OBJECT: The temperature dependence of the proton resonance frequency (PRF) is often used in MR thermometry. However, this method is prone to even very small changes in local magnetic field strength. Here, we report on the effects of susceptibility changes of surrounding air on the magnetic field inside an object and their inferred effect on the measured MR temperature. MATERIALS AND METHODS: MR phase thermometry was performed on spherical agar phantoms enclosed in cylindrical containers at 7 T. The air susceptibility inside the cylindrical container was changed by both heating the air and changing the gas composition. RESULTS: Changing the temperature of surrounding air from 23 to 69°C caused an apparent MR temperature error of 2 K. When ambient air was displaced by 100% oxygen, the MR temperature error increased to 40 K. The magnetic field shift and therefore error in inferred MR temperature scales linearly with volume susceptibility change and has a strong and nontrivial dependence on the experimental configuration. CONCLUSION: Air susceptibility changes associated with oxygen concentration changes greatly affect PRF MR thermometry measurements. Air temperature changes can also affect these measurements, but to a smaller degree. For uncalibrated MR thermometry, air susceptibility changes may be a significant source of error.
OBJECT: The temperature dependence of the proton resonance frequency (PRF) is often used in MR thermometry. However, this method is prone to even very small changes in local magnetic field strength. Here, we report on the effects of susceptibility changes of surrounding air on the magnetic field inside an object and their inferred effect on the measured MR temperature. MATERIALS AND METHODS: MR phase thermometry was performed on spherical agar phantoms enclosed in cylindrical containers at 7 T. The air susceptibility inside the cylindrical container was changed by both heating the air and changing the gas composition. RESULTS: Changing the temperature of surrounding air from 23 to 69°C caused an apparent MR temperature error of 2 K. When ambient air was displaced by 100% oxygen, the MR temperature error increased to 40 K. The magnetic field shift and therefore error in inferred MR temperature scales linearly with volume susceptibility change and has a strong and nontrivial dependence on the experimental configuration. CONCLUSION: Air susceptibility changes associated with oxygen concentration changes greatly affect PRF MR thermometry measurements. Air temperature changes can also affect these measurements, but to a smaller degree. For uncalibrated MR thermometry, air susceptibility changes may be a significant source of error.
Authors: K Kuroda; R V Mulkern; K Oshio; L P Panych; T Nakai; T Moriya; S Okuda; K Hynynen; F A Jolesz; F A Joles Journal: Magn Reson Med Date: 2000-02 Impact factor: 4.668
Authors: Terry S Yoo; Michael J Ackerman; William E Lorensen; Will Schroeder; Vikram Chalana; Stephen Aylward; Dimitris Metaxas; Ross Whitaker Journal: Stud Health Technol Inform Date: 2002
Authors: Evdokia M Kardoulaki; Richard R A Syms; Ian R Young; Kaushal Choonee; Marc Rea; Wladyslaw M W Gedroyc Journal: Med Phys Date: 2015-03 Impact factor: 4.071
Authors: Mingming Wu; Hendrik T Mulder; Paul Baron; Eduardo Coello; Marion I Menzel; Gerard C van Rhoon; Axel Haase Journal: Magn Reson Med Date: 2020-05-05 Impact factor: 4.668