Questions tagged [mri]
The mri tag has no usage guidance.
29
questions
1
vote
2
answers
45
views
What is the most likely imaging processing step associated with the term 'Riesz' in clinical MRI?
I understand that it is an odd question, and this is arguably not the ideal forum, but I am at a loss.
Some of you may be familiar with DICOM as a consensus or standard format for medical image ...
- 455
1
vote
0
answers
146
views
Bring two Fourier transforms to same range to add them
I have Fourier transforms of two images which I wish to add (Basically I have an input Fourier transform which I mask, reconstruct the underlying image using an algorithm, and then try to replace the ...
- 71
0
votes
0
answers
5
views
kSpace data manipulation
I have access to GE MRI scanner data and have been trying to convert the raw kspace data to image format using ifftshit(ifft2(.)). However, the reconstructed images don't match the expected outcome:
...
0
votes
0
answers
24
views
Beginner question about MRI
I am used to process PET/CT scans currently I am starting working on magnetic resonance imaging and I have simple question that I can not find answer for.
I have files in Dicom and multiple series. ...
0
votes
0
answers
17
views
removing stripy artifact from fMRI
I have fMRI images, some of which have a stripy artifact that looks like a Gabor filter. Removing this kind of noise is not, to my knowledge, a standard part of any fMRI processing pipeline. I am ...
- 101
0
votes
0
answers
13
views
Spatial encoding in MRI and k-space
I am trying to understand how an MR image is formed, how k-space works and how spatial encoding works.
My current understanding based on basic medical physics lectures is:
slice select in the Z-axis ...
- 1
1
vote
1
answer
122
views
T1 Mapping in Python?
I'm trying to write a simple program to perform T1 mapping of a few MRI Images.
My understanding is that all I need is to plot the pixel intensity values by inversion time then fit a curve. The output ...
- 13
1
vote
1
answer
76
views
Adding noise to real MRI data
I designed an algorithm for MRI data denoising which has good properties under heavy Rician noise (sigma is greater than 80). The method was tested on some phantoms and Rician noise generators. Now I ...
- 27
1
vote
0
answers
36
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 ...
-1
votes
1
answer
311
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
1
vote
1
answer
102
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 ...
- 653
2
votes
1
answer
158
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
1
answer
54
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 ...
- 167
0
votes
0
answers
63
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 ...
- 455
-1
votes
1
answer
45
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, ...
- 3
2
votes
1
answer
646
views
Bloch equation: adding gradients
I have a bloch simulation that I have implemented in Python. The implementation is very simple as:
...
- 185
0
votes
0
answers
152
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 ...
- 185
0
votes
1
answer
63
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 ...
- 185
1
vote
1
answer
741
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 ...
- 185
0
votes
1
answer
36
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 ...
- 185
0
votes
0
answers
118
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 ...
- 185
0
votes
2
answers
180
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 ...
- 185
0
votes
1
answer
78
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 ...
- 185
0
votes
0
answers
273
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:
<...
- 185
0
votes
1
answer
70
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:
$$
\...
- 185
0
votes
1
answer
311
views
Slice selection in MRI
Looking at some examples in the "handbook of MRI Pulse Sequences" by Bernstein, I see the following:
So if I can generate an RF pulse with a bandwidth of 2 kHz and I want a 3 mm slice thickness, the ...
- 185
1
vote
1
answer
131
views
Gradient echo MRI. Do the gradients have to be the same duration?
I currently got hold of the book "Handbook of MRI Pulse Sequences" and am looking into computing the duration, gradient strength and ramp times for the phase encoding gradient, readout prehasing and ...
- 185
0
votes
1
answer
228
views
area under the phase encoding gradient in MRI
I have a question about how I could compute the area (duration and amplitude) for the phase encoding gradient in a typical MRI gradient echo sequence. So, let us assume that my field of view in the ...
- 185
0
votes
1
answer
232
views
Confusion with regards to units in Sinc pulse
I am currently reading a section in the Handbook for MRI Pulse Sequence book where it says that the time-bandwidth product for a SINC pulse is given by:
$$
T \Delta f = Z
$$
where $T$ is the length ...
- 185