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Influence of water and fat heterogeneity on fat‐referenced MR thermometry
Author(s) -
Baron Paul,
Deckers Roel,
Bouwman Job G.,
Bakker Chris J. G.,
de Greef Martijn,
Viergever Max A.,
Moonen Chrit T. W.,
Bartels Lambertus W.
Publication year - 2016
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.25727
Subject(s) - chemistry , ultrasound , nuclear magnetic resonance , approximation error , chicken breast , analytical chemistry (journal) , materials science , mathematics , physics , chromatography , acoustics , statistics , food science
Purpose To investigate the effect of the aqueous and fatty tissue magnetic susceptibility distribution on absolute and relative temperature measurements as obtained directly from the water/fat (w/f) frequency difference. Methods Absolute thermometry was investigated using spherical phantoms filled with pork and margarine, which were scanned in three orthogonal orientations. To evaluate relative fat referencing, multigradient echo scans were acquired before and after heating pork tissue via high‐intensity focused ultrasound (HIFU). Simulations were performed to estimate the errors that can be expected in human breast tissue. Results The sphere experiment showed susceptibility‐related errors of 8.4°C and 0.2°C for pork and margarine, respectively. For relative fat referencing measurements, fat showed pronounced phase changes of opposite polarity to aqueous tissue. The apparent mean temperature for a numerical breast model assumed to be 37°C was 47.2 ± 21.6°C. Simulations of relative fat referencing for a HIFU sonication (ΔT = 29.7°C) yielded a maximum temperature error of 6.6°C compared with 2.5°C without fat referencing. Conclusion Variations in the observed frequency difference between water and fat are largely due to variations in the w/f spatial distribution. This effect may lead to considerable errors in absolute MR thermometry. Additionally, fat referencing may exacerbate rather than correct for proton resonance frequency shift–temperature measurement errors. Magn Reson Med 75:1187–1197, 2016. © 2015 Wiley Periodicals, Inc.