Overview of PRF Thermometry

The basis for MR temperature imaging is that the hydrogen electrons shield the nucleus from the magnetic field, decreasing the resonant frequency of the protons. Hydrogen bonds normally existing between water molecules effectively pull electrons away from their protons, increasing the resonant frequency. But, as the temperature of the tissue rises, hydrogen bonds in the tissue stretch, bend, and break. Where this happens, the electrons shield the protons from the magnetic field a little bit more, reducing the net field seen by the protons, and the overall resonant frequency. The effect has been shown to be the same for all aqueous tissues and linear within the temperature range of interest, with a temperature coefficient of alpha = 0.01 ppm/°C. Use of this relationship to measure temperature is referred to as the proton resonant frequency shift (PRF) thermometry. In practice, the temperature change in tissue is found from the change in phase in a series of gradient echo images by the following relationship,

where the echo time TE, the field strength B0, and the gyromagnetic ratio gamma are known.

In practice, PRF thermometry is easily performed in stationary tissues and MR thermometry has become integral in focused ultrasound treatments in the United States. One of the advantages of using MRI has been that it could be used to make sure the ultrasound system is properly calibrated and focused. This has been done with the application of a “test shot” with a temperature rise of a few degrees. In addition, MRI can be used to assess the treatment immediately, and evaluate if the treatment needs to be immediately extended.

Our lab has been working on MR thermometry techniques for various applications. For example, we have developed methods specifically for the case of motion, such as respiratory motion. Specific methods are needed in this case because the background phase in the heating image and the preheating image are not the same.

Relevant Lab Publications

Vigen KK, Daniel BL, Pauly JM, Butts K. Triggered, navigated, multi-baseline method for proton resonance frequency temperature mapping with respiratory motion. Magn Reson Med. 2003 Nov;50(5):1003-10.

V. Rieke, K. Vigen, G. Sommer, B. Daniel, J. Pauly, K. Butts, Referenceless PRF Shift thermometry, MRM, 2004 Jun;51(6):1223-31.

Pisani L, Ross A, Diederich C, Nau W, Sommer G, Glover G, Butts K, Effects of Spatial and Temporal Resolution for MR Image-guided Thermal Ablation of Prostate with Transurethral Ultrasound, JMRI, 2005 Jul;22(1):109-18.

Vigen K, Jarrard J, Rieke V, Frisoli J, Daniel B, Butts Pauly K, In Vivo Porcine Liver Radiofrequency Ablation with Simultaneous MR Temperature Imaging, JMRI, 2006; 23(4): p578-584.

Chen J, Daniel B, Butts Pauly K, The Temperature Dependence of The Proton Density of Ex Vivo Tissues, JMRI. 2006 Mar; 23(3): p430-434.

Butts Pauly K, Diederich CJ, Rieke V, Bouley D, Chen J, Nau WH, Ross AB, Kinsey A, Sommer G, MR-guided High Intensity Ultrasound Ablation of the Prostate, Topics in Magnetic Resonance Imaging 2006 June17(3):p195-207.

Rieke V, Diederich CJ, Nau WH, Ross AB, Kinsey A, Sommer G, Butts Pauly K, Referenceless MR Thermometry for Monitoring Thermal Ablation in the Prostate, IEEE Transactions on Medical Imaging, 2007; 26(6): p813-821.

Van den Bosch M, Daniel BL, Rieke V, Butts-Pauly K, Kermit E, Jeffrey SS. MRI-guided radiofrequency ablation of breast cancer: preliminary clinical experience. JMRI. 2008 Jan;27(1):204-8.

Rieke V, Butts Pauly K, Echo Combination to Reduce PRF Thermometry Errors From Fat, JMRI, 2008 Mar;27(3):376-90.

Rieke V, Butts Pauly K, MR Thermometry, Invited Review paper for the special issue, “Interventional MRI Update,” JMRI, 2008 Feb; 27(2):376-90.

Grissom W, Kerr A, Holbrook A, Pauly J, Butts Pauly K, Maximum Linear-Phase Spectral-Spatial RF Pulses for Fat-Suppressed PRF-Shift MR Thermometry, MRM, in press.

Additional Work Presented only in Abstracts

Rieke V, Ross AB, Nau WH, Diederich CJ, Sommer G, Butts K, MRI temperature mapping during ultrasound prostate ablation using fat for phase estimation, IEEE EMBS, San Francisco, 2004.

Rieke V, Butts K, Referenceless Thermometry in the Presence of Phase Discontinuities Between Water and Fat, 13th Scientific Meeting of the International Society for Magnetic Resonance in Medicine. Miami, Florida, May 2005, p.147.

Rieke V, Kinsey AM, Nau WH, Diederich CJ, Sommer G, Butts Pauly K, Referenceless PRF thermometry with multi-echo processing to monitor prostate ablation. 6th International Symposium on Therapeutic Ultrasound, Oxford, England, September 2006. Poster

Rieke V, Hargreaves B, Butts Pauly K, RF shift thermometry using multiple-acquisition phase-cycled balanced SSFP, ISMRM, Berlin Germany May 2007, p.1133. Poster

Rieke V., Butts Pauly K. Contribution of temperature dependent T1-change, slice thickness and positioning to an artifact in temperature images of FUS heating. ISMRM, Toronto, Canada, 2008 p. 1224.

King R, Rieke V, Butts Pauly K, MR-Guided Focused Ultrasound Ablation of the Rat Liver, ISMRM 2009

Rieke V, King R, Swaminathan A, McConnell M, Butts Pauly K, MR-Guided Focused Ultrasound Ablation Through the Ribcage, ISMRM 2009

Holbrook A, Santos J, Kaye E, Rieke V, Butts Pauly K, Real Time MR Thermometry for Monitoring Focused Ultrasound in the Liver, ISMRM 2009

Grissom W, Lustig M, Rieke V, Holbrook A, Pauly J, Butts Pauly K, Reference-Less MR Thermometry Using Iteratively-Reweighted L1 Regression, ISMRM 2009

Grissom W, Rieke V, Pauly J, McDannold N, Butts Pauly, K, Regularized Multicoil MR Thermometry, ISMRM 2009