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CVNT > imaging > Flashcards

imaging Flashcards

1
Q

properties of X-rays

A

high energy:
- short wavelength
- high frequency

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2
Q

how are x-rays produced?

A

the interaction of fast moving electrons with a metal target

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3
Q

production of x-rays

A
  1. contains anode and cathode (tungsten)
  2. cathode heats up, cloud of e- forms
    • thermionic emission
  3. p.d is applied sending the e- to a target/focal spot on the anode producing x-rays
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4
Q

general x-ray emission

A
  • e- interact with tungsten atoms e-
  • energy lost through x-radiation
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5
Q

characteristic/minor emission

A
  • one of incoming e- knocks an e- from tungston atom
  • an e- from outer shell drops to inner shell to fill gap
  • energy is released as x-ray
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6
Q

x-ray tube

A
  • anode and cathode are in pyrex tube
  • tube is immersed in oil to aid conduction of heat
  • tube surrounded by lead except small window
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7
Q

exposure factors of x-ray

A
  • kV control (voltage)
    • higher energy x-ray for thicker parts of body
  • mA control (current)
    • heats the cathode, higher frequency of x-rays
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8
Q

setting up an exposure chart

A

when you get a good x-ray, record exposure factors used and measure thickness of the anatomy x-rayed

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9
Q

control panel of x-ray machine

A
  • kV control
  • mA control
  • timer
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10
Q

collimation definition and prupose

A

reducing the size of the x-ray beam using diaphragm
- reduces unnecessary radiation of the patient
- reduces production of scattered radiation
- improved image quality
- less exposure to staff

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11
Q

effect of distance on x-ray intensity

A

intensity is inversely proportional to the square of distance from the x-ray tube
- important to keep distance the same to get same result with the same exposure factors

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12
Q

3 possibilities of interaction of x-rays with matter

A
  1. photons pass through unchanged (black/darker on image)
  2. photons are absorbed (white on image)
  3. photons are scattered (degrades image quality)
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13
Q

purpose of a grid

A
  • useful when x-raying thick areas
  • reduces scattered radiation reaching the film
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14
Q

grid structure

A
  • thin strips of lead
  • allows primary beam travelling in straight line pass through
  • needs high exposure factors
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15
Q

grid ratio

A
  • height of the lead strips divided by the width of the spacing material
  • higher ratio removes more scatter but also removes some of primary beam
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16
Q

grid factor

A

number by which the mAs must be multiplied if a grid is used

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17
Q

types of grid

A
  1. parallel
  2. focused
    - must be used right way up, strips slope more towards edge
  3. pseudo-focused
    - compensates for grid cut-off which occurs in parallel grid
  4. cross hatched
    - require very high exposures
  5. moving/potter-bucky
    - parallel grid mounted beneath table top
    - removes fine lines that appear when using stationary grid
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18
Q

effects of ionising radiation

A

carcinogenic- tumor development of cells
somatic- direct changes in body tissues that occur not long after exposure has occured
genetic/mutation- chromosomal mutation

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19
Q

sources of radiation hazard

A
  • tube head
  • primary beam
  • scatter radiation
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20
Q

safety measures to protect staff from exposure

A
  • lead apron, gloves and thyroid shield
  • tight collimation
  • chemical restraint so no need for staff to be present
  • dosimeters to measure exposure
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21
Q

how should dosimeters be worn?

A
  • on neck or chest area
  • area that faces radiation source
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22
Q

digital radiography

A

direct capture of x-ray image displayed on computer

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23
Q

digital radiography advantages

A
  • decreased running costs
  • reduced repeat rate
    • time saving
    • decreased radiation dose
  • improved images due to manipulation
  • portable (field x-rays)
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24
Q

digital radiography disadvantages

A
  • set up costs
  • limited by availability of computers
  • ensuring adequate back-up of files
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25
Q

radiographic opacity definition

A

how black or white overall?

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26
Q

radiographic contrast definition

A

differences in black/white/grey

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27
Q

radiographic sharpness definition

A

clarity of image

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28
Q

what are contrast media?

A

agents that are more or less opaque than surrounding tissue

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29
Q

what do contrast media do?

A

delineate organs/cavities within body to see structures that are usually poorly visable

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30
Q

types of contrast media

A
  • positive contrast
    • barium, white on radiograph
  • negative contrast
    • gases, black on radiograph
31
Q

barium as contrast agent

A
  • used in GI tract
  • reasonably palatable
  • cheap
  • non toxic
32
Q

ionic iodinated contrast

A
  • irritant extra-vascularly
  • toxic in large doses
  • viscous
33
Q

non-ionic iodinated contrast

A
  • more expensive
  • viscous
  • side effects can still occur (anaphylaxis, nephrotoxicity)
34
Q

negative contrast media advantages

A

air/CO2
- free
- simple, relatively safe
- can combine with positive contrast agents
(double contrast)

35
Q

negative contrast media disadvantages

A
  • risk of air embolism
  • poor mucosal detail
  • less contrast than positive contrast agents
36
Q

barium swallow technique

A

indications= dysphagia, suspected rupture
- shows pharynx and oesophagus
- care if cant swallow (aspiration risk)

37
Q

barium ‘follow-through’ technique

A
  • shows stomach and small intestine
  • liquid barium (stomach tube or mouth)
  • take x-ray immediately then at intervals
38
Q

barium enema technique

A
  • evaluates large intestine
  • liquid barium infused into rectum post-enema
  • messy/difficult to interpret
  • superseded by endoscopy
39
Q

contrast in urinary tract

A
  • never barium (bladder irritant)
  • use water-solule iodinated contrast
40
Q

cystography techniques

A
  • pneumocystogram
  • positive contrast cystogram
  • double contrast cystogram
41
Q

myelography

A
  • delineates subarachnoid space
  • localised lesions of spinal cord
  • non-ionic water-soluble contrast
42
Q

production of ultrasound

A
  • high frequency sound wave
    piezoelectric effect
    1. voltage applied to disc within transducer
    2. disc expands or contracts
    3. sound wave produced
43
Q

recieving the ultrasound signal

A
  • sound returns from tissues to transducer
  • pressure of sound wave distorts disc which creates voltage
  • voltage processed by machine and displayed
44
Q

acoustic impedance

A

density of tissue x speed of sound in tissue

45
Q

ultrasound specular reflection

A
  • soundwaves hit large smooth surface giving a bright/mirror reflection line
46
Q

ultrasound non-specular reflection

A
  • beam hits small structures with re-radiates in all directions giving texture to organs
47
Q

ultrasound B-mode

A
  • images a slice through the patient
48
Q

ultrasound M-mode

A
  • used in cardiac work
  • movement of points along line followed
49
Q

ultransound abdomen clipping site

A

xiphisternum to pubis
- follow costal arch up to lumbar muscles

50
Q

ultrasound heart clipping site

A
  • right side
  • 4th-6th intercostal space
  • costochondral junction to sternum
51
Q

ultrasound left kidney clipping site

A
  • behind last rib below lumbar muscles
52
Q

ultrasound right kidney clipping site

A
  • last 2-3 intercostal spaces below lumbar muscles
53
Q

advantages of ultrasound

A
  • good soft tissue detail
    • internal structure of organs
  • functional information (movement)
54
Q

disadvantages of ultrasound

A
  • expensive equipment
  • need to clip hair
  • difficult to interpret
  • gas/fat/bone hinders examination
55
Q

types of ultrasound transducer

A
  • phased array
  • convex
  • linear
56
Q

advantages of phased array transducer

A
  • easy to manipulate
  • small contact area
  • wide field at depth
57
Q

advantages of linear transducer

A
  • large contact area
  • large field of view near skin
  • good for superficial structures
58
Q

positioning aids

A
  • radiolucent wedges and plastic troughs
  • sandbags (will be seen on radiograph)
  • tape
59
Q

naming of projections

A

describe the path of the x-ray beam from the tube to the image receptor
- ventrodorsal
- plantarodorsal
lateral projections named after side animal is lying on

60
Q

CT/MRI

A
  • slices through the animal
61
Q

scintigraphy

A

functional remodelling activity of bone

62
Q

principles of CT

A
  • ionising radiation
  • similar to radiography
  • rotating x-ray machine to take 360 degree view
63
Q

uses of CT

A
  • gives multiple detailed reconstructions from one scan
  • used to make custom made surgial implants
  • 3D models for surgical planning
64
Q

disadvantages of CT

A
  • limited availability/expensive
  • uses higher doses of ionising radiation than x-ray
65
Q

scintigraphy principles

A
  • uses radioisotope
  • bound to another substance which determines where in the body it will localise
    e.g. HDP binds to bone
  • bound isotope is injected into patient
66
Q

uses of scintigraphy

A
  • dectection of skeletal injury in horses in areas difficult to radiograph
  • cases where its difficult to localise source of lameness
  • detection of thyroid nodules in hyperthyroid cats
67
Q

disadvantages of scinitgraphy

A
  • uses ionising radiation
  • patient remains radioactive after scan
  • poor anatomical detail (difficult interpretation)
68
Q

how does MRI work?

A
  • nuclei with odd no. of protons and/or odd no. neutrons it will spin creating its own magnetic field
  • when the patient enters the feld, the neutrons line up
  • patient bombarded with radiowaves and nuclei become disorientated
  • this emits a radiosignal
69
Q

advantages of MRI

A
  • good contrast resolution
  • excellent anatomical detail of soft tissues
  • doesn’t use ionising radiation
70
Q

MRI uses

A
  • neurology cases
  • soft tissue lesions
71
Q

disadvantages of MRI

A
  • not widely available/expensive
  • requires GA
  • powerful magnetic field
72
Q

physical safety in aquisition of radiographs in horses

A
  • be ready to move x-ray equipment out of way
  • avoid touching horse with equipment
73
Q

radiation safety in aquisition of radiographs in horses

A
  • minimise number of people around horse
  • PPE

CVNT (7 decks)

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