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Feasibility of absolute quantification for (31)P MRS at 7 T
PURPOSE: Phosphorus spectroscopy can differentiate among liver disease stages and types. To quantify absolute concentrations of phosphorus metabolites, sensitivity calibration and transmit field ([Formula: see text]) correction are required. The trend toward ultrahigh fields (7 T) and the use of mul...
Autores principales: | , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
John Wiley and Sons Inc.
2019
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6492160/ https://www.ncbi.nlm.nih.gov/pubmed/30892732 http://dx.doi.org/10.1002/mrm.27729 |
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author | Purvis, Lucian A. B. Valkovič, Ladislav Robson, Matthew D. Rodgers, Christopher T. |
author_facet | Purvis, Lucian A. B. Valkovič, Ladislav Robson, Matthew D. Rodgers, Christopher T. |
author_sort | Purvis, Lucian A. B. |
collection | PubMed |
description | PURPOSE: Phosphorus spectroscopy can differentiate among liver disease stages and types. To quantify absolute concentrations of phosphorus metabolites, sensitivity calibration and transmit field ([Formula: see text]) correction are required. The trend toward ultrahigh fields (7 T) and the use of multichannel RF coils makes this ever more challenging. We investigated the constraints on reference phantoms, and implemented techniques for the absolute quantification of human liver phosphorus spectra acquired using a 10‐cm loop and a 16‐channel array at 7 T. METHODS: The effect of phantom conductivity was assessed at 25.8 MHz (1.5 T), 49.9 MHz (3 T), and 120.3 MHz (7 T) by electromagnetic modeling. Radiofrequency field maps ([Formula: see text]) were measured in phosphate phantoms (18 mM and 40 mM) at 7 T. These maps were used to assess the correction of 4 phantom 3D‐CSI data sets using 3 techniques: phantom replacement, explicit normalization, and simplified normalization. In vivo liver spectra acquired with a 10‐cm loop were corrected with all 3 methods. Simplified normalization was applied to in vivo 16‐channel array data sets. RESULTS: Simulations show that quantification errors of less than 3% are achievable using a uniform electrolyte phantom with a conductivity of 0.23‐0.86 S.m(−1) at 1.5 T, 0.39‐0.58 S.m(−1) at 3 T, and 0.34‐0.42 S.m(−1) (16‐19 mM KH(2)PO(4(aq))) at 7 T. The mean γ‐ATP concentration quantified in vivo at 7 T was 1.39 ± 0.30 mmol.L(−1) to 1.71 ± 0.35 mmol.L(−1) wet tissue for the 10‐cm loop and 1.88 ± 0.25 mmol.L(−1) wet tissue for the array. CONCLUSION: It is essential to select a calibration phantom with appropriate conductivity for quantitative phosphorus spectroscopy at 7 T. Using an 18‐mM phosphate phantom and simplified normalization, human liver phosphate metabolite concentrations were successfully quantified at 7 T. |
format | Online Article Text |
id | pubmed-6492160 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2019 |
publisher | John Wiley and Sons Inc. |
record_format | MEDLINE/PubMed |
spelling | pubmed-64921602019-05-06 Feasibility of absolute quantification for (31)P MRS at 7 T Purvis, Lucian A. B. Valkovič, Ladislav Robson, Matthew D. Rodgers, Christopher T. Magn Reson Med Full Papers—Spectroscopic Methodology PURPOSE: Phosphorus spectroscopy can differentiate among liver disease stages and types. To quantify absolute concentrations of phosphorus metabolites, sensitivity calibration and transmit field ([Formula: see text]) correction are required. The trend toward ultrahigh fields (7 T) and the use of multichannel RF coils makes this ever more challenging. We investigated the constraints on reference phantoms, and implemented techniques for the absolute quantification of human liver phosphorus spectra acquired using a 10‐cm loop and a 16‐channel array at 7 T. METHODS: The effect of phantom conductivity was assessed at 25.8 MHz (1.5 T), 49.9 MHz (3 T), and 120.3 MHz (7 T) by electromagnetic modeling. Radiofrequency field maps ([Formula: see text]) were measured in phosphate phantoms (18 mM and 40 mM) at 7 T. These maps were used to assess the correction of 4 phantom 3D‐CSI data sets using 3 techniques: phantom replacement, explicit normalization, and simplified normalization. In vivo liver spectra acquired with a 10‐cm loop were corrected with all 3 methods. Simplified normalization was applied to in vivo 16‐channel array data sets. RESULTS: Simulations show that quantification errors of less than 3% are achievable using a uniform electrolyte phantom with a conductivity of 0.23‐0.86 S.m(−1) at 1.5 T, 0.39‐0.58 S.m(−1) at 3 T, and 0.34‐0.42 S.m(−1) (16‐19 mM KH(2)PO(4(aq))) at 7 T. The mean γ‐ATP concentration quantified in vivo at 7 T was 1.39 ± 0.30 mmol.L(−1) to 1.71 ± 0.35 mmol.L(−1) wet tissue for the 10‐cm loop and 1.88 ± 0.25 mmol.L(−1) wet tissue for the array. CONCLUSION: It is essential to select a calibration phantom with appropriate conductivity for quantitative phosphorus spectroscopy at 7 T. Using an 18‐mM phosphate phantom and simplified normalization, human liver phosphate metabolite concentrations were successfully quantified at 7 T. John Wiley and Sons Inc. 2019-03-20 2019-07 /pmc/articles/PMC6492160/ /pubmed/30892732 http://dx.doi.org/10.1002/mrm.27729 Text en © 2019 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. |
spellingShingle | Full Papers—Spectroscopic Methodology Purvis, Lucian A. B. Valkovič, Ladislav Robson, Matthew D. Rodgers, Christopher T. Feasibility of absolute quantification for (31)P MRS at 7 T |
title | Feasibility of absolute quantification for (31)P MRS at 7 T |
title_full | Feasibility of absolute quantification for (31)P MRS at 7 T |
title_fullStr | Feasibility of absolute quantification for (31)P MRS at 7 T |
title_full_unstemmed | Feasibility of absolute quantification for (31)P MRS at 7 T |
title_short | Feasibility of absolute quantification for (31)P MRS at 7 T |
title_sort | feasibility of absolute quantification for (31)p mrs at 7 t |
topic | Full Papers—Spectroscopic Methodology |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6492160/ https://www.ncbi.nlm.nih.gov/pubmed/30892732 http://dx.doi.org/10.1002/mrm.27729 |
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