Questions tagged [nuclear-magnetic-resonance]
For questions about Nuclear Magnetic Resonance
56
questions
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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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14 views
Spin-flip of electrons in non-neutral hydrogen atoms in water and fat molecules
What is the Spin-flip of electrons in non-neutral hydrogen atoms in water and fat molecules?
I know there is known spin-flip RF of electrons in neutral hydrogen atoms (hydrogen line).
Thanks,
Cheers
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1answer
28 views
Why would giving a 90 degree Radiofrequency pulse to a ZERO longitudinal magnetisation cause zero transverse magnetisation in MRI?
Let's imagine in my scenario the (a) in the picture above has no net longitudinal magnetization (therefore 0 longitudinal). Why would giving an 90° RF pulse in my scenario not cause the Protons to ...
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1answer
27 views
Can nuclear spin interactions drive nuclear transitions?
The atomic nucleus is often treated as monolithic from the perspective of atoms and molecules, but NMR demonstrates that nuclear states can be affected through external means.
Especially the ...
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5 views
Equilibrium density matrix for a homonuclear spin system in NMR
I'm currently reading this paper. In the paragraph under fig. 3 on page 2, they write:
The equilibrium density matrix for a homonuclear spin system is a sum of $n=5$ terms: $IIIIZ+IIIZI+IIZII+IZIII+...
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1answer
20 views
How to calculate Steady state nuclear magnetization in NMR [closed]
https://en.m.wikipedia.org/wiki/Bloch_equations
In the Bloch Equations M0 is supposed to represent the steady nuclear magnetization. What determines this M0 value and how do you calculate it? Is it ...
2
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2answers
54 views
Parallel and Anti-parallel Protons in NMR
I'm an Alevel Student trying to understand the concept of NMRI, I understand that when an external magnetic field is applied, the protons either line up with (parallel) or line up against (...
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12 views
On the origin of spin-lattice relaxation
According to P.J. Hore in the Oxford Chemistry Primer "Nuclear Magnetic Resonance" p57, 'the dipolar coupling, modulated by molecular motions, causes nuclear spins to experience time-dependent local ...
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12 views
Relation between NMR relaxations times to pure/mixed quantum states
in my quantum studies we were asked to define the relationship between pure/mixed quantum states to T1,T2 relaxation times.
I can't find information about it or perhaps i found it but didn't ...
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23 views
Can multiple NMR spectra integrals be added?
I am new to NMR, so this may be a basic question. Can multiple NMR integrals be added (weighted average)? Attached are NMR integrals of pure propane and pure isobutane. Suppose I have a real chemical ...
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75 views
NMR spectroscopy
I was wondering how many times larger is the magnetic moment of an electron compared to a proton? How come the electrons magnetic moment play no role in NMR and MRI? Edit Electron Spin Spectroscopy ...
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19 views
NMR Bloch equations in 4D?
I'd like to apologize for the purely theoretical question in advance, but I find this an interesting thought-excercise. So basically me and my coworkers asked how the Bloch-equation would look like "...
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1answer
29 views
Why is the image complex in magnetic resonance imaging? (and how does partial Fourier imaging work?)
The MRI image is reconstructed using inverse Fourier transform from k-space data measured during a pulse sequence. According to some online sources the resulting image is complex-valued and usually (...
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1answer
10 views
What is responsible for large ppm shifts in HNMR analysis of paramagnetic compounds?
In H-NMR spectra of paramagnetic metal acetylacetonate compounds M(III)(acac)3, large ppm shifts are observed. This is seen with other organometallic compounds as well. What is the origin of this ...
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36 views
Quantum Mechanical Treatment of the Spin Echo
I'm trying to find the expectation value of the spin in the $y$ direction after applying a $\pi/2$-$\pi/2$ sequence of pulses. In Slichter's Principles of Magnetic Resonance, he does a $\pi/2$-$\pi$ ...
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1answer
49 views
Nuclear relaxation time in absence of a magnetic field
It seems that after reading about how MRI scans work, and it appears that I had a misconception of what T1 relaxation times mean. From what I think I understand now, the T1 relaxation time refers to ...
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37 views
MRI T1 contrast and k-space understanding
I have a couple of questions regarding MRI theory; I have read around but am struggling to find and answer and move on in my understanding; as such any help would be much appreciated:
When designing ...
2
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1answer
239 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
50 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 ...
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1answer
43 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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23 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: ...
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35 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 {...
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1answer
221 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 ...
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1answer
31 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 ...
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20 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....
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2answers
103 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 ...
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1answer
18 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,...
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1answer
132 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
37 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}...
2
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1answer
265 views
How can a frequency-specific interference in MRI be limited to a single stripe on the corresponding image (zipper artifact)?
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 the acquisition of the image, a certain ...
4
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1answer
268 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 ...
3
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1answer
75 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 ...
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1answer
130 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 ...
2
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1answer
188 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
94 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
26 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 ...
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21 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 ...
2
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2answers
160 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
167 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 ...
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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
384 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 ...
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1answer
79 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:
$$\langle M_1(t)\rangle = {\rm tr}\left [\rho(0)\sigma_+^{(1)}\exp\left(i\frac{...
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2answers
500 views
Hyperfine Interaction Hamiltonian
I didn't had any course on hyperfine interactions and now I am having trouble in solving the Anisotropic Hyperfine Hamiltonian. The problem is of matrix dimensions that have to be considered in the ...
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0answers
51 views
magnetism in NMR spectroscopy
How do electrons reduce the effective magnetic field felt by protons? This is the explanation given to chemical shift, how does it work?
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49 views
Nonlinearities arising from linear equations
I have sources that tell me that the Bloch Equations, which describe the magnetization vector in nuclear magnetic resonance, are nonlinear. In vector form, without relaxation, they are: $$ \partial_t \...
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0answers
39 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
46 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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55 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 ...
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1answer
318 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 ...
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287 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 ...
