224 - 25 MRI EXTRA Flashcards
What is nuclear magnetic resonance image based on?
Resonance absorption of electromagnetic radiation by a sample placed in a magnetic field
to observe the effect of nuclear magnetic resonance image
→ What is required?
The use of radio frequency range electromagnetic radiation
The purpose of NMR
- Measure the mobility of membrane components
- The investigation of the structure of macromolecules, such as enzymes
What is spin?
The intrinsic angular momentum of elementary particles (and their composites)
What is gyroscope model?
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
What is the value of spin for nuclei of odd mass number
An integer multiple of ½
The value of spin of nuclei of even mass number if the charge of nucleus even?
They lack spin
The value of spin of nuclei with even mass number if the charge is odd?
The spin quantum number has an integer value
The simultaneous presence of charge and spin of nuclei results in ____, which depends on the magnitude of spin
an intrinsic magnetic moment through rotation
___ results in an intrinsic magnetic moment through rotation, which depends on the magnitude of spin
The simultaneous presence of charge and spin of nuclei
The simultaneous presence of charge and spin of nuclei results in an intrinsic magnetic moment through rotation, which depends on___
the magnitude of spin
Does neutrons possess intrinsic magnetic momentum (MN)
Yes
What is precession of the gyroscope?
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.
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 the ground state of particles
→ The other corresponds to the excited state
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)___
- an external magnetic field (H0)
- two levels
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
the energy levels of the proton (and likewise, electron)
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)___
- the ground state of particles
- the excited state
What does the splitting of energy levels of proton (or electron) depend on?
The magnitude of applied external field
Applying electromagnetic radiation of frequency f0
→ we can ____ between the energy levels of the proton (nuclear spin)
Induce transitions
If we fix a frequency
→ the different nucleus, having different g factors and spins
→ will show (1)___ at different (2)_____
- resonance
- different magnetic field strengths
Is the energy the only difference between the ground state and excited state of a proton in an external magnetic field?
No
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?
The spin and magnetic momentum vectors
The spin and magnetic momentum vectors can describe the intrinsic angular momentum of the proton assume
- The position ____ in the ground state, parallel to ___
- The opposite direction __ in the excited state
- Alpha; external magnetic field
- Beta
The spin and magnetic momentum vectors can describe the intrinsic angular momentum of the proton assume
- The position alpha in the ___ state, parallel to external magnetic field
- The opposite direction beta in the __ state
- ground
- excited
The spin and magnetic momentum vectors can describe the intrinsic angular momentum of the proton assume
- The position alpha in the ground state, parallel to external magnetic field
- 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)___
- precess
- the external magnetic field
- the resonance condition
In the absence of external magnetic field, what happen to nuclear spins?
They point in random directions
In the NMR experiment, the external magnetic field is applied, what happen to nuclear spins?
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
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 ___
the absorption of a portion of the irradiating energy
What is NMR spectrum?
The frequency dependence of the intensity of absorbed electromagnetic radiation
What does the electron cloud surrounding the nuclei influence?
The external magnetic field
What does the electron cloud surrounding the nuclei influence The external magnetic field
→ What does this mean?
The nuclei will experience the a local magnetic field, slight different from external magnetic field
What does chemical shift mean in NMR spectrum?
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
In this PMR spectrum, why are the signals of chemical groups are not simply absorption lines?
Because the interaction with neighboring spins split lines into doublets or quadruplets
Operation of a typical NMR Spectrometer
- The sample placed in the spectrometer surrounded by magnetic field (which is produced by electromagnet)
- The oscillator provides the electromagnetic radiation of desired frequency, which is relayed to the sample by the coupling coil
- 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)
Which mode that modern NMR spectrometers are usually operated in?
Fourier transform Mode
The radio frequency field can be rotated.
→ Therefore, what do scientists used to express this angle?
Pulses of length 90 degree, 180 degree, etc.
The roles of 90 degree pulse
- 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
What is spin-spin relaxation time?
(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
What is FID signal?
The observed signal of the free response of the spin system in the time domain (free induction decay)
What does the spin system do 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”
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?
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
Why do we need to have relaxation time?
Not to distort our results by starting an initial state that doesn’t correspond to the thermal equilibrium
Why do we need to have relaxation time?
Not to distort our results by starting an initial state that doesn’t correspond to the thermal equilibrium
What happen if we have already collected FID?
These signals can be converted to the conventional NMR spectrum of early continuous wave spectrometers, with Fourier transformation (FT)
