Evaluation of a Workflow to Define Low Specific Absorption Rate MRI Protocols for Patients With Active Implantable Medical Devices.

Background MRI exams for patients with MR-conditional active implantable medical devices (AIMDs) are contraindicated unless specific conditions are met. This limits the maximum specific absorption rate (SAR, W/kg). Currently, there is no general framework to guide meeting a lower SAR limit. Purpose To design and evaluate a workflow for modifying MRI protocols to whole-body SAR (WB-SAR <= 0.1 W/kg) and local-head SAR (LH-SAR <= 0.3 W/kg) limits while mitigating the impact on image quality and exam time. Study Type Prospective. Population Twenty healthy volunteers on head (n = 5), C-spine (n = 5), T-spine (n = 5), and L-spine (n = 5) with IRB consent. Assessment Vendor-provided head, C-spine, T-spine, and L-spine protocols (SAR(RT)) were modified to meet both low SAR targets (SAR(LOW)) using the proposed workflow. in vitro SNR and CNR were evaluated with a T-1-T-2 phantom. in vivo image quality and clinical acceptability were scored using a 5-point Likert scale for two blinded readers. Field Strength/Sequences 1.5T/spin-echoes, gradient-echoes. Statistical Analysis In vitro SNR and CNR values were evaluated with a repeated measures general linear model. in vivo image quality and clinical acceptability were evaluated using a generalized estimating equation analysis (GEE). The two reader's level of agreement was analyzed using Cohen's kappa statistical analysis. Results Using the workflow, SAR limits were met. LH-SAR: 0.12 +/- 0.02 W/kg, median (SD) values for LH-SAR were 0.12 (0.02) W/kg and WB-SAR: 0.09 (0.01) W/kg. Examination time did not increase <= 2x the initial time. SAR(RT) SNR values were higher and significantly different than SAR(LOW) (P < 0.05). However, no significant difference was observed between the CNR values (value = 0.21). Median (IQR) CNR values were 14.2 (25.0) vs. 15.1 (9.2) for head, 12.1 (16.9) vs. 25.3 (14.2) for C-spine, 81.6 (70.1) vs. 71.0 (26.6) for T-spine, and 51.4 (52.6) vs. 37.7 (27.3) for L-spine. Image quality scores were not significantly different between SAR(RT) and SAR(LOW) (median [SD] scores were 4.0 [0.01] vs. 4.3 [0.2], P > 0.05). Data Conclusion The proposed workflow provides guidance for modifying routine MRI exams to achieve low SAR limits. This can benefit patients referred for an MRI exam with low SAR MR-conditional AIMDs. Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2020.