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Imaging in Biomedical Research > Radiography and CT > Flashcards

Radiography and CT Flashcards

1
Q

How was the X-ray discovered?

A
  • By accident
  • Trying to improve the cathode ray tube by making stronger electric fields to cause electron beams
  • Accidently exposed a photographic film that was in the line of the cathode
  • Some non-visable radiation more penetrating more than visable light
  • Wilhelm Conrad Rontgen (1901)
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2
Q

What did they find out that the new radiation could do?

A
  • Penetrate tissues but the body absorbs to varying degrees
  • Different levels of exposure on film revealed the internal structure of the body
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3
Q

Where do X-rays sit on the electromagnetic spectrum?

A
  • Very small wavelengths- the shorter the wavelength, the higher the energy it carries
  • The ionising radiation has enough energy to harm tissue
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4
Q

What are the components of electromagnetic waves?

A

Partly electric and partly magnetic

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5
Q

What is the range of a radio wave?

A

M

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6
Q

What is the range of a microwave?

A

cm

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7
Q

Outline the components of the cathode ray tube

A
  • Electron beam
  • Cathode
  • X-rays
  • Tungsten anode
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8
Q

How does the cathode ray tube work?

A
  • Pump out the internal air to create a vacuum
  • Apply a voltage between the negative anode and positive cathode
  • The voltage (when high enough) causes electrons to be dislodged from the cathode and then accelerates toward the anode
  • As it accelerates, it suddenly stops as it hits the high density metal material
  • All the energy gathered over the path of acceleration is released in an instant
  • This energy dissipates as heat and x-rays
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9
Q

What determines the different strengths of the x-ray?

A

The voltage between the anode and the cathode

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10
Q

What are the two ways that x-rays can be produced?

A

First
- Electron collides with a tungsten atom

  • Tungsten atom loses electron from lower from lower orbit
  • Electron from higher orbit falls to lower orbit
  • Excess energy released as an X-ray

Second
- Nucleus may attract speeding electron

  • Electron slows and changes course
  • Braking action slows electron which releases excess energy
  • Excess energy released as an X-ray
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11
Q

How is it so the x-ray beam can be focused?

A

Tungsten anode geometry is such that the angle creates the x-ray going out the window

The light determines the field of exposure

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12
Q

How is heat produced by the x-ray dealt with?

A
  • Is normally suspended in an oil bath (high density medium to dissipate the heat)
  • The tungsten filament is a plate which slowly rotates presenting a different area and preventing overheating
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13
Q

What is penetration in terms of x-rays?

A

The higher the energy, the easier penetration of the tissue is

There is less interaction with the tissue

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14
Q

What is attenuation in terms of x-rays?

A

Inverse to penetration

Good penetration means harder to interact with the tissue

Whereas interaction with the tissue means it is absorbed

Attenuation increases with atomic number of exposed material

  • Attenuation falls with increasing energy of photons
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15
Q

What happens to penetration and attenuation when there is low energy (soft)?

A

Allow the visualisation of fatty tissue

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16
Q

What happens to penetration and attenuation when there is high energy (hard)?

A

Can visualise bones and not tissue

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17
Q

How does analogue imaging work?

A
  • Through film
  • The light exposes crystals on the film
  • Gets developed and can see areas where crystals have been exposed
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18
Q

How does digital imaging work?

A
  • Have individual pixels
  • Sharper image is smaller pixels
  • Independent of the size of the pixels (within the pixel is only a single grey (or colour) value)
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19
Q

How does film radiography work?

A
  • X-rays are converted to visible light by an intensifier
  • Visible light oxidises radio-sensitive crystals producing a latent
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20
Q

Why did origional film x-rays need longer exposure?

A
  • The images that are generated to visualise film are high energy, high penetration and low attenuation
  • X-rays are poor at interacting with thin film so need longer exposure- however this increases an individual’s radiation dose
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21
Q

What was invented to reduce exposure time and radiation in film X-rays?

A

An intensifier- converts the x-rays into visable light which is good for film exposure and safer

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22
Q

How is film radiography visualised?

A
  • Exposed radiosensitive crystals are converted to black metalic silver
  • Unexposed crystals are washed out of the emulsion
  • Uses a developer, a fixer and then a washer
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23
Q

What do the light and dark areas represent in film radiography?

A
  • Dark indicate low tissue density (muscle)
  • Light indicate high tissue density (bone)
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24
Q

How does digital radiography work?

A
  • A layer of phospher (encased in plastic) is exposed to X-rays
  • The phosphor absorbs enery and releases it over time (latent image)
  • The intensity is read by a light detector of certain locations and the computer puts the image back together again
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25
Q

How does the phosphor layer work in digital x-rays?

A

A bit like fluorescence but stores the light for longer

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26
Q

What is the phosphor layer scanned by in digital radiography?

A
  • Scanned by a laser which causes the screen to emit light
  • Then energy is proportional to the magnitude of x-ray exposure
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27
Q

What is the digital radiograph made up of?

A
  • Pixels
  • Pixels are segments each assigned a different grey (or colour value)
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28
Q

What are 4 benefits of conventional film radiography?

A
  • Radiologists and doctors must have adequete access to computers for digital
  • Computer equiptment is expensive in digital
  • No problems associated with virus or hacker software
  • Better spatial resolution than digital images
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29
Q

What are 5 benefits of digital radiography?

A
  • No film or film jackets to purchase or a processor to maintain
  • Lower dosage as decreased retakes (can manipulate the exposure)
  • No time spent filing/searching for old films
  • Increased efficiency
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30
Q

What is lifetime exposure of radiation made up of?

A
  • 50% from radon in the earth- makes up 84% natural
  • 15% medical imaging- makes up 16%
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31
Q

What is radiation dosage measured in?

A

millisieverts (mSv)

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32
Q

What is angiography?

A
  • Inject a liquid dye into the blood stream
  • Contains metal particles
  • These show up on angiographs of radiography and CT scans
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33
Q

What does tomography do?

A

Capture three-dimentional data on the internall structure of an object by using serial sections

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34
Q

What is computed tomography (CT)?

A

Tomographic medical imaging method where a three-dimensional image of the internal structure of an onject is generated using a large series of radiographic sections (x-rays)

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35
Q

What length are CT waves?

A
  • Short (10^-10m)
  • Try and optimise frequencies of the x-rays we use
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36
Q

What is the path of each photon considered to be?

A

A ray

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37
Q

What is the quantity of photons reaching the plate called?

A
  • Detector measures the degree of attenuation (photons that are absorbed or scattered)
  • Called the ray sum
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38
Q

What is an issue with using X-rays to visualise structures?

A
  • Only provides us with a 2D image of a 3D structure
  • Difficult to interpret
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39
Q

WHat did Godfrey Hounsfiled do?

A
  • Was an electrical engineer in the 60s
  • Realised there must be a wat to capture information from many viewpoints using x-rays
  • Then process together
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40
Q

What is the view of a CT scan?

A
  • Detector measures attenuation of every beam (ray sum) from different viewpoints
  • Then get a complete set of ray sums
  • Attenuation of each ray sum is correlated with ray position (attenuation profile) for each view
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41
Q

What is a back projection?

A

Collates data from attenuation profiles to produce an image

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42
Q

What is a phantom structure?

A

A structure with a known density used to see how accurate a scan is

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43
Q

Who was Allan MacLeod Cormack and what did he do?

A
  • South African physicist
  • Worked with Hounsfield (made the machine to produce x-ray souces and detect attenuation profile) to do the mathematics for CT reconstruction
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44
Q

Who created the computed axial tomography (CAT)?

A

Hounsfield and Cormack

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45
Q

What is the general structure of a CAT scanner?

A
  • X- ray source on one side
  • Detector on the other side
  • They move aroynd the head to gather different views
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46
Q

What is slice construction in CT?

A

Computer generation of a large series of two-dimensional x-ray slices based on x-ray attenuation coefficients (i.e back projections)

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47
Q

What is the 3D reconstruction in CT scans?

A

Computer reconstruction of a large series of 2D x-ray slices to generate a 3D image of an object’s internal structure (i.e stacking slices)

48
Q

What is windowing in CT?

A

The window is the range of CT numbers that will be displayed with the different shades of grey, ranging from black to white

49
Q

What is segmentation in CT?

A

Method to select part of a 3D reconstruction using CT numbers

50
Q

What does a collimator do?

A
  • Is a dense metal to focus the x-ray beam and avoid scattering inside the scanner (which would subject the patient to non-diagnostic ionising radiation)
  • Also, the x-ray source produces different energies, the low ones are unhelpful as they are absorbed by all the patients tissues, the collimator removes these low energy rays
51
Q

What does the x-ray tube do in CT?

A
  • Emits x-rays
  • Which pass through a collimator and produces and x-ray beam in a fan or a cone shape (modern), older produce a beam
52
Q

What is the fan or beam directed at in CT?

A

The object, e.g. patient skull

53
Q

What does the attenuation after the beam has passed through the object allow a computer to do?

A

Can be used by a computer to work out the relative density of the tissues examined (profile generated)

54
Q

How is a 360 image of the object gathered in CT?

A
  • The object can be rotated incrementally (e.g. steps of 1 degrees) within the beam
  • More commonly, the beam can be rotated incrementally around the object (steps of 1 degrees)
55
Q

In CT what does a thinner slice provide?

A

Thinner slice is more information but is slower to take and patient will habe more ionising radiation.

56
Q

What happens in CT once a scan of a slice has been taken?

A

The x-ray set up will be moved down/up by tthe depth we want to capture another 360 attenuation profile until the entire area is sectioned

This information can be used by a computer to work out the relative density of the tissues examined

57
Q

What is important to consider in terms of angles of sectioning in a CT?

A
  • Need to consider what information we want to capture and what is the best view to section
  • Tend to have better refistration between the slices in the plane where the information was collected
  • Using a transverse plane to see sagittal for example won’t be as accurate as seeing transverse
58
Q

What are the usual thickness of body CT slices?

A

0.05-30mm

59
Q

Why does a CT need to be calibrated?

A

Need to work out the density of surrounding materials so it is accurate

60
Q

Outline what a pencil beam scanner (1st generation) is

A
  • X-ray beam
  • Uses a single source and detector
  • Rotate by small amount and then repeat
  • 180 decree arc covered
  • Then gantry moved to next location for following slice
  • Step and shoot
61
Q

What is a gantry in CT?

A

The setup of the x-ray source and detector

62
Q

What are 2 advantages of the 1st generation scanner?

A
  • Easy calibration and little noise
  • Small steps mean that there is sufficient data
63
Q

What are 2 disadvantages with the 1st generation scanner?

A
  • Slow, so not good for lungs or heart where they change shape rapidly
  • Is no longer used
64
Q

Why are 1st and 2nd generaiton CT scanners limited to a 180 degree rotation?

A
  • The x-ray source and detector array were powered by cables
  • Thats why the gantry could only be rotated a certain amount
65
Q

How are 3rd generation onwards CT scanners able to perform 360 degree rotation?

A
  • Slip-rings were invented
  • They are contacts that could slide apart from one another and could move 360
66
Q

Outline the fan beam incremental CT scanner (2nd generation)

A
  • X-ray fan
  • Array of detectors
67
Q

What are three disadvantages with the 2nd generation CT scanner?

A
  • Did not cover full field of view
  • Faster than 1st generaiton but still slow
  • No longer used
68
Q

Outline the rotate-rotate scanners (3rd) generation

A
  • X-ray fan
  • Array of detectors
  • Full field of view covered
  • Source and detector array able to move in a circle within the scanner
  • All readings of view collected simultaneously
69
Q

What are 3 advantages of the 3rd generation CT scanner?

A
  • Fast
  • Reduces artefacts from patient motion
  • Still used
70
Q

What is a disadvantage of the 3rd generation scanner?

A

Ring artefacts if detector array is misaligned in relation to the source

71
Q

Outline the rotate only scanners (4th generation)

A
  • Fixed 360 degree detector array
  • Rather than moving the array, the source is rotated
  • Is fast
72
Q

What are 2 disadvantages of 4th generation scanners?

A
  • Motion artefacts are problematic
  • Can be addressed but increases radiation dose
73
Q

Outline ultrafast CT (5th generation)

A
  • 1980s
  • Neither source nor detectors move
  • Suitable for cardiac imaging
74
Q

What are three disadvantages of 5th generation CT?

A
  • Poorer spatial resolution
  • High cost
  • Not used in routine imaging
75
Q

Outline dual source CT scanners (6th generation)

A
  • Two sources and detector arrays at 90-95 degrees to each other
  • Often one whole field of view and the other a partial field of view
  • X-rays from each source can be at different energy levels- see different densities therefore views of the same structure
76
Q

Outline 7th generation CT scanners

A
  • Similar to 3rd generation
  • Cone rather than fan of x-rays
  • Flat plate rather than multirow detector
  • Used for dental imaging
  • Still in development
77
Q

Outline helical CT (spiral/overlap CT)

A
  • Fast scan
  • Slow processing
  • Standard for medical diagnostic CT
  • Single source
  • Detectors in array
  • Source and detectors rotate whilst bed moves patient- therefore helical scan
78
Q

What is a voxel?

A

Volume element

Rather than pixel ‘squares’, more like 3D cubes

79
Q

What is the CT number proportional to?

A

Proportional to the mean relative linear attenuation in a voxel

80
Q

What is the CT number dependent on?

A

Energy (spectrum)

81
Q

What is airs CT number (hounsfield unit)

A

-1000

82
Q

What is waters CT number (hounsfield unit)

A

0

83
Q

What is fats CT number (hounsfield unit)

A

-10s

84
Q

What is muscles CT number (hounsfield unit)

A

10-low 100s

85
Q

What is bones CT number (hounsfield unit)

A

1000-3000

86
Q

What does the CT number want to relfect?

A
  • The nature of the tissue in that voxel
  • usually assumed but calibration needed (work out what 0 and 1000 are as a reference reading)
87
Q

Outline how windowing (opacity manipulation) works?

A
  • Voxels are all assigned a CT number
  • These are not helpful to visualise structures however (arbitrary)
  • Represent these CT numbers as shades of grey
  • Assign grey scale values to the voxels- least dense are given darker, going down to air as being black
88
Q

What is a problem with assigning grey scale values to voxels in windowing?

A
  • There are at least 2000 CT numbers but humans can only see 40 shades
  • We need to think about the structures that we are interested in and assign these 40 shades (a window)
  • Work out the averal density (level/depth of the window) of the things we are interested in and whether we need a wide or narrow window (range)
89
Q

Page 3, CT 2 for examples of common CT scans

A
90
Q

What was a study done using CT into non-invasive diagnosis of tumours?

A
  • Looked at lung cadavers, cancer tumours
  • Scan post mortem to see the position of the different tumours
  • Then dissected out to see if they could find them
  • Was a good way of identifying the tumours but can also be used when treating tumours using radiotherapy
  • Can 3D scan the tumours and focus the x-rays on the right area preserving surrounding tissue
  • De Clerk et al 2004
91
Q

What is effective radiation dose measured in?

A

Millisieverts (also rad, rem, roetgen, sievert)

92
Q

Why do we need to consider radiation when scanning different body areas?

A

They have varying sensitivities to radiation

93
Q

What does effective dose refer to (radiation)?

A

Refers to the dose averaged over the entire body

94
Q

What is the mSv of chest x-rays?

A

0.1

95
Q

What is the mSv of cranial CT?

A

1.5

96
Q

What is the mSv of abdominal CT?

A

5.3

97
Q

What is the mSv of chest CT?

A

5.8

98
Q

What is the mSv of chest, abdominal and pelvic CT?

A

13.9

99
Q

What is the mSv of cardiac CT (angiogram)?

A

6.7-13 depending on how much data we want to collect

100
Q

What is the mSv of naturally occuring doses from cosmic rays and radioactive substances?

A

3

101
Q

What is a study into anatomical research using existing patient data of lung shape and sexual dimorphism?

A
  • Interested in sexual differences in lung size, shape and breathing mechanics
  • In order to optimise treatment and diagnoses for males and females, need to understand the dtails
  • Used prevoiusly taken CT scans and found that there was a different in lung shape
  • More pointed apex for men (more diaphragm usage)
  • More columnar for women (more intercostal muscle usage)- might be due to pregnancy inhibiting diaphragm use
  • Torres-Tamayo et al 2018
102
Q

What is a study into anatomical research using existing patient data of the size of pterygomaxillary fissures?

A
  • The trigeminal nerve is important for general sensation from the cranial cavity
  • If have a headache, trigeminal nerve is conveying the information
  • Cluster headaches can be treated with a microstimulator in the pterygomaxillary fissure to stimulate the corresponding ganglion
  • Wanted to see if the microsimulator would actually fit in the ganglion
  • Found it was of sufficient size in both men and women
  • Puche-Torres et al 2017
103
Q

What is a study into anatomical research using existing patient data of hepatic vein variations?

A
  • Hepatic vein in the liver has different patterns of attributes
  • These can be subdivided into subtypes for drainage passage
  • Important for transplants and re-sectioning
  • Anything over 3cm in diameter needs to be reconstructed for proper drainage
  • Lin et al 2023
104
Q

What is comparative anatomy research important for?

A
  • Zoological
  • Archaelogical
  • Palaentological
105
Q

What is an example of a zoological approach of comparative anatomy research?

A
  • Found variations in the bony labarynth of the inner each shape in humans and chimpanzees
  • Gunz et al 2013
106
Q

Why are dried skulls unuseful for MRI studies?

A

They don’t have hydrogen atoms which are important in MRI reconstruction

107
Q

What is an example of a palaeontological approach of comparative anatomy research?

A
  • Fossilised remains are the bones or skeleton elements replaced by minerals inside a rocky matrix
  • Rocky matrix is either too hard to break apart without damaging the fossil or too crumbly
  • Therefore can use CT scans and form a 3D reconstruction which can be rotated to see different bones and aspects that we couldn’t physically extract
  • E.g. the skeletal anatomy of the early diapsid, Feralisaurus corami from the middle Triassic- Cavicchini et al 2020
108
Q

How are CT’s useful in visualising voids?

A
  • CT provides a non-invasive and non-destructive way to investigate the shape and volume of voids
  • Can fill voids with wax and then destroy the specimen (disruptive however)
  • With CT’s we can visualise and fill the voids with a virtual cast
109
Q

What are 3 advantages of CT and voids?

A
  • Non-destructive
  • Can determine shape as well as size (either volume or cross-sectional area)
  • Readily distinguishes bine from air or fluid
110
Q

What are 3 advantages of CT in image reconstruction?

A
  • Both 2D slices and 3D reconstructions produced
  • Slices can be stacked to ‘reconstruct’ 3D visualisations
  • 3D visualisations can be segmented to show internal features
111
Q

How was CT helpful in visualising the maxillary sinus of macaques?

A
  • Allowed visualisation of the maxillary sinys shape and measurement of its volume
  • (voidal reconstruction)
  • Marquez and Laitman 2008
112
Q

How was CT helpful in imaging the frontal sinuses of bovids?

A
  • Goat and sheep sinuses go into the bony core of their horns in order to lighten them
  • So there is a hollow space in the horns which is hard to visualise the shape of this space
  • CT shows complex, small interconnected chambers of this sinus void
  • Farke 2010
113
Q

How can you use CT to visualise volumes?

A
  • If 2D techniques are used it is easy to add slices together to produce 3D reconstructions
  • i.e. go from displaying cross-sectional areas to displaying spatial information
  • CT allows non-invasive vivisection
  • We can examine structrues as if they were dissected straight out of the body
114
Q

How does segmentation or the extraction of 3D representation work in CT?

A
  • Identifying voxels based on their CT number that are occupied by structures of interet
  • Space occupied by that structure or tissue can be regarded as the union of voxels associated with those pixels where the x-ray attenuation is above the appropriate theshold (thresholding)
  • Easy when thresholds are very different
  • But also means object has multiple boundaries if surface rendering for example outer surface compared to voidal trabeculae in the bone
115
Q

What are two applications of mobile CT scanners?

A
  • For clinical purposes (like patients who don’t normally have access to a facility with a CT scanner)
  • For research (like bringing a CT scanner to a museum rather than take the specimen to the scanner)

Imaging in Biomedical Research (9 decks)

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