Abstract 13253: Remotely-Controlled Cantilevered Cardiac Shim Coil (CSS) Corrects Cardiac MRI Magnetic-Field Inhomogeneities Due to Implanted Cardioverter Defibrillators (ICDs): Preclinical Validation

Abstract

Introduction: 1.4M people (US) have implanted ICDs, which reduce risk of sudden death due to ventricular arrhythmias. Cardiac MRI (cMR) is used in patients with ICDs to diagnose conditions that predispose to sudden death and to plan and guide ablation therapy. However, all ICDs contain a ferromagnetic transformer which imposes a large inhomogeneous (>100 parts-per-million, ppm) magnetic field in sections of the heart, creating large image voids that can mask pathology, such as myocardial scar. Wide-band Late Gad. Enhancement (LGE) imaging has improved evaluation of ICD patients, handling < 25ppm artifacts, leaving unreadable voids in ~30% of patients. Hypothesis: ICD artifacts can be reduced with a remotely-displaced cardiac shim system (CSS), allowing clinical CMR imaging. Methods: The CSS system (Fig. 1A- C). A shim coil, placed in the bore, was designed to correct 75ppm fields at 15cm distances, using currents supplied from the MRI operator room (OpRm). The coil is immune to magnetic forces. A cantilevered beam holds the shim coil over the patient’s chest above the cardiac imaging coil allowing unrestricted imaging. MR-conditional motors, remotely-controlled from the OpRm, allow 2mm-resolution 3D shim-coil positioning. Experiments : swine (N=3) with chest-overlaid ICDs, emulating patients, were imaged. Magnetic-field maps were used to estimate shim-coil positioning, and current magnitude & polarity. Fine-tuning of location and current was performed during continuous 2D ECG-gated breath-held GRE/SSFP imaging. 2D/3D LGE cMR was subsequently acquired and evaluated. Results: CSS reduced field inhomogeneities due to implanted ICDs by 30ppm in 2D and 3D cMR sequences, correcting ICD-related image distortions in several heart regions (Fig. 1D, E). Conclusion: An externally-controlled shim-coil localization and drive system reduced artifacts without requiring entry into the scanner room, supporting efficient, higher quality cMR imaging of ICD patients.