Radiography Flashcards
Outline the restraint of small animals for radiography
- Chemical and physical
- Sedation/GA
- Positioning aids
- Never manual restraint
- Positioning may depend on condition-
Outline the restraint of large animals for radiography
- Most radiographed sedated and standing
- Manual restraint usually required
- Occasionally GA for some body areas e.g. pelvis
What is the importance of movement blur in radiography?
- Leads to poor image quality
- Can be due to voluntary or involuntary movements
How can movement blur be minimised?
- Correct machine settings
- Use of good restraint
- Short exposure (increase mA, decrease exposure time)
Outline sedation for radiography
- Suitable for most thoracic and abdominal radiography
- May be used for some MSK studies
- A2A and butorphanol commonly used
- Close monitoring required, oxygen supplementation often also important
Outline general anaesthesia for radiography
- Some MSK radiography as require critical positioning
- Required for good quality, inspiratory thoracic radiographs
- Most contrast studies except oral barium
- May be safer for patient vs sedation
What are the Roentgen signs?
- Number
- Location
- Size
- Shape
- Margination
- Radiopacity
- Internal architecture and function in some cases
What are the characteristics of a good radiograph?
- Accurate portrayal
- Easy perception (sharp shadows, wide range of shades of grey)
- No misleading artefacts
- Consistent results
- No unnecessary risks taken
Outline positioning for radiogrpahy
- Part of interest as close as possible to cassette to minimise distortion
- Use standard radiographic positions first
How is axial rotation in the thorax assessed?
- Look at rib heads overlying as opposed to the ribs
- The caudodorsal rib heads should be superimposed
Outline centring for radiography
- Centre primary beam over area of interest
- Means that x-rays will go through area of interest vertically minimising distortion
Outline the importance of collimation for radiography
- Scatter contributes to general image opacity and increases radiation hazard
- Collimation means minimum size beam is used and so reduces scatter
What is the collimation required for joints and long bones?
- Joints: include associated 1/3rd of adjacent bones
- Long bones: include whole bone including both adjacent joints
Outline how to appraise collimation
- Primary beam must be contained within area of cassette, so 4 unexposed borders should be visible if are not shuttered by digital machine -
- Collimation described by number of unexposed borders seen on plate, given as percentage i.e. 0%, 25%, 50%, 75%, 100%
- Then describe how closely the image has been collimated to the area of interest
Outline the considerations regarding exposure factors in radiography
- Cannot tell correct exposure from visual appearance of a digital image
- Need to use minimum exposure possible
Why are grids used in radiography?
- X-ray scatter more significant with thicker animal
- Presents safety issue and poorer image quality
- Grids reduce scattered radiation reaching the cassette and improve radiographic contrast
How do grids reduce the scattered radiation reaching the cassette?
- Alternating strips of palstic and leda in a thin sheet
- Filter out x-ray photons not passing in a forward direction
- Absorbs proportion of primary beam
- Width and height of lead strips determine how much scattered radiation is filtered
Describe how to use a grid in radiography
- Only legally allowed for body regions greater than 10-15cm thick
- Placed between patient and cassette
- Focused grids must be aligned with centre of primary beam, correct way up and correct film focal distance used
- Increase exposure (called grid factor, usually increased by 2-3 times)
What are the different types of grids available?
- Parallel
- Focused
- Pseudofocused
Describe the labelling of a radiographic image
- Patient and date may be entered into computer and embedded in digital image file and linked to radiograph
- Side markers should always be exposed on the image
Why is radiography an important part of many imaging work-ups?
- Time and cost effective
- Easy
- Can be easily submitted for a second opinion (teleradiology)
- Useful where bone or air/gas is present
What are the disadvantages of radiography?
- Less useful where fluid and soft tissue structures are present and in contact
- Patients need to be well restrained
- Good radiographic technique needed for diagnostic images
- Hazards of ionising radiation to personnel
What conditions are likely to give the best imaging results?
- Chonic, and where clinical signs are severe or persistent/recurrent despite treatment
- Significant changes will have taken place in the patient
What is the general principle for radiographic views taken and why?
- 2 perpendicular orthogonal views
- To fully evaluate any body area
- Certain views may hide certain pathologies
What are the routine views taken for the thorax for:
a: routine radiography
b: lung metastasis screening
c: specifically lung pathology?
a: RLR and DV
b: RLR, LLR and DV or VD
C: RLR (+/- LLR) and VD
What are the routine views taken for abdominal radiography?
RLR or LLR and VD
What are the routine views taken for pelvic or spinal radiography?
RLR or LLR and VD
What are the routine views taken for limb radiography?
Mediolateral and CrCd/CdCR/DP/PD
What are the routine views taken for skull radiography?
RLR or LLR and DV
Why are 3 views taken when screening for lung metastases?
- Lung closest to table will collapse
- This will hide any soft tissue pathologies
Why is a VD view better for abdominal radiography?
Allows the intestines to spread out more and so improves visualisation
Why is a DV view commonly used for imaging of the skull?
Easier to get the skull and spine straight on DV
What views are taken for limb radiography of the horse?
- 4 orthogonal views
- Lateromedial
- Dorsopalmar/dorsoplantar
- 2x45 degree oblique views
- e.g. for carpus: DorsoLateral-PalmaroMedial Oblique (DLPMO) and DorsoMedialPalmaroLateral Oblique (DMPLO)
What is adjusted to improve the contrast of a radiograph?
kV (changes the power of the beam and so changes the proportions that x-rays can penetrate through tissues)
When should thoracic images be taken in relation to the patient’s breathing?
At peak inspiration to prevent the diaphragm obscuring the view, and to prevent the lung fields appearing opaque where they are not
When should abdominal images be taken in relation to the patients breathing?
At the expirational pause to ensure there is enough space in the abdomen for the intestines to spread out
What is the purpose of radiographic contrast studies?
Provide increased detail of organ size, shape, position, internal detail and sometimes function
Outline the properties of negative contrast agents
- Low physical density agents
- Radiolucent appearance
- Air, gases
Outline the properties of positive contrast agents
- High atomic number therefore high radiographic opacity
- Radiopaque on radiographs
- E.g. barium, meglumine diatrozoate, iohexol
List the ideal properties of radiographic contrast agents
- Differ from tissues under examination in terms of capacity to absorb x-rays
- Accurately delineate the body part being examined
- Be neither toxic nor irritant
- Persist for the duration of the study
- Be totally eliminated afterwards
- Easily administered
- Cost effective
Why should a plain (survey) radiograph be taken before a contrast study?
- Assess adequate radiographing technique
- Inform if contrast media is contra-indicated
- May give a diagnosis
- Assess patient preparation e.g. presence of faeces
- Decide on suitable technique
- Comparison with study films
How many views should be taken for contrast studies?
- 4
- Contrast agent moves with gravity, each view will put the contrast agent into a different position
- Will show or hide different things
Where are negative contrast agents commonly used?
Bladder and Gi tract
What are the advantages of negative contrast studies?
- Cheap
- Quick
- Convenient
- Relatively safe
What are the disadvantages of negative contrast studies?
- Poor mucosal detail if used alone
- Air slowly eliminated from the body which may confuse later studies
- Theoretical risk of air embolus in blood strem e.g. if have ulceration
What are barium sulphate studies common used for? How is it administered?
- GI contrast studies
- Administered as suspension, paste or mixed with food
What are the advantages of barium sulphate contrast studies?
- Low toxicity
- Inert
- Excellent mucosal detail
- Therapeutic for V&D
- Relatively cheap
What are the disadvantages of barium sulphate contrast studies?
- Care with aspiration, cannot be used under GA
- Cause granulomatous reaction in the lungs if refluxed
- Irritant if enters body cavities so care with suspected perforation
What are water-solube iodine preparation contrast studies commonly used for?
- Cardiovascular system
- Urinary tract
- Joints
- Salivary glands
- Tear ducts
- Fistulas/sinuses
- GIT
- Myelography
What are the 2 types of water soluble iodine preparations?
- Non-ionic
- Ionic
- (also gastrointestinal preparations)
What are ionic water soluble iodine preparation contrast studies used for?
- Suitable for IV administration, or directly administered
- NOT myelography
- e.g. meglumine diatrozoate
What are non-ionic water soluble iodine preparation contrast studies used for?
Suitable for myelograpy and any other use, recommended for all applications as has few side effects vs ionic
- e.g. iohexol
What are the advantages of water-soluble iodine preparation contrast studies?
- Versatile (can be injected IV or directly administered)
- Rapidly absorbed and excreted by the liver if leak into body cavity and blood stream
What are the disadvantages of water-soluble iodine preparation contrast studies?
- Ionic are hyperosmolar so get unprelant side effects if conscious (nausea, vomiting)
- Ionic are irritant if injected direclty
- Large doses of iodine are toxic
- Contra-indicated IV in hypovolaemia, hypotension, cardiac or severe renal failure
- Rarely may cause iodine-induced acute renal failure
What is myelography?
Contrast radiography of the spine and subarachnoid space
What is intravenous urography?
- Excretion urography
- iv injection of contrast excreted by kidneys
Outline cystography
- COntrast radiography of the bladder
- Can be positive contrast (infusion of positive contrast into bladder)
- Pneumocystography: infusion of air into bladder
- Double contrast cystography: infusion of positive contrast into bladder followed by air
What is cardio-angiography?
Contrast radiography of heart and blood vessels
What sis arthrography?
Contrast radiography of the joints
What is dacryocystography?
Contrast study of the lacrimal sacs
What are the advantages of advanced imaging methods e.g. CT and MRI?
- Avoid superimposition as give cross sectional images
- Superior to radiography and ultrasonography for some conditions
- Useful for surgical planning
What are the disadvantages of advanced imaging methods e.g. CT and MRI?
- Radiography and ultrasonography may be more efficient
- Long periods of restraint needed
- High cost
- Limited availability
What regions/tissues is CT particularly useful for?
- Bone
- Nasal cavities
- Middle ear
- Some joints e.g. elbow
- Pharynx
- Lungs
- Thoracic and abdominal masses
- Portosystemic shunts (angiography)
What regions/tissues is MRI particularly useful for?
- Soft tissues
- Nervous system
- Middle ear
- Soft tissue masses e.g. in the head
- Some joints e.g. shoulder, stifle and muscles/tendons
What are the key principles of a radiological report?
- Must enable someone else to look at radiograph and understand what you are talking about
- Focus on important points
- Use radiographic (Roentgen) signs for accurate descriptions
- Normal structures mentioned
- All abnormalities listed and prioritised in terms of likely significance
- Differential diagnoses ordered in terms of likelihood
- Consider further diagnostic tests
What are the requirements for radiographic viewing equipment?
- Must have enough luminance and spatial resolution
- Applies to all screens for diagnosis
- Good quality, high brightness and high resolution LCD screens fill requirements
Outline the standardised orientation for radiograph interpretation
- Cranial portion towards left of image
- Proximal towards top of image
- VD: cranial to top, look at image as though looking at patient i.e. left marker on the right
- Lateral: dorsal edge to top of image, cranial to the left
Outline the basic principles of radiographic image interpretation
1: Put radiograph in correct orientation
2: Assess whether or not the radiograph is of diagnostic quality
3: Make observations on what can be seen
4: Summarise and establish differentials and interpretation
5: Assess whether any other tests are needed in order to establish a firm diagnosis
Outline the initial observation stage of radiograph interpretation
- Simply describe
- Be systematic, work outside in
- Roentgen signs
- Comment on normals
- Comparison to normal if available
- Do not let clinical signs influence observations
- Be aware of possible superimposition
- Evaluate visibility of borders
- Consider potential shadowing/border obliteration
Outline the summarising and differentials stage of radiographic interpretation
- Summarise all observations
- Differentials should lead on from conclusions
- Rank in order of likelihood
- Connect observations to clinical signs
- Eliminate differentials as a result of radiograph
- Unusual findings usually unusual presentation of common condition
- Usually single differential covers all or most abnormalities, more likely to be several conditions in old patients
List some common pitfalls in radiographic interpretation
- Search errors
- Lack of methodical search
- Judgement or analysis errors
- Not taking enough time
- Not considering effects of limitations of radiographic technique
- Not looking at all of radiograph
- Distraction by an obvious lesion
- Not knowing normal radiographic anatomy
- Allowing clinical details to influence observation
- Not considering clinical details of case when formulating differentials list
- Not placing differentials in likelihood order
Explain how under-reading a radiograph may occur
Failure to recognise poor technique, lack of knowledge, committing to a diagnosis before radiography, interpreting a certain combination of signs as indicating a specific diagnosis
Explain how over-reading a radiograph may occur
- Misinterpreting normal anatomy e.g. fat separating lungs from thoracic wall misinterpreted as pleural effusion
- Classification of incidental findings as signficiatn
- Mistaking artefacts for pathology
- Faulty reasoning (e.g lesion identified but incorrectly localised)
Describe the somatic effects of radiation on individuals
- Skin erythema
- Bone marrow hypoplasia
- Testicular/ovarian sterility
- Abortion
- Cataracts
- Life-shortening with very high doses
Outline some genetic effects of radiation
- Increased risk of DNA mutation and inherited abnormalities
- Carcinogenic effects
What cell types and therefore tissues and individuals are most susceptible to the risks of radiation?
- Rapidly dividing cells
- Bone marrow, gonadal tissue, germinal layers of skin/GIT
- Persons under 18, pregnant women/foetus
Outline the risk from scattered radiation to staff
- Scatter can travel in any direction
- Consists of lower energy radiation produced in the patient’s body tissues
- Same risks as radiation
Outline gamma scintigraphy
- Aka physiological imaging, commonly used for MSK diseases in horses
- Injection of unstable radioactive nucleotide (usually technetium 99m) into patient
- Decays, releasing gamma rays
- Detected using gamma camera, converts into light and produces computer image
- Uptake in areas of disease increased by carrier e.g. methylene diphosphonate (MDP_
Outline safety issues related to gamma scintigraphy
- Animals injected with radioactive substance
- Technetium has a short half life (6 hours) and decays rapidly (12-48 hours)
- Minimise handling during procedure and isolate after
- Excreted urine must be caught and stored for 48 hours
Describe radioiodine treatment
- Treatment for feline hyperthyroidism
- Iodine 131 injected and concentrated in thyroid gland
- Emits beta-particles and gamma rays, only travel a few mm in tissue
- Half life of 8 days
Outline the safety issues associated with radioiodine treatment
- Radioiodine excreted from body in urine mostly so must be caught and stored until safe
- Cat is a radiation hazard so must be isolated and hospitalised for at least 14 days
What legislations control the use of ionising radiation?
- Ionising Radiations Regulations 2017 (governs use of radiation in workplace)
- Ionising Radiation (Medical Exposure) Regulations 2018
Outline the main points of the legislation relating to ionising radiation
- Notify Health and Safety Executive if practice owns/uses an x-ray machine
- Appoint Radiation Protection Adviser and Radiation Protection Supervisor
- Define and identify controlled area
- Draw up and follow local rules
- Justify need for radiation
- Minimise exposure to personnel (ALARP)
- No dose limit should be exceeded
Describe the Radiation Protection Advisor (RPA)
- External to practice, expertise in radiation safety
- Advanced knowledge of radiation safety e.g. Radiation physicist, Veterinary Diploma holder
- RPA Certificate of Competence
- Initially helps design and set up radiography facilities
- Establishes Local Rules
- Annual visits for monitor safety and advice on: room design, layout, shielding, siting and use of equipment, local rules, dosimetry
Describe the Radiation Protection Supervisor (RPS)
- Member of staff within practice
- Responsible for day-to-day supervision and enforcement of rules
- Makes sure Local Rules are followed
- Keeps Local Rules and paperwork up to date
- Understands legal requirements
- Ensures radiation doses are kept to a minimum
- Manage radiation emergencies
- Consults with RPA where necessary
Describe the controlled area for radiation
- Area of risk of significant radiation exposure
- Determined by RPA
- Dependent on facilities and type of radiographic studies
- Clearly defined with warning signs
- Extends 2m from primary beam if performed outdoors
- Usually constitutes x-ray room in small animal practice
What materials stop x-ray beams?
- Primary beam: 4.5 inches of brick (double layer of brick), or 1 mm lead
- Scattered radiation: single layer of brick
- Not stopped by wood or glass
Describe the Local RUles of rradiation
- Code of Conduct for performing radiography
- Placed in easily visible place
- Read and understood by every member of staff involved in radiography
- Details equipment, procedures and access restrictions
- Lists RPA, RPA and any staff involved in radiography
- Defines control areas
- Includes written arrangements for making radiographs, including restraint, record keeping and protective clothing
How can radiation exposure be monitored?
- Most commonly film badges or thermoluminescent dosimeters (TLDs)
- Worn by all staff regularly involved with radiography
- Regularly checked
Describe PPE used in radiogaphy
- Only protects against scattered radiation
- Aprons and gloves to protect hands and arms (0.25mm lead for aprons, 0.35mm lead for gloves)
- Also thyroid protectors available
- Stored flat to prevent cracking of lead rubber
- Regularly checked for cracks or other defects
What are the potential sources of radiation that may affect staff/
- Direct beam
- Leakage from tube head
- Scatter from patient
- Some primary beam will pass through patient, plate and table top i.e. go all the way through to the floor (or foot)
How can radiographic procedures be optimised?
- Minimise risk to personnel
- Follow Local Rules
- Consider and prepare carefully for each procedure (e..g direction of primary beam, scatter)
- Good positioning, centring, collimatin, labelling, avoid artefacts
- Correct exposure
- Good processing
- Reduce need for repeats
- Avoid exposure creep
How can risk to the public/other staff from radiation be minimised?
- Warning lights and signs
- Written arrangements
- Staff familiar with safety and procedures
- Regular servicing of equipment
What are the provisions for manual restraint of large animals for radiography?
- Must be wearing adequate protective clothing
- Stand as far outside of primary beam as possible
- 1 person may hold head
- Use self supporting boxes or cassette holder or long-handled cassetter holders if it is necessary to hold
- Use chemical restraint where possible
Outline the practical measures that can be used to limit access to radiation exposure in small animal practice
- Mostly suing vertical primary beam
- Always use good chemical restraint where possible
- Appropriate physical restraint
- Should not need to be in the same room for most small animal procedures
In what circumstances is manual restraint for radiography permitted?
- Animal is critically ill and cannot be sedated/anaesthetised
- Radiography must be essential to teh case managemetn
How can scattered radiation be controlled?
- Reduce amount produced using adequate collimation, using lowest possible kV that will still produce a diagnostic image
- Use grid in patients deeper than 10-15cm
- reduce effect of scatter on personnel by increasing distance and using appropriate PPE
What is the importance of the inverse square law with regards to radiation safety?
- Intensity of x-ray is inversely proportional to the distance^2 from their source
- So if double the distance from the source of x-rays, reduce intensity to a quarter
- Therefore distance is a good way of reducing hazard
What views are commonly taken for radiographs of the following joint scenarios in small animals?
a: caudal aspect of elbow
b: carpus fractures
c: hips dysplasia screening
d: tarsus OCD
a: flexed lateral view
b: oblique views
c: only ventrodorsal required
d: oblique views
How is a decubitus lateral view performed?
Patient in lateral recumbency, x-ray film place perpendicular to the table at the patient’s spine, supported by snadbags. Machine head rotated to be parallel to the table,i.e. x-ray beams will be horizontal
When might a decubitus lateral view of the abdomen be performed?
To look for free abdominal gas, as this will move to the top of the abdomen
What are key challenges when acquiring a thoracic radiograph?
- Accurate positioning to avoid axial rotation
- Achieving adequate lung inflation
- Avoiding movement blur
Outline the advantages and disadvantages of a ventrodorsal thoracic radiograph
- Disadvantages: heart rotates to one side and distorts shadow
- Advantages: may produce better pulmonary detail, more sensitivity for the detection of small amounts of pleural fluid
What are the advantages of right lateral thoracic radiographs?
- Heart position more consistent
- More lung between heart and chest wall
- Diaphragm obstructs less of the lung field
What are the advantages of dorsoventral thoracic radiographs?
- Safer in dyspnoeic animals
- Heart lies in anatomically correct position
