Magneto-inductive catheter receiver for magnetic resonance imaging.

A catheter-based RF receiver for internal magnetic resonance imaging is demonstrated. The device consists of a double-sided thin-film circuit, wrapped around a hollow catheter and sealed in place with heat-shrink tubing. Signals are detected using a resonant LC circuit at the catheter tip and transmitted along the catheter using an array of coupled LC circuits arranged as a magneto-inductive waveguide, a form of low frequency metamaterial. Coupling to a conventional RF system is accomplished using a demountable inductive transducer. Protection against external B 1 and E fields is obtained by using figure-of-eight elements with an electrical length shorter than that of an immersed dipole. The system is primarily designed for biliary imaging, can pass the biopsy channel of a side-opening duodenoscope, and is guidewire-compatible, potentially allowing clinicians to implement MR image guided procedures without changing their standard practice. Decoupling against B 1 and E fields is verified, and in vitro (1)H magnetic resonance imaging with submillimeter resolution is demonstrated at 1.5 T using phantoms.

In vivo 31P magnetic resonance spectroscopy using a needle microcoil.

Batch fabrication methods have been used to produce low-cost microcoils for magnetic resonance spectroscopy (MRS) that could be discarded after applications such as insertion into tissue during interventional surgery. Needle-shaped microcoils were constructed using electroplated conductors buried in shafts formed with different combinations of silicon and plastic and used to acquire in vivo (31)P spectra of rat thigh muscle at 81 MHz. The designs in this study achieved a maximum signal-to-noise ratio (SNR) for phosphocreatine (PCr) of 10.4 in a 10-min acquisition, with the three adenosine triphosphate (ATP) multiplets also clearly visible. An average 20% reduction in PCr occurred over a 60-min period, and intracellular pH was estimated to be 6.6, which are both evidence of ischemia. A needle microcoil design could have applications in real-time MRS of tumors or in evaluating pathology in general during surgical investigations.