Longitudinal gradient coil optimization in the presence of transient eddy currents

Area of Science:

• Medical Imaging
• Electromagnetism
• Computational Physics

Background:

• Magnetic Resonance Imaging (MRI) gradient coil switching induces eddy currents in conductive components like cryostats.
• These eddy currents degrade the spatial and temporal performance of gradient coils, necessitating compensation methods.

Purpose of the Study:

• To theoretically investigate and demonstrate a novel approach for optimizing gradient coil designs by incorporating induced eddy currents.
• To achieve spatially homogeneous gradient fields that accurately follow input pulses by combining coil and eddy current fields.

Main Methods:

• A theoretical study incorporating eddy currents into the gradient coil optimization process.
• Simulation of transient eddy currents in a realistic cryostat vessel using a low-frequency finite-difference time-domain (FDTD) method with a total-field scattered-field (TFSF) scheme.
• Exemplification using shielded and unshielded longitudinal gradient coils.

Main Results:

• Demonstrated the effectiveness of the proposed method in modifying gradient coil designs to counteract eddy current distortions.
• Achieved a combination of coil fields and eddy current fields that produce a spatially homogeneous gradient following the input pulse.
• Validated the approach through simulations of eddy current behavior in a cryostat.

Conclusions:

• Incorporating eddy current effects into coil optimization is a viable strategy for enhancing MRI gradient performance.
• The proposed method offers a way to design gradient coils that inherently compensate for eddy current-induced distortions.
• This approach can lead to improved spatial and temporal accuracy in MRI gradient fields.