Magnetic resonance imaging (MRI) is a popular diagnostic technique that enables non-invasive examination of human anatomy. Recent advancements in metasurfaces have demonstrated their potential to enhance MRI performance by improving signal-to-noise ratio (SNR) without increasing static magnetic field. By confining and amplifying local magnetic fields in the region of interest, metasurfaces serve as effective clinical accessories that can be placed between patient body and MRI transceiver arrays. Numerous designs of metasurfaces have been explored to enhance RF magnetic fields and improve SNR in 1.5T MRI systems. However, these structures interact with RF signals during both transmission (Tx) and reception (Rx) phases. During Tx phase, this interaction can amplify RF power delivered to the tissues, increasing risk of tissue heating by elevating specific absorption rate. To mitigate these challenges, a smart metasurface-inspired wrap, composed of diode loaded interconnected rectangular spirals and split ring resonators, is developed. This design selectively enhances RF signals during Rx phase while remaining inactive during Tx phase. The incorporation of diodes in each unit cell of the designed novel metasurface enables a shift in resonance frequency during Tx phase, detuning it from 63.8 MHz. During Rx phase, the metasurface resonates like a high-Q circuit, amplifying received magnetic field. This approach achieves a nearly four times improvement in SNR and improved RF field homogeneity (with only 6.3 % spatial variation) in magnetic field within human head models during Rx phase. Inactivity of the metasurface during Tx phase ensures patient safety by limiting RF signal interactions only during Rx phase.
Gupta et al. (Fri,) studied this question.