Correction for EPI distortions using multi-echo gradient-echo imaging

Chen, Nan‐kuei; Wyrwicz, Alice M.

doi:10.1002/(sici)1522-2594(199906)41:6<1206::aid-mrm17>3.0.co;2-l

Cited by 123 publications

(105 citation statements)

References 14 publications

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“…Correction of these artifacts has been studied extensively. For example, to mitigate these artifacts, we can use field mapping to investigate the spatial distribution of the off-resonance effects and then use this information to reduce the susceptibility artifacts (Chen et al, 2006;Chen and Wyrwicz, 1999;Zeng and Constable, 2002). It is also possible to use parallel imaging techniques with EPI acquisitions to limit geometric distortion (Weiger et al, 2002), by systematically skipping multiple integer lines in the continuous sampling of different phaseencoding lines and then reconstructing the skipped phase encoding lines using spatial information embedded inside different array channels.…”

Section: Spatial Distortionmentioning

confidence: 99%

Event-related single-shot volumetric functional magnetic resonance inverse imaging of visual processing

et al. 2008

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Developments in multi-channel radio-frequency (RF) coil array technology have enabled functional magnetic resonance imaging (fMRI) with higher degrees of spatial and temporal resolution. While modest improvement in temporal acceleration has been achieved by increasing the number of RF coils, in parallel data acquisition techniques, the maximum attainable acceleration is intrinsically limited only by the amount of independent spatial information in the combined array channels. Since the geometric configuration of a large-n MRI head coil array is similar to that used in EEG electrode or MEG SQUID sensor arrays, the source localization algorithms used in MEG or EEG source imaging can be extended to also process MRI coil array data, resulting in greatly improved temporal resolution by minimizing k-space traversal during signal acquisition. Using a novel approach, we acquire multi-channel MRI head coil array data and then apply inverse reconstruction methods to obtain volumetric fMRI estimates of blood oxygenation level dependent (BOLD) contrast at unprecedented whole-brain acquisition rates of 100 ms per sample. We call this combination of techniques magnetic resonance Inverse Imaging (InI), a method that provides estimates of dynamic spatially-resolved signal change that can be used to construct statistical maps of task-related brain activity. We demonstrate the sensitivity and inter-subject reliability of volumetric InI using an eventrelated design to probe the hemodynamic signal modulations in primary visual cortex. Robust results from both single subject and group analyses demonstrate the sensitivity and feasibility of using volumetric InI in high temporal resolution investigations of human brain function.

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Section: Spatial Distortionmentioning

confidence: 99%

Event-related single-shot volumetric functional magnetic resonance inverse imaging of visual processing

et al. 2008

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“…In the first, the principles of acquisition of specific phase-encoded echo trains is extended to reconstruct a series of phase images, each one containing the phase accumulation between successive gradient echoes (25,26). While this method does allow for correction of all off-resonance artifacts, it does so at the detriment of the acquisition time, which is multiplied by the number of phase encoding steps (25,26) or half the number of phase encoding steps (27). The second approach requires the measurement of the point spread function in the phase-encoded direction in each voxel of the image (28).…”

mentioning

confidence: 99%

A new EPI‐based dynamic field mapping method: Application to retrospective geometrical distortion corrections

Lamberton¹,

Delcroix²,

Grenier³

et al. 2007

Magnetic Resonance Imaging

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Purpose: To retrospectively correct for geometrical distortions, a new dynamic field mapping method suitable for dynamic single-shot gradient-echo type echo-planar imaging (GRE-EPI) is proposed. Materials and Methods:The method requires a single volume additional acquisition and allows the extraction of a field map from each phase volume, assuming invariance across time of the echo time-independent phase component. Performances of the method are assessed using three sets of experiments: the first tests the prerequisite and the modeling; the second tests the method with time-dependent geometrical distortions; and the third presents a comparison with two other methods. Results:Our results legitimize the modeling procedure and demonstrate that the dynamic method is less sensitive to noise than the other methods. A theoretical explanation for this is proposed in the discussion section. Conclusion:Given the minor increase in the acquisition time, this method is well suited for functional magnetic resonance imaging; prospective direction.

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“…The slopes estimated from the even and odd echo images are averaged, and Δ y (x,y) readily calculated by multiplying the result by N echoes /2π. The multi-channel modulation method proposed by Chen and Wyrwicz [7] also avoids the necessity of phase unwrapping. However, this method is much more computationally expensive, and may not be feasible if immediate viewing of the data is desired in clinical applications.…”

Section: Correction For Geometric Distortionmentioning

confidence: 99%

“…Methods to correct for geometric distortion involve collecting conventional gradient echo, offset spin-echo, or EPI images at different values of TE in order to estimate the B 0 field inhomogeneity [4,5,6]. A method using a multi-echo reference scan was recently proposed by Chen and Wyrwicz [7]. However that method is very computationally intensive.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous correction of ghost and geometric distortion artifacts in EPI using a multiecho reference scan

Schmithorst

Dardzinski

Holland

2001

IEEE Trans. Med. Imaging

189

154

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A computationally efficient technique is described for the simultaneous removal of ghosting and geometrical distortion artifacts in echo-planar imaging (EPI) utilizing a multi-echo, gradient-echo reference scan.Nyquist ghosts occur in EPI reconstructions because odd and even lines of k-space are acquired with opposite polarity, and experimental imperfections such as gradient eddy currents, imperfect pulse sequence timing, B 0 field inhomogeneity, susceptibility, and chemical shift result in the even and odd lines of k-space being offset by different amounts relative to the true center of the acquisition window. Geometrical distortion occurs due to the limited bandwidth of the EPI images in the phaseencode direction. This distortion can be problematic when attempting to overlay an activation map from a functional MRI (fMRI) experiment generated from EPI data on a high-resolution anatomical image.The method described here corrects for geometrical distortion related to B 0 inhomogeneity, gradient eddy currents, radiofrequency pulse frequency offset, and chemical shift effect. The algorithm for removing ghost artifacts utilizes phase information in two dimensions and is thus more robust than conventional one-dimensional methods. An additional reference scan is required which takes approximately 2 minutes for a matrix size of 64 × 64 and a TR of 2 seconds. Results from a water phantom and a human brain at 3 Tesla demonstrate the effectiveness of the method for removing ghosts and geometric distortion artifacts.

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Correction for EPI distortions using multi-echo gradient-echo imaging

Cited by 123 publications

References 14 publications

Event-related single-shot volumetric functional magnetic resonance inverse imaging of visual processing

Event-related single-shot volumetric functional magnetic resonance inverse imaging of visual processing

A new EPI‐based dynamic field mapping method: Application to retrospective geometrical distortion corrections

Simultaneous correction of ghost and geometric distortion artifacts in EPI using a multiecho reference scan

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