Magnetic resonance visualization of conductive structures by sequence-triggered direct currents and spin-echo phase...

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging (MRI)
• Interventional Radiology

Background:

• Traditional instrument visualization in interventional MRI relies on susceptibility artifacts.
• Susceptibility artifacts have limitations including poor conspicuity in inhomogeneous tissues and disturbed spatial encoding.
• Current methods offer limited control over artifact generation, being solely dependent on sequence parameters.

Purpose of the Study:

• To present a novel visualization method for interventional MRI instruments.
• To overcome limitations of susceptibility artifacts by applying sequence-triggered direct current (DC) pulses.
• To enable background-free current path localization using spin-echo (SE) phase images.

Main Methods:

• Sequence-triggered DC pulses were applied during spin-echo (SE) imaging between radiofrequency excitation and refocusing.
• Transient field inhomogeneities were induced by DC pulses, creating a phase offset.
• DC pulses were applied during inactive read-out or slice-encoding gradients to avoid false spatial encoding.
• Feasibility was demonstrated using a water phantom with a brass conductor and a titanium needle.

Main Results:

• Pulsed DC application near the conductor resulted in a visible phase offset in SE phase images.
• SE phase images remained homogenous, allowing reliable conductor position determination even in inhomogeneous fields.
• Artifact characteristics were controllable via amperage, independent of sequence parameters.
• Visualization remained effective even at a 30° angle between current and static magnetic field.

Conclusions:

• Spin-echo phase images effectively display conductors carrying pulsed DC without artifacts from persistent field inhomogeneities.
• Magnitude and phase images are acquired simultaneously, requiring no additional measurement time.
• This technique offers significant advantages for precise instrument localization in interventional MRI.