Fast Three-Dimensional Magnetic Resonance Thermometry Using an Echo-Shifted Gradient-Recalled Sequence

Abstract

High-intensity focused ultrasound (HIFU) is a noninvasive thermal ablation therapy. Thermometry techniques with high precision and temporal resolution are needed to ensure the safety and effectiveness of HIFU. The magnetic resonance thermometry (MRT) technique based on proton resonance frequency shift (PRFS) shows good linearity with and high sensitivity to temperature change, and is frequently used in HIFU therapy. In practice, HIFU may have a potential danger of causing unwanted skin burns far away from the focus of ultrasound irradiation. It is therefore desirable to increase the spatial coverage of MRT measurements to include the skins. In this work, a fast three-dimensional (3D) MRT technique was developed based on an echo-shifted gradient-recalled sequence with controlled aliasing in volumetric parallel imaging. Phantom experiments were first used to calibrate the accuracy and precision of temperature measurements made by the proposed technique to those obtained by an optical fiber thermometer. Pork tissues were then scanned at room temperature to determine the precision of temperature measurements before and after imaging acceleration. The pork tissues were also scanned under the condition of HIFU heating to compare the accuracy of temperature measurements with or without imaging acceleration.

Keywords

• magnetic resonance thermometry
• echo-shifted gradient-recalled sequence
• volumetric parallel imaging
• proton resonance frequency shift