Questions tagged [mri]
The mri tag has no usage guidance.
23
questions
1
vote
0answers
24 views
Why do we not encode frequency in 3 dimensions in MRI?
If I understand correctly, to select a particular slice (of an object, during an MRI scan) that is orthogonal to the direction of the main magnetic field applied, we apply a magnetic field that varies ...
0
votes
0answers
3 views
How to detect slices with circular crops in volumetric mri data
Ive got some MRI volumetric data I am trying to do some image analysis on. Ive got an issue right now where the first and last 2-4 slices of the data are cropped circularly. Here is an example of what ...
0
votes
0answers
17 views
How to calculate the echo magnitude of an hanh echo using bloch simulation?
Stanford provided all basic functions/M-files needed for Bloch simulation. The following MATLAB code snippet was made on top of these M-files to simulate the Hanh Echo:
...
0
votes
1answer
44 views
Will the phase of the reconstructed data using a single MRI k-space point show any curvature?
Some courses tell that each point in k-space (spatial-frequency domain) represents a certain stripe pattern in spatial domain.
Reference: https://www.sciencedirect.com/science/article/pii/...
1
vote
1answer
64 views
Quadrature signal acquisition simulation
Bottom-line: how to create a 90 degrees out of phase signal from the real part of the fourier transform of a 1D signal (i.e., fft of a line of an image). ? *(I *(I think the Fourier shift thm can help ...
0
votes
1answer
128 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 de-noising and the results are nothing that great. I can't see how ...
2
votes
1answer
40 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 ...
1
vote
0answers
57 views
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 ...
-1
votes
1answer
40 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, ...
2
votes
1answer
519 views
Bloch equation: adding gradients
I have a bloch simulation that I have implemented in Python. The implementation is very simple as:
...
0
votes
0answers
144 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 ...
0
votes
1answer
53 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 ...
0
votes
1answer
582 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 ...
0
votes
1answer
34 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 ...
0
votes
0answers
108 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 ...
0
votes
2answers
162 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 ...
0
votes
1answer
71 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 ...
0
votes
0answers
243 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:
<...
0
votes
1answer
65 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:
$$
\...
0
votes
1answer
282 views
Slice selection in MRI
Looking at some examples in the "handbook of MRI Pulse Sequences" by Bernstein, I see the following:
So if I can generate an RF pulse with a bandwidth of 2 kHz and I want a 3 mm slice thickness, the ...
1
vote
1answer
121 views
Gradient echo MRI. Do the gradients have to be the same duration?
I currently got hold of the book "Handbook of MRI Pulse Sequences" and am looking into computing the duration, gradient strength and ramp times for the phase encoding gradient, readout prehasing and ...
0
votes
1answer
176 views
area under the phase encoding gradient in MRI
I have a question about how I could compute the area (duration and amplitude) for the phase encoding gradient in a typical MRI gradient echo sequence. So, let us assume that my field of view in the ...
0
votes
1answer
143 views
Confusion with regards to units in Sinc pulse
I am currently reading a section in the Handbook for MRI Pulse Sequence book where it says that the time-bandwidth product for a SINC pulse is given by:
$$
T \Delta f = Z
$$
where $T$ is the length ...
