Coaxial capacitor (COCA) coil for stretchable arrays in ultrahigh-field MRI

Stretchable RF coils offer the potential to improve MRI performance by conforming closely to patient anatomy, regardless of patient size, thereby enhancing both signal-to-noise ratio (SNR) and patient comfort. In this work, we investigate a stretchable receive array design based on the coaxial capacitor (COCA) coil for 7 T MRI, constructed primarily from ultra-flexible Litz wire stitched onto elastic fabric substrates. The COCA coil eliminates the need for lumped capacitors and maintains stable decoupling performance under transverse stretching, provided that the overlapped area and the coil area change proportionally as the coil is stretched. Bench tests and phantom imaging experiments demonstrate that elliptical COCA coils (in the non-stretched state) maintain consistent decoupling characteristics across stretch ratios up to ×1.3 and outperform fixed arrays in SNR across varying phantom sizes. The proposed design shows strong potential for integration into wearable coil arrays, enabling improved imaging quality and adaptability for diverse patient anatomies.