Mid-Semester Flashcards
What is the atomic number?
Number of protons
What is the mass number?
Protons + neutrons
What are isotopes?
Atoms of the same element with different numbers of neutrons
What are photons?
no mass or electrical charge - pure energy
What are 2 types of radiation?
Waves -> light, x rays or gamma rays represented by photons or quanta
Particles -> alpha or beta particles - travel slower than waves
Alpha particles like helium nuclei
Beta particles like electrons/positrons
What is radioactive decay?
spontaneous radioactive disintegration of an atomic nucleus resulting in the release of energy -> radiation
Emissions from the unstable nucleus can be in the form of particle (alpha/beta) or electromagnetic (wave) radiation
What is electromagnetic radiation?
Visible light, radio, gamma and x rays
Move at speed of light in straight line
Different forms distinguished by wavelength and frequency - smaller the wavelength the higher the frequency (hz) and by amount of energy they transfer
What are 2 types of radiation in electromagnetic spectrum?
- Non-ionising radiation - light, radio and microwave
- Ionizing radiation - high energy + frequency -> can remove an electron from an atom (x rays and gamma rays) -> ionization is process where atom can gain pos or neg charge by losing electrons (causes DNA damage)
What are 5 types of ionising radiation?
- Alpha particles
- Beta particles
-> these particles are not part of electromagnetic spectrum but carry energy particles, they are not photons like as in electromagnetic radiation
- X and gamma rays
- Cosmic radiaiton
- Neutrons
What are sources of ionizing radiation in vet?
X rays -> radiography, fluoroscopy, radiotherapy, computed tomography (CT)
Gamma rays -> nuclear scintigraphy (bone scans)
When X rays pass through matter what can they do?
- Be absorbed by atoms in subject
- Pass straight through to x ray plate
- Change direction and scatter (30% do this in a normal x ray)
Efects of ionizing radiation on living cells
Creates free radicals in water reacting with DNA to cause damage
Proteins can repair DNA sometimes but if not cell death or permanent mutation occurs
3 classifications of X ray damage to cells
Somatic -> affects physical structure of body and cells change quickly
Genetic -> mutation of genes and inherited abnormalities, some lethal some recessive
Carcinogenic -> affects cell so cancer forms often decades later
What are deterministic or non-stoachastic affects?
Occur when radiation dose is large enough to cause extensive cell death
Severity is proportional to the dose
There is a threshold level of exposure, above which certain affects like radiation burns occur
What are probabilistic or stochastic effects?
Where effects have no threshold level and every exposure increases the risk that disease occurs
“no safe dose” effects - eg sun
What are the most sensitive tissues to ionising radiation?
young animals and feotus -> Organogenesis and rapid growth
Thyroid gland - high metabolic activity
Gut -> rapid proliferation
Skin - squamous or basal cell carcinoma, red dry scaly skin
Bone marrow -> Decrease rbc, platelet and lymphocyte production
gonads -> decrease sex hormones and increase genetic mutations
Eye -> cataracts in the lens
What is the purpose of radiation protection standards?
Understand that it is not possibke to eliminate all radiation exposure but provide system of control to avoid unnecessary exposure and keep doses in low range
What are 3 dose quantities to measure radiation exposure?
Absorbed dose - energy deposited in a kilogram of substance by radiation
Equivalent dose - absorbed dose weighted for harmful effects of different radiation
Effective dose - equivalent dose weighted for susceptibility to harm of different tissues
How do we measure radiation exposure?
Landauer OSL dose badges
Optically stimulated luminescence
Detector is aluminium when stimulated by laser becomes luminescent in proportion to amount of radiation exposure
Wear in centre of chest under lead gown
What is the dose limit for a member of the public and occupationally exposed persons?
Public -1mSv
Us - less than 100mSv over 5 years (20mSv per year) effective dose
Who is responsible for looking after dose exposure?
Practice owner or principal vet
What are 3 questions to ask before taking a radiograph
Justification - benefit the animal and outweight risk + cost of irradiation
Optimisation - use lowest possible exposure to obtain radiograph
Compliance in limits - operators must not exceed max allowed exposure for the year
What are tthe 3 tenets of radiation safety?
Radiation dose determined by amount of:
- Time person is exposed to ionizing radiation
- Distance between person and radioactive substance
- Shielding used to protect person
What are factors involved in radiation protection - time?
Less time in radiography or fluoroscopy rooms
GA animals so no one holds them
No one in room when radiograph taken
Minimise time with patients undergoing nuclear medicine procedures
What are factors for radiation protection - distance?
More distance = less exposure
Inverse square law -> double distance reduce exposure by 4x
General rule -> 3-4m from source then dose insignificant
Describe shielding from radiation
Lead aprons 0.3-0.5mm
Thyroid/eye shielding during high risk procedures or fluoroscopy
Lead glove 0.5mm if hands near beam
Lead glass for windows, lead sheets in doors or plaster board, brick or concrete walls
Animal restraint for radiation protection
No exposure made until animal restrained
Not held unless for clinical reasons immobilisation is not practical other ways
Where can the primary beam penetrate?
0.5mm lead gowns and gloves - never be exposed to primary beams
Who should never go into a x ray room
Anyone <16 years
Potentially pregnant women
3 types of x ray machine
Portable, mobile or fixed
Explain the x ray table
Can move or float to position patient
On or under table top image plate
Inbuilt bucky system
Lead lined base
Describe the x ray tube
Produces and uses electrons
Source -> tungsten filament at front of cathode
Free electron cloud -> head filament with mA current
Focused electron beam -> shaped nickel focusing cup around filament
Way to accelerate electrons without obstacles -> kilovoltage potential between -ve cathode and +ve anode in a vacuum
Place to crash electrons - tungesten alloy target on anode
What is the purpose of oil in the x ray tube?
To minimise temperature rising
How can we increase speed of electron movement?
Increase KPB difference between anode and cathode to increase speed of electron movement
How are x rays produced?
When free electrons crash into target at the anode some hit or deflect electrons around the target nuclei and their energy is released as x rays (1%)
99% miss and dissipate their movement energy released as heat - dispersed into glass envelope and insulating oil
Describe the anode
Positively charged
2 types - stationary and rotating
stationary - single exposure can heat metal target to over 1000 degrees C
Rotating - spread heat over larger area allowing for higher current and higher x ray output 10-15x that of stationary - used for thicker objects
What is a focal spot? what is the heel effect?
On the anode - AKA the target angled at 5-15 degrees
Heel effect - due to angle useful when radiographing thick + thin areas together - put thicker part towards cathode to even out x rays
When would we use larger and smaller focal spots?
Small - better detail, bigger heel effect, overheats easily - used on head and extremities <10cm to increase detail
Large -> poorer more blurry edge image, disperses heat over larger area so can use high exposure factors - used on thorax, abdomen, spine, pelvis to reduce exposure time, reduce overheating
Describe the X ray tube housing
Lead lined with:
A window - allow x rays to exit tube head
A collimator - controls spread of primary x ray beam as it exits tube head
Illuminator light - show the spread of x rays as they exit
Filtration -> filters produce cleaner image by absorbing lower energy x ray photons more prone to scatter
How do we care for the x-ray tube?
Avoid sudden heat increases in cold tube = >6h warm up
Don’t exceed 80% max number of heat units the x-ray tube can handle
Rotor bearings can wear out - wait 30sec between starts of the rotor
What is kVp?
Controls quality of x rays
Higher -> produces higher energy x rays with more tissue penetration. Greater voltage difference between anode and cathode = faster electrons move + more energy when they crash
What is mAs?
Miliamperes
Controls quantity of x-rays
Higher mAs -> Greater the current is through filament, more x-rays are produced at greater beam intensity
What is SID?
Source-image plate distance - should always be 70-100cm
Measured from origin centre of tube
Affects intensity of beam (no. x-rays reaching plate)
How is SID related to the penumbra effect?
Shorten SID -> cause image magnification and blurring of the edges (penumbra effect)
What is the rule about changing SID?
To maintain radiographic density (blackness) we apply the inverse square law
If SID is x2 then mAs is x4
If SID is x4 then mAs is x16
kVp stays the same as SID changes as it does not effect the penetrating power of the x-ray beam
What is OID?
Object to image plate distance
Distance from subject to the image plate
Should be as short as possible to minimise penumbra effect and magnification
Object needs to be parallel to the plate to avoid shape distortion
What 3 things does X-ray penetration vary with?
Atomic weight -> hydrogen vs lead
Tissue density -> gas vs liquid
Tissue thickness
Attenuation = absorption + scatter
Describe the difference between radio opaque and radiolucent
Radiolucent -> black (air) allows x ray through
Radio-opaque -> white (bone) absorbs x-rays
What is radiographic density influenced by?
= degree of blackness
Quantity (mAs) and quality (kVp) of x-ray
SID
Thickness and type of tissue
What is radiographic contrast?
Contrast = difference in blackening between adjacent structures on an image
-> different shades of grey allows differentiation of different structures on radiograph
What scale of contrast will low kVp produce?
Shorter scale of contrast (high contrast) -> more black and white and less grey
Density difference is greatest
What scale of contrast does high kVp produce?
Longer scale of contrast (low contrast)-> more shades of grey and density difference is small
What is the kVp 15% rule with mAs compensation?
Increase the kVp by 15% and cut mAs in half to get the same exposure
Decrease the kVp by 15% and double the mAs to get same exposure
Do this to reduce patient dose and reduce exposure time and movement blur
Santes Rule
kVp = (2 x tissue thickness in cm) + SID inches + grid factor
What does scatter cause and what is it increased by?
Causes reduced contrast -> more shades of grey (happens with high kVp also)
Caused by high kVp, long exposure times, x-ray larger areas
How do we reduce scatter?
Use correct kVp - if we need to use high then use a grid
Collimate primary beam -> reduce field size and increase collimation
Reduce backscatter with tabletop lead
What is extrafocal radiation?
When the x rays originate from outside the focal spot (when they dont hit the target)
What are 2 causes of a shadow outside the patient?
Scatter from the patient (if the splash is larger when patient is large and not there when patient is small)
Or extrafocal radiation -> created by x rays outside the focal spot caused by collimator defects or too high Kvp or mAs
What is the purpose of a grid?
Allows most of primary beam to pass through but 85-95% scatter absorbed
Between the patient and plate
Used for abdomen and thorax - thick tissue >10cm
Define grid frequency, grid ratio and grid factor
Frequency -> no. strips per cm
Ratio -> height of strip/thickness of interspace material
Higher ratio + frequency = more x-ray absorbed
Factor -> amount mAs increased to compensate for effects of grid
New mAs with grid = old mAs x grid factor
Name 4 grid types
- Parallel - used with small field or long SID - can get grid cutoff
- Focused - allows diverging peripheral rays to pass through grid to film
- Cross hatched - 2 parallel grids perpendicular (high grid cutoff if its off centre)
- Pseudo-focused - combo of parallel and focused
How to achieve grid focus
X ray must be centered to focal point of grid
Grid focal distance -> get with angulation of lead strips and distance from x ray source (manufacturer recommends)
Use within this distance to avoid grid cut off
What is a Bucky grid?
Cross hatched pattern and removes lines by shaking back and forth to blur them
4 things to care for a grid
- Wipe down regularly
- Store in box
- Handle by edges and corners
- Protect from soiling in plastic bag
What is the air gap technique?
Imaging thick tissues, increase imaging plate distance so scatter doesn’t reach the film and form an image
What affects the image quality?
Imaging method and variables (mAs, kVp)
radiographic quality dependent on image contrast and definition
What affects contrast?
Absorption differences, exposure factors and scatter radiation
What affects image detail?
Motion of patient, table or x ray unit
Patient positioning and makeup
Focal spot size
Scatter
What does computed radiography use?
A cassette processed on a separate unit
Cassette contains:
Lead/aluminium backing
Antistatic felt protecting for dust
The imaging plate
Cassettes are scanned to form a digital image
5 ways to care for a cassette
Dont drop or stack
Store upright
Wipe outside clean with damp cloth or mild soap and dry
Put them in plastic bags when doing animals that might leak fluids
What is the imaging plate?
Thin sheet of plastic with photostimulable phosphors (PSP) - trap excited electrons during x-ray exposure, stored as latent energy
Size of phosphor grain affects resolution on the screen
How are CR images read?
Placed in CR reader and stored energy released as visible light due to stimulation of atoms on phosphor plates with infrared beam
How does direct and indirect digital imaging work?
Uses a detector plate connected to processing computer - captures image by electronic array with x-ray absorption material (photoconductors) and transmits directly to computer to generate image
Direct -> uses photoconductors to convert x ray to electronic signal
Indirect -> x-ray converted to light then electric signal
What is a pixel?
Contained in a matrix within a digital image
Each pixel has a grey value
smaller pixel - higher resolution
typically 5-10pixels/mm
What is a matrix?
Rectangle or square table of numbers representing the pixel intensity on screen
Size of matrix determines size of pixel
Increase matrix size with same image area = smaller pixels
What is bit depth?
Number of bits used to store info on each pixel - determines levels of grey
DR -> 14 bit depth
How are digital images processed?
Electronic signal to processor that is manipulated by software to make a histogram
Histogram evaluates contrast and brightness for a specific anatomical region to maximise image for each area
What is spatial resolution?
Detail
Smaller pixel = better resolution
Expressed in line pairs per mm
3 sources of blurring
Motion
Pixel size
Digital image processing
What is contrast resolution?
The dynamic range -> highest contrast is purely black and white
Why are digital radiographs better?
Contrast optimisation - wide dynamic range
Independence of image quality on exposure factors and user technique -> reduces retakes
What do kVp and mAs do?
Optimal kVp only controls contrast
Adjust mAs to avoid pixel starvation or quantum mottle - ideally as low as possible whilst avoiding this
What is the exposure index?
Amount of exposure recieved by image receptor
what is noise?
Anything interfering with formation of the image - anatomy and equipment cause it
Cant control equipment noise
What is moire effect?
Grid lines with similar frequency (lines/cm) as the laser cause wavy moire pattern on image
What is windowing?
WIndow width -> narrow window = higher contrast, wider window = lower contrast (more shades of grey)
Window level -> density/brightness enhancing. Level increased = overall blackness increases whilst subject tissue contrast remains the same
What is DICOM?
Digital imaging communication in media
Image file format
What is PACS?
Picture archiving and communication system
Allows images to be viewed on multiple computers
What are the 3 principles of ALARA?
Time - minimise exposure
Distance - inverse square law
Shielding (lead)
What are some things we can do to prepare equipment prior to taking radiograph?
Switch on and position machine Get technique chart and callipers ready to measure animal depth Get imaging plate, grid and labels ready Positioning aids and PPE Check SID Enter patient details
How is the machine warmed?
60kVp
100mAs
1/10th second
Close collimater, make exposure, wait 30 seconds and repeat
How do we prepare animals?
Clean dry coat Premedication fasting, enemas remove collars measure thickness Restraint -> dont leave sedated animal unattended
List some restraining devices
troughs
rolled towels
foam wedges
ropes to stretch limbs
What is a cassette holder?
Holds the x-ray film when working with horses
Equine foot preparation
Shoe left on for LM view of foot, removed for most other views
Trim and clean hoof and sole
Upright views - pack sulci with plasticine
How can we use magnification to determine what side a dog is laying on?
Further the cassette is from the object -> more magnified and less crisp the image is
So two humerus bones on top of each other -> blurry one is closest to x ray machine and crisp sharp one is closest to table
What part of the animal should be placed closest to the cathode?
Thickest part
What should be included information on a radiograph?
Name of vet or vet hospital
Name of animal + owner
Date
Body markers
How do we place L and R markers?
Thorax + abdomen
Spine/pelvis
Extremities
If animal laying on its left, we put L onto cassette (made of lead)
For the thorax and abdomen - marker placed ventrally
For spine/pelvis - marker placed dorsally
Extremities -> for lateral projections marker placed on cranial or dorsal aspect of limb
All others -> marker on lateral aspect of limb
When are horizontal beam views used?
Normally in horses
To see free air in abdomen, mediastinal masses, spinal fractures
What is the difference in views between a horse and small animal extremity image?
Horse -> Lateral-medial
Small animal -> medial-lateral
What is an orthogonal view?
3 dimensional object displayed as 2 dimensional image
An image taken at 90 degrees to the original
Causes problems - magnification, distortion, summation of shadows, silhouetting, loss of depth perception
How do we display or hang radiographs?
Cranial portion of image at top of screen
patients left on viewer’s right
For lateral views -> dorsal portion at top of screen and cranial portion to viewer’s left
For lateromedial extremities -> proximal portion at top of screen, cranial part to viewer’s left
What are the 5 basic opacities?
- Air (most radiolucent)
- Fat
- Soft tissue/fluid
- Bone
- Metal (most radio opaque)
Radio-opacity is related to thickness as well as density (finger bone less white than vertebrae)
What is superimposition negative and positive summation effect?
Negative summation -> Means that areas of radioluscency overlap and cause increased black (radioluscent) appearance
Positive summation -> Areas of opacity overlap causing increased radioopacity (superimposition of regions of opacity)
What is border effacement/silhouette sign?
2 objects of same opacity touch each other and lose their margins
What are 3 things we can do to manipulate an image?
Shuttering - remove white borders
Windowing- optimise contrast + blackness
Magnification
3 steps to assess radiographic quality
- Identify subject - species, age, gender, breed, clinical history
- Radiographic exam technique - date and time, anatomic part, which projection, nature and type of drugs or contrast
- PLACE (positioning, labelling, artifacts, collimated and centered, exposure and detail adequate)
What is considered when talking about exposure factors?
Good subject contrast for body part - adequate bone and soft tissue visualisation
Good detail and sharp edges
What can cause grains on an image?
Low mAs and quantum mottle
Quantum mottle increases when number of x-rays reaching screen are decreased
