Questions tagged [nuclear-magnetic-resonance]

For questions about Nuclear Magnetic Resonance

Filter by
Sorted by
Tagged with
18
votes
3answers
1k views

How specifically does an MRI machine build an image from received radio waves?

Unlike the excellent Wikipedia page on ultrasound imaging, the one on MRI only explains the principle theory behind MRI - that oscillating strong magnetic fields cause water molecules to emit ...
15
votes
2answers
487 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 ...
11
votes
1answer
509 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. $$\frac{\partial M_x}{\partial t}=({\bf M} \times \gamma {\bf H_0})_x-\frac{M_x}{T_2} $$ $$...
4
votes
1answer
111 views

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 ...
4
votes
1answer
345 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 ...
4
votes
1answer
187 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 ...
4
votes
0answers
317 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 ...
3
votes
1answer
54 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 ...
3
votes
1answer
80 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 ...
2
votes
1answer
501 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 ...
2
votes
1answer
160 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
votes
1answer
31 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 ...
2
votes
1answer
230 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
votes
1answer
1k views

What is Rabi nutation in NMR?

What is the mathematical and physical significance of Rabi Nutation in terms of NMR?
2
votes
1answer
332 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 ...
2
votes
1answer
131 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 $\...
2
votes
2answers
191 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 ...
2
votes
1answer
50 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 ...
2
votes
0answers
165 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 ...
1
vote
1answer
57 views

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 ...
1
vote
1answer
63 views

Phonons and radiation [closed]

I have heard (or misheard) from a reputable Theoretical Physicist from Bell Labs who specialized in Quantum Mechanics that random photon activity can cause decoherence of an entangled or under ...
1
vote
2answers
229 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 (...
1
vote
1answer
31 views

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, ...
1
vote
1answer
84 views

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 ...
1
vote
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 ...
1
vote
1answer
150 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 ...
1
vote
1answer
175 views

Time-domain NMR or: When is the Fourier-Transformation not appropriate?

My question has two parts: One is general and has to do with the Fourier-Transformation, one has to do with Time-Domain NMR. Both parts are interlinked, of course. I tried to find out, why people do ...
1
vote
1answer
281 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 ...
1
vote
0answers
17 views

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 ...
1
vote
0answers
13 views

$j$-$j$ 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 ...
1
vote
2answers
71 views

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 ...
1
vote
1answer
35 views

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 ...
1
vote
0answers
19 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
1
vote
1answer
37 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 ...
1
vote
1answer
54 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 ...
1
vote
0answers
47 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 ...
1
vote
1answer
41 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
vote
1answer
320 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 ...
1
vote
0answers
21 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....
1
vote
0answers
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 ...
1
vote
1answer
100 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{...
1
vote
0answers
52 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
vote
0answers
50 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
vote
0answers
42 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 ...
1
vote
0answers
59 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 ...
1
vote
1answer
510 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 ...
0
votes
1answer
14 views

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{...
0
votes
1answer
35 views

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, ...
0
votes
1answer
33 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 (...
0
votes
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,...