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Quantifying tissue damage due to focused ultrasound heating observed by MRI
1Sunnybrook & Women's College Health Sciences Centre, and Department of Medical Biophysics, University of Toronto, Ontario, Canada. sgraham@sten.sunnybrook.utoronto.ca
Abstract:
Focused ultrasound heating of ex vivo bovine kidney and liver was monitored using magnetic resonance imaging (MRI) to investigate the quantitative relationship between time-dependent temperature elevations and altered contrast in MR images due to thermal coagulation. Proton resonance frequency shift MR thermometry was performed during heating at 10 sec intervals (single-slice fast spoiled GRASS [FSPGR], theta/TE/TR 30 degrees/11/39 msec, field of view 8 cm, 256 x 256, 3 mm slice thickness, 1 NEX); post-heating MR images were T1-weighted (3D-FSPGR, theta/TE/TR 60 degrees/25/200 msec, 1 mm slice thickness, 3 NEX). Analysis of the resulting temperature versus time data using the Arrhenius relationship and a simple binary discrimination model showed that thermal coagulation occurred with heating at approximately 54 degrees C for 10 sec in both tissues and could be predicted with approximately 625 microm spatial resolution. These results suggest that quantitative MR guidance of thermal coagulation therapy is feasible, and they provide information useful for designing future investigations in vivo.
Insights
Magnetic resonance imaging (MRI) can guide thermal coagulation therapy by monitoring temperature changes during focused ultrasound heating. This study shows MRI can predict tissue coagulation at 54°C for 10 seconds with 625 microm resolution.
Area of Science:
- Biomedical Engineering
- Medical Imaging
- Thermal Ablation
Background:
- Focused ultrasound (FUS) enables non-invasive tissue heating.
- Magnetic resonance imaging (MRI) offers real-time monitoring capabilities.
- Thermal coagulation is a key mechanism in FUS therapies.
Purpose of the Study:
- To investigate the quantitative relationship between temperature elevation and MR image contrast changes during FUS-induced thermal coagulation.
- To assess the feasibility of MRI-guided thermal coagulation therapy.
Main Methods:
- Ex vivo bovine kidney and liver tissues were heated using focused ultrasound.
- Proton resonance frequency shift MR thermometry was employed for real-time temperature monitoring at 10-second intervals.
- Post-heating MR images were acquired using T1-weighted sequences.
- Arrhenius relationship and binary discrimination models were used for data analysis.
Main Results:
- Thermal coagulation was observed at approximately 54°C for 10 seconds in both kidney and liver tissues.
- MRI accurately predicted thermal coagulation with a spatial resolution of approximately 625 micrometers.
- A quantitative relationship between temperature elevation and altered MR contrast was established.
Conclusions:
- Quantitative MRI guidance for thermal coagulation therapy is feasible.
- The findings provide valuable data for designing future in vivo investigations of MRI-guided FUS therapies.