High-Throughput RF Coils for High-Field MRI

Improvements in signal to noise ratio (SNR) and ease of use of magnetic resonance imaging (MRI) rf coils are needed to improve image quality and patient throughput in high-field MRI. The goal of this Phase II project is to continue the development of novel rf coil topologies and rf balancing circuits that have demonstrated substantially improved technical performance, reduced cost, and greatly simplified tuning procedures. The success of the Phase I effort demonstrated the unique contributions possible with our advanced, proprietary, simulation software and patented coil technology. The circular polarization (CP) coils built and tested during Phase I demonstrated an improvement of a factor of 3 to 15 (depending on the reference CP technology) in tunability (ability to tune and match efficiently over a wide range of sample loading conditions at very high fields) for equivalent B1 homogeneity. Also, much higher B1 homogeneity is maintained over the full range of load conditions. Significant improvements were also achieved in SNR and passive B0 shimming, and further gains are expected here during Phase II. We denote these coils "litzcages", as they embody both paralleled conductor elements with insulated crossovers similar to that in our prior "litz coil" technology and capacitively segmented phase shifts and four-point drive to achieve highly stable circular polarization. We have demonstrated feasibility of a quadrature, single-tuned, semi-open, passively shimmed rf litzcage with an axially asymmetric field profile. The Phase I saw the development and bench testing of numerous linear and CP litz coils, including one for human knee studies at 3 to 6 T, two for small-animal research at 470 MHz, one for singleresonance human head MRI at 2 to 4.2 T, and one for double-resonance human head MRI at 1.5 T. Field testing of a 3 T H head coil will begin early in Phase II at the Hershey Medical Center, Hershey, PA, followed by final produtizing and initial FDA approval procedures. The Phase II will continue model optimizations and development and field testing of CP single-resonance litzcages for knee, neck, and torso at 3-7 T, as well as smaller CP litzcages for animal research at the highest fields. Preliminary development of a 3 T double-resonance multinuclear H/X head coil utilizing our linear litz coils is also planned. The primary objectives are to permit a substantial increase in MRI patient throughput (thereby reducing scan costs) via relatively inexpensive upgrades of head, knee, neck, and torso rf coils in existing high-field MRI scanners, and/or to enable the more detailed diagnostic studies that are currently not practical because image acquisition time would be excessive.