Jessica A. Martinez;Alessandro Arduino;Oriano Bottauscio;Luca Zilberti
{"title":"Evaluation and Correction of $B_{1}^+$-Based Brain Subject-Specific SAR Maps Using Electrical Properties Tomography","authors":"Jessica A. Martinez;Alessandro Arduino;Oriano Bottauscio;Luca Zilberti","doi":"10.1109/JERM.2023.3236153","DOIUrl":null,"url":null,"abstract":"The specific absorption rate (SAR) estimates the amount of power absorbed by the tissue and is determined by the electrical conductivity and the E-field. Conductivity can be estimated using Electric Properties Tomography (EPT) but only the E-field component associated with \n<inline-formula><tex-math>$B_{1}^+$</tex-math></inline-formula>\n can be deduced from \n<inline-formula><tex-math>$B_{1}$</tex-math></inline-formula>\n-mapping. Herein, a correction factor was calculated to compensate for the differences between the actual SAR and the one obtained with \n<inline-formula><tex-math>$B_{1}^+$</tex-math></inline-formula>\n. Numerical simulations were performed for 27 head models at \n<inline-formula><tex-math>$128 \\,\\mathrm{M}\\mathrm{Hz}$</tex-math></inline-formula>\n. Ground-truth local-SAR and 10g-SAR (SAR\n<sub>GT</sub>\n) were computed using the exact electrical conductivity and the E-field. Estimated local-SAR and 10g-SAR (SAR\n<sub>EST</sub>\n) were computed using the electrical conductivity obtained with a convection-reaction EPT and the E-field obtained from \n<inline-formula><tex-math>$B_{1}^+$</tex-math></inline-formula>\n. Correction factors (CFs) were estimated for gray matter, white matter, and cerebrospinal fluid (CSF). A comparison was performed for different levels of signal-to-noise ratios (SNR). Local-SAR/10g-SAR CF was 3.08 \n<inline-formula><tex-math>$\\pm$</tex-math></inline-formula>\n 0/06 / 2.11 \n<inline-formula><tex-math>$\\pm$</tex-math></inline-formula>\n 0.04 for gray matter, 1.79 \n<inline-formula><tex-math>$\\pm$</tex-math></inline-formula>\n 0/05 / 2.06 \n<inline-formula><tex-math>$\\pm$</tex-math></inline-formula>\n 0.04 for white matter, and 2.59 \n<inline-formula><tex-math>$\\pm$</tex-math></inline-formula>\n 0/05 / 1.95 \n<inline-formula><tex-math>$\\pm$</tex-math></inline-formula>\n 0.03 for CSF. SAR\n<sub>EST</sub>\n without CF were underestimated (ratio across [\n<inline-formula><tex-math>$\\infty$</tex-math></inline-formula>\n - 25] SNRs: 0.52 \n<inline-formula><tex-math>$\\pm$</tex-math></inline-formula>\n 0.02 for local-SAR; 0.55 \n<inline-formula><tex-math>$\\pm$</tex-math></inline-formula>\n 0.01 for 10g-SAR). After correction, SAR\n<sub>EST</sub>\n was equivalent to SAR\n<sub>GT</sub>\n (ratio across [\n<inline-formula><tex-math>$\\infty$</tex-math></inline-formula>\n - 25] SNRs: 0.97 \n<inline-formula><tex-math>$\\pm$</tex-math></inline-formula>\n 0.02 for local-SAR; 1.06 \n<inline-formula><tex-math>$\\pm$</tex-math></inline-formula>\n 0.01 for 10g-SAR). SAR maps based on \n<inline-formula><tex-math>$B_{1}^+$</tex-math></inline-formula>\n can be corrected with a correction factor to compensate for potential differences between the actual SAR and the SAR calculated with the E-field derived from \n<inline-formula><tex-math>$B_{1}^+$</tex-math></inline-formula>\n.","PeriodicalId":29955,"journal":{"name":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","volume":null,"pages":null},"PeriodicalIF":3.0000,"publicationDate":"2023-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/iel7/7397573/10138047/10044569.pdf","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","FirstCategoryId":"1085","ListUrlMain":"https://ieeexplore.ieee.org/document/10044569/","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"ENGINEERING, ELECTRICAL & ELECTRONIC","Score":null,"Total":0}
引用次数: 0
Abstract
The specific absorption rate (SAR) estimates the amount of power absorbed by the tissue and is determined by the electrical conductivity and the E-field. Conductivity can be estimated using Electric Properties Tomography (EPT) but only the E-field component associated with
$B_{1}^+$
can be deduced from
$B_{1}$
-mapping. Herein, a correction factor was calculated to compensate for the differences between the actual SAR and the one obtained with
$B_{1}^+$
. Numerical simulations were performed for 27 head models at
$128 \,\mathrm{M}\mathrm{Hz}$
. Ground-truth local-SAR and 10g-SAR (SAR
GT
) were computed using the exact electrical conductivity and the E-field. Estimated local-SAR and 10g-SAR (SAR
EST
) were computed using the electrical conductivity obtained with a convection-reaction EPT and the E-field obtained from
$B_{1}^+$
. Correction factors (CFs) were estimated for gray matter, white matter, and cerebrospinal fluid (CSF). A comparison was performed for different levels of signal-to-noise ratios (SNR). Local-SAR/10g-SAR CF was 3.08
$\pm$
0/06 / 2.11
$\pm$
0.04 for gray matter, 1.79
$\pm$
0/05 / 2.06
$\pm$
0.04 for white matter, and 2.59
$\pm$
0/05 / 1.95
$\pm$
0.03 for CSF. SAR
EST
without CF were underestimated (ratio across [
$\infty$
- 25] SNRs: 0.52
$\pm$
0.02 for local-SAR; 0.55
$\pm$
0.01 for 10g-SAR). After correction, SAR
EST
was equivalent to SAR
GT
(ratio across [
$\infty$
- 25] SNRs: 0.97
$\pm$
0.02 for local-SAR; 1.06
$\pm$
0.01 for 10g-SAR). SAR maps based on
$B_{1}^+$
can be corrected with a correction factor to compensate for potential differences between the actual SAR and the SAR calculated with the E-field derived from
$B_{1}^+$
.