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PHYS4010: Functional Medical Imaging > MR 1 > Flashcards

MR 1 Flashcards

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USMLE® Step 1 flashcards
1
Q

Matter is composed of atoms, which are made of ________ and ______ (containing _______ and ________).

A

Electrons
Nuclei
Protons
Neutrons

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2
Q

What are the 4 fundamental properties of nuclei?

A
  • Spin
  • Charge
  • Mass
  • Magnetic moment
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3
Q

Give the equation for the mass number

A

A = mass number
N = number of protons/neutrons

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4
Q

Give the equation for the atomic number

A

Z = atomic number
N = number of protons

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5
Q

What type of nuclei have spin?

A

Nuclei with an odd number of protons or neutrons.

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6
Q

Give 7 examples of elements with spin

A

C-13
F-19
Na-23
P-31
K-39
H-1
H-2

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7
Q

What nuclei are used for magnetic resonance imaging?

A

Hydrogen nuclei

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8
Q

Nuclei with spin possess ____ _______ _______ (J) and a _______ ______ (µ)

A

Spin angular momentum
Magnetic moment

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9
Q

Give the equation for magnetic moment

A

µ = magnetic moment
γ = Gyromagnetic ratio
J = spin angular momentum

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10
Q

Nuclear spin and charge give rise to a _______ ______.

A

Magnetic moment

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11
Q

What is the longitudinal direction in NMR?

A

The direction that the B₀ field (the static magnetic field) is aligned with. This is normally the z-axis.

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12
Q

What is the transverse plane in NMR?

A

The xy-plane, perpendicular to the static magnetic field.

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13
Q

What property causes a bar magnet to align with an applied magnetic field?

A

Torque (τ)

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14
Q

How do nuclear magnetic moments respond when they experience torque?

A

The nuclei precess because they have a spin.

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15
Q

Give the equation for the torque on a magnetic dipole in a magnetic field

A

τ = torque
µ = magnetic moment
B = magnetic field

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16
Q

Give the equation for precession

A

µ = magnetic moment
t = time
γ = Gyromagnetic ratio
B = magnetic field

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17
Q

Describe the shape of precessional motion for a magnetic dipole in a magnetic field

A

It exhibits gyroscopic motion.
- Pression occurs about B₀
- Spin occurs about µ, J

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18
Q

Give the equation for precession frequency

A

ω = Larmor frequency (frequency of precession)
γ = Gyromagnetic ratio
B = magnetic field

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19
Q

What is the name for the frequency of precession

A

Larmor frequency

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20
Q

What direction is the precession of H-1?

A

Clockwise

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21
Q

Define spin angular momentum

A

An intrinsic property of atoms with spin, described by a vector quantity (J).

It is the product of the nuclear spin quantum number, I, and reduced Planck’s constant, ħ.

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22
Q

Define the nuclear spin quantum number

A

A characteristic property of the nucleus that can take on integer and half-integer values. It is represented by the letter I.

23
Q

Give the equation for the magnitude of spin angular momentum

A

J = spin angular momentum
I = nuclear spin quantum number

24
Q

How many eigenstates (spin states) does spin angular momentum, J, have?

A

2I + 1

25
Q

What is the name for the spin states of spin angular momentum?

A

The azimuthal spin quantum number, mₗ

26
Q

What is the range for the azimuthal spin quantum number?

A

mₗ = I, (I - 1), (I - 2), …, -I

27
Q

What are the spin states for a proton?

A

I = 1/2 so mₗ = ±1/2

28
Q

Give the equation for the z-component of spin angular momentum

A

Jz = z-component
mₗ = spin quantum number

29
Q

What are the z-component values of spin angular momentum for protons?

A
30
Q

Is spin angular momentum quantised?

A

Yes

31
Q

The potential energy of a magnetic moment is the ____ _____ to rotate the magnetic moment in a magnetic field.

A

Work done

32
Q

Give the equation for the energy of a spin magnetic field

A

E = energy
µ = magnetic moment
B = applied magnetic field
γ = Gyromagnetic ratio
J = spin angular momentum

33
Q

When is potential energy lowest for a magnetic moment in a magnetic field?

A

When the magnetic moment is parallel to the magnetic field.

34
Q

What do spin states correspond to energetically?

A

Zeeman energy levels

35
Q

How many Zeeman energy levels do H-1 atoms occupy?

A

2

36
Q

Why is electromagnetic radiation applied in NMR?

A

To cause a transition between the Zeeman energy levels.

37
Q

What frequency is the applied electromagnetic radiation for NMR equal to?

A

The Larmor precession frequency

38
Q

Spins are distributed amongst energy levels according to the _______ ________, depending on the ______ ______ in the system.

A

Boltzmann distribution
Thermal energy

39
Q

Give the equation for the Boltzmann distribution

A

∆E = difference between energy levels
kB = Boltzmann constant
T = temperature
γ = Gyromagnetic ratio
B = applied magnetic field

40
Q

What two factors determine how many protons there are in each energy state?

A
  • Magnetic field
  • Temperature
41
Q

Is the spin-up state high or low energy?

A

Low

42
Q

Is the spin-down state high or low energy?

A

High

43
Q

When are spins detectable with MR?

A

When there are more protons in the spin-up than the spin-down state, generating a net nuclear equilibrium magnetisation (M₀) that is detectable.

44
Q

Give the equation for the number of excess spins in the spin-up state

A

n = spin-up - spin-down (excess spins)
kB = Boltzmann constant
T = temperature
γ = Gyromagnetic ratio
B = applied magnetic field
N = spin-up + spin-down (total number of spins)

45
Q

How many spins will be in the high energy state (spin-down) if the temperature is reduced to 0?

A

Zero spins

46
Q

How many spins would be aligned in the absence of an external magnetic field?

A

There would be no net alignment as the spins are randomly oriented.

47
Q

What is the level of spin alignment in a 1T magnetic field at 310K?

A

~3 ppm aligned

48
Q

Give the equation for the fractional difference in the population of up and down spin states

A

n = spin-up - spin-down (excess spins)
N = spin-up + spin-down (total number of spins)
T = temperature
γ = Gyromagnetic ratio
B = applied magnetic field

49
Q

What is the impact of spins precessing incoherently in an applied magnetic field?

A

There is no net magnetisation in the xy-plane as the spins aren’t in phase and cancel one another out.

50
Q

Give the equation for the net magnetisation vector in the longitudinal direction

A

M₀ = net magnetisation
Σµ = sum of magnetic moments
n = excess up spins
N = total number of spins

51
Q

Give the equation of motion for magnetisation

A

M = magnetisation
t = time
γ = Gyromagnetic ratio
B = applied magnetic field

52
Q

What does the equation of motion for magnetisation represent?

A

A net magnetisation that precesses about B (the direction of the applied magnetic field).

53
Q

Give 4 safety precautions that have to be followed around MRI scanners

A
  • Don’t bring metals close to the scanner
  • No pacemakers
  • No metallic implants (e.g. stents)
  • No neurostimulators
54
Q

Give 4 effects of a static magnetic field

A
  • Sensory effects (e.g. dizziness)
  • Reaction to the noise from generation of the magnetic field
  • Minor changes to chemical reaction rates
  • Peripheral nerve stimulation (PNS)

PHYS4010: Functional Medical Imaging (8 decks)

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