A phase-cycled temperature-sensitive fast spin echo sequence with conductivity bias correction for monitoring of mild RF hyperthermia with PRFS
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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.
During the phantom heating experiment, on average TFSE temperature maps achieved double temperature-to-noise ratio (TNR) efficiency 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 efficiency improved by around 25% for in vivo data.
A novel TFSE method has been adapted to monitor temperature during mild HT.
KeywordsMR thermometry Hyperthermia Proton resonance frequency shift Fast spin echo Double echo gradient echo Intervention Conductivity
This project was funded by the European Commission under Grant Agreement Number 605162. Research support was received from GE Global Research. The authors would like to thank Abdelali Ameziane for technical support and Fatih Süleyman Hafalir for helpful discussions.
Wu, Mulder, Zur and Menzel contributed to the design of the study. Conceptual work on the method was performed by Zur and Wu. Wu and Mulder performed the measurements and acquired the data. The analysis and interpretation of data was done by Wu and Zur. Wu drafted the manuscript. Mulder, Zur, Lechner-Greite, Menzel, Paulides, van Rhoon and Haase were involved in critical revision of the manuscript.
Compliance with ethical standards
Conflict of interest
Yual Zur, Silke Lechner-Greite, and Marion Menzel were employed with GE Healthcare during the generation of the presented work. The remaining authors have no conflict of interest to declare.
For the in vivo feasibility study, three healthy subjects were scanned with approval by the Erasmus Medical Center Ethics Review Board (METC 2005-340).
Informed written consent was obtained from each volunteer prior to the study.
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