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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
radiographic opacity definition
how black or white overall?
26
radiographic contrast definition
differences in black/white/grey
27
radiographic sharpness definition
clarity of image
28
what are contrast media?
agents that are more or less opaque than surrounding tissue
29
what do contrast media do?
delineate organs/cavities within body to see structures that are usually poorly visable
30
types of contrast media
- positive contrast - barium, white on radiograph - negative contrast - gases, black on radiograph
31
barium as contrast agent
- used in GI tract - reasonably palatable - cheap - non toxic
32
ionic iodinated contrast
- irritant extra-vascularly - toxic in large doses - viscous
33
non-ionic iodinated contrast
- more expensive - viscous - side effects can still occur (anaphylaxis, nephrotoxicity)
34
negative contrast media advantages
air/CO2 - free - simple, relatively safe - can combine with positive contrast agents (double contrast)
35
negative contrast media disadvantages
- risk of air embolism - poor mucosal detail - less contrast than positive contrast agents
36
barium swallow technique
indications= dysphagia, suspected rupture - shows pharynx and oesophagus - care if cant swallow (aspiration risk)
37
barium 'follow-through' technique
- shows stomach and small intestine - liquid barium (stomach tube or mouth) - take x-ray immediately then at intervals
38
barium enema technique
- evaluates large intestine - liquid barium infused into rectum post-enema - messy/difficult to interpret - superseded by endoscopy
39
contrast in urinary tract
- never barium (bladder irritant) - use water-solule iodinated contrast
40
cystography techniques
- pneumocystogram - positive contrast cystogram - double contrast cystogram
41
myelography
- delineates subarachnoid space - localised lesions of spinal cord - non-ionic water-soluble contrast
42
production of ultrasound
- high frequency sound wave piezoelectric effect 1. voltage applied to disc within transducer 2. disc expands or contracts 3. sound wave produced
43
recieving the ultrasound signal
- sound returns from tissues to transducer - pressure of sound wave distorts disc which creates voltage - voltage processed by machine and displayed
44
acoustic impedance
density of tissue x speed of sound in tissue
45
ultrasound specular reflection
- soundwaves hit large smooth surface giving a bright/mirror reflection line
46
ultrasound non-specular reflection
- beam hits small structures with re-radiates in all directions giving texture to organs
47
ultrasound B-mode
- images a slice through the patient
48
ultrasound M-mode
- used in cardiac work - movement of points along line followed
49
ultransound abdomen clipping site
xiphisternum to pubis - follow costal arch up to lumbar muscles
50
ultrasound heart clipping site
- right side - 4th-6th intercostal space - costochondral junction to sternum
51
ultrasound left kidney clipping site
- behind last rib below lumbar muscles
52
ultrasound right kidney clipping site
- last 2-3 intercostal spaces below lumbar muscles
53
advantages of ultrasound
- good soft tissue detail - internal structure of organs - functional information (movement)
54
disadvantages of ultrasound
- expensive equipment - need to clip hair - difficult to interpret - gas/fat/bone hinders examination
55
types of ultrasound transducer
- phased array - convex - linear
56
advantages of phased array transducer
- easy to manipulate - small contact area - wide field at depth
57
advantages of linear transducer
- large contact area - large field of view near skin - good for superficial structures
58
positioning aids
- radiolucent wedges and plastic troughs - sandbags (will be seen on radiograph) - tape
59
naming of projections
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
CT/MRI
- slices through the animal
61
scintigraphy
functional remodelling activity of bone
62
principles of CT
- ionising radiation - similar to radiography - rotating x-ray machine to take 360 degree view
63
uses of CT
- gives multiple detailed reconstructions from one scan - used to make custom made surgial implants - 3D models for surgical planning
64
disadvantages of CT
- limited availability/expensive - uses higher doses of ionising radiation than x-ray
65
scintigraphy principles
- 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
uses of scintigraphy
- 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
disadvantages of scinitgraphy
- uses ionising radiation - patient remains radioactive after scan - poor anatomical detail (difficult interpretation)
68
how does MRI work?
- 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
advantages of MRI
- good contrast resolution - excellent anatomical detail of soft tissues - doesn't use ionising radiation
70
MRI uses
- neurology cases - soft tissue lesions
71
disadvantages of MRI
- not widely available/expensive - requires GA - powerful magnetic field
72
physical safety in aquisition of radiographs in horses
- be ready to move x-ray equipment out of way - avoid touching horse with equipment
73
radiation safety in aquisition of radiographs in horses
- minimise number of people around horse - PPE

CVNT (7 decks)

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