Correcting image distortions from a nonlinear B1+-gradient field in frequency-modulated Rabi-encoded echoes

Paul P Wang; Taylor W Froelich; Efrain Torres; Lance DelaBarre; Parker Jenkins; Jerahmie Radder; Michael F Mullen; Michael Garwood

doi:10.1002/mrm.29549

Correcting image distortions from a nonlinear B₁⁺-gradient field in frequency-modulated Rabi-encoded echoes

Paul P Wang, Taylor W Froelich, Efrain Torres, Lance DelaBarre, Parker Jenkins, Jerahmie Radder, Michael F Mullen, Michael Garwood

Research output: Contribution to journal › Article › peer-review

3 Scopus citations

Abstract

PURPOSE: To correct image distortions that result from nonlinear spatial variation in the transmit RF field amplitude ( B 1 + $$ {B}_1^{+} $$ ) when performing spatial encoding with the method called frequency-modulated Rabi encoded echoes (FREE).

THEORY AND METHODS: An algorithm developed to correct image distortion resulting from the use of nonlinear static field (B 0 ) gradients in standard MRI is adapted herein to correct image distortion arising from a nonlinear B 1 + $$ {B}_1^{+} $$ -gradient field in FREE. From a B 1 + $$ {B}_1^{+} $$ -map, the algorithm performs linear interpolation and intensity scaling to correct the image. The quality of the distortion correction is evaluated in 1.5T images of a grid phantom and human occipital lobe.

RESULTS: An expanded theoretical description of FREE revealed the symmetry between this B 1 + $$ {B}_1^{+} $$ -gradient field spatial-encoding and standard B 0 -gradient field spatial-encoding. The adapted distortion-correction algorithm substantially reduced image distortions arising in the spatial dimension that was encoded by the nonlinear B 1 + $$ {B}_1^{+} $$ gradient of a circular surface coil.

CONCLUSION: Image processing based on straightforward linear interpolation and intensity scaling, as previously applied in conventional MRI, can effectively reduce distortions in FREE images acquired with nonlinear B 1 + $$ {B}_1^{+} $$ -gradient fields.

Original language	English (US)
Pages (from-to)	2100-2108
Number of pages	9
Journal	Magnetic resonance in medicine
Volume	89
Issue number	5
DOIs	https://doi.org/10.1002/mrm.29549
State	Published - May 2023

Bibliographical note

Funding Information:
This research was supported by the Minnesota Lions Diabetes Foundation, and the Malcolm B. Hanson Endowed Chair in Radiology. Additional support was provided by the National Institutes of Health grants U01 EB025153 and P41 EB027061. PW is grateful to the Schott Family Foundation, the Minnesota Lions Diabetes Foundation, and the University of Minnesota Medical Scientist Training Program for supporting his graduate student assistantship. PJ is grateful to Mr. Tom Olsen for supporting his graduate student assistantship. The authors are grateful to the referees for their insightful comments that improved this paper.

Publisher Copyright:
© 2022 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.

Keywords

B-gradient encoding
B-nonlinearity correction
distortion correction
low-cost MRI
radiofrequency imaging
surface coil

Center for Magnetic Resonance Research (CMRR) tags

IRP
MRE

PubMed: MeSH publication types

Journal Article
Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

Publisher link

10.1002/mrm.29549

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@article{d7e6b9b70f854deab95a18b1b5b1b5f1,

title = "Correcting image distortions from a nonlinear B1+-gradient field in frequency-modulated Rabi-encoded echoes",

abstract = "PURPOSE: To correct image distortions that result from nonlinear spatial variation in the transmit RF field amplitude ( B 1 + $$ {B}_1^{+} $$ ) when performing spatial encoding with the method called frequency-modulated Rabi encoded echoes (FREE). THEORY AND METHODS: An algorithm developed to correct image distortion resulting from the use of nonlinear static field (B 0 ) gradients in standard MRI is adapted herein to correct image distortion arising from a nonlinear B 1 + $$ {B}_1^{+} $$ -gradient field in FREE. From a B 1 + $$ {B}_1^{+} $$ -map, the algorithm performs linear interpolation and intensity scaling to correct the image. The quality of the distortion correction is evaluated in 1.5T images of a grid phantom and human occipital lobe. RESULTS: An expanded theoretical description of FREE revealed the symmetry between this B 1 + $$ {B}_1^{+} $$ -gradient field spatial-encoding and standard B 0 -gradient field spatial-encoding. The adapted distortion-correction algorithm substantially reduced image distortions arising in the spatial dimension that was encoded by the nonlinear B 1 + $$ {B}_1^{+} $$ gradient of a circular surface coil. CONCLUSION: Image processing based on straightforward linear interpolation and intensity scaling, as previously applied in conventional MRI, can effectively reduce distortions in FREE images acquired with nonlinear B 1 + $$ {B}_1^{+} $$ -gradient fields. ",

keywords = "B-gradient encoding, B-nonlinearity correction, distortion correction, low-cost MRI, radiofrequency imaging, surface coil",

author = "Wang, {Paul P} and Froelich, {Taylor W} and Efrain Torres and Lance DelaBarre and Parker Jenkins and Jerahmie Radder and Mullen, {Michael F} and Michael Garwood",

note = "Funding Information: This research was supported by the Minnesota Lions Diabetes Foundation, and the Malcolm B. Hanson Endowed Chair in Radiology. Additional support was provided by the National Institutes of Health grants U01 EB025153 and P41 EB027061. PW is grateful to the Schott Family Foundation, the Minnesota Lions Diabetes Foundation, and the University of Minnesota Medical Scientist Training Program for supporting his graduate student assistantship. PJ is grateful to Mr. Tom Olsen for supporting his graduate student assistantship. The authors are grateful to the referees for their insightful comments that improved this paper. Publisher Copyright: {\textcopyright} 2022 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.",

year = "2023",

month = may,

doi = "10.1002/mrm.29549",

language = "English (US)",

volume = "89",

pages = "2100--2108",

journal = "Magnetic resonance in medicine",

issn = "0740-3194",

publisher = "John Wiley and Sons Inc.",

number = "5",

}

TY - JOUR

T1 - Correcting image distortions from a nonlinear B1+-gradient field in frequency-modulated Rabi-encoded echoes

AU - Wang, Paul P

AU - Froelich, Taylor W

AU - Torres, Efrain

AU - DelaBarre, Lance

AU - Jenkins, Parker

AU - Radder, Jerahmie

AU - Mullen, Michael F

AU - Garwood, Michael

N1 - Funding Information: This research was supported by the Minnesota Lions Diabetes Foundation, and the Malcolm B. Hanson Endowed Chair in Radiology. Additional support was provided by the National Institutes of Health grants U01 EB025153 and P41 EB027061. PW is grateful to the Schott Family Foundation, the Minnesota Lions Diabetes Foundation, and the University of Minnesota Medical Scientist Training Program for supporting his graduate student assistantship. PJ is grateful to Mr. Tom Olsen for supporting his graduate student assistantship. The authors are grateful to the referees for their insightful comments that improved this paper. Publisher Copyright: © 2022 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.

PY - 2023/5

Y1 - 2023/5

N2 - PURPOSE: To correct image distortions that result from nonlinear spatial variation in the transmit RF field amplitude ( B 1 + $$ {B}_1^{+} $$ ) when performing spatial encoding with the method called frequency-modulated Rabi encoded echoes (FREE). THEORY AND METHODS: An algorithm developed to correct image distortion resulting from the use of nonlinear static field (B 0 ) gradients in standard MRI is adapted herein to correct image distortion arising from a nonlinear B 1 + $$ {B}_1^{+} $$ -gradient field in FREE. From a B 1 + $$ {B}_1^{+} $$ -map, the algorithm performs linear interpolation and intensity scaling to correct the image. The quality of the distortion correction is evaluated in 1.5T images of a grid phantom and human occipital lobe. RESULTS: An expanded theoretical description of FREE revealed the symmetry between this B 1 + $$ {B}_1^{+} $$ -gradient field spatial-encoding and standard B 0 -gradient field spatial-encoding. The adapted distortion-correction algorithm substantially reduced image distortions arising in the spatial dimension that was encoded by the nonlinear B 1 + $$ {B}_1^{+} $$ gradient of a circular surface coil. CONCLUSION: Image processing based on straightforward linear interpolation and intensity scaling, as previously applied in conventional MRI, can effectively reduce distortions in FREE images acquired with nonlinear B 1 + $$ {B}_1^{+} $$ -gradient fields.

AB - PURPOSE: To correct image distortions that result from nonlinear spatial variation in the transmit RF field amplitude ( B 1 + $$ {B}_1^{+} $$ ) when performing spatial encoding with the method called frequency-modulated Rabi encoded echoes (FREE). THEORY AND METHODS: An algorithm developed to correct image distortion resulting from the use of nonlinear static field (B 0 ) gradients in standard MRI is adapted herein to correct image distortion arising from a nonlinear B 1 + $$ {B}_1^{+} $$ -gradient field in FREE. From a B 1 + $$ {B}_1^{+} $$ -map, the algorithm performs linear interpolation and intensity scaling to correct the image. The quality of the distortion correction is evaluated in 1.5T images of a grid phantom and human occipital lobe. RESULTS: An expanded theoretical description of FREE revealed the symmetry between this B 1 + $$ {B}_1^{+} $$ -gradient field spatial-encoding and standard B 0 -gradient field spatial-encoding. The adapted distortion-correction algorithm substantially reduced image distortions arising in the spatial dimension that was encoded by the nonlinear B 1 + $$ {B}_1^{+} $$ gradient of a circular surface coil. CONCLUSION: Image processing based on straightforward linear interpolation and intensity scaling, as previously applied in conventional MRI, can effectively reduce distortions in FREE images acquired with nonlinear B 1 + $$ {B}_1^{+} $$ -gradient fields.

KW - B-gradient encoding

KW - B-nonlinearity correction

KW - distortion correction

KW - low-cost MRI

KW - radiofrequency imaging

KW - surface coil

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