Dynamic field map estimation using a spiral-in/spiral-out acquisition

Bradley P. Sutton, Douglas C. Noll, Jeffrey A. Fessler

Research output: Contribution to journalArticlepeer-review

Abstract

The long readout times of single-shot acquisitions and the high field strengths desired for functional MRI (fMRI) using blood oxygenation level-dependent (BOLD) contrast make functional scans sensitive to magnetic field inhomogeneity. If it is not corrected during image reconstruction, field inhomogeneity can cause geometric distortions in the images when Cartesian k-space trajectories are used or blurring with spiral acquisitions. Many traditional methods to correct for field inhomogeneity distortions rely on a static field map measured with the use of images that are themselves distorted. In this work, we employ a regularized least-squares approach to jointly estimate both the undistorted image and field map at each acquisition using a spiral-in/spiral-out pulse sequence. Simulation and phantom studies show that this method is accurate and stable over a time series. Human functional studies show that the jointly estimated field map may be more accurate than standard field map estimates in the presence of respiration-induced phase oscillations, leading to better detection of functional activation. The proposed method measures a dynamic field map that accurately tracks magnetic field drift and respiration-induced phase oscillations during the course of a functional study.

Original languageEnglish (US)
Pages (from-to)1194-1204
Number of pages11
JournalMagnetic Resonance in Medicine
Volume51
Issue number6
DOIs
StatePublished - Jun 2004

Keywords

  • Field inhomogeneity
  • Functional MRI
  • Image reconstruction
  • Iterative methods
  • Spiral

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging
  • Radiological and Ultrasound Technology

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