A How can a zipper MRI artifact be limited to a single line?

M

member 664596

Summary
The presence of a stripe of artifact on the final MRI image would logically entail multiple points of frequency information on the actual (Fourier space) data acquisition; however, a zipper artifact is the result of a systematic corruption of a specific frequency. Why wouldn't it, then, manifest itself throughout the entire final image, as opposed to a single vertical stripe?
he so-called [herringbone or spike MRI artifact][1] 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 RF wave emitted by the patient (providing the info about diseased or normal anatomy) had become distorted by some extraneous RF interference, and sampled as such through a DFT process into Fourier space (k space). After producing the reverse FFT, that dot of artifact affected the whole image in a striped pattern:

sUbsh.png


There is another RF-interference artifact in MRI, called [zipper-artifact][3], manifested on the clinical images is as a thin stripe up and down:

EzWjA.png


In the case of the zipper artifact there is a corruption of the signal sent back to the RF antenna from the patient being scanned, affecting a particular, specific frequency, which logically matches the polluting source. This frequency-specific phenomenon would affect each signal collected in the process of filling in k space. In contradistinction, a zipper artifact occurs at a single point in time, showing a dot in k-space.

The question is:

If every point of information in k-space (Fourier space) in MRI affects the entire reconstructed image after performing a reverse FFT, how can a frequency-specific problem in Fourier space produce a single vertical stripe on image space - as opposed to affecting the whole image as in the herringbone artifact above?
 
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What do you get when you take the FFT of a single frequency?
 
M

member 664596

What do you get when you take the FFT of a single frequency?
Are you referring to a single point in 2D Fourier space? That would yield a stripped pattern on image space. But I know you are most likely not making reference to this.
 
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Are you referring to a single point in 2D Fourier space?
No, I am asking for what you get when you transform a pure sin wave.
 
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Klystron

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[text removed] In the case of the zipper artifact there is a corruption of the signal sent back to the RF antenna from the patient being scanned, affecting a particular, specific frequency, which logically matches the polluting source. This frequency-specific phenomenon would affect each signal collected in the process of filling in k space. In contradistinction, a zipper artifact occurs at a single point in time, showing a dot in k-space.

The question is:

If every point of information in k-space (Fourier space) in MRI affects the entire reconstructed image after performing a reverse FFT, how can a frequency-specific problem in Fourier space produce a single vertical stripe on image space - as opposed to affecting the whole image as in the herringbone artifact above?
Were the patients in the herringbone and zipper artifact examples enclosed in a Faraday cage during imaging?
 

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