Ponente
Descripción
This work is part of an interdisciplinary research that joins the area of electromagnetic metamaterials and the area of magnetic resonance imaging for medical imaging. Ultra-high field magnetic resonance imaging systems provide an increased signal-to-noise ratio and resolution in comparison with high field systems, and the only drawback of ultra-high field systems is the inherent inhomogeneity of the radiofrequency excitation field. The transmit field B1+ in a 7 T birdcage coil is inherently inhomogeneous due to the effects of wavelengths on tissue. In the literature, there are several approaches addressing the issue of homogenizing this field. This work investigates the homogenization of this field through metasurfaces that consist of a two-dimensional planar array of capacitively loaded conducting rings. Electromagnetic simulations are carried out with the software CST Studio Suite for a 7 T birdcage loaded with metasurfaces to validate the proof-of-concept. The metasurfaces are placed in the intermediate space between the head model and the birdcage on either side of the head. The periodical structure of this type of metasurface supports magnetoinductive waves because of the mutual inductive coupling existing between the elements of the array. The analysis takes advantage of this coupling and exploits the excitation of a standing magnetoinductive wave across the arrays, which creates a strong local field that contributes to homogenize the field of the birdcage. The presence of the arrays does not detune the birdcage, so that they can be used with commercial birdcages that operate both to transmit and to receive. The figures show screenshots of the implementation in CST of the model under study and the results of the simulation for the transmit field B1+ in the absence and in the presence of the metasurfaces.
