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Imaging Human Brain Structure

William Chapman Techniques in Neuroscience 2nd Year English 74 cards

does a CT scan rotate 360 degrees round the patient?

Cards in this deck (74)

  1. 1what are x-rays?form of radiation that can be used at low levels to produce an image of the body
    usually used to detect cancer or brain damage
  2. 2what is computerised tomography? (CT/CAT)a computerised axial tomography uses a computer that merges many x-rays from several angles into a single picture
  3. 3what are the 4 types of static imaging?1) x-ray
    2) angiogram
    3) CT scan
    4) MRI
  4. 4what is an angiogram?an x-ray image of blood vessels made after the injection of a radiopaque (contrast) substance
  5. 5what is magnetic resonance imaging?an imaging technique that uses a magnetic field and radio waves to produce highly detailed electrical images of the body
  6. 6what are the characteristics of an x-ray?can pass through objects
    beams are scattered by molecules
    denser materials show greater scattering (dense= reflect more rays) appear white (bones)
  7. 7how can x-rays be detected?using photographic emulsion or electronic detectors
  8. 8what are the 4 basic densities for x-rays?air (black)
    soft tissue
    fat
    bone (white)
  9. 9why do some x -rays have grids between the specimen and the film?prevents too much scattering of the photons
  10. 10why must there be protection from x-rays?x-rays cause biological damage and the operator and patient must be protected from radiation
  11. 11what is the protection mechanism against x-rays?LEAD
    used to absorb radiation
  12. 12how does the modern x-ray differ from the radiograph?1) uses high energy photons
    2) x-ray machinery can move round the person rather than the person moving
    3) ionising radiation
    4) exposes film/detector
    5) projection data is collected
  13. 13advantages of x-rays?1) is fast - the results = available within the hour
    2) painless and non-invasive
    3) inexpensive
    4) low amount of ionising radiation for image
    5) good contrast (air and bones)
    6) identify cracks, infections, injury and abnormal bones
    7) identify bone cancer and locating alien objects
  14. 14x-ray disadvantages?1) x-rays increases the levels of hydrogen peroxide in the blood - toxic
    2) high risk of getting cancer after continuous exposure
    3) x-rays are able to change the base of the DNA --> mutations
    4) 2-D only
    5) POOR DIFFERENTIATION BETWEEN SOFT TISSUE
  15. 15what is contrast radiography?injection, ingestion or other placement of opaque material within the body
  16. 16why might you have to wait a while before taking a radiography image?takes a while for it to reach target are
  17. 17give two examples of contrast agents1) barium
    2) iodine
  18. 18give 2 advantages of contrast radiography1) improve visualisation and tissue separation
    2) can demonstrate functional anatomy and pathology
  19. 19characteristics of a CT/CAT scan?multiple low energy x-rays
    use an array of several detectors
    a 3D image is created by computer analysis
    image is represented as a series of slices (tomographs)
    x rays are beamed and received at many different points
  20. 20does a CT scan rotate 360 degrees round the patient?does a CT scan rotate 360 degrees round the patient?
  21. 21why are x-rays able to pass through matter?short wavelength
  22. 22what are the advantages of CT scan?1) good resolution
    2) faster than MRI
    3) most systems can be scanned (brain--> leg)
  23. 23what are the disadvantages of CT?1) requires breath holding - hard for some patients
    2) artefacts created by metal chips (common)
    3) CT scans of brain can be affected by bone nearby
    4) high doses of radiation
    5) NO PREGNANT PATIENTS - causes childhood cancer and leukaemia
  24. 24what does angiography do?used to study blood vessels, through the use of contrast to make the vessels visible under fluoroscopic procedures
  25. 25what is a cerebral angiography?specifically vessels of brain
    detects abnormalities, blockages, bleeding or therapeutic reasons
  26. 26how can an angiogram image be enhanced?subtraction --> making negative image
    remove negative image from the positive
  27. 27what are the main things angiography is able to detect?narrowing/blocking --> bulges in arterial walls
    aneurysms
    acute stroke (blood clots in brain)
  28. 28what are the risks of angiography?1) internal bleeding or haemorrhage
    involves puncturing an artery to inject the contrast (usually done in the leg)
    2) stroke/ heart attack
    blood clots of plaque dislodge forming a blockage
    3) allergic reaction
    to contrast
  29. 29what contrast substances did we use to use in the past?ionic iodinated contrast
  30. 30what do we now use as contrast substances for angiography?nonionic iodinated contrast:
    1) iohexol
    2) iopamidol
    3) ioversal
    4) imagopaque
  31. 31what doe the amount of contrast substance injected depend on? what factors?condition/age/weight/pathology of vessels
  32. 32what are the following imaging - arteriography venography angiocardiography lymphographyartery
    vein
    heart
    lymphatic system
  33. 33when is digital subtraction angiography useful?1) imaging vessels which can't be seen due to overlapping bony structures
    2) detecting small lesions which are almost completely undetectable on routine films
  34. 34what is PET and what does it measure?measures metabolic activity of cells in the human body
  35. 35what is injected before you can perform a PET scan?fluorodeoxyglucose (18F) (FDG)
    radiotracer
  36. 36why is fluorodeoxyglucose used?linked to receptor ligands
    gives good and non-harmful window (110 mins)
  37. 37how do PET produce images?radio tracer goes to the area where the substance it has tagged is used. the radiotracer undergoes NUCLEAR DECAY (emission of protons) as the nuclei is unstable
    positron hits electron and they completely annihilate each other resulting in converting all their masses into energy --> 2 gamma rays sent in opposite directions (180 degrees) out of body
    PET scanner detects the gamma rays and we can detect where these events occur
  38. 38what does the computer do with the detected gamma rays?computer and reconstruction algorithms allow us to build an image since millions of the decay events happen/second
  39. 39what are PET scans used to detect?increased, decreased metabolic activity - for example cancers use more glucose/ have a higher metabolic rate than healthy tissues
  40. 40how is the radioactive tracer introduced into the body?as a radioactive solution
  41. 41PET scanner diagramPET scanner diagram
  42. 42give four position emitting isotopes and their respective half-livesgive four position emitting isotopes and their respective half-lives
  43. 43half life of 11C?20 mins
  44. 44half life of 15 0?2 mins
    SMALLEST
  45. 45half life of 13N?9.9 mins
  46. 46why are the radio tracers usually deoxyglucose?1) metabolised in brain
    2) appropriate half life
  47. 47what are the advantages of PET scans?1) allows us to evaluate body function - detect biochemical alterations that suggest disease
    2) because the radioactivity is very short-lived, the radiation exposure is low (amount is low and doesn't affect the normal processes of the body)
    3) imaging improves detection of a variety of cancers and useful for identifying small tumours in patients with PARANEOPLASTIC neurological disorders
  48. 48what are paraneoplastic neurological disorders?collateral damage to nervous system as immune cells attack tumour as it sees it as an invasion
  49. 49PET risks?1) any exposure = potential tissue damage --> cancer
    2) pregnancy- infants that are breast-fed could be exposed to 18F radiation
  50. 50PET scan limitations?1) can give false positives if a patient's chemical balances are not normal
    eg diabetic that has eaten recently will have an elevated blood sugar and insulin
    2) because radioactive substance decays quick and is effective for a short period of time --> must be produced in a lab nearby
    TIMING IS EVERYTHING
  51. 51how is the value of a PET scan enhanced?when it is part of a larger diagnostic work up
    eg. combined with CT or MRI
  52. 52how do MRIs work?use strong magnetic fields and radio waves to produce detailed images of the inside of the body
    rely on the magnetic properties of hydrogen atoms (positively charged proton and no neutron)
  53. 53what can be an advantage of using PET and MRI when looking at tumours?PET localises the tumour and MRI helps to identify how much of the tissue needs to be removed
  54. 54—xx
  55. 55how long does an MRI take?45 mins
  56. 56explain the principles behind MRImagnetic waves causes all the hydrogen atoms to align in the same orientation
    radio frequency waves pass through the protons and disrupt them. when the protons stop spinning they emit electromagnetic energy which is detected by the received coils
    computer reconstructs image
  57. 57what does the primary magnetic field (Bo) cause the protons to do? what is the proportion that along and what is the proportion that don't?a greater proportion aligns parallel (low energy) than antiparallel (high energy)
    this is the NET MAGNETIC VECTOR and in the z-axis
  58. 58what does the radio frequency coil burst of energy do?when turned off, nuclei return to resting state and release the energy stored during the pules --> detected by scanner
  59. 59explain polarisation of the protonsprotons are like little magnets
    spins are normally oriented randomly (a)
    in an applied magnetic field, the spins align with the applied field in the equilibrium state (b)
  60. 60parallel to Bo the lower energy state? Bo = PRIMARY MAGNETIC FIELDyes
    MAGNETIC FIELDS ALIGNS ALL THE HYDROGEN PROTONS
    majority align parallel as this is a lower energy state
  61. 61—the hydrogen protons are found in tissue and in bloodthe hydrogen protons are found in tissue and in blood
  62. 62what does the Larmor equation state?the stronger the applied external magnetic field, the higher the precession frequency (alignment)
  63. 63what is spin precession?the movement of the axis of a spinning body around another axis due to torque acting to change the direction of the first axis
    direction of spin which generates a magnetic field in that direction
  64. 64—protons spin along the long axis of the primary magnetic field = precession
    precession rate is termed Larmor frequency    protons spin along the long axis of the primary magnetic field = precession precession rate is termed Larmor frequency
  65. 65how does a strong magnetic field include in terms of precession frequency?increase in precession frequency
  66. 66—has both magnetic fields and radio frequency coilshas both magnetic fields and radio frequency coils
  67. 67T1 and T2?LOOK AT LECTURE NOTES
  68. 68what is fMRI? what does it measure?functional MRI
    measures brain activity - measure BOLD (blood oxygen level dependent activity)
  69. 69what do you have to determine first before performing an fMRI?basal brain activity as a point of comparison
  70. 70is fMRI quick?yes - 5 seconds
  71. 71what principle does fMRI depend on?oxyhaemoglobin and deoxyhaemoglobin differ in terms of their signal
  72. 72what do you have to be careful of when determining brain activity?changes in blood flow can change signal --> important to check that changes in blood flow are a result of the activity you are interested in
  73. 73fMRI advantages?1) non-invasive
    2) no radiation risk (unlike CT and PET scan)
    3) high spatial resolution
    4) record signal from all regions of the brain, unlike EEG/MEG which are based towards cortical surfaces
  74. 74fMRI disadvantages?1) poor temporal resolution - very slow
    2) images must be interpreted carefully since brain processes are complex and often non-localised
    3) the BOLD signal is only an indirect measure of neural activity and is thus susceptible to influence by non-neural changes in the body

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2nd Year Techniques in Neuroscience (Neuroanatomical, Imaging and Biochemical Techniques) Flashcards on Imaging Human Brain Structure, created by William Chapman on 12/05/2016.
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