Simultaneous T₂ -weighted real-time MRI of two orthogonal slices

Area of Science:

• Medical Imaging
• Radiotherapy Technology
• Magnetic Resonance Imaging

Background:

• Magnetic resonance (MR) guidance is crucial for detecting and compensating for lesion motion during therapy.
• T2-weighted MR imaging offers superior lesion contrast compared to T1-weighted real-time imaging.

Purpose of the Study:

• To design a rapid T2-weighted magnetic resonance imaging (MRI) sequence.
• To enable simultaneous acquisition of two orthogonal slices for real-time lesion tracking.

Main Methods:

• Developed the Ortho-SSFP-Echo sequence for simultaneous T2-weighted spin echo signal acquisition in two orthogonal slices.
• Implemented slice selection and phase-encoding direction swapping for unique signal conditions.
• Incorporated flow-compensation strategies to minimize motion-related signal dephasing.
• Acquired time-series data using the sequence in phantom and in vivo experiments, tracking target centroids.

Main Results:

• Successfully identified and delineated lesions in dynamic phantom images.
• Visualized the kidney with T2 contrast at 0.45s temporal resolution under free-breathing conditions in volunteers.
• Demonstrated strong correlation between respiratory belt data and kidney centroid motion.
• Confirmed that a saturation band did not impede lesion tracking.

Conclusions:

• The Ortho-SSFP-Echo sequence provides real-time, T2-weighted images in two orthogonal slices.
• Simultaneous acquisition capability is advantageous for real-time motion tracking in radiotherapy and interventional MRI.