Technical Note: Four-dimensional deformable digital phantom for MRI sequence development.

Area of Science:

• Medical Physics
• Magnetic Resonance Imaging
• Radiotherapy

Background:

• MR-guided radiotherapy requires specialized imaging sequences distinct from diagnostic radiology.
• Existing MRI simulation software lacks features for optimizing novel sequences.
• Development of advanced simulation tools is crucial for advancing MR-guided radiotherapy.

Purpose of the Study:

• To present a novel digital framework for testing MRI sequences.
• To incorporate anatomical structure, respiratory motion, and MR physics into the simulation.
• To facilitate the development of new imaging sequences for MR-guided radiotherapy.

Main Methods:

• Utilized extended Cardiac-Torso (XCAT) software for anatomical phantom creation (T1, T2, proton density maps).
• Developed a respiratory motion model based on XCAT deformation vector fields and a respiration signal.
• Employed JEMRIS (an open-source Bloch simulator) with a custom extension for independent spin motion calculation, enabling deformable motion simulation.

Main Results:

• Successfully simulated 2D cine acquisitions and demonstrated motion ghosts in T2-weighted spin echo images.
• Simulation results aligned with previously published literature findings.
• Deformable motion simulations exhibited comparable computational time to rigid motion simulations.

Conclusions:

• Introduced a deformable 4D digital phantom framework for MR sequence development.
• The framework accurately simulates MRI by integrating anatomical structure, realistic breathing, deformable motion, and Bloch simulation.
• This tool is highly relevant for optimizing novel MRI sequences for lung and abdominal MR-guided radiotherapy.