Das Priyanka, Gupta Jegyasu, Sikdar Debabrata, Bhattacharjee Ratnajit
iHUB DivyaSampark, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India.
Department of Electronics and Electrical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India.
Magn Reson Imaging. 2023 Jul;100:1-9. doi: 10.1016/j.mri.2023.03.005. Epub 2023 Mar 15.
Magnetic resonance imaging (MRI) is an increasingly popular non-invasive technique for clinical diagnosis. Signal-to-noise ratio (SNR) is a crucial performance metric of MRI, improvement of which can be exchanged for increased image resolution or decreased scan time. Besides the progress in various hardware and software techniques for improving SNR in MRI scanners, use of metasurfaces as accessories has recently shown potential towards enhancing SNR by boosting local magnetic field in the scanned volume. Magnetic field enhancement over a larger depth from the skin is essential for imaging of deeper tissues, which can be facilitated by a specifically designed metasurface. Here we present such a metasurface with complementary-type resonant structures on the two sides of a high-permittivity dielectric, which substantially increases magnetic flux density on the skin (forty-five fold) that decays down to unity at a depth of 95 mm from the skin. This results in boosting of SNR up to forty-fold on the skin in 1.5 T MRI, while keeping tissue heating below the safety limit. An original analytical approach is formulated to readily estimate the SNR enhancement factor of this metasurface. Using the designed metasurface as an accessory for MRI scanners could help making MRI scans more efficient and affordable.
磁共振成像（MRI）是一种在临床诊断中越来越受欢迎的非侵入性技术。信噪比（SNR）是MRI的一项关键性能指标，提高信噪比可以换取更高的图像分辨率或更短的扫描时间。除了在各种硬件和软件技术方面取得进展以提高MRI扫描仪的信噪比外，使用超表面作为附件最近已显示出通过增强扫描体积中的局部磁场来提高信噪比的潜力。从皮肤到更大深度的磁场增强对于深层组织的成像至关重要，这可以通过专门设计的超表面来实现。在这里，我们展示了一种在高介电常数电介质两侧具有互补型谐振结构的超表面，它显著增加了皮肤表面的磁通密度（45倍），该磁通密度在距皮肤95毫米深处衰减至1。这使得在1.5T MRI中皮肤表面的信噪比提高了40倍，同时保持组织加热低于安全极限。我们制定了一种原始的分析方法，以方便地估计这种超表面的信噪比增强因子。将设计的超表面用作MRI扫描仪的附件有助于使MRI扫描更高效且更经济实惠。
