Double-tuned Cryogenic Imaging Platforms for Pre-clinical MRS

DESCRIPTION (provided by applicant): The goal of this project is to develop a series of ultra-high-performance, double-tuned, cryogenic, cost-effective, MRI rf coil platforms, especially for improved MR spectroscopy (MRS) in pre-clinical studies in small animals at high-fields. Substantial gains in S/N appear likely for a wide range of pre-clinical, single- organ, MRS applications, both single-resonance and double-resonance, at fields at least up to 600 MHz, from the use of cryogenically cooled, circular-polarization RF coils. Examples include mouse and rat-brain H/31P 1 studies of malignant tumors, brain metabolism in small animals, plaque formations in mouse and rat models of Alzheimer's disease, and mouse models of cardiac and liver disease. The S/N gains for many single- resonance applications are expected to range from 2 to 5, and will often be greater than the gain in going from 4.7 T (200 MHz) to 11.7 T (500 MHz) ? and at a small fraction of the cost. In addition, these gains will be achieved in a platform which permits routine double-resonance, thereby enabling cross-polarization, de- coupling, indirect, and C hyperpolarization methods for even greater gains in S/N and spectral resolution in 13 MRS. Ultimately, human MRS applications where sample losses are not dominant will also benefit from Cry- oMR coils, such as extremity bone marrow evaluations in children, where MRS (1H, P, and C) may prove 31 13 useful in evaluating metabolic changes that are important indicators of leukemia progress and response. Preliminary designs will be carried out for several applications during Phase I, and a mouse MRS plat- form will be designed in detail, fabricated, and tested at 100 K. A novel hybrid coil design will reduce sample losses, minimize SAR, and improve S/N significantly. The coil design will be based on full-wave, finite element simulations of the loaded coil using well validated full-wave software. The effort will build on our extensive experience in double-tuned MRI/NMR RF coils for small-animal studies and our extensive experience in cryogenic NMR rf coils. During the Phase II, two second-generation (40 K) platforms for H/13C at 7 T and 11.7 T will be developed, fabricated, and then tested at other institutes, yet to be finalized, but likely the NCI Small Animal Imaging Resource Program at Washington University and Duke University. For mouse brain MRS, the H S/N 1 of the proposed Phase II double-tuned cryogenic platform at 11.7 T is projected to exceed that of state-of-the- art, room-temperature, short, double-tuned birdcages of 25 mm diameter by a factor of 3; and the C S/N will 13 exceed state-of-the-art RT double-tuned birdcages by a factor of 4, which can lead to a factor of 16 reduction in signal acquisition time for constant resolution. For the more common field of 7 T, S/N gains will be even greater.