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Bio-Med > MRI > Flashcards

MRI Flashcards

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Biology 101 flashcards
1
Q

What is MRI?

A

a spectroscopic imaging technique used in medical settings to produce images of the inside of the human body

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2
Q

How does MRI work?

A

absorption + emission of energy of the RF EM Spectrum

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3
Q

Adv of MRI (4)

A
  • Utilises non ionizing radition
  • ability to image in any plane
  • very low incidents of side effects
  • ability to diagnose, visualize + evaluate various illnesses
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4
Q

Components of MRI (4)

A
  • Magnet - powerful uniform magnetic field
  • Gradient magnet (lower in strength)
  • RF equipment
  • Powerful Computer
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5
Q

Field strength of MRI magnet

A

.5 - 2.0 T

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6
Q

Types of magnets used in MRI (4)

A
  • Resistive Magnets
  • Permanent Magnets
  • Super conducting magnets
  • Gradient Magnets (used to create variable field)
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7
Q

Proton and neutron spins are known as …

A

… nuclear spins

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8
Q

What is spin?

A

A small magneti field, either + or - and mathematical value of 1/2

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9
Q

An unpaired component has a spin of 1/2 and two particles …

A

… with opposite spis cancel out

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10
Q

In NMR, the magnetic field is produced by …

A

… the unpaired nuclear spins

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11
Q

Why are Protons important to MIR? (4)

A
  • +’ve charge
  • spin about central axis
  • a moving (spinning) charge creates a magnetic field
  • straight arrow (vector) indicates the direction of the magnetic field
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12
Q

When placed in a large magnetic field, hydrogen atoms have …

A

… a strong tendancy to align in the direction of the magnetic field

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13
Q

The magnetic field runs down the …

A

… centre of the tube, so the hydrogen protons will align at either the head or feet

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14
Q

Majority of protons will …

A

… cancel out, but the net number of protons is sufficient to produce an image

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15
Q

MRI machine applies a RF pulse that is …

A

… specific to hydrogen

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16
Q

RF pulse are applied through a coil that is …

A

… specific to the part of the body being scanned

17
Q

The gradient magnets are …

A

… rapidly turned on and off which alters the magnetic field

18
Q

Larmor Equation

A
19
Q

What does the Larmor Frequency?

A

Frequency need to excite transverse magnetization (precession)

20
Q

When the RF pulse is turned off, the hydrogen protons …

A

… slowly return to their natural alignment within the magnetic field and release their excess stored energy

21
Q

What happens to the released energy? (3)

A
  • Released as heat
  • Exchanged and absorbed by other protons
  • Released as Radio Waves
22
Q

Measuring the MR Signal (3)

A
  • Moving proton vector induces a signal in the RF antenna
  • Signal is picked up by coil and sent to computer
  • Computer uses Fourier transform to convert to an image
23
Q

Magnetisation State (2)

A

A

  • Protons spinning in nature, w/o external mag field.
  • Directions of spins are random and cancel out each other
  • Net magnetisation is 0

B

  • Large magnetic field, B_0, spins align themselves either
    • against (high energy state)
    • along (low energy state)
  • Slight abundance of spins aligned in low energy state
24
Q

Proton Alignment (4)

A

A - spin of a proton aligned to B0 in the z-axis

B - An external perturbing magnetic field, B1, knocks the vector out its axis, which is now aligned at a new angle w.r.t B0

C - As the pertubing field B1 is removed, the vector gradually starts returning back to its original state

D - begins to wobble

25
Q

Resonance Eqn

A

v - resonant frequency

gamma - gyromagnetic ratio

B_0 - magnetic field

26
Q

T1 Parameter

A

the spin-lattic relaxation time-scale for the longitudinal magnetisation to come back to its original value

27
Q

T2 Parameter

A

the spin-spin relxation time for the transverse magnetisation to come back to its initial value

28
Q

T1 weighted imaging has …

A

… higher spatial resolution

29
Q

T2 weighted imaging has …

A

…. higher tissue contrast

30
Q

What does the image represent?

A

Every tissue layer has a different volume of water thus a different number of hydrogen atoms which produce different images based on the # hydrogen atoms

Bio-Med (9 decks)

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