Veterinary Imaging Flashcards
What are the veterinary imaging modalities
- Radiography
- Ultrasound
- Fluoroscopy
- Computed tomography (CT)
- Magnetic Resonance Imaging (MRI)
- Scintigraphy
What type of radiation do X-rays use?
- Electromagnetic radiation
- X-rays (and gamma rays) cause ionisation in atoms (ours &
the patient’s)
In which processes are X-rays used?
- Radiography
- CT
- Fluoroscopy
What is ionising radiation?
- Ionisation = this is when an electron is ejected from the atom
when the x-ray strikes it (see the image) - A “free radical” atom is formed that lacks an electron so it pulls electrons off surrounding atoms, and the damaging process goes on (‘free
radical cascade’)
What does ionising radiation cause?
- Damage that causes breaks in chemical bonds
- DNA is often damaged as it is large and has little redundancy
- DNA damage in somatic cells causes effects in the individual (eg cancer)
- DNA damage in a germ cell (ova, sperm) can cause DNA mutation that can be passed on to future generations
What modalities omit ionising radiation?
- Radiography
- Radiography - Contrast studies
- Fluoroscopy
- Computed tomography (CT)
- Scintigraphy
X-rays:
Pass through the patient to a digital detector which records the digital image and sends it to a computer
In X-rays, each tissue absorbs a ____ amount of x-rays
* If more x-rays are absorbed = ____
* If more x-rays pass through = ____
different; whiter; blacker
Radiopaque
whiter
Radiolucent
blacker
The 5 Radiographic Opacities:
- Gas opacity
- Fat opacity
- Soft tissue opacity
- Mineral opacity
- Metal opacity
How radiopaque or radiolucent a structure is helps us determine…
the type of tissue it is comprised of
What is a contrast agent?
Something instilled into an organ in the patient to see that organ better
Contrast agents either cause the organ to look ____ or ____
radiolucent; radiopaque
Radiographs are _____ so always take _ views
‘2-dimensional’; 2
What is Fluoroscopy?
An x-ray “movie”
- There is an x-ray tube producing a continuous x-ray beam
The opacity in fluoroscopy is ____ compared to radiographs
reversed
What is fluoroscopy used for?
- Collapsing trachea
- Swallowing studies
- Orthopaedic surgery
- Stent placement - cardiovascular
Fluoroscopy is the ____ risk for radiation exposure in practice
as the x-rays are ____ and staff are in the room
biggest; continuous
Both MR & CT are _____images - slices of the body
“cross-sectional”
Cross sectional imaging is about….
simplifying complicated anatomy by eliminating superimposition of structures
How is a CT image formed?
- The CT machine has an x-ray tube that rotates around the patient & the patient moves through the CT machine (through the donut).
- The x-rays are detected by detectors. Each one represents a slice of tissue. Each detector is about
0.6mm wide. Multiple detectors/slices are acquired at once so it is quick. - The slices and therefore the voxels are very small (approx 0.6mm) so essentially a ‘volume’ of tissue
is scanned.
How are CT’s used in practice?
- In every referral practice
- In some general practices
- Licence is required as it emits radiation
- Cats and dogs - used for all areas of the body; poor for the brain
- Equine - used for anything that can fit in - just the distal limbs & head.
It can be standing CT or conventional CT. - Also in all other species eg rabbits, birds, snakes, zoo animals etc
How is an MRI image formed?
- MRI is a map of the electrical signal from hydrogen atoms (H+).
- H+ is abundant in fat and water in the body so it is good for imaging soft tissues. MRI is not good for imaging bone.
- H+ are positively charged.
and spin at random orientation. - When they are put in an MRI machine, the orientation of the spinning aligns to the magnetic field of the MRI machine.
- A radio-frequency pulse is applied which causes the hydrogen atoms to no longer spin aligned to the magnetic field
- When the radio-frequency pulse is turned off, the alignment gradually returns (‘relaxes’) back to be aligned with the MRI machine’s magnetic field
- As the H+ atoms realign, they release energy which is collected as a ‘signal’ which forms the image
- The time this realignment takes is different for each H+ atom depending on which tissue it is in.
What two things can manipulate the appearance of the soft tissues in an MRI?
- different radio-frequency pulses
- the timing of when the energy signal is collected during realignment/relaxation
MRI safety: During an MRI, …
Any ferrous metallic (ferromagnetic) object can become a projectile and kill people
- REMOVE metal from the body
MRI vs CT:
- CT is cheaper
- CT is quicker
- CT is good for all areas, except the brain. MRI is good for brain and spine
- Both usually require referral
How is an ultrasound image made?
- Made by sound being sent into the tissue and the tissue reflecting sound back.
- It can reach a depth of approximately 10cm. So the whole abdomen of large animal like a horse cannot be examined.
- Movement can be seen, such as the heart beating, so the function of some organs can be evaluated as well as the appearance.
Ultrasound sound echos each have their own ____. The longer the echo takes to return, the ____ it is displayed on the image
Amplitude; deeper
What 3 things can happen when an X-ray interacts with a patient?
- Pass through the patient to the x-ray detector plate
- Absorbed in the patient
- Scattered from the patient
What is acoustic impedance?
The resistance a sound wave encounters when it passes through a tissue
What determines if the sound is reflected in an ultrasound?
- The density of the tissue and the speed of sound in that tissue
- Sound is reflected at an interface between tissues of different acoustic impedance. Large difference = bright dot
What are ultrasound transducers?
Devices that convert electrical energy into mechanical energy
What are the types of ultrasound transducers?
- Linear
- Curvilinear
- Phased array
How do ultrasound transducers work? (2)
- Convert electrical energy into sound waves, which are then sent into the body,
- Receiving the reflected sound waves, converting them back into electrical signals for image creation
Ultrasound is considered …
Safe
What is scintigraphy?
- Injection of a carefully chosen radioactive substance that can be seen on a gamma camera
- The radioactive substance is linked to a substance that is physiologically active in the body.
- The physiologically active substance is part of the physiologic process in the body that is being assessed.
- Therefore, it is a function test.
What can scintigraphy be used for?
- Assessing function such as:
- Kidney
- Thyroid
- Liver
- Cardiac - Portosystemic shunt detection
- Pulmonary thromboembolus
Scintigraphy uses ….
ionising radiation
Contrast agents use gas and metal opacity contrast agents because…
contrast agents are used at either extreme of the 5 radiographic opacities
Why are 2 orthogonal views required for a radiograph?
Because they are 2D
What are the advantages to cross sectional imaging?
- Can be made in any plane
(transverse, dorsal & sagittal planes) - Ability to visualise internal structures in 3D, providing detailed “slices” of the body
What are curvilinear transducers used for?
Scanning the abdomen
What are linear transducers used for?
For scanning things close to the surface (up to 4cm deep)
What are phased array transducers used for?
for scanning the heart (echocardiography)
Echocardiography
Scanning the heart
Advantages and disadvantages of ionising radiation
- Quick and readily available imaging for bones
- Limited soft tissue visualisation
What are MRI’s used for in veterinary practice?
- Advanced imaging of soft tissues, especially the brain and spinal cord,
- Diagnosing conditions like tumours, infection and inflammation
What are ultrasounds used for in veterinary practice?
- Evaluating the heart, abdomen, and reproductive system
- Visualising internal organs, soft tissues, and blood flow in animals
