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W/Biophysics > 34. Radio spectroscopies > Flashcards

34. Radio spectroscopies Flashcards

1
Q

What did the stern gerlach experiment prove?

A

quantization of e- spin in 2 orientations

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2
Q

What happens to the dipole in a homogenous magnetic field?

A

opposite sides of a dipole cancel each other out

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3
Q

Why were silver atoms used in the S-G experiment?

A

because AG atoms have one single outer shell electron, so we can study the properties of 1 electron

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4
Q

When does the magnetic moment emerge?

A

when there is a charge and a net spin

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5
Q

What is magnetic resonance?

A

Resonance-absorbtion of EM energy by a material placed in a magnetic field

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6
Q

Magnetic moment formula

A

M = gamma * L
gamma : gyromagnetic ratio
L : nuclear spin (quantum number)

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7
Q

What is the gyromagnetic ratio?

A

ratio of magnetic moment and angular momentum

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8
Q

What is the Zeeman effect?

A

splitting of a spectrum line into several components by the application of a magnetic field. Distortion of e- orbitals by the magnetic field

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9
Q

What is angular momentum?

A

the quantity of rotation of a body. Product of its moment of inertia (a tendency to remain unchanged) and its angular velocity

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10
Q

In how many levels does each E level split into?

A

2l+1 levels (E of atom changes when put in a magnetic field)

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11
Q

What is a precession?

A

in a magnetic field, protons spin around the long axis of the primary magnetic field (change in the orientation of the rotational axis)

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12
Q

What happens to the protons when there is no external magnetic field applied?

A

They are oriented randomly (still have a spin bc of their charge)

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13
Q

What is the precession rate?

A

The rate of precession of the magntic moment of the proton around the external magnetic field

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14
Q

Which relationship does the Larmor equation describe?

A

Relationship between rate of precession (larmor frequency) and strength of magnetic field

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15
Q

What is paramagnetism?

A

magnetism emerging in external magnetic field (caused by dipole orientation)

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16
Q

What is net magnetization (also called macroscopic magnetization)?

A

Vector sum of parallel and antiparallel orientation i

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17
Q

What determines the ratio of low and high energy spin populations?

A

Boltzman distribution : Nantipar/Npar = e^(-dE/kT)

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18
Q

Which electromagnetic radiations are employed for resonance?

A

radiofrequencies (electromagnetic)

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19
Q

What is resonance?

A
  • A perturbation of the nuclear spin orientation will occur when an oscillating magnetic field is applied whose frequency closely matches the larmor precession frequency
  • applying an EM radiation of a certain freq, we can induce transitions between the E levels of the proton
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20
Q

What is the basic process of NMR?

A

Magnetic pulses are applied to excite transitions between Zeeman energy levels, and then they relax

21
Q

What are T1 and T2 relaxation?

A

T1 : relaxation in long axis (spin-lattice)

T2 : relaxation in transverse axis (spin-spin)

22
Q

What is relaxation?

A

an excited magnetic moment back to equilibrium on the Z axis

23
Q

What happens during T2 relaxation?

A

After the 90° excitation pulse all spins will be pointing in the Y axis direction, and rotating in synchronized phase.
Spin vectors will disperse and distribute themselves uniformly in the the plane and lose their phase.

24
Q

What does T2 relaxation time depend on?

A

on interaction between elementary magnets (spins, protons)

25
Q

What is the net magnetization at T2?

A

0

26
Q

What happens during T1 relaxation?

A

relaxation of the Z-axis vectorial component towards the direction of the external magnetic field. Give up the extra energy to their surroundings : the lattice.

27
Q

What does T1 time depend on?

A

on the interaction between elementary magnet and its environment

28
Q

What is FID?

A

Free induction decay. Magnetic moments dephase due to magnetic field inhomogeneity, creating a damped sine wave (Mr signal does not continue forever)

29
Q

What is NMR spectroscopy used for?

A

determining the content and purity of a sample, as well as its molecular structure

30
Q

What does NMR measure?

A
  • measures local magnetic field around a nuclei by measuring resonance frequency
  • measures energy emitted when the spin returns to its base level
31
Q

What is the NMR spectrum?

A

intensity of absorbed radiation as a function of frequency

32
Q

What does ESR stand for?

A

electron spin resonance

33
Q

What is the area under the NMR line proportional to?

A

proportional to the number of absorbing nuclei

34
Q

What does the energy gap bw parallel and antiparallel correspond to?

A

corresponds to radiofrequency

35
Q

What is “chemical shift”?

A
  • electron cloud surrounding nuclei influences the external magnetic field, so the nuclei will experience a slightly different local magnetic field than the external.
  • changes the resonance frequency of given nucleus : NMR lines shift slightly
36
Q

What does ESR measure?

A

the absorbtion of microwave radiation corresponding to the energy splitting of an unpaired electron when it is placed in a strong magnetic field

37
Q

What is the ESR spectrum?

A

intensity of EM radiation as a function of magnetic field

38
Q

What are the differences in magnetic field and frequencies bw ESR and MSR?

A

ESR : lower magnetic field, higher frequency radiation

39
Q

How does space encoding work?

A

using phase shift to determine the contribution of different voxels

40
Q

How does proton density contrast work?

A

signal is weighted to reflect the actual density of protons, since nuclear magnetic resonance is the basis of MRI

41
Q

What is proton density contrast ideal for?

A

for distinction between fluid, cartilages… so for joints

42
Q

What does T1 reflect? How does this affect the brightness/darkness?

A

T1 reflects time it takes for regrowth of Mz signal. Tissues with short T1 recover more quickly. Their Mz value is larger so it is a stronger signal (brighter)

43
Q

What does T2 reflect? How does this affect the brightness/darkness?

A

T2 reflects time it takes for MR signal to decay in the transverse plane. Short T2 means signal decays rapidly. Shorter T2s have smaller signals and appear darker.

44
Q

What is pixel brightness or darkness related to?

A

To magnitude of MR signal detected

45
Q

In T1 weighted images, which will be darker, and which will be brighter?

A

long T1 materials will be darker

46
Q

In t2 weighted images which will b darker and which will be brighter?

A

Long T2 materials will be brighter

47
Q

How do we get T1 weighted image?

A

short TR/ short TE

48
Q

How do we get T2 weighted image?

A

long TR/ long TE

49
Q

How do we get PD weighted image?

A

long TR / short TE

W/Biophysics (24 decks)

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