Simultaneous acoustic radiation force imaging and MR thermometry based on a coherent echo-shifted sequence

Area of Science:

• Medical Imaging
• Biophysics
• Ultrasound Technology

Background:

• Simultaneous magnetic resonance (MR) acoustic radiation force imaging (ARFI) and MR thermometry (MRT), termed STARFI, is crucial for monitoring thermal therapies.
• Existing radiofrequency (RF)-spoiled gradient echo (spGRE) STARFI methods have limitations in efficiency and sensitivity.
• A novel coherent echo-shifted (cES) sequence was developed to enhance STARFI performance.

Purpose of the Study:

• To propose and evaluate a new cES sequence for simultaneous MR-ARFI and MRT (cES STARFI).
• To comprehensively compare the performance of cES STARFI against the conventional spGRE STARFI.
• To assess the sequence's utility during pulsed high-intensity focused ultrasound (HIFU) applications.

Main Methods:

• A cES sequence was designed with delayed echoes and a displacement encoding gradient (DEG).
• Interleaved high-intensity focused ultrasound (HIFU) pulses (ON/OFF) separated displacement and temperature phase changes.
• Bloch simulations and ex vivo experiments on porcine muscle and brain were conducted for comparison.

Main Results:

• The cES STARFI sequence demonstrated a shorter minimum repetition time (TR), indicating higher time efficiency.
• cES STARFI exhibited significantly higher phase sensitivity to displacement compared to spGRE STARFI in ex vivo experiments.
• Both displacement-induced phase-to-noise ratio (PNRd) and temperature uncertainty were improved with cES STARFI in porcine brain (P<0.05).

Conclusions:

• The cES STARFI sequence enables simultaneous MR-ARFI and temperature measurements during pulsed HIFU.
• Despite not quantifying exact displacement, cES STARFI offers superior phase sensitivity and focal spot visualization over spGRE STARFI.
• cES STARFI presents a promising alternative for practical applications requiring simultaneous ARFI and MRT.