Questions tagged [nuclear-magnetic-resonance]

For questions about Nuclear Magnetic Resonance

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8 views

What affects spin-lattice and spin-spin relaxation times?

I'm performing NMR on common substances like mineral oil, water, and a copper sulfate solution. I know that the ions cause low spin-lattice and spin-spin relaxation times in copper sulfate solution. ...
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17 views

Data augmentation in $k$-Space

I am working on denoising data in $k$-space for MRI (magnetic reasonance imaging) using Convolutional neural networks, and I am wondering what would be some suitable data augmentation techniques ...
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Ramsey technique and spin echos

Assuming we use a laser of frequency very close to resonance, in the Ramsey technique (say for 2 level atoms) the $\pi/2$ pulse would put the Bloch vector in the equatorial plane, along the y axis, ...
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33 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, ...
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22 views

Visualizing dynamics of a two-level atom on the Bloch Sphere

I am trying to use the Bloch Sphere to understand how applying resonant sequences of $\pi/2$ and $\pi$ pulses changes the state of a two-level system initially in the ground state. Specifically, I am ...
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25 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, ...
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53 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 ...
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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 ...
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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 ...
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62 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 ...
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26 views

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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80 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 ...
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Was NMR/ESR spin flip-flop line ever measured?

Let $a$,$b$ be two unlike spins in a uniform magnetic field and RF excitation, and let $B_0$ be the magnetic field for which some transition energies of the spins coincide $E_a^{i,j}(B_0)=E_b^{k,l}(...
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Q-Populations difference using Boltzmann distribution

Question- Calculate the difference in the populations of the two nuclear spin states of $1H$ nuclei in a magnetic field of $10T$ at a temperature of $298K$ Answers to chose from (it’s a multiple ...
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101 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 ...
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33 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 ...
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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
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79 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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30 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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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 ...
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2answers
199 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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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 ...
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133 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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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 (...
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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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40 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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52 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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45 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 ...
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1answer
474 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 ...
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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 ...
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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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28 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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38 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
301 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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33 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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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....
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164 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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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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388 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 ...
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1answer
39 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}...
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1answer
327 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 ...
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336 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 ...
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1answer
79 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
150 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 ...
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1answer
224 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 ...
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1answer
123 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 $\...
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27 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 ...
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2answers
184 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 ...
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183 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 ...