Minimal artifact actively shimmed metallic needles in MRI

Area of Science:

• Medical Imaging
• Biophysics
• Magnetic Resonance Imaging

Background:

• Metallic needles used in interventional MRI procedures cause significant magnetic field distortions (ΔB₀).
• These distortions lead to signal voids, hindering visualization and monitoring during procedures.
• Current methods lack effective solutions for mitigating needle-induced artifacts in real-time MRI.

Purpose of the Study:

• To develop and evaluate an active shim insert for needles to correct magnetic field disturbances in MRI.
• To assess the effectiveness of the active shim in restoring signal loss around metallic needles.
• To determine the sequence independence and potential applications of this novel shimming technique.

Main Methods:

• Modeled the ΔB₀ induced by a 4 mm titanium needle at 3T.
• Designed and fabricated a two-coil orthogonal shim set to counteract the ΔB₀.
• Assessed signal recovery in a water phantom and phase stability in ex-vivo porcine tissue using dynamic gradient echo sequences.
• Evaluated shim insert heating during continuous operation.

Main Results:

• Achieved an average signal recovery of ~63% around the needle across various orientations.
• Demonstrated that signal recovery and ΔB₀ correction are independent of the MRI pulse sequence.
• Successfully minimized needle-induced phase gradients outside the signal void.
• Observed a maximum temperature rise of 0.9°C during 8 minutes of continuous 1A operation.

Conclusions:

• Presented a sequence-independent method using an active shim insert to minimize signal loss caused by metallic needles in MRI.
• The active shim insert effectively corrects magnetic field disturbances, improving signal visualization.
• This technology holds significant potential for enhancing various qualitative and quantitative interventional MRI applications.