Methods for improving MR thermometry in focused ultrasound

Overview

This master’s thesis, authored by Yu Weng at the Cyprus University of Technology, addresses advanced methods for improving magnetic resonance (MR) thermometry in the context of focused ultrasound (FUS) therapies. MR thermometry is a non-invasive imaging technique that enables real-time temperature mapping during thermal therapies, such as high-intensity focused ultrasound (HIFU) treatments. These therapies are increasingly used for precise ablation of pathological tissues, including tumors, without the need for surgical incisions. The integration of MR imaging with focused ultrasound allows clinicians to monitor and control the delivery of thermal energy, ensuring both efficacy and safety. However, MR thermometry faces several technical challenges, especially in dynamic or heterogeneous tissue environments, which this thesis aims to address.

Key Contributions

• Analysis of Current MR Thermometry Techniques: The thesis provides a comprehensive review of existing MR thermometry methods, including the widely used proton resonance frequency (PRF) shift technique, and discusses their limitations in the presence of tissue motion, magnetic field variations, and susceptibility changes.
• Proposed Improvements: Building on the limitations identified, the thesis explores advanced acquisition and processing strategies such as parallel imaging, sparse sampling, and robust signal processing algorithms. It also evaluates multibaseline, referenceless, and hybrid thermometry techniques that enhance measurement accuracy in challenging scenarios.
• Motion Tracking and Compensation: Recognizing the impact of organ motion (e.g., in the liver, kidney, or heart), the work investigates motion tracking solutions, including anatomical image atlases, optical-flow displacement detection, navigator echoes, and rapid vessel tracking. These techniques are crucial for maintaining spatial accuracy during temperature monitoring.
• Alternative Imaging Approaches: The thesis reviews alternative MR-based methods like MR acoustic radiation force imaging (MR-ARFI), which can identify the focal spot and sound beam path, offering a complementary approach to conventional thermometry, particularly in heterogeneous or transcranial applications.

Impact and Relevance

The advancements proposed in this thesis have significant implications for the field of image-guided thermal therapies. By improving the robustness and accuracy of MR thermometry, especially in the presence of motion or complex tissue environments, these methods enhance the safety and effectiveness of focused ultrasound treatments. The integration of advanced motion compensation and alternative imaging strategies broadens the clinical applicability of MR-guided FUS, enabling the treatment of a wider range of anatomical targets with greater precision. Ultimately, the research contributes to the ongoing evolution of non-invasive therapeutic technologies, supporting better patient outcomes and expanding the role of MR-guided interventions in modern medicine.