Magnetic resonance acoustic radiation force imaging.

Area of Science:

• Biomedical Imaging
• Medical Physics
• Ultrasound Technology

Background:

• Acoustic radiation force impulse (ARFI) imaging is an elastography technique using ultrasound to map tissue mechanical properties.
• Current ARFI methods provide stiffness-weighted images based on displacements from focused ultrasound pulses.

Purpose of the Study:

• To evaluate the feasibility of magnetic resonance acoustic radiation force imaging (MR-ARFI).
• To assess MR-ARFI's capability in detecting and quantifying displacements induced by ultrasound pulses.

Main Methods:

• Quasistatic MR elastography was employed to measure focal displacements using a 1D MRI sequence.
• Ultrasound pulses from a 1.5/1.63 MHz transducer were synchronized with MRI hardware before displacement-encoding gradients.
• Displacements were mapped in a tissue phantom and ex vivo bovine kidney.

Main Results:

• Displacements were successfully observed in the phantom and kidney, increasing linearly with acoustic power in the phantom (R²=0.99).
• Higher acoustic power led to increased displacement and irreversible phantom changes, with detectable transverse components.
• Displacements in the kidney increased post-thermal ablation.

Conclusions:

• MR-ARFI is feasible for detecting small displacements induced by low-power ultrasound pulses.
• The efficient MRI sequence is compatible with dynamic ultrasound focal spot tracking.
• MR-ARFI holds promise for advanced elastography and guiding ultrasound therapies like drug delivery.