Diagnostic Imaging Flashcards
What is the physical basis and what do the images show for the 4 main types of imaging?
Radiography and computed tomography - physical basis is x-rays images show variations in physical density
Scintigraphy - physical basis is gamma rays - images show metabolic activity
MRI - physical basis is radiowaves - images show magnetization
Ultrasonography - physical basis is high frequency sound - images show echogenecity (how many echos are produced by different structures)
Define radiography
Making images representing the shadow of an object or patient in the x-ray beam
What does the level of greyness in a radiograph show?
How much of the x-rays are absorbed into a material
What is the order of density of tissues within the body when doing a radiograph?
Air<Fat<Tissue<Bone
What is the main problem when doing a radiograph of an animal?
Superimposition - x-rays have to go through the whole animal making it difficult to distinguish features
What is tomography?
Images that represent a section through the body
Define scintigraphy
Images representing the distribution of radioactivity injected into a patient
Describe the process of scintigraphy
Molecule usually metabolised by bone injected with a radioactive atom which fuses into boneA gamma camera detects the atom and generates an image showing the distribution of bone metabolism
Why do we carry out scintigraphy instead of radiography?
Some lesions don’t show up on a radiograph
Define magnetic resonance imaging
Images by applying pulsed magnetic energy to the patient and collecting radiowaves emitted between pulses
What is MRI only really used for?
Neurology patients
Define ultrasonography
Images made by firing pulses of high frequency sound into body and collecting returning echoes
When may imaging be useful?
When a patient has a suspected internal condition likely to alter body structure
What are the 3 outcomes of diagnostic imaging?
Description of gross morphological features of a conditionFeatures may be characteristic of a diagnosis but other tests usually requiredCan also be used to guide biopsy or to facilitate treatment
What are x-rays?
Form of electromagnetic radiation - particularly penetrating form of light that can go through light opaque materials
How are x-rays produced?
Fast electrons collide with atoms of a heavy metal (tungsten)
What are the 3 key requirements for x-ray production?
Source of electronsMethod for accelerating themTarget
Describe a basic x-ray tube
Source of electrons with low voltage through it facing a target made of tungsten backed with copper to prevent over-heatingThis is placed in a vacuum tube and a moulding placed around the electron emitter to better direct the electronsA high voltage is then passed through the target end and the electrons pass across the vacuum and collide with the tungsten producing x-rays
What 3 things does x-ray absorption depend upon and why?
Tissue densityAtomic number of elements in tissueTissue thicknessThese factors increase number of electrons in x-rays path
What two words are used to describe how things appear on a radiograph?
Lucent - more see through (air)Opaque - less see through (metal)
What are the 5 types of tissue that can normally be distinguished on a radiograph and what are some examples?
Air - in lung or intestineFat - between abdominal organsSoft tissue - parenchymal organs, muscle and fluidsBone - other mineralised tissuesMetal - left/right marker or foreign body
What is one limitation of looking for soft tissue with a radiograph?
Cannot distinguish between them without a contrast medium
How does radiograph opaqueness vary with thickness?
The more thick an object the more radio opaque it becomes
What are kVp and mAs?
kVp = kilovoltage peak - high voltage across the x-ray tubemAs = total no. electrons crossing the tube
What is Bremsstrahlung radiation?
Fast electrons slow as they approach a tungsten nucleusThe difference in kinetic energy causes x-rays to be produced from the loss of energy from the electrons
What does Bremsstrahlung radiation result in?
Broad, continuous range of x-ray energies
What does increasing mAs do?
More x-rays are produced with the same median energy
How would increasing mAs look on a radiograph?
Makes it darker
What are the typical mAs ranges used when radiographing small animals?
25-300mA and 0.01-0.03s
When is it useful to adjust the mA setting?
When you need to minimise exposure time and avoid motion blur high mA settings are useful
What does increasing kVp result in?
More x-rays with higher energy
What is used to filter out low energy x-rays and why?
Aluminium filter to reduce radiation exposure as low-energy x-rays are useless
What kVp settings do we use for different body parts?
Low kVp for very small parts - extremititesHigh kVp for thicker body parts - thorax
What is contrast medium?
Inert compounds that are visible radiographically
What is the primary beam?
X-rays that originate from the target following a defined path
What is scattered radiation?
X-rays that have been deflected by interaction with the patient
Why is scattered radiation a problem?
Radiographs affected by excessive scatter look indistinct and greyX-rays travelling in a variety of directions could hit animal handlers
What happens to the image with random low-level exposure over the entire film?
Darkens image and reduces contrast
What 3 ways can be used to minimise scattered radiation?
Minimise volume of tissue irradiated by collimating size of the primary beamPutting a layer of lead-rubber between cassette and table topUse high kVp exposures
What are x-ray grids?
Series of fine lead strips aligned parallel to the direction of the primary beam with strips of material between that allow most x-rays through
What is the purpose of an x-ray grid?
Reduce the amount of scattered radiation by absorbing scattered radiation within the grip
What is the grid factor?
The amount you need to increase the exposure when using a grid to compensate for increased absorption - usually by about 2 or 3
What is radiation exposure and what is it measured in?
Ability of radiation to ionise the air - measured in Roentgens
What is the unit that measures the rate of radioactive decay?
Becquerel
What is the unit of absorbed doses of radiation?
Gray
What is the dose equivalent and what is its unit?
Measure of the effect of radiation - measured in Sieverts
What is the maximum permissable dose for persons at work aged 18 years or more?
20mSv per year
What are the two common types of detector used to monitor personnel levels of radiation?
Film badgeThermoluminescent detector
Describe the use of monitoring devices
Worn for either 4,8 or 13 weeks then returned for processing who send back new dosimeters and give report on previous readings
What are 4 practical points about dosimeters that must be remembered?
Badges must not be sharedMust be worn all day at work but not outside workWorn at waist level and under lead apronsRecords must be kept for 2 years minimum
What are the three basic ways to minimise radiation exposure?
TimeDistanceBarriers
How can time be utilised to minimise radiation exposure?
Spend the minimum time using radiation and minimise retakes
How can distance be used to minimise radiation exposure?
Inverse square rule (2m distance is 1/4 less radiation)Use 2m cable on exposure buttonLeave room when possibleHold things at arms length
What ways can barriers be utilised to minimise radiation exposure?
Personal - lead gloves or apronsMobile - lead plywood doorsWalls - lead sheet, barium-plaster or brick
Define the controlled area
Area around the primary beam where average radiation dose rate exceeds the permissible limit2m radius of the x-ray tube or usually the roomRadiation signs must be positioned at the entrance to the controlled area
What is a designated person?
Someone named in the Local Rules as permitted to making x-ray exposures
Who is the radiation protection advisor?
DVR or hospital physicistInspects facilities and provides reportProvides Local Rules as a guide to proceduresSource of advice when planning modifications
Who is the Radiation Protection Supervisor?
Partner, CertVR or DVRNotifies HSE that radiography is performedResponsible for adminstering Local RulesRoutinely monitors dosimeter readingsPerson to whom problems should be reported
What should never enter the primary beam of an x-ray?
Any part of the human body when restraining - lead gloves don’t offer adequate protection either
What is a long-term consequence of occupation exposure to x-rays?
Skin cancer
What should you ensure are removed from any animal before radiographing?
All collars, identification tags bells etc.
What is it important to do when manually restraining an animal?
Collimate the primary beam so hands are not included
What can cause spurious shadows on a radiograph?
Fogging during handling in the darkroom - either wrong colour or intensity safelight or by a light leak into dark room
What is required for radiography of large dogs with thick parts?
Needs high exposure so should use a grid and the cassette put under the table in the Bucky
What would cause an uneven film blackening and streaky appearance?
Something wrong with the grid - absorbed too many x-rays along its sidesFocussed grid used at wrong distance, upside down or an unfocussed grid was used
What are the ways in which a double exposure can occur on a radiograph?
Person may not hear the audible signal that accompanies emission of x-raysMultiple casettes might be in use and someone has re-exposed a cassette thinking it hadn’t been used
How can motion blur on a radiograph occur?
Involuntary movements of the patient or voluntary movementsLoose x-ray tube mounting or wobbly table would also contribute
What does a grey background on a radiograph indicate?
Light exposure to x-rays or under-development
How can you improve a radiograph with a grey background?
Lower kVp and higher mAs exposureIf other radiographs are also grey then check temperature of the developer tank, chemicals etc.
How can you improve an xray with excessively high contrast?
Increase kVp and/or mAs
What error has occured when a radiograph appears brown or yellow?
Chemicals haven’t been removed by washing and allowed to oxidise on the radiograph causing the brown/yellow colour
Why is a scratched red light a problem?
White light will escape through the gaps and could expose the film
What is the first imaging technique used in GI disease?
Survey radiography
Why can we normally see the GI tract with radiography?
Stomach and intestine contain gas and colon contains faeces
What should be used to see more detail with the GI tract?
Contrast radiography
Name and describe 5 contrast radiography techniques used in the GI tract
Pneumogastrogram - air into stomachFood and barium gastrogram - assess gastric emptyingDouble contrast gastrogram - combine air and barium to identify lesionsUpper GI contrast study (barium) - identify stomach, intestine, assess GI motility/obstructionBarium enema - identify colon, intussusception and mural lesions
Why is barium a good choice for gastric contrast radiographs?
High atomic number and blandTime passing through is increased with barium
What may be a reason not to use barium for GI diagnoses?
Rupture as may leak into abdomen - would do a exploratory laparotomy anyway so can clean out
What does local dilatation usually mean on a radiograph?
Key sign of obstruction - diameter shouldn’t be greater than 1.6x depth of mid-centrum of L5
What can be confused with dilatation of the intestine on a radiograph?
Dilated uterus - dog in 44 days of pregnancy
What types of foreign material may be visible radiographocally?
MetallicMineralisedOpaque materialsNon-opaque materials
What can cause abnormal luminal shape of the GI tract?
Disordered motility or a filling defect
What are abnormal mucosal surfaces only visible on and what does presence suggest?
Only visible on contrast studiesSuggests infiltration or ulceration
How many hours do contrast mediums (Barium suplhate and barium meal) take to empty from the stomach of the dog? Cat?
Barium sulphate - 1-3h in dog and 0.25-2h in catBarium meal - 4-16h in dog and 4-17 hours in cat
What shuold we be able to see during ultrasonography in the GI wall?
5 layers of the GI tract - normal thickness of 3mm
At what rate is peristalsis normally observed at during ultrasonography?
4-5 waves a minute
