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principles of disease > imaging week 10 > Flashcards

imaging week 10 Flashcards

1
Q

what is an X ray

A

an electromagnetic energy with a short wavelength between 0.1-10 nm

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2
Q

how does X ray tube work

A
  • electrons accumulate on filament on cathode with heat applied to it
  • then the electrons emit which is called thermionic emission
  • electrons move from cathode to rotating anode
  • X rays generated as photons and released through small window with filter on it
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3
Q

what are X rays interactions with matter

A

the X rays can either be absorbed, transmitted or deflected

- deflection causes scattered radiation

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4
Q

what is attenuation

A

the process by which radiation loses power as it travels through matter and interacts with it
- increases with atomic number, density and thickness

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5
Q

order of densities for X rays (starting most dense to least)

A
  • contrast agents/metal implants
  • bone
  • muscle
  • fat
  • air
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6
Q

what is X ray film made up of

A

3 layers:
luminescent screen
film emulsion
luminescent screen

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7
Q

how does X ray film work

A

when the photons come through and strike the luminescent film this results in light emission onto the film emulsion and therefore image is generated
emulsion contains silver halide, clumps form after exposure to light generated on luminescent screens

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8
Q

what is digital radiography

A
  • same X ray tube generation
  • digital acquisition
  • scintillation counters detect the photons and count them and based on how many they count will result in the image that’s seen on the screen through the PAC system (picture archiving communication system)
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9
Q

how does the ultrasound probe work

A
  • the probes have generation crystals and detection crystals in one device and dependent on the tissue they encounter you get various patterns returned back to the probe and converted into an image that is seen on the screen
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10
Q

what contrast agent is used for outlining GI tract

A

barium

- it’s high atomic number absorbs more X ray photons than surrounding tissues do

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11
Q

what is barium used for in clinical investigation

A

swallow and meal - oesophagus, stomach and duodenum
small bowel study - small bowel
enema - large bowel
(barium is in declining use)

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12
Q

what are the complications of barium use

A
  • bowel disturbance (common)

- colonic perforation at enema (very rare)

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13
Q

what is a CT scan

A
  • rotating X ray tube
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14
Q

when do you get given an iodinated contrast

A
  • can be given this for CT scan
  • can be given orally or intravenously
  • although IV contrast can lead to kidney failure but benefits outweigh risks
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15
Q

what are CT scans used for

A
  • trauma
  • cancer staging and response to treatment
  • guidance for procedures
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16
Q

what unit is used for describing the absorption of radiation in the body

A

sieverts

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17
Q

what is ionising radiation

A

a particle with sufficient energy to ionise a neutral atom or molecule and leave them with either a positive or negative charge

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18
Q

what are the biological effects of ionising radiation

A

leads to cell damage which can lead to;

  • repair
  • cell death
  • transformation (mutation)
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19
Q

how do you minimise exposure to radiation

A
  • keep a distance
  • use a shield
  • minimise time exposed
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20
Q

what techniques can be used for diagnosing and staging cancer

A
  • plain radiographs
  • barium studies
  • CT
  • MRI
  • PET
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21
Q

what are conventional diagnostic modalities

A
  • don’t require computers
  • endoscopy and biopsy
  • barium examinations
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22
Q

what is the fluoroscopic examination machine used for

A

barium examinations

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23
Q

what specific barium study has CT replaced

A

barium enema used to look at large bowel

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24
Q

what is barium follow-through

A
  • used to look at small bowel

- AKA small bowel study

25
Q

how is CT colonography done

A
  • insufflating carbon dioxide gas into the colon and taking CT scan images and then visualising them through special software
26
Q

what imaging techniques are cross sectional

A
  • CT
  • MRI
  • PET
27
Q

what is cross sectional imaging used for

A
  • initial diagnosis and staging of disease
  • biopsy of lesions
  • monitoring response to treatment
  • recognition of compications to treatment
  • when there is concern for disease relapse
  • sometimes treatment
28
Q

how does CT scan work

A
  • while the CT scanner rotates it produces photons every time
  • every time the photons cross the tissues some get lost
  • the computer at the other end of the detectors find out how much is lost
29
Q

what are pixels in CT

A

the 2D depiction of the structure that you normally see on the screen

30
Q

what is a voxel in CT

A

the 3D component which actually contributes to the 2D pixel

31
Q

what are the CT contrast agents

A

oral - dilute iodine based contrast (gastrografin) can be given to outline the GI tract
intravenous - iodine based contrast (omnipaque) injected into the veins to demonstrate blood vessels or the vascularity of different tissues

32
Q

what is diagnosis and staging with CT

A
  • position of tumour
  • depth of penetration of tumour
  • relationship to adjacent structures (T)
  • involvement of regional lymph nodes (N)
  • presence of distant metastases (M)
33
Q

what kind of tumours can CT diagnose

A

lung, pancreatic, renal, adrenal, brain, retroperitoneal (behind lining of abdominal wall)

34
Q

what is ablation of tumours

A
  • treatment
  • cryoablation or renal tumours
  • microwave ablation of liver metastases
  • radio frequency/microwave ablation of lung tumours
  • protein electrophoresis of pancreatic tumours
35
Q

what is ALARA principle

A

as low as reasonably achievable

  • ensure whether examination is necessary
  • adequate clinical info is essential for appropriate protocol
  • avoid repeat examinations
36
Q

how does MRI imaging work

A
  • radio frequency pulse displaces protons and image is created by displaying time taken for protons to ‘relax’ back to original alignment
  • so resting state of proton is aligned parallel to magnetic field
  • energy sent and now proton alignment perpendicular to magnetic field
  • time taken to relax again differs if different tissues and this is how image is created
37
Q

do heavier or lighter molecules take a longer time to relax in MRI

A

lighter take longer to go back to original alignment

38
Q

what can you get images of with MRI

A
  • excellent bone soft tissue detail
  • vessels
  • brain, spine and musculoskeletal
  • abdomen and pelvis
  • cardiac imaging
    (vessels shown without contrast)
39
Q

disadvantages of MRI

A
  • claustrophobic and noisy
  • motion artefact (moving organs e.g. bowel cannot be pictured because patient has to be still)
  • cannot image patients with pacemakers, aneurysm clips, etc.
40
Q

what are some MRI contrast agents

A
  • gadolinium DPTA is intravenous contrast which causes changes in local magnetic field and so alters tissue signal
  • vascular lesions and some tumours can be seen more easily
41
Q

what are the benefits of screening

A
  • diagnose disease at an earlier stage before symptoms start
  • cancer is easier to treat and more likely to be curable
42
Q

what are some NHS screening programmes

A
  • breast
  • bowel
  • cervix
43
Q

what are the WHO principles of screening

A
  • the condition should be an important health problem
  • there should be a latent stage of disease
  • there should be a test or examination for condition
  • the test should be accessible to the population
  • there should be a treatment
  • facilities for diagnosis and treatment should be available
44
Q

what are the rules for the test in screening

A
  • test should detect disease at early stage
  • test should cause no harm
  • test should have high sensitivity and specificity
  • benefits should outweigh costs
45
Q

what is artificial intelligence

A

programming systems to perform tasks which usually require human intelligence

46
Q

what is machine learning

A

training algorithms to solve tasks by pattern recognition instead of specifically programming them how to solve the task

47
Q

what is deep learning

A

training algorithms by using deep neural networks with multiple layers

48
Q

what is molecular imaging

A
  • radionuclide imaging
  • PET
  • MRI
  • optical imaging
49
Q

how does radionuclide imaging work

A

radiopharmaceutical injected into patient, that produces gamma rays, patient is now radioactive and the gamma rays are detected by lead collimator connected to gamma camera and an image is formed that is sent to PAC system

50
Q

what is a radiopharmaceutical

A

radioactive element attached to a pharmaceutical element

51
Q

what are the properties of an ideal isotope

A
  • half-life similar to length of examination
  • gamma emitter (rather than alpha or beta)
  • energy of gamma rays should be 50-300 keV
  • radionuclide should be readily available at hospital site
  • easily bound to pharmaceutical component
  • radiopharmaceutical should be simple to prepare
  • radiopharmaceutical should be eliminated in similar time to half life
52
Q

how does gamma camera work

A

patient injected with pharmaceutical
they’re emitting gamma rays
gamma rays pass through a collimator that will improve the spatial resolution and then image crystal produces flash of light
image is boosted by photomultiplier tubes and computer applies algorithm to produce image

53
Q

what is SPECT

A
  • single photon emission computed tomography
  • nuclear medicine version of CT
  • gamma cameras rotate around area of interest
  • commonly used for brain and cardiac studies
54
Q

what is PET scan

A
  • positron emission tomography
  • uses radionuclides that decay by positron emission
  • can be used to image biologically interesting processes
  • can be used for absolute quantitation but requires arterial sampling
  • all scanners now PET CT
55
Q

what is a positron

A

positively charged electron

proton converts to neutron and emits positron

56
Q

how does PET scan work

A
  • proton converts into neutron and emits positron
  • when positron comes into contact with electron they annihilate each other producing energy and two high energy gamma rays are sent out in opposite directions and these are detected by PET machine
57
Q

what is a cyclotron

A

enables us to produce proton to neutron decay for PET

58
Q

how do you detect cancer in PET

A

areas that are highly metabolic will have accumulation of fluorine 18 (pharmaceutical)

principles of disease (19 decks)

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