Questions tagged [mri]
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urgent: MRI calculations question
I have a biomedical imaging exam tomorrow and I'm struggling quite a bit with this question below (from b-d). I was hoping someone could help answer these questions or at. I'll describe my approach to ...
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1answer
48 views
Machine learning for denoising MRI images
I'm currently a sophomore in college and pretty new to the field of research. I'm currently working on an existing algorithm for MRI denoising and the results are nothing that great. I can't see how I ...
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1answer
27 views
MRI image reconstruction - reduced scan pecentage
I have an MRI kspace from a siemens 1.5 T scanner with reduced scan percentage ( sampled truncation by not acquiring the most peripheral lines in kspace). The kspace plot in matlab look like below.
I ...
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From Fourier (k space) to wavelet domain in MRI sensing
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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27 views
Order of MR Imaging Encoding Steps
Why is it so important to have the phase gradient encoding step come before the frequency gradient encoding step when collecting MR Images? Currently, the phase encoding step is turned on briefly, ...
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1answer
353 views
Bloch equation: adding gradients
I have a bloch simulation that I have implemented in Python. The implementation is very simple as:
...
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99 views
Bloch equations in MRI rotating field
I am trying to understand the workings of an MRI scanner and wanted to figure out how to simulate it by solving Bloch equations in the rotating frame of reference.
I have a small query regarding the ...
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1answer
38 views
Question about MRI signal construction
As I understand it, in MRI, a line in k-space is usually acquired while the readout gradient is applied. So during the application of this gradient the protons spin at different frequencies along the ...
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1answer
395 views
MRI reconstruction using windowing based apodization
I am trying to apply windowing to do MRI reconstruction. I have a 256 point one dimensional k-space samples which look as follows:
Here, the real part(green) is flat around 0 and the blue curve is ...
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1answer
27 views
Effect on T1 relaxation due to the application of the gradient
In MRI, the T1 relaxation constant for a tissue type is defined as the time taken for the longitudinal relaxation to recover approximately to 63% of its initial value.
Is there any modification of ...
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98 views
reconstruction of MRI signal
I have written a small simulator where I am trying to simulate the MRI signal generation process. I have a SINC RF Pulse to excite the spins and a readout gradient and k-space sampling during the ...
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2answers
137 views
Effective field in MRI when solving for Bloch equations
I have a confusion regarding MRI signal formation. So, as I understand it, we need to solve the Bloch equations for the excitation and the relaxation stages:
So, in the excitation stage, let us ...
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1answer
58 views
The description of the MRI signal from the magnetization vector
I have been working on simulating the MRI signal and what I have done so far is simulate the actions of the RF pulse and the required localization gradients.
So, in the simulation, I am looking at a ...
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187 views
phase evolution of MRI signal during RF excitation
I am trying to compute the phase evolution of a proton spin in the presence of a slice selection gradient. I have the following properties for the slice selection gradient and the RF excitation:
<...
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1answer
54 views
Figuring out how an RF pulse affects the MRI spins
So, I understand how the slice selection gradients work in MRI. So, the frequency offset introduced by the slice selection gradient at a location $z$ relative to the MRI isocenter is given by:
$$
\...
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1answer
209 views
Slice selection in MRI
Looking at some examples in the "handbook of MRI Pulse Sequences" by Bernstein, I see the following:
So if I can generate an RF pulse with a bandwidth of 2 kHz and I want a 3 mm slice thickness, the ...
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1answer
103 views
Gradient echo MRI. Do the gradients have to be the same duration?
I currently got hold of the book "Handbook of MRI Pulse Sequences" and am looking into computing the duration, gradient strength and ramp times for the phase encoding gradient, readout prehasing and ...
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1answer
150 views
area under the phase encoding gradient in MRI
I have a question about how I could compute the area (duration and amplitude) for the phase encoding gradient in a typical MRI gradient echo sequence. So, let us assume that my field of view in the ...
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1answer
79 views
Confusion with regards to units in Sinc pulse
I am currently reading a section in the Handbook for MRI Pulse Sequence book where it says that the time-bandwidth product for a SINC pulse is given by:
$$
T \Delta f = Z
$$
where $T$ is the length ...
