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Transrectal ultrasound applicator for prostate heating monitored using MRI thermometry
N B Smith1, M T Buchanan, K Hynynen
1Brigham and Women's Hospital, Harvard Medical School, Department of Radiology, Boston, MA 02115, USA.
International Journal of Radiation Oncology, Biology, Physics
|February 16, 1999
Summary
A novel MRI-compatible ultrasound applicator enables precise, non-invasive hyperthermia for prostate tumors. Real-time MRI thermometry accurately guides temperature control during treatment.
Area of Science:
- Medical physics
- Biomedical engineering
- Oncology
Background:
- Localized hyperthermia is a promising cancer treatment modality.
- Integrating hyperthermia with Magnetic Resonance Imaging (MRI) allows for real-time temperature monitoring and precise treatment delivery.
- Developing MRI-compatible applicators is crucial for safe and effective MRI-guided hyperthermia.
Purpose of the Study:
- To develop and evaluate a nonmagnetic, MRI-compatible ultrasound applicator for localized prostate tumor hyperthermia.
- To assess the applicator's ability to control energy deposition and achieve therapeutic temperatures in vivo.
- To validate MRI thermometry using the proton resonant frequency (PRF) shift for accurate temperature monitoring.
Main Methods:
- A 16-element, partial-cylindrical intracavitary ultrasound transducer operating at 1.5 MHz was constructed.
- Spatial and temporal temperature elevations were measured using MRI thermometry (PRF shift) during ultrasonic heating.
- The applicator's performance was tested ex vivo and in vivo on rabbit muscle tissue, with comparisons to thermocouple measurements.
Main Results:
- The ultrasound applicator demonstrated MRI compatibility, allowing simultaneous imaging and sonication.
- Real-time monitoring of radiofrequency (RF) power to each element enabled precise control of the induced temperature distribution.
- Therapeutic temperatures (45°C) were achieved in vivo at approximately 16% of maximum system power.
- MRI thermometry using the PRF shift showed an average error of 0.34±0.36°C compared to thermocouples.
Conclusions:
- The developed MRI-compatible intracavitary applicator effectively controlled the ultrasound field and temperature distribution in vivo.
- MRI thermometry utilizing the PRF shift is a sufficiently accurate and stable method for guiding hyperthermia treatments.
- This technology holds potential for precise, image-guided thermal ablation of localized tumors, particularly in the prostate.