Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, California, USA.
Magn Reson Med. 2012 Aug;68(2):606-13. doi: 10.1002/mrm.23235. Epub 2011 Dec 28.
Radiofrequency induced pacemaker lead tip heating is one of the main reasons magnetic resonance imaging (MRI) is contraindicated for patients with pacemakers. The objective of this work was to evaluate the dependence of pacemaker lead tip heating during MRI scanning on the electrical conductivity of the medium surrounding the pacemaker lead tip. The effect of conductivity was measured using hydroxyethyl cellulose, polyacrylic acid, and saline with conductivities ranging from 0 to 3 S/m which spans the range of human tissue conductivity. The maximum lead tip heating observed in polyacrylic acid was 50.4 °C at 0.28 S/m, in hydroxyethyl cellulose the maximum was 36.8 °C at 0.52 S/m, and in saline the maximum was 12.5 °C at 0.51 S/m. The maximum power transfer theorem was used to calculate the relative power deposited in the solution based on the characteristic impedance of the pacemaker lead and test solution impedance. The results demonstrate a strong correlation between the relative power deposited and pacemaker lead tip heating for hydroxyethyl cellulose and saline solutions. Maximum power deposition occurred when the impedance of the solution matched the pacemaker lead impedance. Pacemaker lead tip heating is dependent upon the electrical conductivity of the solution at the lead tip and should be considered when planning in vitro gel or saline experiments.
射频引起的起搏器导线尖端加热是磁共振成像（MRI）对起搏器患者禁忌的主要原因之一。这项工作的目的是评估在 MRI 扫描期间起搏器导线尖端加热对起搏器导线尖端周围介质电导率的依赖性。使用羟乙基纤维素、聚丙烯酸和导电率范围为 0 至 3 S/m 的生理盐水来测量电导率的影响，该范围跨越了人体组织的电导率范围。在 0.28 S/m 时，聚丙烯酸中观察到的最大导线尖端加热为 50.4°C，在 0.52 S/m 时，羟乙基纤维素中的最大加热为 36.8°C，在 0.51 S/m 时，生理盐水的最大加热为 12.5°C。最大功率传输定理用于根据起搏器导线和测试溶液阻抗计算溶液中相对功率的沉积。结果表明，羟乙基纤维素和生理盐水溶液的相对功率沉积与起搏器导线尖端加热之间存在很强的相关性。当溶液的阻抗与起搏器导线的阻抗匹配时，最大功率沉积发生。起搏器导线尖端加热取决于导线尖端溶液的电导率，在计划体外凝胶或生理盐水实验时应予以考虑。
