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

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Discussion Overview

The discussion revolves around the zipper MRI artifact, specifically how it can manifest as a single vertical stripe in an image despite the principle that every point in Fourier space (k-space) influences the entire reconstructed image. Participants explore the nature of this artifact, its relation to RF interference, and the implications of Fourier transformations in MRI imaging.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes the zipper artifact as a corruption of the signal from the patient, affecting a specific frequency that corresponds to the source of interference, leading to a single vertical stripe in the image.
  • Another participant questions the outcome of taking the FFT of a single frequency, suggesting that this could yield a striped pattern in image space.
  • Further clarification is sought regarding whether the reference is to a single point in 2D Fourier space or a pure sine wave transformation.
  • A participant reiterates the question about how a frequency-specific issue in Fourier space can result in a single stripe rather than affecting the entire image, contrasting it with the herringbone artifact.
  • There is a query regarding whether patients were enclosed in a Faraday cage during imaging, implying a consideration of external interference factors.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between frequency-specific artifacts in k-space and their manifestation in image space. The discussion remains unresolved, with multiple competing interpretations of the zipper artifact's behavior.

Contextual Notes

The discussion highlights potential limitations in understanding the transformation processes involved, particularly regarding the assumptions about frequency effects in Fourier space and their implications for image reconstruction.

member 664596
TL;DR
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?
 
Dale said:
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.
 
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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member 664596 said:
[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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