Mattei Eugenio, Lucano Elena, Censi Federica, Angelone Leonardo M, Calcagnini Giovanni
Annu Int Conf IEEE Eng Med Biol Soc. 2016 Aug;2016:2361-2364. doi: 10.1109/EMBC.2016.7591204.
High dielectric materials (HDM) have been proposed in magnetic resonance imaging (MRI) to increase the signal-to-noise ratio (SNR) of the images acquired while reducing the radiofrequency (RF) absorption in tissue. The aim of this study is to assess the potential merit of using HDM to reduce power induced at the tip of an endocardial lead in patients undergoing MRI. Numerical simulations were performed using a commercial finite-differences time-domain (FDTD) software to model the RF field generated by a birdcage body coil at 64 MHz on a human body model. Two HDM pads were placed between the coil and the body model, and their effect was evaluated in terms of local induced power at the tip of a pacemaker lead. Two different patient imaging positions inside the coil (i.e., head & thorax) were studied. In both cases, the use of HDM allowed reducing the induced power (i.e., 57% reduction with head landmark, 68% with thorax landmark), while maintaining the same magnitude of B RMS at the isocenter of the coil. Additionally, when the HDM pads were placed at the head landmark, there was a significant decrease in the local-induced power at the tip of the implant path (58%). Conversely, there was only a 9% decrease when pads were placed at the thorax landmark. In conclusion, the study shows that when the implant is not included in the volume surrounded by the HDM, pads placed between the RF coil and the patient allow obtaining the same magnitude of B1-field with a lower input power of the RF coil, reducing significantly the local induced power around the implant. Conversely, if the implant is included in the volume surrounded by the HDM, the use of HDM can still reduce the input power necessary to obtain the same magnitude of B-field, but the effect on the local induce power at the implant is lower in magnitude.
在磁共振成像（MRI）中，人们提出使用高介电常数材料（HDM）来提高所采集图像的信噪比（SNR），同时减少组织中的射频（RF）吸收。本研究的目的是评估在接受MRI检查的患者中使用HDM降低心内膜导线尖端感应功率的潜在优点。使用商业时域有限差分（FDTD）软件进行数值模拟，以在人体模型上模拟64MHz鸟笼式体线圈产生的RF场。在体线圈和人体模型之间放置两个HDM垫，并根据起搏器导线尖端的局部感应功率评估其效果。研究了线圈内两种不同的患者成像位置（即头部和胸部）。在这两种情况下，使用HDM都能降低感应功率（即头部标记时降低57%，胸部标记时降低68%），同时保持线圈等中心处B RMS的大小不变。此外，当HDM垫放置在头部标记处时，植入路径尖端的局部感应功率显著降低（58%）。相反，当垫放置在胸部标记处时，仅降低了9%。总之，该研究表明，当植入物不包含在HDM包围的体积内时，在RF线圈和患者之间放置垫子可以在较低的RF线圈输入功率下获得相同大小的B1场，显著降低植入物周围的局部感应功率。相反，如果植入物包含在HDM包围的体积内，使用HDM仍可降低获得相同大小B场所需的输入功率，但对植入物局部感应功率的影响幅度较小。
