Questions tagged [nuclear-magnetic-resonance]
For questions about Nuclear Magnetic Resonance
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Does the RF magnetic field have to be uniformly constant for a coherent EPR signal
Consider a loop gap resonator for electron paramagnetic resonance which has static (but sweepable) magnetic field in one direction, "x", and a GHz RF magnetic field in a direction "z&...
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Larmor precession with an oscillating field?
With a non-polar molecule like CO2, presumably Larmor precession doesn't apply.
However, CO2 has a mode of vibration that induces an oscillating dipole moment.
Could something similar to Larmor ...
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Does a moving atom with a nuclear magnetic moment generate an electric field?
I have read that moving ions generate a magnetic field as it moves.
Similarly, is this also true regarding the nuclear magnetic moments of the atom? In other words, would a moving atom with a nuclear ...
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Why is water diamagnetic, but water protons align with external field in NMR?
I recently re-learned today that water is diamagnetic. I don't believe I totally understand why, but I will accept it as true.
However, I remember that in NMR of water, the protons of water form ...
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An embarassing question about photon power, Hamiltonians, and converting units
I am a hapless experimentalist, and desperate for a bit of advice.
I am trying to do a spin-density calculation building on some of the ideas contained in this paper. In brief, it's describing a ...
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Working of MRI in detection of tissues for imaging
why we consider the rotational axis of proton under the action of magnetic field in MRI not electron?
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Why is a CPMG sequence more resilient to errors in the pulse amplitudes than a CP sequence?
In the context of NMR (or in general qubits nowadays), a CP sequence is a refocussing sequence that looks like X/2 - X^n - X/2. A CPMG sequence instead is X/2 - Y^n - X/2. This change of axes is in ...
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What is the "envelope" of the magnetic field, in NMR?
Let $B_1$ be RF pulse.
According to the following lecture, $B_1^e$ represents the "envelope" of $B_1$ and under the labo-frame coordination, following be satisfied;
$B_1\left(t\right)=B_1^e\...
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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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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 ...
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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 ...
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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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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 ...
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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 ...
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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 ...
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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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Berry phase for nuclear magnetic resonance
I am sure that I am making some dumb mistake somewhere here so please bear with me. I have the Hamiltonian for $B>0$
\begin{equation}
\hat{H}(t) = B[\underbrace{\cos(\theta) \hat{\sigma}_z}_{\hat{H}...
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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 ...
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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 $T2$ ...
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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 Bloch sphere visualisation
As seen on wikipedia, (https://en.wikipedia.org/wiki/Two-state_quantum_system#Evolution_in_a_time-dependent_field:_Nuclear_magnetic_resonance)
a spin-$\frac{1}{2}$ particle in magnetic field $${\...
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Magnetic Resonance in quantum mechanics [closed]
Using the identity ($I$) and the Pauli operators ($\sigma_{i}$) as a basis, the Hamiltonian of any two-level system (of basis states $\{|0\rangle,|1\rangle\}$) can be expressed as follows
$$
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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Magnetic field strength of EM radiation
In the study of nuclear magnetic resonance, I have been assuming that the magnetic field component of the radio frequency radiation is what causes the nuclear spins to deviate from their equilibrium ...
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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 ...
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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 ...
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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, ...
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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 ...
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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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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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Why gyromagnetic ratios of different nuclei are different?
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 $\...
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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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Is there an equivalent Larmor precession that is non-magnetic in nature?
Can the magnetic moment of a particle be manipulated without magnetic fields? Could one accomplish this with electromagnetic radiation or even "Atom Lasers"?
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Integration of Bloch equation in magnetic resonance
From Bloch equation we have
\begin{equation}\label{bloch_01}
\tag{1}
\frac{d M_z}{dt} = \frac{M_0-M_z}{T_1}
\end{equation}
from there we can integrate and we get
\begin{equation}\label{bloch_02}
\tag{...
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is room temperature quantum (qubit) nuclear magnetic resonance possible?
I know it is possible to do room temperature NMR. Not just that but one can also use the earth's magnetic field for the nuclei to precess about. If done this way, one gets precession at about the KHz ...
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What does it mean that the Cauchy probability distribution is connected to the solution of the differential equations of forced resonance?
I have read this (or something like this) in Wikipedia, and found some modelling of inhomogeneities in magnetic fields in clinical magnetic resonance imaging (MRI) through the Cauchy distribution, ...
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Short pulses in NMR - what is their shape?
In the Wikipedia article Nuclear magnetic resonance, section Fourier-transform spectroscopy, it says the following:
Fourier-transform spectroscopy
Most applications of NMR involve full NMR spectra, ...
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Effects of a rotation on a Hamiltonian of a 1/2-spin particle in a magnetic field [closed]
The problem: find how the Hamiltonian $$ H= -\frac{\hbar\omega_0}{2}Z-\frac{\hbar \omega_1}{2}(\sigma_+e^{i\omega t}+\sigma_- e^{-i\omega t}) $$ where $\sigma_{\pm}=\frac{1}{ 2}(X\pm i Y)$ changes ...
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$j$-$j$ coupling interaction in Magnetic Resonance Spectroscopy
I am studying Magnetic Resonance Spectroscopy and I have some difficulties in understanding the j-j coupling interaction. What does actually happen from the physical point of view to the electronic ...
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Do protons and electrons actually precess?
I know that protons and electrons do not actually spin, although they have the property of spin.
I was learning about MRI. I was introduced to the idea that you have the spin of the proton in the ...
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Tip angle in NMR
Tipping the magnetisation $\vec{M}$ with a $\vec{B}_1$ field for the time $\tau$, results in a tip angle of $\alpha = \omega \tau$ where $\omega$ is the frequency of the $\vec{B}_1$ field. I think I ...
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Angular momentum and magnetic moment [duplicate]
I have just started studying MRI physics and was reading F.Bloch’s paper on Nuclear Induction.
https://doi.org/10.1103/PhysRev.70.460
In page 463, it is mentioned,
To obtain this variation does not ...
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Why nuclear spin is ignored in Stern-Gerlach experiment?
I can't sure what isotopes of silver(107 or 109) was used.
But Silver has non-zero nuclear spin since the number of proton and neutron are not even.
Since we use Silver atom not electron in SG ...
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Why do 180 degree NMR pulses not violate Einsteins laws for absorption and emission?
So, in Laser theory I learned that a two-level laser is not possible, because it would violate Einsteins equations and the Boltzmann distribution, which in a nutshell say that I cannot cause ...
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