Abstract
Introduction The susceptibility contrast between frozen and unfrozen tissue disturbs the local magnetic field in the proximity of the ice-ball during cryotherapy. This effect should be corrected for in real time to allow PRFS-based monitoring of near-zero temperatures during intervention. Material and methods Susceptibility artifacts were corrected post-processing, using a rapid numerical algorithm. The difference in bulk magnetic susceptibility between frozen and non-frozen tissue was approximated to be uniform over the ice-ball volume and was determined from the isothermal principle applied to the phase-transition frontier of compartments. Subsequently, the magnetic perturbation field was calculated rapidly in 3D using a Fourier-convolution. Experimental studies were performed for two scenarios: tissue defrosting in a water bath and induction of an ice-ball by a MR-compatible cryogenic probe. Results The susceptibility artifacts yielded PRFS temperature errors as high as 10-12?C proximal to the ice-ball, positive or negative depending on the relative orientation of the position vector from the Bo direction. These effects were fully corrected for to within the noise range. The susceptibility-corrected PRFS temperature values were consistent with the phase-transition isothermal condition, irrespective of the local orientation of the position vector. Conclusion By implementing on-line the post processing algorithm, PRFS MRT may be used as a safety tool for noninvasive and accurate monitoring of near-zero temperatures during MR-guided clinical cryotherapy.
Original language | English (US) |
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Pages (from-to) | 23-31 |
Number of pages | 9 |
Journal | Magnetic Resonance Materials in Physics, Biology and Medicine |
Volume | 25 |
Issue number | 1 |
DOIs | |
State | Published - Feb 2012 |
Keywords
- Interventional
- MR-guided cryoablation
- Magnetic susceptibility
- PRFS thermometry
- Real-time correction
- Safety
ASJC Scopus subject areas
- Biophysics
- Radiological and Ultrasound Technology
- Radiology Nuclear Medicine and imaging