Diagnostic Imaging Flashcards
Wavelength and frequency are __ proportional
Inversely
List 3 properties of x-rays
- Short wavelength
- High frequency
- High energy
Which materials can x-rays penetrate?
Materials that absorb or reflect visible light
How do x-rays cause direct tissue damage?
By direct interaction with DNA
How do x-rays cause indirect tissue damage?
By the ionization of water molecules leading the formation of radicals
Which tissues are more affected by x-rays?
List 3
- Bone marrow
- Epithelial cells of the GI tract
- Early stage embryonic cells
What are the 2 classes of biological effects of x-rays?
- Stochastic effects
- Deterministic effects
Define stochastic effects
Give one example
Effects that have a random probability of distribution, and cannot be predicted precisely
Cancer or genetic effects
Define deterministic effects
Give one example
Effects that happen because of certain known conditions
Erythema, hematopoietic damage or cataracts
What does ALARA stand for?
As low as reasonably achievable
What are the units for absorbed radiation?
Gray (Jkg-1)
What are the units for effective dose of radiation?
Sievert
Define radiation exposure
Amount of ionization per mass air
Define absorbed radiation
Amount of energy transferred by radiation per mass
Define effective dose
A measure of radiation and organ system damage in humans
I.e. doses that are NOT received as a patient
What is the annual dose limit of radiation for the public vs a professional?
Public: 1mSv
Professional: 20mSv
What are 3 exceptions for the UK Veterinary Radiation Protection Regulations?
I.e. when can you go in to manually restrain the patient?
- Critical illness in which sedating the animal is dangerous
- Specific radiographic technique is required
- Patient type (i.e., large animal)
List 6 methods of radiation protection
- Filtration of the x-ray tube
- Time
- Distance
- Sheilding
- Collimation
- Personnel monitoring
What is the inverse square law when relating to the distance of radiographic imaging?
If the distance from the primary source is doubled, the intensity will decrease by a factor of four
List 3 ways you can sheild yourself from radiation
- Lead gloves
- Lead aprons
- Lead thyroid collar
What is a collimator?
A light beam diaphragm (like a view finder)
What are 2 types of dosimeters?
- Film badge
- Thermoluminescent (TLD)
How are x-rays produced?
Through conversion of kinetic energy of accelerated electrons into electromagnetic radiation
What is the source of electrons in an x-ray?
A cathode
Define x-ray tube current
Number of electrons flowing per second from the filament to the target
What is the source of deceleration in radiography?
The anode
A high potential difference leads the to __ of the electrons in a vacuum towards the anode
Acceleration
What is the charge of an anode
Positive
What is the function of the actual focal spot of an anode
It reduces over heating
What is the function of the effective focal spot of an anode
Improves detail
Compare small and large filament size in x-ray production
Small: finer detail and concentrates heat
Large: reduced detail but can use higher exposures
An x-ray beam is __
Polychromatic
List 3 things that happen when you increase KVp
(i.e., what else does it increase)
- Increases electron velocity
- Increases number of x-ray photons
- Increases energy
List 2 things that happen when you increase mA
(i.e., what else increases)
- Increases filament heating and tube current
- Increases number of x-rays being produced
Define attenuation
Decrease in intensity of an x-ray beam as it passes through matter
Define transmission
When an x-ray passes through matter without interaction
Define scatter
When the photon changes direction
What creates the image in an x-ray?
I.e., the shadowgram
The attenuation of the x-ray beam by the different tissues in the patient
Describe the photoelectric effect
When the x-ray photon is completely absorbed, and a photoelectron is removed from the shell of the tissue atom (it is ionized)
This gives off some radiation, but not enough to leave the body so it is not a safety hazard
Describe the compton effect
When the x-ray photon ejects an electron from the outer shelll of the tissue atom and the photon is scattered
The scattered photon has a lower energy than the x-ray photon and this may fog the film or be a safety hazard (scatter radiation)
The photoelectric effect is seen with __ radiation, and the compton effect is seen with __ radiation
Photoelectric: low range (up to 30kVp)
Compton: high range
Which form of x-ray absorption provides the best image contrast?
Photoelectric
What are the purpose of grids?
Bonus: when would you use them?
To reduce scatter & improve radiographic contrast
When using high range radiation (producing the compton effect)
What do you need to change about your x-ray when using grids?
Think lighting
Increase exposure
What are the 3 types of radiography?
- Conventional
- Computed
- Digital
Define latent image
The image that reflects the pattern of the part being radiographed
What are the 3 steps in manual film processing?
- Developer
- Fixer
- Wash
When is it recommended to use a grid?
When body part thickness is greater than 10 cm
Why do you need to increase the exposure when using a grid?
Bonus: how much do you need to increase exposure by?
To compensate for the portion of the primary beam absorbed by the grid
Increase exposure by a factor of 2-3
List 3 advantages of using an intensifying screen
- Reduce personnel exposure
- Reduce patient exposure
- Increase image contrast
Where is the image captured in computed radiography?
I.e., what is in the x-ray cassette?
A cassette containing a phosphor storage layer (no film)
List 3 advantages of computed radiography
- Time efficient
- Lower radiation dose
- Cost effective
List 3 disadvantages of computed radiography
- Laser reader is sensitive to dust
- Maintenance
- Manual labour required
How is the image produced in computed radiography?
- Cassette is put into a laser film reader
- Laser beam stimulates phosphor crystals to release stored light energy
- Computer generates a digital image in DICOM format
List 3 advantages of digital radiography
- Quick
- Good quality
- Lower radiation dose
List 2 disadvantages of digital radiography
- More expensive
- Fragile
How is the image produced in digital radiography?
There is an imaging receptor plate containing many small detector elements that transform x-rays into an electrical signal
Explain the difference between direct and indirect digital radiography
Direct: x-ray photon hits a selenium plate and the charges are transmitted to a computer for image construction
Indirect: x-ray photon hits a flat panel that creates visible light, the light photon then stimulates a photocathode which transmits energy to a computer for image construction
Describe image stiching
Bonus: how big can an image get?
When an x-ray tube takes multiple radiographs and fuses images together
Image size up to 1.2m
Describe the process of fluoroscopy
X-rays are directed into a cathode ray vacuum tube to produce an image
What is an advantage of using dynamic digital radiography over fluoroscopy?
DDR produces higher image quality
What is the main advantage of using computed or digital radiography over conventional radiography
Computed and digital radiography do not require film or development, and all images are viewable from computers
What does DICOM stand for?
Digital Imagine & Communication in Medicine
What does PACS stand for?
Picture Archiving & Communication System
Where are computed and digital radiographs sent after they are developed?
To PACS
List 3 things an x-ray can/will do when it interacts with matter
- Absorbed
- Scattered
- Transmitted
The photoelectric effect (for x-ray absorbtion/scatter) depends on __
Think principles of image formation
The atomic number of the tissue atoms
The compton effect (for x-ray absorption/scatter) depends on __
Think principles of image formation
The density of the tissue
Define radiolucent
Appears dark on radiographs
Define radiopaque
Appears light on radiographs
How can you visualize a 3D structure in 2D images like radiographs?
By taking at least 2 radiographic views of a given area
Define penumbra
The partially shaded outer region of the shadow cast by an opaque object
Define summation
The superimposition of structures in different planes
Remember: resulting image is the summation of opacities
What is a DMPLO radiographic view?
Dorsomedial-palmaro/plantarolateral oblique
Explain border effacement
When two structures of the same radiopacity are in contact with each other (their margins cannot be identified)
What is a DLPMO radiographic view?
Dorsolateral-palmaro/plantaromedial oblique
Which side of the patient does the marker annotate?
The anatomical side (right maker notes right side of patient)
Means the patient left will always be the image right
To which side do we always position the patients head?
To the left of the image
What do the markers annotate when the patient is in lateral recumbancy?
The side the patient is laying on (right marker means right lateral recumbency)
Increased motion means you need to __ exposure time
Decrease
What does kV represent
Penetrating power
Kilovoltage
What does mA represent
Hint: exposure, but not exposure
Number of x-ray photons
List 5 signs you are looking for to identify abnormalities on an x-ray
Bonus: what are the names of these signs
- Size
- Shape
- Opacity
- Location
- Number
Rontgen signs
List 2 methods for radiograph interpretation
- Systematic (logical approach)
- Pattern (intuitive approach)
What are Mach lines?
Thin light and dark grey lines at square borders on radiographs
These are visual inaccuracies
List the following order of increasing radiopacities:
Fat, mineral/bone, gas, metallic, soft tissue
Gas < fat < soft tissue < mineral/bone < metallic
Describe the fluorescent effect when using an intensifying screen
When using a screen, 95% of the film exposure is from the light given off by the screen
Define contrast
The degree of perceptible difference between two colour tones
Define object contrast
The difference in radiographic gray tones between two structures
Define film contrast
The ability of an x-ray film to produce a degree of image contrast
List 2 things that will decrease an image contrast
Think about settings on an x-ray
- Under/over exposure
- High kVp
What is kVp?
The potential difference applied to an x-ray tube (the penetrating power)
The kilovoltage peak or kilovoltage
How can fat increase and decrease contrast?
I.e., in which situations would it do one or the other
Normal fat provides contrast by prevent silhouetting
An excess amount of fat decreases contrast because you need a high kVp for penetration (high kVp decreases contrast)
Gas surrounding abdominal organs __ contrast
Increases
Define contrast medium
A substance applied to a patient to enhance the natural contrast of the organ of interest
What is a negative contrast medium?
Provide an example
A medium that does not absorb x-rays (is radiolucent)
Air, CO2
What is the purpose of using a negative contrast medium
To outline hollow organ walls
What is a positive contrast medium?
Provide an example
A medium that absorbs lots of x-rays (radiopaque)
Barium sulphate or iodinated compounds
What is the purpose of using a positive contrast medium
To outline the internal surface of hollow organs, vessels & ducts
List 2 ways barium sulfate can be used and why
- Orally (for an upper GI study)
- Rectally (for an enema study)
List 1 advantage and 1 disadvantage of barium sulfate
Advantage: provides a mucoprotective coating of the GI tract
Disadvantage: can be aspirated
What is the main difference between ionic and non-ionic contrast media?
Bonus: What is the difference in their osmolarities?
Ionic: dissociates into cations and anions
Non-ionic: do not dissociate
Ionic: hyperosmolar
Non-ionic: iso- or low osmolar
How is iodinated contrast media excreted?
Where is it excreted if this organ fails?
Mostly by the kidneys (glomerular filtration)
Via biliary or GI tract
What are 2 types of iodinated contrast media?
- Ionic
- Non-ionic
List 3 abdominal applications for iodinated contrast media
- Positive contrast cystography
- Angiography
- Portography
What is a double contrast study?
Where would it be used?
When positive and negative contrast media are used
Esophagus, stomach, colon, urinary bladder
What is the advantage of a double contrast study?
It highlights the mucosal detail with positive contrast while providing a dark background with negative contrast
What is myelography?
When contrast medium is injected into the subarachnoid space outlining the spinal cord
What are 3 advantages of myelography?
- Relatively inexpensive
- No special equipment
- Localizes spinal cord lesions
What are 3 disadvantages of myelography?
- Invasive
- Technically challenging
- May be non-diagnostic
How is contrast medium used in computed tomography?
IV iodinated contrast media is used, usually following a survery scan
How is contrast media in magnetic resonance tomography?
Gadolinium is used as a paramagnetic substance to enhance the magnetic properties of neighouring molecules and provide contrast
Iodine is not used
How is contrast media used in ultrasound?
IV injection of contrast media (ex. agitated saline) to enhance blood flow, and ultrasound is produced by the reflection of sound off gas bubbles produced by this enhanced blood flow
List 3 clinical applications of a contrast ultrasound
What are they good at looking for?
- Portosystemic shunt
- Perfusion imaging
- Echocardiography
List 3 clinical applications of contrast magnetic resonance tomography
What are they good at looking for?
- Increased vascularity
- Leaky vessels
- Selective distruption of BBB
List 3 applications of contrast computed tomography
What are they good at looking for?
- Neoplasia
- Inflammation
- Abscess & cyst
What is nuclear scintigraphy?
How are the images formed?
A branch of nuclear medicine that allows us to image the extent of a disease based on cellular function and physiology
Images formed by the detection of gamma radiation
List 5 uses of muscuoloskeletal imaging
What can it identify?
- Lameness
- Swelling
- Localised mass
- Known trauma
- Pain
List 3 soft tissue changes you can identify on an x-ray
- Generalized or localized swelling
- Soft tissue masses
- Calcification of soft tissues
List the 4 types of new bone formation
- Osteophytosis
- Enthesophytosis
- Periosteal reaction
- Hyperostosis
Define osteophytosis
New bone at joint surfaces
Define enthesophytosis
What can it indicate?
New bone formation related to ligament/tendon attachments
Indicates soft tissue disease
Define periosteal reaction
What can it indicate?
New bone formation resulting from stimulation of periosteum
Can indicate the aggression of the disease
Define hyperostosis
An excessive growth of bone
List 2 examples of hyperostosis
- DISH (Diffuse Idiopathic Skeletal Hyperostosis)
- Craniomandibular osteopathy
Define osteosclerosis
Increase in bone density without a change in shape
List 2 diseases where you will see osteosclerosis
- Osteopetrosis
- Canine panosteitis/equine enostosis
What is osteopetrosis?
Defective osteoclastic resportion with loss of medullary cavity
Define osteopenia
A reduction in bone mineral density
What are the 2 types of osteopenia?
- Metabolic
- Disuse
Describe the mechanism of metabolic osteopenia
In which condition can this occur?
Excessive Ca resorption from bone to maintain blood Ca levels results in a reduction in density
Hyperparathyroidism
What is Wolff’s law?
The bone of a healthy person or animal will adapt to the loads under which it is placed
List 3 types of fractures
- Traumatic
- Pathological
- Fatigue (stress)
How do you classify fractures?
List 6 ways
- Location
- Transverse, oblique or spiral
- Complete vs incomplete
- Simple, comminuted, segmental
- Open vs closed
- Displaced vs non-displaced
List the 5 steps of fracture healing
- Haematoma formation
- Woven bone + cartilage
- Ossification of cartilage
- Lamellar bone
- Recontoured lamellar bone
List 3 things you should look for to assess fracture healing
- Reduction
- Alignment
- Soft tissues
Define osteomyelitis
Inflammation of bone with medulla
Define osteitis
Inflammation of bone without medulla
Which pathologies are generally seen in infectious osteomyelitis
Periosteal reaction and osteolysis
List 5 things you can see on a radiograph to indicate joint disease
- Osteophytosis
- Alterations in the subchondral bone
- Altered joint space
- Subluxation/luxation
- Periarticular structures
How can you distinguish between an aggressive vs non-aggressive osteolytic lesion?
List 3 ways
- Look at the zone of transition
- Look at the rate of progression
- Look at the associated periosteal reaction
Describe how cysts/slow growing lesions can lead to bone atrophy
Cysts can exert chronic pressure on adjacent bone resulting in thinning and deviation of adjacent bone structures
Define sequestrum
A small avascular bone fragment from a fracture
What is the name for a new bone formed surrounding a fracture?
Involucrum
