetlock?
4 standard views
210
What views are radiographed for horses carpus?
4 standard views
Flexed to separate radial and intermediate carpal bones and see more joint surface
Can skyline dorsoproximal-dorsodistal obliques to shoe dorsal surface of each bone
211
What views are radiographed for horses tarsus?
4 standard views
| Can flex to see calcaneus and sustentaculum tali
212
What views are radiographed for horses stifle?
Lateromedial
| Caudocranial
213
What views are radiographed for horses elbow/shoulder?
Mediolateral
Craniocaudal
Leg normally pulled forwards
214
How are horses upper limbs and pelvis x-rayed and what are the limitations?
Lying with legs extended
| Hard to view and produces lots of scatter as thick tissue
215
What views are radiographed for horses thorax?
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4 images taken as too large for one image
Dorsocranial
Dorsocaudal
Ventrocranial
Ventrocaudal
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216
What views are radiographed for horses head?
Lateral
Dorsoventral
Obliques
217
What are issues regarding equine ultrasounds?
Lots of hair
Thick skin
Dirty
Large so need low frequency which produces low image quality
218
How are horses prepared for ultrasound?
Clipped
Lots of scrub
Spirit to degrease
Gel applied
219
What are equine ultrasounds used for?
Musculoskeletal system
| Abdomen
