Fast PRF-based MR thermometry using double-echo EPI: in vivo comparison in a clinical hyperthermia setting
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To develop and test in a clinical setting a double-echo segmented echo planar imaging (DEPI) pulse sequence for proton resonance frequency (PRF)-based temperature monitoring that is faster than conventional PRF thermometry pulse sequences and not affected by thermal changes in tissue conductivity.
Materials and methods
Four tumor patients underwent between one and nine magnetic resonance (MR)-guided regional hyperthermia treatments. During treatment, the DEPI sequence and a FLASH PRF sequence were run in an interleaved manner to compare the results from both sequences in the same patients and same settings. Temperature maps were calculated based on the phase data of both sequences. Temperature measurements of both techniques were compared using Passing and Bablok regression and the Bland–Altman method.
The temperature results from the DEPI and FLASH sequences, on average, do not differ by more than ΔT = 1 °C. DEPI images showed typically more artifacts and approximately a twofold lower signal-to-noise ratio (SNR), but a sufficient temperature precision of 0.5°, which would theoretically allow for a fivefold higher frame rate.
The results indicate that DEPI can replace slower temperature measurement techniques for PRF-based temperature monitoring during thermal treatments. The higher acquisition speed can be exploited for hot spot localization during regional hyperthermia as well as for temperature monitoring during fast thermal therapies.