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Radiography > Mid-Semester > Flashcards

Mid-Semester Flashcards

1
Q

What is the atomic number?

A

Number of protons

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2
Q

What is the mass number?

A

Protons + neutrons

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3
Q

What are isotopes?

A

Atoms of the same element with different numbers of neutrons

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4
Q

What are photons?

A

no mass or electrical charge - pure energy

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5
Q

What are 2 types of radiation?

A

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

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6
Q

What is radioactive decay?

A

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

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7
Q

What is electromagnetic radiation?

A

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

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8
Q

What are 2 types of radiation in electromagnetic spectrum?

A
  1. Non-ionising radiation - light, radio and microwave
  2. 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)
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9
Q

What are 5 types of ionising radiation?

A
  1. Alpha particles
  2. Beta particles

-> these particles are not part of electromagnetic spectrum but carry energy particles, they are not photons like as in electromagnetic radiation

  1. X and gamma rays
  2. Cosmic radiaiton
  3. Neutrons
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10
Q

What are sources of ionizing radiation in vet?

A

X rays -> radiography, fluoroscopy, radiotherapy, computed tomography (CT)

Gamma rays -> nuclear scintigraphy (bone scans)

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11
Q

When X rays pass through matter what can they do?

A
  1. Be absorbed by atoms in subject
  2. Pass straight through to x ray plate
  3. Change direction and scatter (30% do this in a normal x ray)
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12
Q

Efects of ionizing radiation on living cells

A

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

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13
Q

3 classifications of X ray damage to cells

A

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

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14
Q

What are deterministic or non-stoachastic affects?

A

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

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15
Q

What are probabilistic or stochastic effects?

A

Where effects have no threshold level and every exposure increases the risk that disease occurs

“no safe dose” effects - eg sun

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16
Q

What are the most sensitive tissues to ionising radiation?

A

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

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17
Q

What is the purpose of radiation protection standards?

A

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

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18
Q

What are 3 dose quantities to measure radiation exposure?

A

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

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19
Q

How do we measure radiation exposure?

A

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

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20
Q

What is the dose limit for a member of the public and occupationally exposed persons?

A

Public -1mSv

Us - less than 100mSv over 5 years (20mSv per year) effective dose

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21
Q

Who is responsible for looking after dose exposure?

A

Practice owner or principal vet

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22
Q

What are 3 questions to ask before taking a radiograph

A

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

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23
Q

What are tthe 3 tenets of radiation safety?

A

Radiation dose determined by amount of:

  1. Time person is exposed to ionizing radiation
  2. Distance between person and radioactive substance
  3. Shielding used to protect person
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24
Q

What are factors involved in radiation protection - time?

A

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

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25
Q

What are factors for radiation protection - distance?

A

More distance = less exposure
Inverse square law -> double distance reduce exposure by 4x
General rule -> 3-4m from source then dose insignificant

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26
Q

Describe shielding from radiation

A

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

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27
Q

Animal restraint for radiation protection

A

No exposure made until animal restrained

Not held unless for clinical reasons immobilisation is not practical other ways

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28
Q

Where can the primary beam penetrate?

A

0.5mm lead gowns and gloves - never be exposed to primary beams

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29
Q

Who should never go into a x ray room

A

Anyone <16 years

Potentially pregnant women

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30
Q

3 types of x ray machine

A

Portable, mobile or fixed

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31
Q

Explain the x ray table

A

Can move or float to position patient
On or under table top image plate
Inbuilt bucky system
Lead lined base

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32
Q

Describe the x ray tube

A

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

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33
Q

What is the purpose of oil in the x ray tube?

A

To minimise temperature rising

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34
Q

How can we increase speed of electron movement?

A

Increase KPB difference between anode and cathode to increase speed of electron movement

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35
Q

How are x rays produced?

A

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

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36
Q

Describe the anode

A

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

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37
Q

What is a focal spot? what is the heel effect?

A

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

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38
Q

When would we use larger and smaller focal spots?

A

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

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39
Q

Describe the X ray tube housing

A

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

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40
Q

How do we care for the x-ray tube?

A

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

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41
Q

What is kVp?

A

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

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42
Q

What is mAs?

A

Miliamperes
Controls quantity of x-rays

Higher mAs -> Greater the current is through filament, more x-rays are produced at greater beam intensity

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43
Q

What is SID?

A

Source-image plate distance - should always be 70-100cm

Measured from origin centre of tube

Affects intensity of beam (no. x-rays reaching plate)

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44
Q

How is SID related to the penumbra effect?

A

Shorten SID -> cause image magnification and blurring of the edges (penumbra effect)

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45
Q

What is the rule about changing SID?

A

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

46
Q

What is OID?

A

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

47
Q

What 3 things does X-ray penetration vary with?

A

Atomic weight -> hydrogen vs lead
Tissue density -> gas vs liquid
Tissue thickness

Attenuation = absorption + scatter

48
Q

Describe the difference between radio opaque and radiolucent

A

Radiolucent -> black (air) allows x ray through

Radio-opaque -> white (bone) absorbs x-rays

49
Q

What is radiographic density influenced by?

A

= degree of blackness

Quantity (mAs) and quality (kVp) of x-ray
SID
Thickness and type of tissue

50
Q

What is radiographic contrast?

A

Contrast = difference in blackening between adjacent structures on an image
-> different shades of grey allows differentiation of different structures on radiograph

51
Q

What scale of contrast will low kVp produce?

A

Shorter scale of contrast (high contrast) -> more black and white and less grey
Density difference is greatest

52
Q

What scale of contrast does high kVp produce?

A

Longer scale of contrast (low contrast)-> more shades of grey and density difference is small

53
Q

What is the kVp 15% rule with mAs compensation?

A

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

54
Q

Santes Rule

A

kVp = (2 x tissue thickness in cm) + SID inches + grid factor

55
Q

What does scatter cause and what is it increased by?

A

Causes reduced contrast -> more shades of grey (happens with high kVp also)

Caused by high kVp, long exposure times, x-ray larger areas

56
Q

How do we reduce scatter?

A

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

57
Q

What is extrafocal radiation?

A

When the x rays originate from outside the focal spot (when they dont hit the target)

58
Q

What are 2 causes of a shadow outside the patient?

A

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

59
Q

What is the purpose of a grid?

A

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

60
Q

Define grid frequency, grid ratio and grid factor

A

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

61
Q

Name 4 grid types

A
  1. Parallel - used with small field or long SID - can get grid cutoff
  2. Focused - allows diverging peripheral rays to pass through grid to film
  3. Cross hatched - 2 parallel grids perpendicular (high grid cutoff if its off centre)
  4. Pseudo-focused - combo of parallel and focused
62
Q

How to achieve grid focus

A

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

63
Q

What is a Bucky grid?

A

Cross hatched pattern and removes lines by shaking back and forth to blur them

64
Q

4 things to care for a grid

A
  1. Wipe down regularly
  2. Store in box
  3. Handle by edges and corners
  4. Protect from soiling in plastic bag
65
Q

What is the air gap technique?

A

Imaging thick tissues, increase imaging plate distance so scatter doesn’t reach the film and form an image

66
Q

What affects the image quality?

A

Imaging method and variables (mAs, kVp)

radiographic quality dependent on image contrast and definition

67
Q

What affects contrast?

A

Absorption differences, exposure factors and scatter radiation

68
Q

What affects image detail?

A

Motion of patient, table or x ray unit
Patient positioning and makeup
Focal spot size
Scatter

69
Q

What does computed radiography use?

A

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

70
Q

5 ways to care for a cassette

A

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

71
Q

What is the imaging plate?

A

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

72
Q

How are CR images read?

A

Placed in CR reader and stored energy released as visible light due to stimulation of atoms on phosphor plates with infrared beam

73
Q

How does direct and indirect digital imaging work?

A

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

74
Q

What is a pixel?

A

Contained in a matrix within a digital image
Each pixel has a grey value
smaller pixel - higher resolution
typically 5-10pixels/mm

75
Q

What is a matrix?

A

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

76
Q

What is bit depth?

A

Number of bits used to store info on each pixel - determines levels of grey

DR -> 14 bit depth

77
Q

How are digital images processed?

A

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

78
Q

What is spatial resolution?

A

Detail
Smaller pixel = better resolution

Expressed in line pairs per mm

79
Q

3 sources of blurring

A

Motion
Pixel size
Digital image processing

80
Q

What is contrast resolution?

A

The dynamic range -> highest contrast is purely black and white

81
Q

Why are digital radiographs better?

A

Contrast optimisation - wide dynamic range

Independence of image quality on exposure factors and user technique -> reduces retakes

82
Q

What do kVp and mAs do?

A

Optimal kVp only controls contrast

Adjust mAs to avoid pixel starvation or quantum mottle - ideally as low as possible whilst avoiding this

83
Q

What is the exposure index?

A

Amount of exposure recieved by image receptor

84
Q

what is noise?

A

Anything interfering with formation of the image - anatomy and equipment cause it

Cant control equipment noise

85
Q

What is moire effect?

A

Grid lines with similar frequency (lines/cm) as the laser cause wavy moire pattern on image

86
Q

What is windowing?

A

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

87
Q

What is DICOM?

A

Digital imaging communication in media

Image file format

88
Q

What is PACS?

A

Picture archiving and communication system

Allows images to be viewed on multiple computers

89
Q

What are the 3 principles of ALARA?

A

Time - minimise exposure
Distance - inverse square law
Shielding (lead)

90
Q

What are some things we can do to prepare equipment prior to taking radiograph?

A 
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
91
Q

How is the machine warmed?

A

60kVp
100mAs
1/10th second

Close collimater, make exposure, wait 30 seconds and repeat

92
Q

How do we prepare animals?

A 
Clean dry coat
Premedication 
fasting, enemas
remove collars
measure thickness
Restraint -> dont leave sedated animal unattended
93
Q

List some restraining devices

A

troughs
rolled towels
foam wedges
ropes to stretch limbs

94
Q

What is a cassette holder?

A

Holds the x-ray film when working with horses

95
Q

Equine foot preparation

A

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

96
Q

How can we use magnification to determine what side a dog is laying on?

A

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

97
Q

What part of the animal should be placed closest to the cathode?

A

Thickest part

98
Q

What should be included information on a radiograph?

A

Name of vet or vet hospital
Name of animal + owner
Date
Body markers

99
Q

How do we place L and R markers?

Thorax + abdomen
Spine/pelvis
Extremities

A

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

100
Q

When are horizontal beam views used?

A

Normally in horses

To see free air in abdomen, mediastinal masses, spinal fractures

101
Q

What is the difference in views between a horse and small animal extremity image?

A

Horse -> Lateral-medial

Small animal -> medial-lateral

102
Q

What is an orthogonal view?

A

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

103
Q

How do we display or hang radiographs?

A

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

104
Q

What are the 5 basic opacities?

A
  1. Air (most radiolucent)
  2. Fat
  3. Soft tissue/fluid
  4. Bone
  5. Metal (most radio opaque)

Radio-opacity is related to thickness as well as density (finger bone less white than vertebrae)

105
Q

What is superimposition negative and positive summation effect?

A

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)

106
Q

What is border effacement/silhouette sign?

A

2 objects of same opacity touch each other and lose their margins

107
Q

What are 3 things we can do to manipulate an image?

A

Shuttering - remove white borders
Windowing- optimise contrast + blackness
Magnification

108
Q

3 steps to assess radiographic quality

A
  1. Identify subject - species, age, gender, breed, clinical history
  2. Radiographic exam technique - date and time, anatomic part, which projection, nature and type of drugs or contrast
  3. PLACE (positioning, labelling, artifacts, collimated and centered, exposure and detail adequate)
109
Q

What is considered when talking about exposure factors?

A

Good subject contrast for body part - adequate bone and soft tissue visualisation

Good detail and sharp edges

110
Q

What can cause grains on an image?

A

Low mAs and quantum mottle

Quantum mottle increases when number of x-rays reaching screen are decreased

Radiography (1 decks)

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