Single-shot compensation of image distortions and BOLD contrast optimization using multi-echo EPI for real-time fMRI

Nikolaus Weiskopf, Uwe Klose, Niels Birbaumer, Klaus Mathiak

Research output: Contribution to journalArticle

86 Citations (Scopus)

Abstract

Functional magnetic resonance imaging (fMRI) is most commonly based on echo-planar imaging (EPI). With higher field strengths, gradient performance, and computational power, real-time fMRI has become feasible; that is, brain activation can be monitored during the ongoing scan. However, EPI suffers from geometric distortions due to inhomogeneities of the magnetic field, especially close to air-tissue interfaces. Thus, functional activations might be mislocalized and assigned to the wrong anatomical structures. Several techniques have been reported which reduce geometric distortions, for example, mapping of the static magnetic field B0 or the point spread function for all voxels. Yet these techniques require additional reference scans and in some cases extensive computational time. Moreover, only static field inhomogeneities can be corrected, because the correction is based on a static reference scan. We present an approach which allows for simultaneous acquisition and distortion correction of a functional image without a reference scan. The technique is based on a modified multi-echo EPI data acquisition scheme using a phase-encoding (PE) gradient with alternating polarity. The images exhibit opposite distortions due to the inverted PE gradient. After adjusting the contrast of the images acquired at different echo times, this information is used for the distortion correction. We present the theory, implementation, and applications of this single-shot distortion correction. Significant reduction in geometric distortion is shown both for phantom images and human fMRI data. Moreover, sensitivity to the blood oxygen level-dependent (BOLD) effect is increased by weighted summation of the undistorted images.

Original languageEnglish
Pages (from-to)1068-1079
Number of pages12
JournalNeuroImage
Volume24
Issue number4
DOIs
Publication statusPublished - Feb 15 2005

Fingerprint

Echo-Planar Imaging
Magnetic Resonance Imaging
Magnetic Fields
Oxygen
Air
Brain

Keywords

  • BOLD
  • Distortion correction
  • Echo-planar imaging
  • EPI
  • fMRI
  • Functional magnetic resonance imaging
  • Multi-echo
  • Multi-image
  • Real-time
  • Sensitivity
  • Single-shot

ASJC Scopus subject areas

  • Cognitive Neuroscience
  • Neurology

Cite this

Single-shot compensation of image distortions and BOLD contrast optimization using multi-echo EPI for real-time fMRI. / Weiskopf, Nikolaus; Klose, Uwe; Birbaumer, Niels; Mathiak, Klaus.

In: NeuroImage, Vol. 24, No. 4, 15.02.2005, p. 1068-1079.

Research output: Contribution to journalArticle

Weiskopf, Nikolaus ; Klose, Uwe ; Birbaumer, Niels ; Mathiak, Klaus. / Single-shot compensation of image distortions and BOLD contrast optimization using multi-echo EPI for real-time fMRI. In: NeuroImage. 2005 ; Vol. 24, No. 4. pp. 1068-1079.
@article{16a5fdf7d63b4c89ad731d0794c53c26,
title = "Single-shot compensation of image distortions and BOLD contrast optimization using multi-echo EPI for real-time fMRI",
abstract = "Functional magnetic resonance imaging (fMRI) is most commonly based on echo-planar imaging (EPI). With higher field strengths, gradient performance, and computational power, real-time fMRI has become feasible; that is, brain activation can be monitored during the ongoing scan. However, EPI suffers from geometric distortions due to inhomogeneities of the magnetic field, especially close to air-tissue interfaces. Thus, functional activations might be mislocalized and assigned to the wrong anatomical structures. Several techniques have been reported which reduce geometric distortions, for example, mapping of the static magnetic field B0 or the point spread function for all voxels. Yet these techniques require additional reference scans and in some cases extensive computational time. Moreover, only static field inhomogeneities can be corrected, because the correction is based on a static reference scan. We present an approach which allows for simultaneous acquisition and distortion correction of a functional image without a reference scan. The technique is based on a modified multi-echo EPI data acquisition scheme using a phase-encoding (PE) gradient with alternating polarity. The images exhibit opposite distortions due to the inverted PE gradient. After adjusting the contrast of the images acquired at different echo times, this information is used for the distortion correction. We present the theory, implementation, and applications of this single-shot distortion correction. Significant reduction in geometric distortion is shown both for phantom images and human fMRI data. Moreover, sensitivity to the blood oxygen level-dependent (BOLD) effect is increased by weighted summation of the undistorted images.",
keywords = "BOLD, Distortion correction, Echo-planar imaging, EPI, fMRI, Functional magnetic resonance imaging, Multi-echo, Multi-image, Real-time, Sensitivity, Single-shot",
author = "Nikolaus Weiskopf and Uwe Klose and Niels Birbaumer and Klaus Mathiak",
year = "2005",
month = "2",
day = "15",
doi = "10.1016/j.neuroimage.2004.10.012",
language = "English",
volume = "24",
pages = "1068--1079",
journal = "NeuroImage",
issn = "1053-8119",
publisher = "Academic Press Inc.",
number = "4",

}

TY - JOUR

T1 - Single-shot compensation of image distortions and BOLD contrast optimization using multi-echo EPI for real-time fMRI

AU - Weiskopf, Nikolaus

AU - Klose, Uwe

AU - Birbaumer, Niels

AU - Mathiak, Klaus

PY - 2005/2/15

Y1 - 2005/2/15

N2 - Functional magnetic resonance imaging (fMRI) is most commonly based on echo-planar imaging (EPI). With higher field strengths, gradient performance, and computational power, real-time fMRI has become feasible; that is, brain activation can be monitored during the ongoing scan. However, EPI suffers from geometric distortions due to inhomogeneities of the magnetic field, especially close to air-tissue interfaces. Thus, functional activations might be mislocalized and assigned to the wrong anatomical structures. Several techniques have been reported which reduce geometric distortions, for example, mapping of the static magnetic field B0 or the point spread function for all voxels. Yet these techniques require additional reference scans and in some cases extensive computational time. Moreover, only static field inhomogeneities can be corrected, because the correction is based on a static reference scan. We present an approach which allows for simultaneous acquisition and distortion correction of a functional image without a reference scan. The technique is based on a modified multi-echo EPI data acquisition scheme using a phase-encoding (PE) gradient with alternating polarity. The images exhibit opposite distortions due to the inverted PE gradient. After adjusting the contrast of the images acquired at different echo times, this information is used for the distortion correction. We present the theory, implementation, and applications of this single-shot distortion correction. Significant reduction in geometric distortion is shown both for phantom images and human fMRI data. Moreover, sensitivity to the blood oxygen level-dependent (BOLD) effect is increased by weighted summation of the undistorted images.

AB - Functional magnetic resonance imaging (fMRI) is most commonly based on echo-planar imaging (EPI). With higher field strengths, gradient performance, and computational power, real-time fMRI has become feasible; that is, brain activation can be monitored during the ongoing scan. However, EPI suffers from geometric distortions due to inhomogeneities of the magnetic field, especially close to air-tissue interfaces. Thus, functional activations might be mislocalized and assigned to the wrong anatomical structures. Several techniques have been reported which reduce geometric distortions, for example, mapping of the static magnetic field B0 or the point spread function for all voxels. Yet these techniques require additional reference scans and in some cases extensive computational time. Moreover, only static field inhomogeneities can be corrected, because the correction is based on a static reference scan. We present an approach which allows for simultaneous acquisition and distortion correction of a functional image without a reference scan. The technique is based on a modified multi-echo EPI data acquisition scheme using a phase-encoding (PE) gradient with alternating polarity. The images exhibit opposite distortions due to the inverted PE gradient. After adjusting the contrast of the images acquired at different echo times, this information is used for the distortion correction. We present the theory, implementation, and applications of this single-shot distortion correction. Significant reduction in geometric distortion is shown both for phantom images and human fMRI data. Moreover, sensitivity to the blood oxygen level-dependent (BOLD) effect is increased by weighted summation of the undistorted images.

KW - BOLD

KW - Distortion correction

KW - Echo-planar imaging

KW - EPI

KW - fMRI

KW - Functional magnetic resonance imaging

KW - Multi-echo

KW - Multi-image

KW - Real-time

KW - Sensitivity

KW - Single-shot

UR - http://www.scopus.com/inward/record.url?scp=12844268705&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=12844268705&partnerID=8YFLogxK

U2 - 10.1016/j.neuroimage.2004.10.012

DO - 10.1016/j.neuroimage.2004.10.012

M3 - Article

VL - 24

SP - 1068

EP - 1079

JO - NeuroImage

JF - NeuroImage

SN - 1053-8119

IS - 4

ER -