Simultaneous Dual Frequency $^{1}{\rm H}$ and $^{19}{\rm F}$ Open Coil Imaging of Arthritic Rabbit Knee at 3T

Abstract

The combination of sensitive magnetic resonance techniques with a selective site-targeted nanoparticle contrast agent has a demonstrated utility for molecular imaging studies. By detecting a unique signature of the contrast agent, this approach can be employed to identify specific bio-molecular markers and observe cellular-level processes within a large and complex organism (e.g., in vivo rabbit). The objective of the present investigation was to design, fabricate and characterize a radio-frequency (RF) coil for the dual frequency (1H and 19F) simultaneous collection of both nuclei images in a 3T field, in order to facilitate studies of arthritic knee degradation in rabbits. The coil supports both transmit and receive modes. The supporting activities included: 1) establishing a technical database for calculating the required coil parameters, 2) selection of a favorable coil geometry, and 3) adaption of existing RF measurement techniques to the design, development and electrical evaluation of the coil. The coil is used in conjunction with a Philips Medical Systems clinical MRI scanner, requiring all RF simultaneous dual frequency (1H and 19F) coils to operate in both transmit and receive modes. A commercial version of SPICE (simulation program with integrated circuit emphasis) was used to estimate significant operational parameters prior to fabricating the imaging coil. Excellent images were obtained with the fabricated coil and no operational problems were observed that would limit the use of other coil geometries and field strengths.

A generalized strategy for designing 19F/1H dual‐frequency MRI coil for small animal imaging at 4.7 Tesla

“…Identical and homogeneous B1 field distribution at 19 F and 1 H frequencies were observed in bench test and phantom image. Finally, in vivo mouse imaging confirmed the sensitivity and homogeneity of the 19 F/ 1 H dual-frequency coil design.…”

“…A generalized strategy for designing 19 F/ 1 H dual-frequency coils based on the coupled resonator approach was developed and validated. A unique feature of this design is that it preserves the B1 field homogeneity of the RF coil at both resonant frequencies.…”

“…The feasibility to design 19 F/ 1 H dual-frequency RF coil based on coupled resonator model was investigated. A series capacitive matching network enables robust impedance matching for both harmonic oscillating modes of the coupled resonator.…”

“…A series capacitive matching network enables robust impedance matching for both harmonic oscillating modes of the coupled resonator. Two typical designs of 19 F/ 1 H volume coils (birdcage and saddle) at 4.7T were implemented and evaluated with electrical bench test and in vivo 19 F/ 1 H dual-nuclei imaging.…”

“…However, MRI of fluorinated contrast agent suffers principally from low sensitivity especially at clinical field strengths, even despite the fact that 19 F is a high signal nucleus, requiring millimolar quantities of contrast agent per voxel for detetion (2). Because the amount of fluorine achievable by molecular targeting is limited by the concentration of epitopes that bind the contrast agent, which itself is a function of the tissue pathobiology, improvements in sensitivity and speed are better addressed with the use of specialized and dedicated radiofrequency (RF) coils.…”