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QUESTIONS
» Pulse Sequences

How do we change image contrast? What are the effects of parameter changes? This section explores image contrast and image acquisition methods.

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Pulse Sequences Q&A

These questions are concerned with certain image acquisition methods—pulse sequences—and the effects on the MRI image. Manipulation of image quality is considered.

Choose a question...
  1. What are the differences between spin echo (SE) and gradient echo (GE) pulse sequences?
  2. What is spoiling?
  3. Name an instance of gradient spoiling.
  4. Define SNR (with an equation) in terms of voxel volume, number of measurements and receiver bandwidth.
  5. You decide to try and increase the SNR by increasing the voxel size. Why might this work? List also any tradeoffs. (Assume bandwidth is kept constant.)
  6. You decide to try and increase the SNR by increasing the number of phase encoding steps. Why might this work? List also any tradeoffs.
  7. You decide to try and increase the SNR by increasing the number of signal averages. Why might this work? List also any tradeoffs.
  8. You decide to try and increase the SNR by using a smaller receiver bandwidth. Why might this work? List also any tradeoffs.
  9. You decide to try and increase the SNR by decreasing TE. Why might this work? List also any tradeoffs.
  10. You decide to try and increase the SNR by increasing TR. Why might this work? List also any tradeoffs.
  11. This question contains table depicting the relationship between SNR and operator-selectable imaging parameters (excluding pulse timing parameters). Fill in the SNR column with fractions indicating the proportion of the SNR given on the first line. E.g. "1/2" etc.
  12. What "steady state" is reached in GE pulse sequences when the TR is short? Why does it occur?
  13. What is STIR? Briefly describe how it works.
  14. Are there any other ways of nulling the fat signal, besides STIR?
  15. What is the Ernst equation? When would you use it?
  16. Why does a decay in the transverse magnetisation not imply an equal recovery in the longitudinal direction?
  17. (a) Should TE and TR times be short or long to produce a T1-weighted spin-echo image?
    (b) Should TE and TR times be short or long to produce a T2-weighted spin-echo image?
  18. How is voxel size calculated?
  19. Why can't you just keep on reducing the field of view, to keep increasing the magnification in an image? Isn't that just "zooming in"?
  20. Why is blood black on conventional spin echo images, and bright on conventional gradient echo images?
  21. How does Turbo Gradient Echo differ from conventional Gradient Echo?
  22. What is Echo Planar Imaging?
  23. How does Turbo Spin Echo differ from conventional Spin Echo?

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