Use of fast spin echo for phase shift magnetic resonance thermometry

Abstract

Purpose: To propose a modified fast spin echo (FSE) magnetic resonance imaging sequence for MR thermometry, employing the proton resonance frequency (PRF) shift by means of MR phase maps. Despite their obvious advantages of speed and high signal-to-noise ratio (SNR), FSE sequences have not until now been used for this purpose due to the restraints imposed by the Carr-Purcell-Meiboom-Gill (CPMG) conditions. Materials and Methods:The new FSE combines a new phase modulation scheme that maintains magnetization that ordinarily is destroyed under CPMG conditions, while employing conventional FSE gradient waveforms. The echoes are read in a single shot using 128 readouts in 650 msec, with a phase sensitive preparation using an optional time shift before the start of the refocusing gradient waveforms. This feature allows the quantification of temperature dependent phase shifts. We tested the sequence by imaging a heated agar gel phantom while cooling, using different values for . Results:There was good correlation between FSE and fiberoptic-based temperature measurements in the phantom(r 2 Ն 0.95). Temperature sensitivity could be adjusted by varying the value. Conclusion:With the proposed non-CPMG FSE sequence it is feasible to quantify temperature changes by means of the PRF shift.

Why are pretreatment prostate‐specific antigen levels and biochemical recurrence poor predictors of prostate cancer survival?

“…A potential solution to this problem is the incorporation of dual‐band irradiation pulses for the simultaneous excitation of the PCr and Pi peaks (49, 50). Phase images of Pi can be made very sensitive to even small changes in the chemical shift, which is the principle of MR thermometry in 1 H‐MRI (51, 52).…”

Temperature mapping of thermal ablation using MRI

“…Vogel et al have reported on a modified fast spin echo sequence that enables PRF thermometry (41). This can have a particular benefit in generating high SNR images as lower field strengths, typically used for interventional imaging (0.2-0.5T).…”

Auxiliary phase encoding in multi spin-echo sequences: Application to rapid current density imaging

“…However, its application is quite difficult as the method requires precise adjustments of the receiver phase and the procedure for calculating the list of refocusing pulse flip angles and phases is quite complicated. This method has already been successfully applied to MR thermometry [13] in which a temperature map was obtained by mapping magnetization phase shifts caused by the precession frequency shifts induced by temperature changes in the sample.…”