Questions tagged [nuclear-magnetic-resonance]
For questions about Nuclear Magnetic Resonance
2
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1answer
40 views
Why do some protons align against the magnetic field?
I was learning about proton NMR (Nuclear Magnetic Resonance Spectroscopy) which is where protons (with their own spins) are subjected to an external magnetic field and a radio frequency is applied to ...
3
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1answer
21 views
Does diffusion MRI measure diffusion or osmosis?
I am trying to understand the physical property which is measured in diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI). I read that these methods estimate the apparent diffusion ...
0
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1answer
41 views
What is the true way to determine time parameters from semilog graph?
I have experimental nuclear magnetic resonance data that describe T2-relaxation of the nuclei in the sample of interest. The experimental points obey bi-exponential dependence: I = I1*exp(-t/T2_1) + ...
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0answers
19 views
NMR: Link between relaxation time and Chemical shift
I have been taught NMR in both my physics and chemistry high school classes. Everything lines up until they get into how we detect different chemical environments in the compound.
Chemistry class: ...
1
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0answers
33 views
Origin of 2π normalization factor in chemical $J$-coupling compared to the Heisenberg model
In chemistry, particularly the field of NMR spectroscopy, the interaction between two (nucleic) spins (or so I guess?) is governed by the Hamiltonian:
\begin{align}
\mathcal{H}=2\pi\cdot J_{ij}{\vec {...
1
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1answer
95 views
Spin precession for Rabi oscillations : interpretation with magnetic field in rotating frame
The model considered
Consider an atom modeled by a two level system of energy $\hbar \omega$. We assume this atom is interacting with an electric field through electric-dipole interaction.
The full ...
0
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1answer
28 views
How does an magnetic resonance guided focused ultrasound (MRgFUS) machine work?
As a medical application, magnetic resonance guided focused ultrasound (MRgFUS), is new I the treatment of some parkinsonian diseases, prostate cancer, none problems, and more. However, I am not sure ...
1
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0answers
28 views
How is a NMR spectrum obtained?
I am reading about NMR, and from what I'm understanding it should give information on the transition energies in the spectrum of the nuclear spin in a magnetic field.
What I don't understand is how ...
0
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0answers
12 views
Relaxation time of Proton in NMR and sharper peak relationship [duplicate]
I wanted to ask a question about proton NMR.
I understand that NMR involves the idea of an applied magnetic field to a magnetic nuclei e.g. $^1H$ and resulting in $\alpha~$ and $\beta$ states, where ...
1
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0answers
16 views
Continuous NMR Coil arrangement and signal generation
So I am trying to understand how a signal is being produced in CW NMR and I cam across this online
An it talks about how the in CW the spectrum depends only the current being induced in the x-y plane....
0
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2answers
55 views
Why do the matrices in k-space and the final MRI image have to match?
Naturally, there is no correspondence pixel-to-pixel between Fourier space (k-space) and the final 2D image of an MRI - k-space stores the Fourier coefficients, hence each pixel in it affects the ...
0
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1answer
16 views
Dose attenuation decrease frequency
What cause the transveres decay in nmr? From wiki I have an understanding that it has somthing to do with decoherence which is caused by spin of one atom effecting anouther.
That my basic understand,...
0
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1answer
44 views
How does a gradient elicit a RF signal from the stimulated tissue in MRI?
I understand the idea of spatial encoding afforded by the application of a readout gradient along one of the planes (frequency direction) in MRI. In typical 2D image generation, there is also a phase ...
0
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1answer
35 views
How can I calculate the total rotation a detuned pulse will apply a nuclear spin?
I'm trying to model the effect a radiofrequency pulse will have on a nuclear spin at different detunings. The pulse has a sech lineshape, a pulse area (time integral of the pulse envelope) of $\frac{π}...
0
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0answers
79 views
In which specific point of the imaging-acquisition MRI process does a zipper artifact occur?
On this post I was trying to prove that the so-called herringbone or spike MRI artifact on a given example could be traced to a specific point(s) in Fourier space ("k-space").
The idea is that during ...
4
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1answer
133 views
How to identify an MRI artifact on Fourier space? [closed]
I am trying to find the frequency of the artifact on the MRI image of the knee below both manually and with ImageJ:
As you can see the artifact results in a bar pattern extending horizontally along ...
0
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0answers
83 views
Difference between Coherence Transfer, Polarization Transfer & Population transfer
Previously I asked some questions on quantum coherence and the answer helped me to clear the concept. I did some more literature review to understand the basic facts in relation to density matrix. ...
3
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1answer
60 views
Mathematical term for the on/off gradient functions in MRI imaging
The slice selection gradients, as well as the phase and frequency, in MRI imaging are traditionally represented by on/off box or rectangular symbols:
or
My question is what is the mathematical name ...
0
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0answers
19 views
Averaging a tensor in NMR Hamiltonian for infinite speed limit MAS
I'm trying to figure out if there is a simple way to compute what the average Hamiltonian for an NMR experiment at ideal infinite speed MAS would look like. I keep failing, but I'm not sure why. I'll ...
2
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1answer
84 views
From K-space to wavelets in compressed SENSE MRI (cSENSE)
In compressed sensing MRI (cSENSE MRI) technology the idea seems to entail sampling from the Fourier domain (k space) in a way that, when transformed to the wavelet domain ("sparsification"), the ...
1
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1answer
155 views
Heisenberg's uncertainty principle for MRI
In the nuclear magnetic resonance imaging (MRI), the spatial resolution and temporal resolution can not be arbitrarily reduce simultaneously. What would be a simple inequality of the Heisenberg's ...
2
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1answer
79 views
How does spin flip take place?
An electron in a constant magnetic field, say $B_z~ \hat{z}$ starts precessing about $\hat{z}$-direction. One can flip the spin by providing a time-varying field $B_x \sin(\omega t)~ \hat{x}$ in the $\...
0
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1answer
24 views
Amplitude of a signal from it's function
If I have the equation of a light pulse in the form
$$L(ω)=\frac{1}{π}\frac{\frac{1}{2}Γ}{((ω−ω_0)^2+(\frac{1}{2}Γ)^2)}$$
where $\Gamma$ is the linewidth of the pulse and $\omega_0$ is its resonant ...
1
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0answers
20 views
Effect of a Lorentzian pulse on a non-resonant spin particle
I'm looking into rotation of a nuclear spin particle using a pulse with a Lorentzian lineshape. If the pulse has an area of $\frac{\pi}{2}$ and the nuclear spin frequency is on resonance with the ...
1
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1answer
117 views
Why are spins initially coherent after 90 degree pulse in NMR?
In NMR we apply a 90 degree radio frequency pulse to the sample. This causes magnetization vector to fall into transverse plane. Then the relaxation of initial phase coherence occurs. Why are the ...
3
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1answer
125 views
How to explain spin-spin relaxation in MRI/NMR in terms of quantum mechanics?
I noticed two approaches to explanation of MRI/NMR. The most popular classical approach exploits the notion of magnetization vector and Larmor precession. Everything then is described as oscillations ...
0
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1answer
40 views
Modelling a radiofrequency pulse
I'm looking into NMR at the moment and am trying to work out a way of modelling the action of a radiofrequency pulse on nuclear spins. Specifically, if I apply a pulse to rotate the spin by $\pi/2$ I ...
0
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1answer
205 views
Why do nuclei precess in magnetic fields?
I understand that a classical bar magnet will precess about the axis of an external magnetic field. Whilst researching NMR, I have read that nuclei with half-integer spin which are subject to an ...
1
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1answer
76 views
Distributive property of tensor product
I have a homework problem in nuclear magnetic resonance. After a bunch of calculations, I have arrived at the expression:
$$\langle M_1(t)\rangle = {\rm tr}\left [\rho(0)\sigma_+^{(1)}\exp\left(i\frac{...
0
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2answers
330 views
Hyperfine Interaction Hamiltonian
I didn't had any course on hyperfine interactions and now I am having trouble in solving the Anisotropic Hyperfine Hamiltonian. The problem is of matrix dimensions that have to be considered in the ...
1
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0answers
45 views
magnetism in NMR spectroscopy
How do electrons reduce the effective magnetic field felt by protons? This is the explanation given to chemical shift, how does it work?
1
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0answers
48 views
Nonlinearities arising from linear equations
I have sources that tell me that the Bloch Equations, which describe the magnetization vector in nuclear magnetic resonance, are nonlinear. In vector form, without relaxation, they are: $$ \partial_t \...
1
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0answers
33 views
NMR Chemical shift and the electron distribution
We explain the position of a hydrogen environment as being downfield if it is deshielded by its proximity to an electron withdrawing group. The electrons around the nucleus protect said nucleus from ...
2
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1answer
42 views
How to excite high spin nuclear state from ground state?
For example, the ground state of a nuclei is $0^+$, and we can excite $1^-$ state with a circular polarized gamma photon, which has a spin angular momentum $1\hbar$. This satisfies the selection rule ...
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0answers
48 views
is alternating field really needed for NMR/ESR?
Consider a two level system - say a single spin-1/2 electron in a magnetic field. To make transition between the spin-split levels the usual advice is to apply an alternating transverse magnetic field ...
0
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1answer
232 views
In Nuclear Magnetic Resonance what is the Rotating Frame?
My understanding is that there's an initial precession frequency ($\omega_0$) about the direction of magnetization ($z$). Then when you excite the nucleus into the spin state with the radio frequency ...
3
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0answers
228 views
Good books on NMR
I need some help in finding a good book on NMR spectroscopy that focuses more on the physical aspects of the phenomenon and not so much on the chemical application. All the books I've read on that ...
1
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1answer
1k views
What is Rabi nutation in NMR?
What is the mathematical and physical significance of Rabi Nutation in terms of NMR?
1
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1answer
236 views
NMR rotating frame
I'm reading about a linearly polarized field (in the context of NMR). The field is given by
$$ {\bf H_{lin}}=2H_1({\bf i}\cos(\omega_zt)).$$
This can be created by having a pulse field plus its ...
11
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1answer
478 views
Nuclear Magnetic Resonance (NMR) Conceptual Questions
Let $M$ be the magnetic moment of a system. Below are the Bloch equations, including the relaxation terms.
$$\frac{\partial M_x}{\partial t}=({\bf M} \times \gamma {\bf H_0})_x-\frac{M_x}{T_2} $$
$$...
2
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0answers
155 views
Correlation function in relaxation in NMR
I am new in this community, I am from a chemistry background. I want to know a detailed solution of a density matrix for a singlet state using the concept of spin lattice relaxation in NMR. I will ...
14
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2answers
437 views
Decoherence and measurement in NMR
It seems that the Bloch equations, or a suitable generalization thereof, are enough to phenomenologically model the measurement process in NMR. Has anyone attempted a fully quantum mechanical model ...
