Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
Biomedical Image Analysis, Eindhoven University of Technology, Eindhoven, The Netherlands.
Magn Reson Med. 2017 Dec;78(6):2449-2459. doi: 10.1002/mrm.26613. Epub 2017 Feb 5.
We introduce a new MR-based method to determine the transfer function (TF) for radiofrequency (RF) safety assessment of active implantable medical devices. Transfer functions are implant-specific measures that relate the incident tangential electric field on an (elongated) implant to a scattered electric field at its tip. The proposed method allows for TF determination with a high spatial resolution in relatively fast measurements without requiring dedicated bench setups from MRI images.
The principle of reciprocity is used in conjunction with the potential to measure currents with MRI to determine TF. Low-flip angle 3D dual gradient echo MRI data are acquired with an implant as transceive antenna, which requires minimal hardware adaptations. The implant-specific TF is determined from the acquired MRI data, with two different postprocessing methods for comparison.
TFs of linear and helical implants can be determined accurately (with a Pearson correlation coefficient R ≥ 0.7 between measurements and simulations, and a difference in field at the tip ΔEtip ≤ 19%) from relatively quick (t < 20 minutes) MRI acquisitions with (several) millimeter spatial resolution.
Transfer function determination with MRI for RF safety assessment of implantable medical devices is possible. The proposed MR-based method allows for TF determination in more realistic exposure scenarios and solid media. Magn Reson Med 78:2449-2459, 2017. © 2017 International Society for Magnetic Resonance in Medicine.
我们介绍了一种新的基于磁共振（MR）的方法，用于确定射频（RF）安全性评估有源植入式医疗器械的传递函数（TF）。传递函数是与植入物特异性相关的量，它将入射切向电场与尖端的散射电场联系起来。该方法允许在不需要专用磁共振成像（MRI）设备的情况下，从 MRI 图像中以相对较快的测量速度获得高空间分辨率的 TF。
利用磁共振成像测量电流的潜力，结合互易原理来确定 TF。采用带有植入物作为收发天线的低翻转角 3D 双梯度回波 MRI 数据采集，这需要最小的硬件适配。从获得的 MRI 数据中确定植入物特异性 TF，并使用两种不同的后处理方法进行比较。
线性和螺旋植入物的 TF 可以从相对较快的（t<20 分钟）MRI 采集（几个）毫米的空间分辨率中准确确定（测量值与模拟值之间的 Pearson 相关系数 R≥0.7，并且尖端处的场差异 ΔEtip≤19%）。
通过 MRI 进行植入式医疗器械 RF 安全性评估的 TF 确定是可行的。所提出的基于 MR 的方法可以在更真实的暴露场景和实体介质中确定 TF。磁共振医学 78:2449-2459, 2017. © 2017 国际磁共振学会。
