B0 Shimming Device Using Adjustable Magnetic Materials

The patent replaces traditional mechanical shim coils with a magnetic field generating apparatus that uses electromagnetic induction. Instead of physically adding multiple coil layers that occupy space, the system uses a single coil structure with controlled current distribution to generate the necessary magnetic field corrections, thereby maintaining free bore space while achieving field uniformity.

The patent changes the operational parameters of the shim coil system by using time-varying currents with specific frequency components. Rather than increasing the number of physical coils, the system modifies the electrical parameters (current amplitude and frequency) to generate multiple magnetic field components from a single coil structure, achieving the effect of multiple coils without the spatial overhead.

The patent replaces the multi-coil thermal system with a single-coil electromagnetic system. By using electromagnetic induction with time-varying currents, the system achieves the same field uniformity correction with significantly reduced resistive heating, as only one coil carries current at any given time rather than multiple coils operating simultaneously.

The patent employs periodic current variation at specific frequencies to generate the necessary magnetic field components. By using alternating currents with different frequency components instead of DC currents in multiple coils, the system reduces continuous heat generation and allows for thermal management through the periodic nature of the operation.

The patent merges the shim coil functionality with the main gradient coil structure. Instead of using separate insert shim coils that need to be handled independently, the shimming capability is integrated into the existing gradient coil assembly, eliminating the need for separate heavy components and complex cabling arrangements.

The patent extracts the shimming function from the physical shim coil hardware and implements it through software-controlled current modulation of the gradient coils. This removes the need for heavy magnetic components and extensive cabling, leaving only the control electronics and software to manage field uniformity.

The patent uses time-varying magnetic fields as an intermediary mechanism. Instead of placing static conductors close to the subject that would continuously interact with RF and gradient fields, the system uses periodically varying fields that can be synchronized and coordinated with the RF and gradient operations, reducing unwanted interactions through temporal separation and coordination.

The patent employs periodic current modulation to generate the shimming fields. By using alternating currents at specific frequencies rather than continuous DC currents, the system creates time-limited electromagnetic interactions that can be coordinated with the pulse sequences, reducing continuous coupling and interference with RF and gradient operations while maintaining low power consumption.