Abstract #1565

Balanced-force shim system for correcting field inhomogeneities due to implanted cardioverter-defibrillators (ICDs): validation in phantoms

Ehud Jeruham Schmidt¹, Mirko Hrovat², Henry R Halperin¹, and Aravindan J Kolandaivelu¹

¹Medicine (Cardiology), Johns Hopkins University, School of Medicine, Baltimore, MD, United States, ²Mirtech Inc., Boston, MA, United States

Synopsis

A resistive-shim system was constructed to correct the >100ppm magnetic-field inhomogeneity caused by implanted ICDs, which leads to signal loss and blurring in cardiac MRI. A plastic platform, held to the MRI stretcher, allows human-subject insertion, and holds a sensitive 720 Ampere*turns dipole-approximating shim-coil on a movable-fixture above the chest. Shim-coil is electronically decoupled from gradients and body-coil-RF. ICD field-inhomogeneity is measured with B0 mapping, and a correction field computed (shim-coil-center-location, DC-current-intensity). Shim-coil is moved to shim-coil-center-location, and a power-supply sends DC-current to the shim-coil. System was tested on phantoms overlaid with ICDs and corrected >75ppm inhomogeneity over 50x50x50mm³ FOV.

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