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