A phase-cycled temperature-sensitive fast spin echo sequence with conductivity bias correction for monitoring of mild RF hyperthermia with PRFS

Objective Mild hyperthermia (HT) treatments are generally monitored by phase-referenced proton resonance frequency shift calculations. A novel phase and thus temperature-sensitive fast spin echo (TFSE) sequence is introduced and compared to the double echo gradient echo (DEGRE) sequence. Theory and methods For a proton resonance frequency shift (PRFS)-sensitive TFSE sequence, a phase cycling method is applied to separate even from odd echoes. This method compensates for conductivity change-induced bias in temperature mapping as does the DEGRE sequence. Both sequences were alternately applied during a phantom heating experiment using the clinical setup for deep radio frequency HT (RF-HT). The B0 drift-corrected temperature values in a region of interest around temperature probes are compared to the temperature probe data and further evaluated in Bland–Altman plots. The stability of both methods was also tested within the thighs of three volunteers at a constant temperature using the subcutaneous fat layer for B0-drift correction. Results During the phantom heating experiment, on average TFSE temperature maps achieved double temperature-to-noise ratio (TNR) efciency in comparison with DEGRE temperature maps. In-vivo images of the thighs exhibit stable temperature readings of ±1 °C over 25 min of scanning in three volunteers for both methods. On average, the TNR efciency improved by around 25% for in vivo data. Conclusion A novel TFSE method has been adapted to monitor temperature during mild HT

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