MRI thermometry in phantoms by use of the proton resonance frequency shift method: application to interstitial laser thermotherapy

Johan Olsrud, Ronnie Wirestam, Sara Brockstedt, Annika M K Nilsson, Karl-Göran Tranberg, Freddy Ståhlberg, Bertil R Persson

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Abstract

In this work the temperature dependence of the proton resonance frequency was assessed in agarose gel with a high melting temperature (95 degrees C) and in porcine liver in vitro at temperatures relevant to thermotherapy (25-80 degrees C). Furthermore, an optically tissue-like agarose gel phantom was developed and evaluated for use in MRI. The phantom was used to visualize temperature distributions from a diffusing laser fibre by means of the proton resonance frequency shift method. An approximately linear relationship (0.0085 ppm degrees C(-1)) between proton resonance frequency shift and temperature change was found for agarose gel, whereas deviations from a linear relationship were observed for porcine liver. The optically tissue-like agarose gel allowed reliable MRI temperature monitoring, and the MR relaxation times (T1 and T2) and the optical properties were found to be independently alterable. Temperature distributions around a diffusing laser fibre, during irradiation and subsequent cooling, were assessed with high spatial resolution (voxel size = 4.3 mm3) and with random uncertainties ranging from 0.3 degrees C to 1.4 degrees C (1 SD) with a 40 s scan time.
Original languageEnglish
Pages (from-to)2597-2613
JournalPhysics in Medicine and Biology
Volume43
Issue number9
Publication statusPublished - 1998

Subject classification (UKÄ)

  • Radiology, Nuclear Medicine and Medical Imaging

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