Fast frequency mapping with balanced SSFP: theory and application to proton-resonance frequency shift thermometry

Area of Science:

• Medical Imaging
• Biophysics
• Magnetic Resonance Imaging

Background:

• Accurate temperature mapping is crucial for various medical applications, including thermal ablation and hyperthermia treatment.
• Existing methods for temperature mapping often face limitations in speed, accuracy, or applicability under specific imaging conditions.

Purpose of the Study:

• To develop and validate a rapid frequency mapping technique using multiecho balanced steady-state free precession (balanced SSFP).
• To assess the accuracy and performance of this new method for temperature change measurements in a gel phantom.
• To compare the balanced SSFP technique against the established multiecho fast low-angle shot (FLASH) method.

Main Methods:

• Acquisition of frequency maps using multiecho balanced SSFP (including True FISP, FIESTA, or FFE sequences).
• Determination of temperature changes by measuring the temperature-sensitive water proton-resonance frequency via phase-based linear fitting.
• Analysis of signal-to-noise ratio (SNR) under varying relaxation times, flip angles, and local field inhomogeneities.

Main Results:

• The balanced SSFP method demonstrated a significant increase in accuracy for frequency/temperature shift estimation compared to the FLASH method, depending on tissue parameters.
• Theoretical and experimental results showed good agreement.
• Balanced SSFP allows for very short repetition times (TRs) without signal loss due to saturation, crucial for real-time temperature mapping.

Conclusions:

• Multiecho balanced SSFP provides a rapid and accurate method for temperature mapping.
• This technique offers superior accuracy over the FLASH method for temperature shift estimation in specific scenarios.
• The ability to use short TRs makes balanced SSFP suitable for real-time temperature monitoring applications.