Effects of air susceptibility on proton resonance frequency MR thermometry
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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.
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.
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.
KeywordsAir Susceptibility Temperature PRF PRFS-based MR thermometry
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- 3.Lepetit-Coiffe M, Laumonier H, Seror O, Quesson B, Sesay MB, Moonen CTW, Grenier N, Trillaud H (2010) Real-time monitoring of radiofrequency ablation of liver tumors using thermal-dose calculation by MR temperature imaging: initial results in nine patients, including follow-up. Eur Radiol 20(1): 193–201PubMedCrossRefGoogle Scholar
- 13.Yoo TS, Ackerman MJ, Lorensen WE, Schroeder W, Chalana V, Aylward S, Metaxas D, Whitaker R (2002) Engineering and algorithm design for an image processing API: a technical report on ITK—the insight toolkit. In: Westwood JD, Hoffman HM, Robb RA, Stredney D (eds) Medicine meets virtual reality 02/10— Digital upgrades: applying Moores Law to Health, vol 85. Studies in health technology and informatics. I O S Press, Amsterdam, pp 586–592Google Scholar
- 17.Kaye GWC, Laby TH (eds) (2005) 2.6.6 Magnetic properties of materials. In: Tables of physical & chemical constants, 16th edn. The National Physical LaboratoryGoogle Scholar
- 21.Streicher MN, Schäfer A, Dhital B, Müller D, Heidemann RM, Pampel A, Ivanov D, Turner R (2010) Chemically selective asymmetric spin-echo EPI phase imaging for internally referenced MR thermometry. Proc Int Soc Magn Reson Med 18: 3018Google Scholar
- 24.Salomir R, Viallon M, Roland J, Terraz S, Morel D, Becker C, Gross P (2010) Reference-less PRFS MR thermometry using a thin open border and the harmonic functions theory: 2D experimental validation. Proc Int Soc Magn Reson Med 18: 247Google Scholar