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Biophysics 2 (Theory) > 224 - 25 MRI EXTRA > Flashcards

224 - 25 MRI EXTRA Flashcards

1
Q

What is nuclear magnetic resonance image based on?

A

Resonance absorption of electromagnetic radiation by a sample placed in a magnetic field

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2
Q

to observe the effect of nuclear magnetic resonance image

→ What is required?

A

The use of radio frequency range electromagnetic radiation

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3
Q

The purpose of NMR

A
  • Measure the mobility of membrane components
  • The investigation of the structure of macromolecules, such as enzymes
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4
Q

What is spin?

A

The intrinsic angular momentum of elementary particles (and their composites)

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5
Q

What is gyroscope model?

A

A model that derives the existence of the intrinsic angular momentum of a particle or the nucleus by supposing a rotational motion of the particle

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6
Q

What is the value of spin for nuclei of odd mass number

A

An integer multiple of ½

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7
Q

The value of spin of nuclei of even mass number if the charge of nucleus even?

A

They lack spin

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8
Q

The value of spin of nuclei with even mass number if the charge is odd?

A

The spin quantum number has an integer value

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9
Q

The simultaneous presence of charge and spin of nuclei results in ____, which depends on the magnitude of spin

A

an intrinsic magnetic moment through rotation

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10
Q

___ results in an intrinsic magnetic moment through rotation, which depends on the magnitude of spin

A

The simultaneous presence of charge and spin of nuclei

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11
Q

The simultaneous presence of charge and spin of nuclei results in an intrinsic magnetic moment through rotation, which depends on___

A

the magnitude of spin

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12
Q

Does neutrons possess intrinsic magnetic momentum (MN)

A

Yes

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13
Q

What is precession of the gyroscope?

A

It describes a change in the direction of the axis of a rotating object, so in this case a change in the spin axis of the gyroscope.

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14
Q

What happen during Zeeman spitting?

A

In the presence of an external magnetic field (H0), the interaction of the magnetic moments and the field cause the energy levels of the proton (and likewise, electron) to split into 2 levels

→ One of which corresponds to the ground state of particles

→ The other corresponds to the excited state

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15
Q

Zeeman splitting

In the presence of (1)____, the interaction of the magnetic moments and the field cause the energy levels of the proton (and likewise, electron) to split into (2)___

A
  1. an external magnetic field (H0)
  2. two levels
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16
Q

Zeeman splitting

In the presence of an external magnetic field (H0), the interaction of the magnetic moments and the field cause___ to split into 2 levels

→ One of which corresponds to the ground state of particles

→ The other corresponds to the excited state

A

the energy levels of the proton (and likewise, electron)

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17
Q

What happen during Zeeman spitting?

In the presence of an external magnetic field (H0), the interaction of the magnetic moments and the field cause the energy levels of the proton (and likewise, electron) to split into 2 levels

→ One of which corresponds to (1)___

→ The other corresponds to (2)___

A
  1. the ground state of particles
  2. the excited state
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18
Q

What does the splitting of energy levels of proton (or electron) depend on?

A

The magnitude of applied external field

19
Q

Applying electromagnetic radiation of frequency f0

→ we can ____ between the energy levels of the proton (nuclear spin)

A

Induce transitions

20
Q

If we fix a frequency

→ the different nucleus, having different g factors and spins

→ will show (1)___ at different (2)_____

A
  1. resonance
  2. different magnetic field strengths
21
Q

Is the energy the only difference between the ground state and excited state of a proton in an external magnetic field?

A

No

22
Q

The energy is the only difference between the ground state and excited state of a proton in an external magnetic field

→ What else can describe the intrinsic angular momentum of the proton?

A

The spin and magnetic momentum vectors

23
Q

The spin and magnetic momentum vectors can describe the intrinsic angular momentum of the proton assume

  1. The position ____ in the ground state, parallel to ___
  2. The opposite direction __ in the excited state
A
  1. Alpha; external magnetic field
  2. Beta
24
Q

The spin and magnetic momentum vectors can describe the intrinsic angular momentum of the proton assume

  1. The position alpha in the ___ state, parallel to external magnetic field
  2. The opposite direction beta in the __ state
A
  1. ground
  2. excited
25
Q

The spin and magnetic momentum vectors can describe the intrinsic angular momentum of the proton assume

  1. The position alpha in the ground state, parallel to external magnetic field
  2. The opposite direction beta in the excited state

→ At the same time, both magnetic momentum vectors (1)___ along a cone that is parallel to (2)____ with the frequency coming from (3)___

A
  1. precess
  2. the external magnetic field
  3. the resonance condition
26
Q

In the absence of external magnetic field, what happen to nuclear spins?

A

They point in random directions

27
Q

In the NMR experiment, the external magnetic field is applied, what happen to nuclear spins?

A

The nuclear spins in the parallel state alpha, while other fall in opposite state beta (more ordered state)

→ precess around the axis of external magnetic field

28
Q

In the NMR experiment, the sample is placed in a homogeneous external magnetic field

→ By tuning the frequency of the electromagnetic radiation, we bring about ___

A

the absorption of a portion of the irradiating energy

29
Q

What is NMR spectrum?

A

The frequency dependence of the intensity of absorbed electromagnetic radiation

30
Q

What does the electron cloud surrounding the nuclei influence?

A

The external magnetic field

31
Q

What does the electron cloud surrounding the nuclei influence The external magnetic field

→ What does this mean?

A

The nuclei will experience the a local magnetic field, slight different from external magnetic field

32
Q

What does chemical shift mean in NMR spectrum?

A

The effect in which the electron cloud surrounding the nuclei influence the external magnetic field

→ changes the actual resonance frequency of the given nucleus and causes the NMR line to be shifted slightly

33
Q

In this PMR spectrum, why are the signals of chemical groups are not simply absorption lines?

A

Because the interaction with neighboring spins split lines into doublets or quadruplets

34
Q

Operation of a typical NMR Spectrometer

A
  1. The sample placed in the spectrometer surrounded by magnetic field (which is produced by electromagnet)
  2. The oscillator provides the electromagnetic radiation of desired frequency, which is relayed to the sample by the coupling coil
  3. The NMR signal coming from the sample → collected by the detector coil (connected to highly selective radio receiver)

(The magnetic field strength is changed slowly to satisfy the resonance condition)

35
Q

Which mode that modern NMR spectrometers are usually operated in?

A

Fourier transform Mode

36
Q

The radio frequency field can be rotated.

→ Therefore, what do scientists used to express this angle?

A

Pulses of length 90 degree, 180 degree, etc.

37
Q

The roles of 90 degree pulse

A
  • Important
  • Macroscopic magnetization is rotated exactly into x - y plane

→ after this pulse the M vector will induce changing electrical voltage or Emf in the detector coil

→ at the end of 90 degree excitation pulse → all spins will point in the direction of the y axis of the revolving coordinate system

→ start rotating synchronized in phase

38
Q

What is spin-spin relaxation time?

A

(After applying 90 degree pulse, the macroscopic magnetization rotates into the x - y plane)

After the pulse ceases, the process of spin-spin relaxation induce an exponentially decaying voltage signal in the standing detector coil

→ The detected signal is the free response of the spin system

39
Q

What is FID signal?

A

The observed signal of the free response of the spin system in the time domain (free induction decay)

40
Q

What does the spin system do after switching off the external electromagnetic field used for excitation?

A

the spin system tries to give off the “excess” energy, transmitting to the environment, the “lattice”

41
Q

After switching off the external electromagnetic field used for excitation, the spin system tries to give off the “excess” energy, transmitting to the environment, the “lattice”

→ What is spin-lattice relaxation time?

A

The macroscopic magnetization returns to its equilibrium state, with growing amplitude in the z direction

→ the process is described by an exponential time course, with characteristics time T1 depending in the sample which is called spin-lattice relaxation time

42
Q

Why do we need to have relaxation time?

A

Not to distort our results by starting an initial state that doesn’t correspond to the thermal equilibrium

42
Q

Why do we need to have relaxation time?

A

Not to distort our results by starting an initial state that doesn’t correspond to the thermal equilibrium

43
Q

What happen if we have already collected FID?

A

These signals can be converted to the conventional NMR spectrum of early continuous wave spectrometers, with Fourier transformation (FT)

Biophysics 2 (Theory) (13 decks)

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