MRI RESPIRATORY ARTIFACT REDUTION METHODS


Respiration Artefact Reduction
 ROPE
  • Respiratory ordered phase encoding collects centre of K-space when respiratory motion is minimal.
  • Moderate scan time penalty (25%) & not entirely effective.
  • Can be useful

Respiratory Gating
  • Data collection restricted to periods of minimal respiratory motion (excitation continues).
  • Moderately effective.
  • High scan time penalty (50%-100%) & not very effective.
  • Increases SAR substantially.
  • Essentially useless
Respiratory Triggering
  • Machine based triggering or user selected TR to match breathing period.
  • Usable for long TR sequences only
  • Quite effective but not robust
Multiple Acquisitions

  • Average motion artefacts over multiple acquisitions
  • Typically only works with NEX >4

  • [repeat phase step n times then increment, average over TR x NEX]
  • Better with "SMART" averaging (Philips)

  • (collect all phase steps then repeat acquisition, average over TR x N.phase x NEX)
  • Only moderately effective
  • Increased scan time and opportunity for other patient motion
  • Breath Hold Sequences
    • Restrict sequence period to <25 seconds
    • Extremely effective (no respiratory artefact or repeat the scan)
    • Presents difficulties for sequence design and parameter choices.
    • Practical application depends on scanner performance specifications.
    • Gives sharper images by avoiding motion induced partial volume averaging effects
    Ultrafast Acquisition
    • Sequential acquisitions of single slice sequences running <1 second
    • Obviates need for breath hold (better with it)
    • Overcomes some limitations of breath hold sequences
    • Practical with high performance equipment

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