Reduction of RF Heating Near Bilateral Deep Brain Stimulation Leads Using Two-Channel RF Shimming at 3T

The use of 3T MRI in patients with bilateral deep brain stimulation (DBS) leads is limited by safety concerns due to radiofrequency (RF) heating. A promising strategy to overcome this problem involves RF shimming using low-specific absorption rate (SAR) calibration scans to estimate the RF-induced currents based on image artifacts near the leads. Although clinically available two-channel RF shimming can suppress RF heating in a single lead configuration, complete nulling is not possible when more than one lead is involved. This study aims to develop a method to minimize rather than null RF heating and optimize imaging performance during 3T MRI in a bilateral DBS lead configuration by using two-channel RF shimming. An anthropomorphic phantom equipped with bilateral DBS leads and fiber-optic temperature sensors was constructed. Optimal RF shim settings were determined in multiple phantom orientations using a low-SAR calibration protocol. These settings were evaluated and compared with the quadrature mode by measuring local RF heating during a high-SAR imaging sequence and inspecting residual image artifacts. Measured heating curves and imaging data confirmed that tailored RF shim settings minimized RF heating and image artifacts for both leads simultaneously in all orientations studied. Two-channel RF shimming on a clinical 3T MRI scanner can thus be optimized in a bilateral DBS lead configuration to minimize RF heating and maximize imaging performance. This workflow could potentially enable a patient-specific workflow for safe imaging in patients with bilateral DBS leads at 3T.