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Carr-Purcell sequences with composite pulses.

M D Hürlimann1

  • 1Schlumberger-Doll Research, Ridgefield, Connecticut 06877-4108, USA. hurlimann@ridgefield.sdr.slb.com

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|September 5, 2001
PubMed
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New nuclear magnetic resonance (NMR) sequences offer enhanced error correction and signal quality in challenging, inhomogeneous magnetic fields. These novel Carr-Purcell-like sequences improve relaxation measurements and signal-to-noise ratios for broader NMR applications.

Area of Science:

  • Magnetic Resonance Spectroscopy
  • Pulse Sequence Design
  • Nuclear Magnetic Resonance (NMR)

Background:

  • Standard Carr-Purcell-Meiboom-Gill (CPMG) sequences face limitations in strongly inhomogeneous magnetic fields.
  • Error correction and signal quality are crucial for accurate relaxation measurements in NMR.

Purpose of the Study:

  • To develop novel Carr-Purcell-like NMR sequences with improved performance in inhomogeneous fields.
  • To retain the intrinsic error correction capabilities of the standard CPMG sequence.
  • To enhance signal-to-noise ratio and enable new applications like B(1) imaging.

Main Methods:

  • Design of composite pulse sequences matching excitation pulses with refocusing cycles.
  • Utilizing specific pulse angles and phase cycling, e.g., (90°(0)-(90°(90-θ/2)-θ(180-θ/2)-90°(90-θ/2))(n)) and (127°(x,y)-(127°(x)-127°(-x))(n)).

Related Experiment Videos

  • Analysis of echo amplitude modulation and signal bandwidth in inhomogeneous fields.

    • Main Results:

    • Novel sequences demonstrate improved performance and error correction in strongly inhomogeneous fields.
    • Sequences with theta ≈ 90° and 270° generate a larger signal bandwidth, enhancing signal-to-noise ratio.
    • A specific sequence (127°(x,y)-(127°(x)-127°(-x))(n)) exhibits bimodal excitation off-resonance.
    • A sequence (22.5°(67.5)-90°(-22.5))-(90°(67.5)-45°(157.5)-90°(67.5))(n) allows for coarse B(1) imaging.

    Conclusions:

    • The developed composite pulse sequences offer significant advantages over conventional CPMG sequences in inhomogeneous fields.
    • These sequences are suitable for relaxation measurements and open possibilities for RF field mapping.
    • The findings contribute to advancing NMR techniques for various scientific applications.