Effect of subject‐specific head morphometry on specific absorption rate estimates in parallel‐transmit MRI at 7 T

Purpose To assess the accuracy of morphing an established reference electromagnetic head model to a subject‐specific morphometry for the estimation of specific absorption rate (SAR) in 7T parallel‐transmit (pTx) MRI. Methods Synthetic T1‐weighted MR images were created from three high‐resolution ope...

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Vydáno v:Magnetic resonance in medicine Ročník 89; číslo 6; s. 2376 - 2390
Hlavní autoři: Jeong, Hongbae, Andersson, Jesper, Hess, Aaron, Jezzard, Peter
Médium: Journal Article
Jazyk:angličtina
Vydáno: United States Wiley Subscription Services, Inc 01.06.2023
John Wiley and Sons Inc
Témata:
Absorption
Circular polarization
Composition
Computer Processing and Modeling
electromagnetic body models
Magnetic resonance imaging
Magnetic Resonance Imaging - methods
Medical imaging
Model accuracy
Morphing
Morphometry
MRI safety
nonlinear registration
parallel transmit
Phantoms, Imaging
Registration
RF transmit
SAR
RF transmit
nonlinear registration
parallel transmit
electromagnetic body models
SAR
MRI safety
ISSN:0740-3194, 1522-2594, 1522-2594
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Shrnutí:Purpose To assess the accuracy of morphing an established reference electromagnetic head model to a subject‐specific morphometry for the estimation of specific absorption rate (SAR) in 7T parallel‐transmit (pTx) MRI. Methods Synthetic T1‐weighted MR images were created from three high‐resolution open‐source electromagnetic head voxel models. The accuracy of morphing a “reference” (multimodal image‐based detailed anatomical [MIDA]) electromagnetic model into a different subject's native space (Duke and Ella) was compared. Both linear and nonlinear registration methods were evaluated. Maximum 10‐g averaged SAR was estimated for circularly polarized mode and for 5000 random RF shim sets in an eight‐channel transmit head coil, and comparison made between the morphed MIDA electromagnetic models and the native Duke and Ella electromagnetic models, respectively. Results The averaged error in maximum 10‐g averaged SAR estimation across pTx MRI shim sets between the MIDA and the Duke target model was reduced from 17.5% with only rigid‐body registration, to 11.8% when affine linear registration was used, and further reduced to 10.7% when nonlinear registration was used. The corresponding figures for the Ella model were 16.7%, 11.2%, and 10.1%. Conclusion We found that morphometry accounts for up to half of the subject‐specific differences in pTx SAR. Both linear and nonlinear morphing of an electromagnetic model into a target subject improved SAR agreement by better matching head size, morphometry, and position. However, differences remained, likely arising from details in tissue composition estimation. Thus, the uncertainty of the head morphometry and tissue composition may need to be considered separately to achieve personalized SAR estimation.
Bibliografie:Funding information
Wellcome Trust, Grant/Award Number: 203139/Z/16/Z; BHF Center of Research Excellence, Oxford, Grant/Award Number: RE/13/1/30181; Dunhill Medical Trust, NIHR Oxford Biomedical Research Center
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Funding information Wellcome Trust, Grant/Award Number: 203139/Z/16/Z; BHF Center of Research Excellence, Oxford, Grant/Award Number: RE/13/1/30181; Dunhill Medical Trust, NIHR Oxford Biomedical Research Center
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ISSN:0740-3194
1522-2594
1522-2594
DOI:10.1002/mrm.29589