Correction of spatial distortion in EPI due to inhomogeneous static magnetic fields using the reversed gradient method

Morgan, Paul S.; Bowtell, Richard; McIntyre, Dominick J.O.; Worthington, B. S.

doi:10.1002/jmri.20032

Cited by 174 publications

(182 citation statements)

References 21 publications

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“…Solving this equation gives coefficients {p n }, from which we can find {z n } as roots of the polynomial in (16). Once {z n } are found, the corresponding unknowns {a n } can be easily computed by solving the following linear equation with a Vandermonde matrix Z:…”

Section: B Harmonic Retrieval Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Joint Estimation and Correction of Geometric Distortions for EPI Functional MRI Using Harmonic Retrieval

Nguyen

Sutton

Morrison

et al. 2009

IEEE Trans. Med. Imaging

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Abstract-Magnetic Resonance Imaging (MRI) uses applied spatial variations in the magnetic field to encode spatial position. Therefore, non-uniformities in the main magnetic field can cause image distortions. In order to correct the image distortions, it is desirable to simultaneously acquire data with a field map in registration. We propose a joint estimation (JE) framework with a fast, non-iterative approach using harmonic retrieval (HR) methods, combined with a multi-echo EPI acquisition. The connection with HR establishes an elegant framework to solve the JE problem through a sequence of one dimensional HR problems in which efficient solutions are available. We also derive the condition on the smoothness of the field map in order for HR techniques to recover the image with high signal-to-noise ratio. Compared to other dynamic field mapping methods, this method is not constrained by the absolute level of the field inhomogeneity over the slice, but relies on a generous pixel-to-pixel smoothness. Moreover, this method can recover image, field map, and T2* map simultaneously.

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Section: B Harmonic Retrieval Methodsmentioning

confidence: 99%

“…Some other methods try to bypass estimation of the field map. For example, in [2] and [16] two images of the same object are acquired with preparation and readout gradients altered by some ratio α. The corrected image is produced by combining and rectifying these two acquired images pixel by pixel.…”

Section: Iω(r)t(k) E −T(k)/t *mentioning

confidence: 99%

Joint Estimation and Correction of Geometric Distortions for EPI Functional MRI Using Harmonic Retrieval

Nguyen

Sutton

Morrison

et al. 2009

IEEE Trans. Med. Imaging

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“…Jezzard et al [7] have demonstrated that deformations due to B 0 field inhomogeneities appear mainly along the PED and are negligible in other directions. More precisely, we follow the distortion model as expressed previously in [17], [18] which assumes that I F and I B are generated from the theoretical corrected image C using a displacement field parallel to the PED:…”

Section: A Distortion Modelmentioning

confidence: 99%

“…This simple method strongly reduces the distortion, however it is sensitive to noise and the computed transformation needs to be smoothed, leading to a trade-off between regularity and precision. Other methods in this category include Morgan et al approach [18], using continuously alternating phase encoding, Weiskopf et al method [19] using a modified multi-echo EPI acquisition with reversed phases, or Holland et al algorithm [9] which performs an intensity-based registration (each line being considered independently). As for Voss et al algorithm, the obtained displacement field is sensitive to noise, especially when large displacements are present.…”

Section: Introductionmentioning

confidence: 99%

Block-Matching Distortion Correction of Echo-Planar Images With Opposite Phase Encoding Directions

Hédouin

Commowick

Bannier

et al. 2017

IEEE Trans. Med. Imaging

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Abstract-By shortening the acquisition time of MRI, Echo Planar Imaging (EPI) enables the acquisition of a large number of images in a short time, compatible with clinical constraints as required for diffusion or functional MRI. However such images are subject to large, local distortions disrupting their correspondence with the underlying anatomy. The correction of those distortions is an open problem, especially in regions where large deformations occur.We propose a new block-matching registration method to perform EPI distortion correction based on the acquisition of two EPI with opposite phase encoding directions (PED). It relies on new transformations between blocks adapted to the EPI distortion model, and on an adapted optimization scheme to ensure an opposite symmetric transformation. We present qualitative and quantitative results of the block-matching correction using different metrics on a phantom dataset and on in-vivo data. We show the ability of the blockmatching to robustly correct EPI distortion even in strongly affected areas.

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“…One simple algorithm compares two separate images acquired traversing k-space in opposite directions along the phase-encode (PE) direction (6). Other approaches use a field map measurement, since the displacement field at any given point is proportional to the susceptibility-induced change in B 0 (7).…”

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confidence: 99%

EPI distortion correction from a simultaneously acquired distortion map using TRAIL

Priest

Vita

Thomas

et al. 2006

Magnetic Resonance Imaging

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Purpose: To develop a method for shot-by-shot distortion correction of single-shot echo-planar imaging (EPI) that is capable of correcting each image individually using a distortion measurement performed during acquisition of the image itself. Materials and Methods:The recently-introduced method known as two reduced acquisitions interleaved (TRAIL) was extended to measure the distribution of the main magnetic field B 0 with each shot. This corresponded to a map of distortion, and allowed distortion to be corrected in the acquired images. Results:Distortion-corrected images were demonstrated in the human brain. The distortion field could be directly visualized using the "stripe" distribution imposed by the TRAIL pulse sequence. This confirmed the success of the correction. Over a time-course measurement of 10 images, variance was reduced by using shot-by-shot distortion correction compared to correction with a constant field map. Conclusion:Shot-by-shot distortion correction may be performed for EPI images acquired using an extension of the TRAIL technique, ensuring that the correction reflects the actual distortion pattern and not merely a previously measured, but possibly no longer valid, distortion field. This avoids errors due to changes in the distortion field or misregistration of a previously measured distortion map resulting from subject motion. ECHO-PLANAR IMAGING (EPI) (1,2) can acquire images very rapidly with a high signal-to-noise ratio (SNR) per unit time. For many applications of EPI, very high main magnetic fields (B 0 ) allow increases in SNR, blood oxygen level-dependent (BOLD) responses, or T1 to be exploited. However, higher magnetic fields also bring greater problems-in particular an increased sensitivity to magnetic susceptibility differences between tissues or between tissue and air, which cause strong variations in B 0 and can thus degrade image quality. The T2* relaxation times are reduced, resulting in rapid signal decay during the EPI readout. Also the susceptibility-related inhomogeneities in B 0 correspond to local variations in the Larmour frequency ( 0 ), which leads to image distortions along the phase-encode direction. For time-course studies, another problem is that the B 0 distribution depends on the subject orientation, therefore, the distortion can change if the subject moves (3-5). These problems have prevented many further applications of single-shot EPI. Effective methods to correct distortion are therefore needed.There are several algorithms that can measure and correct EPI distortion resulting from susceptibility effects (4 -10). One simple algorithm compares two separate images acquired traversing k-space in opposite directions along the phase-encode (PE) direction (6). Other approaches use a field map measurement, since the displacement field at any given point is proportional to the susceptibility-induced change in B 0 (7). A B 0 field map can be calculated from the phase change between two or more separately acquired gradient-echo or EPI images with different echo tim...

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Correction of spatial distortion in EPI due to inhomogeneous static magnetic fields using the reversed gradient method

Cited by 174 publications

References 21 publications

Joint Estimation and Correction of Geometric Distortions for EPI Functional MRI Using Harmonic Retrieval

Joint Estimation and Correction of Geometric Distortions for EPI Functional MRI Using Harmonic Retrieval

Block-Matching Distortion Correction of Echo-Planar Images With Opposite Phase Encoding Directions

EPI distortion correction from a simultaneously acquired distortion map using TRAIL

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