MRI monitoring of interstitial microwave‐induced heating and thermal lesions in rabbit brain in vivo

Abstract

The purpose of this experiment was to use MRI to monitor microwave heating and thermal damage of brain tissue in vivo. Interstitial microwave antennas were implanted into the cerebral hemispheres of seven anesthetized rabbits. Variable power of 30 to 100 W was applied for periods of 5 to 15 minutes and tissue temperature was monitored continuously. MR images were obtained throughout the procedure at 20-second intervals, using a spoiled gradient-echo sequence, without significant artifact. Magnitude, phase, and complex difference images all demonstrated temperature-related signal changes during heating. The findings were better visualized on the phase and complex difference images. Phase difference image analysis revealed an approximately linear relationship between phase change and temperature. Post-treatment thermal lesions measured up to 2.0 cm in size on pathologic specimens and exhibited a zonal pattern on spin-echo MR images.

Heat-source orientation and geometry dependence in proton-resonance frequency shift magnetic resonance thermometry

“…Previous experiments incorporating interstitial microwave heating of polyacrylamide gels have resulted in eccentric temperature-induced phase-shift patterns when the antenna was oriented perpendicular to the main magnetic field (27). Furthermore, subsequent experiments have revealed similar eccentric phase-shift patterns from interstitial microwave heating of in vivo rabbit brain (28), in which it was assumed that the observed eccentricity was simply a result of in vivo anisotropic temperaturediffusion effects, such as those due to blood flow. Other heat-delivery devices for clinical use potentially will give rise to this effect, such as focused ultrasound transducers and, perhaps to a lesser extent, interstitial laser fibres.…”

MR thermometry

“…Microwave heating for thermal ablation uses a small interstitial microwave antenna operated at a frequency of 1-3 GHz (11). For microwave ablation, several antennas can be used simultaneously to create large lesions sizes.…”

Temperature mapping using the water proton chemical shift: Self-referenced method with echo-planar spectroscopic imaging

“…The phase-mapping method has been widely accepted as a convenient tool to monitor tissue temperature change under thermal therapies (7)(8)(9). However, the phase-mapping method is subject to tissue susceptibility change (10 -12) and body movement, because it depends upon a relative change in the phase by taking a subtraction between objective and reference images.…”