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Related Experiment Videos

Real-time autoshimming for echo planar timecourse imaging.

Heidi A Ward1, Stephen J Riederer, Clifford R Jack

  • 1Department of Radiology, Mayo Clinic, Rochester, Minnesota 55905, USA.

Magnetic Resonance in Medicine
|November 6, 2002
PubMed
Summary
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Head motion causes geometric distortions in functional MRI (fMRI) and diffusion tensor imaging. A new "shim NAV" method corrects these motion-induced magnetic field changes in real-time, improving image alignment and reducing artifacts.

Area of Science:

  • Magnetic Resonance Imaging
  • Neuroimaging
  • Medical Physics

Background:

  • Head motion during MRI scans introduces magnetic field distortions.
  • These distortions cause geometric inaccuracies and artifacts in echo planar imaging (EPI), impacting functional MRI (fMRI) and diffusion tensor imaging (DTI).
  • Clinically relevant head motions can lead to >3 mm translations in EPI images.

Purpose of the Study:

  • To develop and validate a real-time method for detecting and correcting head motion-induced magnetic field changes during EPI acquisition.
  • To reduce geometric distortions and image artifacts in fMRI and DTI caused by head motion.

Main Methods:

  • Introduction of a navigator pulse sequence and processing method termed "shim NAV" for real-time detection of linear shim changes.

Related Experiment Videos

  • Development of a shim-compensated EPI pulse sequence for dynamic correction of these shim changes.
  • Validation using phantom and in vivo experiments with applied gradient shims and intentional subject motion.

    • Main Results:

    • Shim NAV accurately detects applied gradient shims.
    • Shim-compensated EPI significantly reduces geometric distortion and image artifacts in phantom studies.
    • In vivo experiments show improved alignment of timecourse EPI images with real-time shim correction during intentional motion.

    Conclusions:

    • The "shim NAV" method effectively detects linear shim changes caused by head motion.
    • Shim-compensated EPI dynamically corrects for these changes, improving EPI image quality and alignment.
    • This real-time correction strategy holds promise for more robust fMRI and DTI acquisitions.