1
Q
Properties of X-rays
A
Invisible
Painless
Effects are latent, not immediate can take yrs
Effects are cumulative
2
Q
Dangers of radiation
A
All ionising radiation poses a risk to health of both humans and animals:
-produces biological effects to living tissue via chemical reactions
-radiation ions kill or damage living cells
-the most susceptible cells are rapidly dividing and growing cells. (Gonads and young animals)
-cell structure is damaged and the genes then mutate
-damage from radiation can be cumulative
Small doses over long periods of time are as serious as one high dose
-Effects may not be apparent until later and can be passed to the next generation
3
Q
Effects of radiation
A
- Generalised inflammation
- Blood disorders, leukaemia
- Death of tissues, necrosis
- Death or mutation of developing of foetus
- Damage to gonads, tumours (esp females as have all their eggs in ovaries at birth, males are constantly producing new sperm).
- Infertility
- Production of tumours
4
Q
Somatic effects (biological)
A
Direct changes to the body, occurring soon after exposure.
- reddening of the skin
- cracking of skin
- blood disorders
- cataract formation
- digestive upsets
5
Q
Carcinogenic effects (biological)
A
Induction of tumours in tissues that have been exposed to radiation
Can be as long as 20-30yrs after exposure
6
Q
Genetic effects (biological)
A
Gonads are irradiated and mutations are induced in chromosomes of germ cells
The mutation may give rise to inherited abnormalities in the offspring
7
Q
IRR 2017
A
Ionising radiation regulation (was 1999) in effect since Jan 2018.
Legal document therefore hardgoing, very detailed, accompanied with second booklet to explain regulations further.
Contains principles of radiation protection in all work activities inc veterinary radiography.
HSE inspectors have the right to inspect xray equipment, facilities and dosemetry
These regulations protect staff and public from harmful effects.
8
Q
Under IRR 2017 when can X-rays be performed?
A
When there is justifiable clinical reason
Exposure to personell is kept to a minimum
Dose limits are not exceeded.
9
Q
Radiation legislation
A
Approved code of practice for the protection of persons against ionising radiation arising from any work activity.
Approved code of practice for all uses of radiation and radioactive materials. Doesn’t refer to veterinary use directly but still quite complex.
Guidance notes for the safe use of ionising radiations in veterinary practice. Published by BVA in 2019 (prev 2002).
10
Q
Sources of potential exposure
A
3 main sources;
- leakage from tube head; faulty equipment
- exposure to the primary beam
- exposure to scattered radiation
11
Q
Tube head
How can you tell if there is cracks?
A
Is lead lined box
Tube window is covered with aluminium filter (2.5mm) this removes low energy x-ray photons form the primary beam
To test for cracks tape a non screen film to the tube head leave for a few exposures and then process it - if any cracks are in the tube head it will cause black lines to appear on the film.
12
Q
Exposure to the primary beam
A
This is the greatest hazard - high energy X-rays
Light beam diaphragm or cones are devices to collimate exposed area
Areas covered by the primary beam should be no larger than the area of the cassette.
All borders of the beam should be visible on the processed radiograph.
13
Q
Exposure to scattered radiation
A
Produced when primary beam strikes a solid object.
Can bounce off objects and travel in any direction - always in straight lines
Energy or strength decreases rapidly (retreat as far away as possible (min 2m)
Low energy; it can be absorbed by lead-rubber protective clothing
14
Q
How to reduce scattered radiation?
A
- collimate the primary beam as tightly as possible
- reduce KV (penetrating power) wherever possible
- use lead backed cassettes
- use lead topped tables or lead lining
-compress large areas of soft tissue - use grids where appropriate; grids reduce scattered radiation from reaching the film, not you.
15
Q
Health and safety executive (HSE)
A
All practices using xray machines must notify HSE, they may have periodic visits by HSE inspectors
Any practice failing to comply with the law may be served with compulsory improvement orders or can be prosecuted and fined.
16
Q
RPS and RPA
A
RPS = radiaton protection supervisor
RPA = radiation protection advisor
RPS; must be appointed within the practice - their role is being responsible for ensuring that radiography is carried out safely and local rules are being obeyed. They do not need to be present for every examination.
RPS; appointed outside the practice. Can either be a vet who holds a diploma in veterinary radiography who has knowledge in radiation physics or a medical physicist with an interest in veterinary radiography. RPA gives advice on all aspects of radiation protection, the demarcation of the controlled areas and the drawing up of local rules and written arrangements.
17
Q
Local rules and SOPs
A
Set of instructions written by RPA.
Includes details of equipment, procedures and restrictions to access to the ‘controlled area’ as well as the designated persons (inc RPA and RPS).
They contain an assessment of the max dose of radiation likely to be received by people working in practice.
Also details of patient restraint and the precautions to be taken if manual restraint is required. All staff involved in radiography should be given a copy, also displayed in the xray room. This needs to be reviewed annually.
18
Q
The controlled area
A
Specific room: thick walls or lead lined
The RPA usually states the extent of the controlled area
The area usually extends to a radius of 2m around the primary beam
Usually the whole x-ray room.
Controlled area must be demarcated physically and clearly by:
- warning sign
-visible lights switched on at the mains or exposure is taking place
-warning buzzer
19
Q
Maximum permissible dose (MPD)
A
This was used in the past to describe the max dose of radiation that felt to be safe for an individual but, it’s no longer used today.
Principle = keeping each individuals dose as low as reasonably practicable ALARP.
18+ = 20 millisieverts (msv) in a calendar year. In special cases employers may apply for a dose in it of 100msv in 5yrs and 50msv in 1yr.
For trainees 6msv in a year.
Anyone else and employees under 18 and not a trainee = 1msv in a year.
Now = limit is for the skin averaged over an area of skin not exceeding 1cm square.
20
Q
Dosimetry
A
Dosemeters record any radiation which the wearer is exposed.
Should be worn on the trunk of the body underneath protective clothing.
Extra dosemeters can be worn on collar or sleeve to monitor levels in unprotected parts
Finger dosemeters beneath lead gloves are used for large animal radiography.
Only to be worn by the person to whom it was issued, they should not be left in the xray room or in direct sunlight or heat
21
Q
Types of dosemeters
A
Film badge = contains small pieces of xray film and are usually blue.
Thermo-luminescent dosemeter badge (TLDB) - contain lithium fluoride crystals that are radiation sensitive; they are purple since November 2006 (were mostly orange).
22
Q
Record book
A
Must include:
- date
- patient details
- region xray’d
- exposure factors
- who is restraining animal
- owner details/case number
- animals breed and weight
- projection/view
- personnel - everyone involved
- image quality (assists in the development and exposure chart).
23
Q
How are X-rays produced
A
By machines when mains electricity is converted/transformed to a high-voltage current, converting some energy to xray energy.
24
Q
What can electromagnetic radiation pass?
A
Can pass through a vacuum (space)
But not visible to naked eye.
Can penetrate some solid materials and are absorbed by some.
Always travel in straight lined and at the same speed.
25
What energy is a given type of radiation?
Directly proportional to the frequency of the radiation.
Inversely proportional to its wavelength.
26
The atom
Made up of a nucleus
Contains protons (positively charged) and neutrons (no charge)
The nucleus has a shell with electrons (negatively charged) orbiting.
27
Atomic number
Number of protons or electrons is unique to thr atoms of each element.
Referred too as the atomic number (symbol Z)
Protons and electrons are usually equal to each other and therefore has no charge.
Elements with a low atomic number = radiolucent
Elements with a high atomic number = radiopaque
28
Ions
If an atom loses electrons it becomes +ve charged = cation
If an atom gains an electron it becomes -ve charged = anion
Atoms that have a charge = ionised
29
Barium + iodine atomic number
Barium = 56 radiopaque - good for contrast studies.
Iodine = 53
30
Production of X-rays
Produced in the machines tube head when fast moving electrons collide with the target element. The electrons that are stopped by the target give up all their energy to form an xray photon
>99% of electron energy is converted to heat and <1% of energy is converted to X-rays.
31
Define anode and cathode and their role in the xray tube head.
Anode = +ve charged electrode, leaving device.
Cathode = -ve charged electrode, entering device
In the tube head the cathode produces a focused beam of high speed electrons and the anode serves as a target that converts the kinetic energy of these electrons into xray photons and heat.
32
Define milliamperage (mA) and kilovoltage (kVp)
mA = measure of the current that passes through an X-ray tube.
If more electrons are produced, more X-rays will be produced and therefore intensity of the beam increases.
Quantity (intensity) of the X-ray!
kVp = max voltage applied to an xray tube, determines the penetrating power and energy of the beam.
Quality or penetrating power of the xray beam!
33
Line focus principle
The anode (target) is slanted to increase surface area and refract the beam to hit straight down and focus the beam and keep clearer image.
Creates a sharper image.
Also dissipates heat and prevents cracking and overheating. The target should be as small as possible.
Target is angled to 20-22.5 degrees from vertical allowing bombardment to be 3x bigger.
34
What is a focal spot?
On some xray machines.
Small focal spot = for fine detail (limbs)
Broad or course focal spot = for areas that require higher exposure (abdo/chest)
35
Rotating anodes
Used in more powerful machines that are capable of much higher exposures bcs they disperse the heat more effectively.
Target is always rotating and consequently the electrons are hitting a changing area on target .
Target is a metal disc with a beveled rim of tungsten onto a molybdenum rod attached to a motor.
Disc rotates at a high speed and whole circumference becomes the focal spot whilst it remains the same size.
Angle = 20-22.5 degrees
36
Tube overload
Maximum load that a tungsten target can take before damaged.
This can happen in 2 ways;
- target can vaporise and coat the glass wall rendering it useless
-target itself can emit electrons and cause a high voltage (anode - cathode) destroying the cathode and its filament.
37
X-ray output
An xray machine must have what before it produces X-rays?
A low current (mA) to heat the filament and release a ‘cloud’ of electrons
A suitable voltage of high tension (kV) to drive the electrons towards the anode.
38
Penumbra effect
An undesirable effect.
Blurring of margins related to the beam geometry.
Caused by a larger focal spot or increased distance between an object or image receptor.
39
What are the 4 exposure factors?
Kilovoltage (kV)
Milliamperage (mA)
Time (s)
Focal - film distance (FFD)
40
Effect of kV
Higher the kV the greater the energy of the X-ray photons produced so greater their penetrating power.
The greater the atomic number and density of the tissues to be examined the higher the kV needed to penetrate it.
41
Effect of mA and time
Higher the mA the more X-ray photons will be produced therefore increasing the beams intensity
mA and exposure length produce mAs - related to the quantity of X-rays producing one exposire
42
What is the 10K rule ?
Increase the kV by 10 then half the mAs and vice versa.
Decrease the kV by 10 then double the mAs and vice versa.
43
What happens when the xray hit the patient?
Degree of absorptions depends on:
tissue thickness
molecular density (atomic number)
- higher number, more X-rays are absorbed
-gas, radiolucent low atomic number
-metal, radiopaque high atomic number
-differences between radiolucent and radiopaque
Bone has higher molecular density than fat
44
Focal-film distance (FFD)
Distance between focal spot and film.
X-ray beam quality (kV) will remain constant whatever the FFD
X-ray beam remains constant as its intensity (mAs) falls as it moves away from the tube, as it spreads over a larger area, the opposite happens if it is closer to the tube.
45
FFD - inverse Square law
If the distance between the film and the tube head is doubled then the intensity (mAs) of the beam is quartered:
New mAs = old mAs/4
If the distance between the film and the tube head is halved the intensity mAs of the beam is quadrupled:
New mAs. Old mAs X 4
46
In X-rays how would you penetrate Plaster of Paris (wet & dry)
Dry X mAs by 2
Wet X mAs by 4
47
What are wavelengths measured in?
Angstrom
48
What does the degree of absorption depend on?
The atomic number
Specific gravity
The depth of tissue
49
What is the Formula for working out mAs?
mAs = mA x s
S = mAs / mA
mA = mAs / s
50
If the kV is increased by 10 what would you do to the mAs?
Half the mAs
51
If the kV is decreased by 10, what would you do to the mAs?
The mAs would be doubled.
52
How would you work out a new mAs using the old mAs and FFD?
New mAs = old mAs X new FFD (squared) / old FFD ( squared)
53
How to work out a new mAs when given a grid factor?
Grid factor X mAs
To remove a grid factor:
mAs / grid factor
54
Functions of traditional film cassettes
To hold intensifying screens and protect them from damage.
To exclude all light from entering the cassette and fogging the film
To maintain a close and uniform contact between the film and screens.
55
Digital radiography
Two forms:
Computed radiography (CR) - imaging plate
Direct digital radiography (DDR) - image is sent instantaneously to the screen
Method of acquiring the image is the same as traditional radiography. The difference is the image is acquired digitally and stored electronically.
56
Digital imaging plates (IP)
Similar to conventional cassettes
Contains an imaging plate accessed by a specific key
Made of photostimulable phosphor that is excited by x-rays and light photons
Used in the same way - either on or beneath table
Labelled electronically
57
How do you clean digital imaging plates?
Ensure image is erased otherwise creates a ‘ghost’ image
More sensitive to scattered radiation so need erasing if not used for a few days to avoid build up of artefacts
Wipe down after use
Periodically cleaned in accordance with manufacturers instructions.
To store keep them secure and rotate use .
58
Digital image storage and display
CR/DR systems (offline & online)
Images are saved in specific format (DICOM)
59
What is DICOM?
Digital imaging and communications in medicine
Prevents tampering with original image
Ensures consistency of file type between all radiographic systems
60
What is scatter radiation?
Scatter is lower energy
Causes poor image quality and blurring
As primary beam passes through patient
- some passes through and forms the image
- some is absorbed by the tissues
- some interacts with tissues and gets scattered in random directions
61
How can scatter be reduced?
Reduce kV
Accurately select exposure factors
Collimate the primary beam
Compression band (not used anymore)
Use a grid
62
What is a grid?
Made up of very thin strips of lead
Separated by plastic or aluminium strips
The plastic/aluminium allow xray photons through
The lead strips absorb a large proportion of scattered radiation travelling at an angle
63
Grid factor
Usually 2.5-3
New mAs = mAs x grid factor
64
Grid ratio
Ratio between the height of the lead strips to the width of the radiolucent interspaces
The larger the grid ratio the more efficient it is at absorbing scatter, but the grid factor is larger
A ratio of 3:1 means that the height of the lead strips is 3X the width of the spacer
65
Lines/cm
The number of lines (lead strips) per cm.
Usually 24 lines to 1cm
Measure of quality:
The greater the number of lines/cm the finer the grid lines on the film
The less obtrusive the grid lines (show on X-rays)
More expensive they are
Higher the grid factor (so higher exposure needed)
66
Types of grids
Stationary - linear - parallel, focussed, pseudo-focussed
Stationary - crossed
Moving - potter-Bucky diaphragm
67
Care of grids
Careful handling
Don’t drop
Clean regularly
Correct storage
68
Labelling methods
(Traditional & digital)
Traditional:
Before exposure = lead letters/numbers, lead-impregnated tape (x-rite)
After exposure = light marker
After processing = hand-written label
Digital:
Patients details are input into the computer
Patients details and views required.
69
Info needed on a general xray and BVA
General = animal identification, date, L/R marker, time if using contrast
BVA = date, kennel club num, L/R marker, chip number
70
Reasons for contrast studies
- certain structures unclear as radiolucent or masked by other structures
- inner lining of hollow, fluid-filled organs cannot be assessed as it’s same radiographic density as fluid contained within the organ.
- contrast studies make these structures more apparent this increases contrast between the structure of interest and surrounding tissue
- allows assessment of shape, sizes, position and internal architecture
- serial films may give indication of function as well (eg rate of gastric emptying).
Aids in visualisation of structures or details otherwise unseen, by increasing the contrast by changing the radiopacity of the structure and radiopacity of surrounding tissues.
71
Ideal properties of contrast studies
Different radiographic density to tissues
Non-irritant or toxic
Accurately delineation of organs
Persistence - for sufficient time to take the radiographs
Total expulsion from the body
72
Types of contrast
(Positive contrast media)
Eg - barium (atomic number 56) and iodine (atomic number 53)
Contain elements of high atomic number
Absorb large proportion of x-ray beam
Relatively radio-opaque
Appear white
Provide positive contrast in comparison to soft tissues
- barium sulphate preparations (GUT ONLY)
- ionic water-soluble iodine preparations
- non- ionic water-soluble iodine preparations.
73
Types of contrast media
(Negative)
Atomic number = lower, so appears black on x-ray
Eg - air, N2), O2, CO2 (gases)
Relatively radiolucent
Used mainly in bladder (pneuocystogram) and gut (pneumogastrogram or pneumocolon)
74
Double contrast studies
Involve positive and negative contrast media in hollow organs to aid mucosal detail
If using negative contrast in bladder the mucosa won’t be outlined so may mask neoplasia but good to see stones, if add positive contrast this will outline lining too.
Small amount of positive contrast is used to coat the lining of the otgan then distended with gas
Useful in = Bladder, stomach, colon
75
Barium sulphate
+VE contrast media
-white chalky material
- mixed with water
- available as liquid, paste, powder or BIPS (barium impregnated polythene spheres)
- GUT ONLY (orally or enema)
- not suitable for inj into bld vessels
-provides very fine mucosal detail
- heavy metal but has such a low solubility patients are prevented from absorbing too much toxic heavy metal
- CONTRAINDICATED IF GUT PERFORATED
- can cause granulomas and adhesions if leaks into thoracic or abdo cavity
- can cause pneumonia if aspirated
- avoid heavy sedation/GA for barium swallow
- no food for 24hrs prior to
- dont give to constipated patients (makes it worse)
- don’t use if surgery is anticipated (leaks from incision)
-barium series - sequence of X-rays taken every 15-60mins following the passage of contrast media from the oesophagus through the colon.
76
Ionic water-soluble iodine preparations
Iodine compounds
Ionic - contain salts
Hypertonic - high osmotic pressure
Water soluble
Therefore can inj into bld stream
Anaphylaxis rare but poss
Excreted by kidney, outlines upper urinary tract
Safe to use in other body parts.
IV inj may cause nausea and retching
Heavy sedation or GA recommended
Due to high osmotic pressure, they absorb fluid when passing though gut so become diluted
Less contrast in gut than barium
Risk of collapse in dehydrated patient
Not routinely used for gut studies
Sodium Diatrizoate (hypaque, urograffin, gastrografin)
Sodium Iothalmate (conray)
Sodium loxaglate (hexabrix)
77
Non-ionic low osmolar water-soluble iodine preparations
Myelography
Some IV studies
Avoids irritation of spinal cord
May be administered by cisternal puncture or lumbar puncture (between 4th and 5th or 5th and 6th lumbar vertebrae)
GA necessary
Shows opacification of the CSF demonstrating the spinal cord
Use in gut if suspect gut perforation
Tumours and prolapsed discs
Iohexol (omnipaque)
Iopamidol (niopam)
Metrizamide (amipaque)
78
Patient preparation of contrast studies
Usually elective procedure
Barium study of stomach, SI & kidneys required 24hr fast
Enema can be used
Plain X-rays should be taken to
Check for pathology
Determine correct exposure
Check adequacy of patient prep and amount of contrast medium required
Compare to subsequent radiographs
79
Barium swallow of oesophagus
Indications = regurgitation, retching, dysphagia
Prep = normal X-rays
Equipment = barium paste or liquid (5-50ml), oral water-soluble iodine preparation if perforation suspected
Liquid barium and tinned food (megaoesophagus)
Restraint - moderate sedation
Technique = paste placed at back of tongue, liquid syringed slowly into buccal cavity giving them time to swallow, xray immediately in lateral (occasional VD)
80
Gastrogram
(Contrast studies)
Indications = persistent vomiting, haematemesis, displacement of the stomach and liver size assessment
Preparation = 24hr fast, enema & norm X-rays
Equipment = barium liquid (20-100ml), BIPS, water soluble iodine if a perforation is suspected, syringe or stomach tube, 3-way tap
Restraint = moderate sedation.
81
Gastrogram techniques (contrast studies)
Pneumogastrogram = shows position, distensibility of stomach, large gastric masses or FBs. Use stomach tube and take 4X x-rays
Barium Gastrogram = position, thickness of wall, also shows SI. FBs can be drowned by contrast, no mucosal detail. Once administered, roll the patient to coat the stomach. 4X X-rays
Double contrast Gastrogram = the latter gives better mucosal detail plus better distension of stomach, can see FBs as filling defects. Give barium first, roll patient and then give air. remove stomach tube.
82
Small intestine (barium study)
Indications = persistent vomiting, haematemesis, abdo mass, malabsorption, weight loss.
Technique = liquid barium, series of radiographs taken at intervals
83
Large intestine (contrast studies)
Indications = tenesmus, melaena, colitis, identification of certain abdo masses
Preparation = 24hr fast, enema (tepid water or saline) plain X-rays
Equipment = cuffed rectal catheter or Foley catheter, 3 way tap and large syringe for pneumocolon. Gravity feed can/hose or barium enema bag for barium or double contrast
Restraint = moderate to deep sedation or GA
84
Large intestine techniques in contrast studies
Pneumocolon = outline soft tissue masses in colon. Rectal catheter is positioned and colon inflated with room air using a syringe and 3 way tape until air leaks around catheter. Take views without removing the catheter.
Barium enema = displacement or compression of colon. Catheter placed, barium allowed to flow in via gravity until it begins to leak around catheter (usually 10-20ml/kg required). Take views without removing catheter
85
Barium doseage guide
Enemata = 10mls/kg
Per os = 8-12mls/kg in cats and small dogs in larger dogs use 5-7mls/kg
Via stomach tube = 15-100mls depending on patient size and rate of gastric emptying
Glucagon may be given to slow rate of gastric emptying.
86
Intravenous Urography (IVU) and Excretion Urography
IV administration of water-soluble iodine (bolus IV Urography or infusion IV Urogram)
Indications = assessment of kidney shape, size and position. Haematuria, urinary incontinence
Preparation = 24hr fast and enema. Plain X-rays
Equipment = IV catheter, bolus IVU (syringe, 3 way tap, concentrated contrast medium), infusion IVU (drip giving set, contrast medium)
87
Cystography
Pneumocystogram - quick and easy but poor mucosal detail - perforation will allow gas to leak but hard to distinguish from GIT gas.
Positive contrast cystogram - good for perforations but masks small lesions and calculi
Double contrast cystogram - methods of choice, good for mucosal detail and identify any filling defects - contrast puddle.
Non-ionic iodine preps are less irritant on inflamed bladder mucosa
88
Cystography steps (contrast studies)
First the bladder is catheterised and the urine drained
Pneumocystogram - bladder is inflated with room air using
Positive contrast cystogram- bladder inflated with diluted iodine contrast medium
Double contrast cystogram - 2-15ml iodine contrast medium (150mg/ml) roll patient to coat mucosa and inflate with air.
89
Urethra
(Contrast studies)
Male - retrograde urethrography
Female - retrograde vagiono-urethography
Indications = haematuria, dysuria, urinary incontinence, urinary retention, prostatic and vaginal disease
Preparation = enema and plain X-rays
Restraint = dogs sedation, bitches/cats GA
Equipment = urinary catheter and syringe and dilute iodine contrast
90
Myelography (spine) contrast study
Injection of positive contrast into the subarachnoid space - water soluble iodine preparations
- iohexol and iopamidol
Cisternal puncture just caudal to skull. Needle inserted into the cisterna Magna. The cranial end of the subarachnoid space.
Lumbar puncture - cauda equina. Needle inserted into dorsal subarachnoid space
GA essential, clip area, spinal needle.
91
Cisternal puncture
Elevate table 10 degrees with head at raised end
Clip and surgically cleanse inj site
Flex head to 90 degree angle with the neck
Insert needle into cisterna Magna
Advance needle until CSF drips out of hub
Collect several mls of CSF
Injection warmed contrast media slowly
Remove needle and extend head again
Series of X-rays taken
92
Lumbar puncture
Clip and surgically cleanse inj site
Flex vertebral column by pulling hindlimbs forward
Insert needle at L5-6
As it passes through cauda equina the animals hindlimbs and anus will usually twitch slightly
Little or no CSF may appear from this site
Inject contrast media after a small test injection
Remove needle
Extend spine
Take X-rays
93
Portal venography - contrast study
Assess blood flow through the liver
Laparotomy - splenic or mesenteric vein catheterised
94
Angiocardiography - contrast studies
Heart
Via jugular or cephalic vein, carotid or femoral artery
Also called arteriography e
95
Bronchography- contrast studies
Lungs
Propyl-iodine which is injected down ET tube
96
Arthography - contrast studies
Joint spaces
Contrast into the joint space, demonstrating distension, rupture or defects in articular cartilage
Negative, positive, double contrast
GA and aseptic prep and technique
97
Fistulography
Inject contrast media into the tract to see where it goes.
98
What are the two types of digital X-rays?
Computed (cassette)
Direct digital
99
Computed radiography (CR)
Uses a specialised cassette which contains an imaging plate and records ‘raw’ image as energy
Exposed plate is placed into specialised reader and a digital image is viewed onto software. Cassette automatically cleared
Cassette compatible with existing X-ray tables
IP coated (photostimulable phosphor)
IPs are more sensitive to radiation
100
Direct digital radiography (DR)
Use film-less xray capture
No plate needed
Two types of DR radiography: flat panel systems (direct & indirect) and charged coupled systems
101
DR - flat panel system direct conversion
A detector is synchronised with the xray equipment and uses a semiconductor, usually amorphous selenium
X-ray hits flat panel — the charge is read by thin film transistor — electronically processed and converted into an electronic file
102
DR - flat panel system indirect conversion
A detector panel is synchronised with the X-ray equipment
A scintillator (usually caesium iodide or gadolinium) built into flat panel detector.
X-ray hits flat panel — energy converted to visible light — converted to a digital signal forming an image
103
DR - charge coupled device systems
Fluorescent screen is positioned directly under table and visible light produced is relayed to monitor via lens/mirrors
X-ray hits fluorescent screen — energy converted to visible light — relayed by lens/mirrors to form image on screen
104
Advantages and disadvantages of digital radiography
A = quicker, saves time and resources, easier for sharing images (DICOM), easy access, minimal storage, manipulate image, reduce exposure to X-rays, harder to go missing.
D = risk of system crashing/losing files, expensive, human error.
105
ID station (CR)
Contactless data transmission to cassette
Connects to PC running ID software
Cassette insertion slot
Can stand alone for space saving or can be integrated into a fully configured ID console
Can have multi or single slots, no intervention, high productivity, ‘dust free’
106
Computed Tomography (CT scanning)
Computer Aided or Axial Tomography
Based on the x-ray principle
X-rays are used to produce highly detailed cross-sectional radiograph of the patients tissues
Much greater tissue contrast than X-rays
Film is replaced by a banana shaped detector which measures the xray profile
Acquires images or slices in an axial plane (transverse plane)
107
How does CT work?
X-ray tube head moves rapidly around the circumference of the ring during exposure
Radiation from the patient is detected
electronically and digitised (producing an image that can be manipulated by computer)
Table moves forward slightly producing many cross sectional slice like images of area under investigation
High doses of radiation mean that manual restraint prohibited
Normal GA equipment and monitoring equipment can be used
108
Applications and CT technique
Applications = much more tissue definition than radiography - differentiating between different types of soft tissue and between fluid and soft tissue.
Grey scale - hounsfield units. Anything outside the ‘window level’ or ‘window width’ appears as white and black.
Technique = GA or heavily sedated. Exposure takes between a few secs-mins
‘Spiral’ or ‘helical’ CT scanners can produce images that can be reformatted into other planes to aid in evaluation of anatomy.
Images can be displayed in 3D to aid surgical planning.
109
Nuclear scintigraphy
Use of radioactive isotopes (gamma)
Governed by the Radioactive Substances Act 1993
Two licenses must be obtained form Environmental Agency: registration for keeping and using isotopes and authorisation for governing the accumulation and disposal of radioactive waste.
Local rules outline safe working procedures
110
Gamma
High energy, high frequency, short wavelength
111
Nuclear scintigraphy pt 2
Involves the production of images demonstrating the distribution of radioactive materials within a patient following the internal administration of a radioactive pharmaceutical
Scintigraphy is a diagnostic branch of nuclear medicine
112
Bone scintigraphy
Evaluation of the skeletal system
Depends on the principle that actively metabolising bone will incorporate certain bone “tracers”
Distribution of these tracers is dependent on the rate of bone turnover and blood flow
Images obtained reveal the relative distribution of these tracers throughout the skeletal system complements X-rays not replaces
Process involves the acquisition of images at various times after administration of the tracer. The tracer usually requires several hrs to be incorporated into the bone and cleared from remaining tissues.
Gives info on blood flow vs soft tissue and bone metabolism
113
Renal scintigraphy
Evaluation of function - uses nuclear medicine
114
Thyroid scintigraphy
Visual display of functional thyroid tissue following administration of a radionuclide that concentrates thyroid tissue.
Provides info regarding anatomy and function - integral role in diagnosis and management of thyroid disease.
Will appear red or ‘hotter’ than salivary glands if abnormal
115
Portal scintigraphy
Transcolonic portal scintigraphy is a new technique available for diagnosing portosystmeic shunts in dogs and cats
116
Scintigraphy summary
Patients must be isolated for 24hrs post procedure
Gamma-ray emitting radioactive substance attached to a molecule (iodine)
injected into the blood stream(molecule is taken up by tissue under investigation)
The emitted gamma photons are detected by hand-held radioactivity counter, large gamma camera. The pattern of emitted radioactivity reflects the activity of tissue
117
Scintigraphy - sources of radiation
Radiopharmaceutical
The injection
The patient
The urine
The bedding
Waste material
PPE/staff rotation
Disposal and handling of excretion and waste
118
Scintigraphy - Precautions
Patients must be isolated until a Geiger counter confirms they are no longer emitting significant amounts of radiation.
Set up a controlled area with signage
Minimal handling and restricted access
Bedding to be checked with Geiger counter
Areas where pharmaceutical was prepared should be routinely monitored
119
Magnetic Resonance Imaging (MRI)
Scanner is a powerful magnet
Magnetising tissues within it, aligning protons in body’s hydrogen atoms
Radio waves from radiofrequency aerial disorientating protons, causing emission of tiny radio signals
Radio signal released by protons are detected by radiofrequency aerial converted to an image by a computer.
120
How is MRI used?
Soft tissue, internal organs which are relatively transparent to X-rays limiting the practical application of other imaging modalities such as CT
MRI has an excellent sensitivity for these tissues with 100% increase in soft tissue resolution compared to its closest competitor CT
Doesn’t use ionising radiation
Superior clarity of the images, particularly of the brain, combined with its non-invasive nature led to its quick acceptance
121
MRI scanning
Safe compared to CT
NO METAL - convention anaesthetic and monitoring equipment cannot be used
Patients must be under GA, ensure still during scan
122
MRI technique and applications of MRI
Technique = many different scans performed, meaning a variety of tissues can be examined
T1 - weighted scan, fluid is dark
T2 - weighed scan, fluid is bright
Images can be taken in any plane (transverse, sagittal, dorsal)
Applications = soft tissue information preferable to CT, complex ‘gating’ techniques (radiofrequency pulses synchronised movement)
Brain and spinal imaging
IV MRI contrast medium containing gadolinium, ‘paramagnetic’, ‘enhancement’ of tissues absorbing contrast, demonstrating vascularity.
123
MRI fields
Open - permanent magnets; C-shaped and opened at the sides, lower magnetic field and scans take longer
Closed - superconducting magnets; tube shaped, moveable table top, higher magnetic field and faster but more expensive
124
MRI pulse sequences
T2 - weighted scan. Fluid & fat hyperintense (white)
T1 - weighted scan. Fluid hypointense (dark), fat hyperintense (white) used with contrast.
Stir sequence - suppress fat whilst retaining bright signal from fluid.
Flair sequence - suppresses fluid while retaining bright signal from fat.
GE sequence - more rapid scanning useful for scanograms
125
What are the sound waves produced in ultrasound?
2.5-15 MHz’s
Higher frequency than detected by human ear
126
What is the piezoelectric effect in ultrasound?
Transducer which produces an electric current which causes crystals to vibrate and change shape.
127
High frequency ultrasound
Better resolution but cannot penetrate far.
Used in superficial structures
Sound waves are passed as pressure waves into patient, some waves return to transducer causing vibration of crystals and convert back to electric impulses to form an image.
128
Linear array transducer
Piezoelectric crystals in line and image is rectangular, good patient contact can be a problem
129
Sector scanner transducer
Crystals close together, small patient contact needed. Triangular image showing deeper tissues more effectively
130
What recumbency should a patient be in for an echocardiography
Lateral as heart sinks to bottom and minimises the effect of the lungs in the way
131
Ultrasound technique: A-mode
Amplitude
Shows a graphic display of distances between tissue interfaces.
It’s used for measurement (foetal skulls and age)
132
Ultrasound technique: B-mode
Brightness
2D Image
Image formed in relation to sound reflections from parenchyma of tissues
133
Ultrasound technique: M-mode
Movement
Quantifies heart motion
134
Ultrasound terminology
Echogenicity
Ability of tissues to reflect ultrasound waves.
Determines how bright or dark structures appear on an image.
With higher reflection (hyperechoic) appearing bright (white) and lower reflection (hypoechoic) appearing dark, while no reflection (anechoic) appears black
135
Ultrasound terminology
Anechoic
Without echos
Areas appear black on ultrasound because they do not send back any sound waves.
Masses are often fluid filled.
136
Ultrasound terminology.
Hypoechoic
An area on an ultrasound image appearing darker than the surrounding tissue because it reflects fewer sound waves (echo’s), indictating its denser or more solid like muscle or tumour rather than fluid filled.
137
Ultrasound terminology
Hyperechoic
Tissue/structure reflects many ultrasound waves back to the transducer appearing brighter or ‘whiter’ on an image compared to surrounding tissue.
Indicates increased echo intensity, often due to fat, fibrosis, calcifications or pathologies such as fatty liver or specific tumours.
138
On ultrasound, if there is a difference in normal architecture how will it appear on the image?
Mottled appearance
139
How does fluid appear on an ultrasound ?
Black - very few reflections.
Free abdo fluid is seen as black around organs (which would be hard to distinguish between with X-rays).
140
On Doppler ultrasonography what do the colours mean
Red- towards transducer. Shorter
Blue - away from transducer. Longer
141
Advantages of ultrasound
Differentiates between soft tissues and fluid
Shows internal architecture of structures
‘Real time’ image, providing information on function of structures
Guides biopsies and FNA
Conscious patient (no sedation or GA)
Avoiding more invasive procedures
142
Disadvantages of ultrasounds
Doesn’t penetrate bone, acoustic shadows radiating black streaks
Doesn’t penetrate air
Not useful from assessing lungs or skeletal systems
Requires interpretation at time; knowledge and skill
Clipping of hair
143
Ultrasound machine checks
Schedule regular service engineer visits
Check machine visually before every use
Check all connections plugged in correctly
Check integrity of wiring, cables and transducers
Wipe transducers and cables after use (specialised cleaner)
Follow recommended cleaning protocol - sterilisation of transducers after certain procedures
Wipe down entire machine after use
Report any problems
144
Is digital radiography indirect or direct?
Direct (DDR)
Refers to direct digital registration of the image at the detector with no intermediate processing step required to obtain the digital signals
145
Is computed radiography (CR) direct or indirect ?
Indirect.
A mechanical system using analogue technology to take X-ray exposures with CR cassettes in place of traditional film cassettes.
146
When labelling digital radiographs what information is needed?
Patient species, name patient ID
Area of study, recumbency, plate size
L/R marker
With KC X-rays:
No patient name but KC number, microchip number, date and L/R marker
147
Viewing digital images
Viewed on CR/DR computer monitor
Post-processing manipulation of image
Rotation/flipping, magnification, adjustment of density/contrast, annotation, measurements.
148
Define subtraction radiography (X-rays)
The method removes distracting material in the ordinary film
149
Define edge enhancement (xrays)
An image processing filter that enhances the edge contrast of an image
150
Define brightness enhancement (xrays)
Is the balance of light and dark shades in a displayed image
151
Define contrast enhancement (xrays)
Determines how many grey levels are displayed and the density determines the intensity.
152
What is tereradiology ?
Transmit digital imaging files in DICOM format
153
What is PACS?
Picture archiving and communication systems.
Refers to host of technologies.
PACS compenents include:
A digital imaging modality or device
A network with reasonable bandwidth
An archive device, diagnostic workstations, archive/routing software
Some interplay with the hospital or radiology information system.
154
Name the PACS principles
1. Acquire images
2. Store into central responsibilities
3. Distribute upon requests
4. Display images
155
advantages and disadvantages of computed radiography (CR)
A - plates are cleared automatically and last for a long time, digital storage, image manipulation, cheaper, prior equipment still compatible.
D - storage needed, plates need cleaning and maintaining, have to wait to be processed before viewing the image, lower spatial resistance compared to DR.
156
Why do bones look white on X-rays?
Due to the density and its high atomic number
157
Why do images appear whiter if the x-rays are unable to penetrate the object?
There aren’t enough photons hitting the imaging plate
Photons aren’t powerful enough to travel straight through the object
The xray beam hasn’t been produced for long enough
If the reverse is true for the above the film will appear darker
158
Density with xrays
This is the degree of blackening of the film.
This is determined by exposure used.
Image blackening affected by the quantity of the x-rays passing though the patient and reaching the film. Factors affecting this; MAs, FFD and kV
If overexposed - reduce exposure factors or inc FFD
If underexposed - increase exposure factors of dec FFD
159
What is quantum mottle?
An exposure fault specific to DR
Underexposure which results in grainy or ‘noisy’ appearance.
Insufficient photons reaching the detectors and the system is unable to differentiate between backround electric noise and low signal xray photons.
160
Overexposure in DR
Tolerated better than underexposure and usually remains diagnostic.
If extreme overexposure the areas with the lowest radiographic density will appear black and cannot be recovered with manipulation.
161
Contrast (penetrating power0
Radiography
Difference between various radiographic densities (shades of grey) on the radiograph
Film showing white image on black background with few intermediate grey shades:
Excessive contrast due to too low kV
Insufficient penetration power
‘Soot and whitewash’
X-rays without extreme density mainly shows grey shades:
Insufficient contrast
‘Flat film’
Caused by underdevelopment during conventional radiography. Overexposure and scatter fogging will result in a flat image (film) but background will be black
162
Definition (xrays)
Sharpness and clarity of the structures visible on radiographs. Good definition is essential if the image is to be diagnostic.
What can affect it?
Movement blur
Scattered radiation
Fog
Focal spot size
Magnification and object-film distance (OFD)
Double exposure
Grid lines
163
Uberschwinger artefact (CR & DR)
Image processing error where there are large differences in radiopacity in adjacent areas (eg orthopaedic implants) are excessively enhanced creating a radiolucent-like appearance or halo around the implant which can be mistaken for loosening of the implant or infection
164
Look-up table errors (CR and DR)
Incorrect selection of the examination algorithm for the body area to be examined or inadequate/no collimation in the region of interest.
165
Moire artefacts (CR & DR)
When a stationary grid has been used fro CR or DR, or if the grid is aligned with the readout of the CR cassette, creating alternating light and dark bands across the image.
It can be corrected by using a Potter-Bucky moving grid or a stationary grid with a higher number of lead strips per cm
166
Recording exposure
Legal requirement to record each exposure and quality of image.
This allows continuous improvement in radiographic safety and quality. Correct information input into imaging software
167
What factors need to be considered when taking radiographs?
Positioning
Comlimation
Centering
Exposure factors
Labelling
Artefacts
168
What is the minimum thickness a lead apron should be?
0.25mm Pb
0.5mm Pb recommended.
169
Define radiopaque
Materials that are dense enough to resist passage of xrays.
Appear white or light on an image.
Have a high atomic number
170
Define radiolucent
Low atomic number.
Appear black or dark on an image.
Allows X-rays to pass through with little to no absorption.
CCOAS - VN
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