# Questions tagged [mri]

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1answer
538 views

### Bloch equation: adding gradients

I have a bloch simulation that I have implemented in Python. The implementation is very simple as: ...
1answer
42 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 ...
1answer
67 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 ...
1answer
123 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 ...
1answer
46 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 ...
1answer
26 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 ...
0answers
26 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 ...
1answer
155 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 ...
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 ...
1answer
604 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 ...
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 ...
2answers
164 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 ...
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 ...
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:  \...
1answer
287 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 ...
1answer
182 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 ...
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 ...
0answers
18 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: ...
1answer
61 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/...
1answer
139 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 ...
0answers
59 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 ...
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 ...
0answers
109 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 ...
0answers
244 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: <...
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, ...