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

• Published in: Journal of magnetic resonance imaging 2020-07, Vol.52 (1), p.91-102
• Main Authors: Martinez, Jessica A., Moulin, Kévin, Yoo, Bryan, Shi, Yu, Kim, Hyun J., Villablanca, Pablo J., Ennis, Daniel B.
• Format: Article
• Language: English
• Subjects: Absorption; Acceptability; active implantable medical devices; Design modifications; Electronic implants; Evaluation; Field strength; Head; Humans; Image quality; low SAR; Magnetic Resonance Imaging; Median (statistics); Medical equipment; Medical imaging; MRI; MR‐conditional; MR‐safety; Patients; Phantoms, Imaging; Population studies; Prospective Studies; Prostheses and Implants; SAR; Spine; Statistical analysis; Statistics; Surgical implants; Workflow
• ISSN: 1053-1807; 1522-2586
• DOI: 10.1002/jmri.27044

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 (SARRT) were modified to meet both low SAR targets (SARLOW) using the proposed workflow. in vitro SNR and CNR were evaluated with a T1‐T2 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. SARRT SNR values were higher and significantly different than SARLOW (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. Level of Evidence: 1 Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2020;52:91–102.