An ultra-flexible 3-channel receive-only coil array for 3T magnetic resonance imaging made of coaxial transmission line resonators

Abstract

Magnetic resonance imaging (MRI) is a well established technique in non-invasive medical imaging with high soft tissue contrast and the advantage of working without ionizing radiation. High-frequency coils are used to excite the nuclear spins as well as to receive the MR signal, which have their resonance frequency at the Larmor frequency of the examined atomic nuclei. A dynamic field of research in this context is the improvement of the achieved signal-to-noise ratio (SNR). For this purpose, several small coil elements can be combined to form a so-called ”array”. By using several coils, undesired couplings occur between them, which can be reduced to a minimum both by a well-thought-out arrangement of the elements (geometric decoupling) within the array and by an appropriate interface (preamplifier decoupling). In addition, the SNR increases if the coils are close to the area to be investigated. Standard coil arrays made of copper wire have a fixed soldered interface and are rigid. Due to the inelastic arrangement of the coil elements, good geometric decoupling is possible. The presented diploma thesis describes the development and construction of an ultra-flexible, 3-channel receive-only coil array for 3 Tesla magnetic resonance imaging. The array consists of three so-called coaxial coils, each with its own interface. In contrast to standard coils, coaxial cables are used as resonators. Through gaps of the inner and outer conductor, the dielectric becomes the capacitance and the entire structure resonates. There are only solder joints at the coil terminal, so this coil design is far more flexible than that of the standard coils, which have soldered capacitances inside the coil wire. If very thin coaxial cables are used, extremely flexible and also very light coils can be built with many new application possibilities for magnetic resonance imaging. One example is the Bracoil-project, which deals with the construction of a T-shirt-like array for breast MR. The flexible elements fit very well to the patients body shape.