Symposium



Real-time MR Thermometry Feedback Control for Prostate Hyperthermia with a Commercial HIFU System


Presenting Author Senior Author
Name: Eugene Ozhinsky Name: Viola Rieke
Email: eugene.ozhinsky@ucsf.edu Email: viola.rieke@ucsf.edu
Presenting Author’s RIG/SRG: Prostate Cancer MRI/MRS Interventional Radiology  
Presenting Author's Lab Location: China Basin   

Abstract Information
Imaging Modality: MR
Disease Application: Prostate Cancer
Complete author list: Eugene Ozhinsky, Vasant A. Salgaonkar, Chris J. Diederich, and Viola Rieke
Abstract highlights: We implemented and evaluated an MR Thermometry feedback control system for hyperthermia therapy using a commercially avail-able prostate ablation system. The experiments demonstrated that this technique allowed to sustain the therapeutic temperature rises (4-8°C) for long durations (>15 min) in large contiguous volumes in-vivo.
 
Introduction
Hyperthermia (40-45°C, 30-60 min) has been combined successfully with several cancer treatment modalities, such as radiation, chemotherapy and drug delivery. Clinical studies have demonstrated feasibility of safe application of prostate hyperthermia with endorectal ultrasound applicators. Previously, the possibility of hyperthermia therapy using a commercially available MR-guided High-Intensity Focused Ultrasound (HIFU) system for prostate ablation was investigated in simulations and phantom experiments. The goal of this project was to develop a real-time MR-thermometry feedback control for prostate HT with the InSightec prostate transducer and measure its performance in ex-vivo muscle and in in-vivo animal model.
 
Methods
The real-time thermometry application was developed for the RTHawk real-time MRI system (Heartvista, Inc., Menlo Park, CA), connected to a 3T MR scanner (GE Healthcare, Waukesha, WI) and the ExAblate 2100 prostate array (InSightec, Haifa, Israel). The application included an SPGR pulse sequence (TE = 13.4 ms, FOV = 28-32 cm, 3 s/slice), a real-time PRFS thermometry reconstruction pipeline and a custom interface for data visualization and prescription (fig.1). The system provided for interleaved simultaneous acquisition of multiple slices at different orientations. Temperature measurement was implemented using a user-adjustable elliptical ROI and served as an input to a PI feedback controller module. The controller automatically adjusted the ultrasound transducer duty cycle using a signal generator (Agilent, Santa Clara, CA), controlled via an Ethernet interface. Three HT beamforming and control patterns were implemented on the ExAblate 2100 prostate phased array ablation system: sharp 4-point focus pattern (Focal dist. = 30 mm, foci: 0.5 cm apart), mild 4-point focus (focal dist. = 40 mm, foci: 1 cm apart), and cylindri-cally diverging (ROC: 40 mm). Max. electrical power was 10 W; target temperature increase: 6 and 8°C. The HT technique was validated in phantom (2 experiments), ex-vivo muscle tissue (2 experiments) and in-vivo in one live pig (6 ex-periments), where the prostate endorectal transducer was placed on the inner thigh of the animal.
 
Results
Multi-Slice MR thermometry and feedback control was integrated with ExAblate Prostate system specific for HT. The experiments demonstrated that MR thermometry feedback control allowed to sustain the therapeutic temperature rises (4-8°C) for long durations (>15 min) in large contiguous volumes in-vivo (fig. 2-3).
 
Conclusions
This study demonstrates the feasibility of using InSightec prostate transducer with real-time MR thermometry feedback control for hyperthermia therapy.