# Questions tagged [nuclear-magnetic-resonance]

For questions about Nuclear Magnetic Resonance

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### Larmor frequency in NMR for nucleus with spin greater than 1/2

I'm reading the theory about NMR and in most textbooks I can see that the Larmor frequency achived as follow: on the one hand from QM we know that $$\Delta E = \hbar \omega$$ on the other hand, if ...
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### Is precessional frequency of hydrogen nucleus in H-NMR equal to angular frequency of magnetic component EM radiation?

I asked the same question on chemistry stack exchange but got no answer over there. So, I'm posting it here in the hopes that I'll find some sort of answer:) Suppose we have a hydrogen nucleus. Now, ...
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### Why the $T_1$ recovery & $T_2$ decay are independent?

In MRI, I was thinking that the decrease in transverse magnetization results in the recovery of longitudinal magnetization. However, recently, I found it was wrong. I saw a diagram (McRobbie 2014. ...
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### Is the generation of NMR signal due to spontaneous emission?

The usual description of how NMR signal is generated is that the sample has some equilibrium magnetisation along the $z$ axis, this is then flipped into the $x$-$y$ plane by a 90° pulse and there it ...
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1 vote
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### Distribution of relaxation time in a stretched exponential function

I'm fitting a stretched exponential function to a saturation recovery experiment, of the following form: $$I(t)=I_0 \left(1-\exp\left(-\frac{t}{T_1}\right)^\beta\right)$$ Where $\beta$ ranges from ...
1 vote
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### How is a 180° RF pulse in NMR?

A 180° pulse appears to be an RF pulse that is equivalent to rotating the direction of the magnetization vector by exactly 180° in MRI or NMR observations; That is, it may invert the direction of the ...
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1 vote
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### What is the required RF power pulse to flip the nuclei from longitudinal to transverse in MRI scanning?

Picture source: Lesics at t=189 and t=205. I recently visited a friend who just had MRI scan. From his explanation, I have some question about magnetic power applied to him. Consider a B magnetic ...
1 vote
100 views

### In MRI, why are outputs of slice selection and frequency encoding different although both use gradient?

I am a cognitive science graduate student who began to study MRI with a little physics background. Please forgive me if I don't use proper verbs or prepositions. I think I understood slice selection ...
1 vote
195 views

### How does one pick Echo time (TE) in MRI machine?

The definition of echo time (TE) in MRI is the time difference between a 90-degree RF signal and the echo peak, which feels like an intrinsic property of the proton. How can we even control how long ...
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1 vote
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### Why is water bright in a T2 weighted image?

I am new to study MRI. Please understand if some terminologies I use are wrong. This might be a silly question, but I wonder why water is bright in a T2 weighted image. T2 relaxation is also called ...
730 views

### What is 90 or 180 "degree" RF pulse in MRI?

I am studying MRI, specifically spin echoes. Now I kind of understand how magnetic resonance imaging works, but what I'm stuck is the definition of "degree" in MRI. What I thought was that ...
71 views

### Recovering Decay Constant from Fourier Transformed Exponential Decay in NMR

I'm currently in a NMR lab for an undergraduate physics class, and I am attempting to determine the decay constant $\tau$ (e.g. $T_2$) associated with a free induction decay signal. However, our ...
1 vote
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### How is NMR different from hyperfine structure?

Essentially I've confused myself by trying to understand NMR (nuclear magnetic resonance) as the transition between hyperfine levels and I seem to encounter a contradiction. I'll describe my ...
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### Why the angle of nuclear magnetic moment of the proton with an external magnetic field is 54,7°?Why it is not completely parallel to the ext field?

When trying to understand the basics of Nuclear Magnetic Resonance I always found that the angle between the nuclear magnetic moment of the proton and the allied external magnetic field is 54,7° but I ...
1 vote
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### Why does transversal magnetization decay and what is actually being measured in an MRI sequence? [closed]

This may be a few questions disguised as one however this may help uncover what's the missing piece in my understanding. $T1$ characterizes the rate at which longitudinal $M_z$ recovers and $T2$ ...
63 views

### Why isn't amplitude modulation used more often in magnetic resonance technologies? [closed]

Optically pumped magnetometers utilize a visible light carrier wave which is amplitude modulated down to a Larmor frequency of ~1000 Hz. This is in contrast to the vast majority of magnetic resonance ...
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### Magnetic Resonance in quantum mechanics [closed]

Using the identity ($I$) and the Pauli operators ($\sigma_{i}$) as a basis, the Hamiltonian of any two-level system (of basis states $\{|0\rangle,|1\rangle\}$) can be expressed as follows  H =\frac{\...
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### What is the oscillation frequency of the observed/measured free induction decay signal in MRI?

I recognize that many articles attempting to describe the basics of MRI under simplify a lot of technical details. I would like to confirm the following understanding about the free induction decay ...
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### Mechanism of NMR

I am doing research into NMR right now in several different sources, and it seems as if there are two competing models which are used to describe how radio waves can impact nuclear spins. The first ...
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### Spectral density of random fluctuations

In nuclear magnetic resonance relaxation theory, in order to determine relaxation rates from transition probabilities, one needs the spectral density of random magnetic field fluctuations around the ...
52 views

### NMR without static magnetic field

NMR is usually conducted by first aligning nuclei to a strong, constant magnetic field, so that you can apply RF radiation with a magnetic component directly perpendicular to the constant field. ...
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### Proton spin precession and alignment to magnetic field in NMR

Precession due to magnetic field occurs when the magnetic moment of a small coil is proportional to its angular momentum ($\vec{m}=g\vec{L}$). This is due to Euler momentum equation, which for such a ...
310 views

### How are the Bloch equations non-linear?

This question is similar to the following, but I have expanded the question moderately: Nonlinearities arising from linear equations The Bloch equations are described by the following vector equation (...
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### How does MRI distinguish information between in-plane localization and slice selection, despite both using frequency encoding?

A MRI machine can generate 3D image of a human brain. A 3D image have three axis x (horizontal), y (vertical) and z (head-foot). First, a slice along z were selected using frequency encoding. Then, ...
292 views

### What is the function of the RF pulse in NMR?

I am slightly confused about the purpose of the RF (radiofrequency) pulse in NMR. The powerpoint of my course mentioned that an RF pulse perturbs the equilibrium magnetization and sets the nucleus ...
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### Is there any summary of cavity QED and spin resonance related effects and splittings?

I recently started working on NMR-based qubits and I have lots of confusion regarding the definitions of different interactions and energy level splitting phenomenon. I wonder if you know any ...
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### At what power of magnetic resonance does metal embedded in a person start to be pulled?

What is the level (number) of magnetic resonance necessary to provide an unsafe environment for a person who has metal embedded in their upper body? At what level do the metal shards start to be ...
136 views

### NMR/EPR with an RF electric field

Is it possible to perform NMR/EPR spin alignment with an oscillating electric field instead of a magnetic field (so with a sample inside the RF electric field of capacitive plates rather than a RF ...
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1 vote
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### NMR: Why does 180 degree pulse turn around direction of lamor precession?

In descriptions of the spin echo measurement sequence, it says first a $90°$ pulse turns the magnetization sum vector into the transversal plane where it rotates with the Larmor frequency spins of ...
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I have recently started reading about NMR spectroscopy. I know the formula $\mu$ = $\gamma.J$, where J is the angular momentum (intrinsic or spin angular momentum) of the particle. I also know the $\... 2 votes 0 answers 17 views ### Is the Larmor precession of$s\$-orbital electrons constant, heedless of additional electronic orbitals as they get added from one element to another?

Understanding how the frequency required in NMR changes from element to element, even if all of them depend on the Larmor precession of the proton, I was wondering if they same applied to electron ...
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### Why thermal tumbling of molecules does not prevent the establishment of magnetization in NMR?

Given the rapid thermal tumbling of water molecules at room temperature, theoretically speaking, why magnetic thermalization of proton nuclear spins is at all possible? Further, how can nuclear spins ...
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