Reference-Free PRFS MR-Thermometry Using Near-Harmonic 2-D Reconstruction of the Background Phase

• Published in: IEEE transactions on medical imaging Vol. 31; no. 2; pp. 287 - 301
• Main Authors: Salomir, R., Viallon, M., Kickhefel, A., Roland, J., Morel, D. R., Petrusca, L., Auboiroux, V., Goget, T., Terraz, S., Becker, C. D., Gross, P.
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.02.2012; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Ablation; Animals; Approximation methods; Body Temperature - physiology; Coils; Focused ultrasound; Formalism; Frequency shift; harmonic functions; High-Intensity Focused Ultrasound Ablation - methods; Image Interpretation, Computer-Assisted - methods; Image reconstruction; In Vitro Techniques; Instability; Magnetic fields; magnetic resonance (MR) thermometry; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; magnetic susceptibility; Mathematical model; Mathematical models; Muscle, Skeletal - pathology; Muscle, Skeletal - physiopathology; Muscle, Skeletal - surgery; Perturbation methods; Polynomials; Reconstruction; Reference Values; Reproducibility of Results; Sensitivity and Specificity; Studies; Surgery, Computer-Assisted - methods; Thermography - methods; tissue motion; Turkeys
• ISSN: 0278-0062; 1558-254X
• DOI: 10.1109/TMI.2011.2168421

Proton resonance frequency shift (PRFS) MR thermometry (MRT) is the generally preferred method for monitoring thermal ablation, typically implemented with gradient-echo (GRE) sequences. Standard PRFS MRT is based on the subtraction of a temporal reference phase map and is, therefore, intrinsically sensitive to tissue motion (including deformation) and to external perturbation of the magnetic field. Reference-free (or reference-less) PRFS MRT has been previously described by Rieke and was based on a 2-D polynomial fit performed on phase data from outside the heated region, to estimate the background phase inside the region of interest. While their approach was undeniably a fundamental progress in terms of robustness against tissue motion and magnetic perturbations, the underlying mathematical formalism requires a thick unheated border and may be subject to numerical instabilities with high order polynomials. A novel method of reference-free PRFS MRT is described here, using a physically consistent formalism, which exploits mathematical properties of the magnetic field in a homogeneous or near-homogeneous medium.