Fast Referenceless PRF Thermometry Using Spatially Saturated, Spatial-spectrally Excited Flyback EPI

摘要

High intensity focused ultrasound (HIFU) is a promising technique for noninvasive treatment of liver tumors. To safely monitor HIFU, accurate temperature measurements must be acquired. However, respiratory motion impairs the performance of conventional MR-guided PRF-thermometry sequences, leading to inaccurate temperature measurements and locations. We developed an MR imaging system to minimize these with the following key elements: imaging at 3.62 frames/sec and utilizing real-time referenceless thermometry processing. A spatially saturated, spectral-spatially excited flyback echo planar readout pulse sequence that allows rapid temperature acquisition was developed. The spatial-spectral pulse ignores lipids, and other off-resonance effects are mitigated with linear delays of the EPI readout. The saturation pulse restricts the field of view in the phase encode direction, allowing for increased resolution without aliasing. The pulse sequence was constructed in RTHawk, a real time MR environment, and tested by creating lesions in a phantom using the ExAblate 2000 (Insightec, Haifa, Israel). The experiment was performed when the transducer and phantom were stationary and when both were manually moved back and forth to simulate respiratory motion. Both lesions mainly followed the same shape, and the lesion appeared as a round growing spot during motion. The real-time sequence in conjunction with referenceless thermometry is promising for HIFU in the presence of motion.