While today’s clinical MRI scanners are limited to magnetic fields of 3 T, researchers visiting the NHMFL now can perform MRI research at 21.1 T in the world’s only 900-MHz ultra-widebore (105-mm) vertical magnet. Several challenges were addressed to perform research using MRI in very high field vertical bore magnets: vertical magnets are thought to be less conducive to maintaining the animal in a low stress environment; typical bore sizes for high field magnets are often too small to house the animal and complex electronics needed to generate the radio frequency (RF) magnetic field (B 1 ) used for MRI; and MRI instrumentation for research must accommodate different- sized samples with widely varying electrical properties that alter RF performance. Each of these challenges is overcome by a tunable 900-MHz transmit/receive volume coil recently constructed for 1 H MR imaging. To accommodate a diverse range of specimens and RF loads at such a high frequency, a sliding-ring adaptation of a low- pass birdcage was implemented. This large volume (33-mm ID) coil can be impedance matched under a variety of loading conditions without sacrificing B 1 homogeneity, maintained by the simultaneous alteration of the distributed capacitance between the copper sliding tuner ring and conductive legs. Further implementations have extended this design to other nuclei, such as sodium & carbon, that are potential biomarkers of cell function. An adjustable sliding ring coil for neuroimaging in vertical high fields: ex vivo and in vivo applications at 21.1 T Chunqi Qian 1,3,*, Ihssan S. Masad 1,2,4, Jens T. Rosenberg 1,2, Malathy Elumalai 1, William W. Brey 1, Samuel C. Grant 1,2 and Peter L. Gor’kov 1 1. National High Magnetic Field Laboratory, 2. Florida State University, 3. National Institutes of Health, 4. King Faisal University Funding Grants: G.S. Boebinger (NSF DMR ); S.C. Grant (NSF-NHMFL User Collaboration Grants Program) Facilities: 900-MHz Widebore NMR Magnet, Tallahassee, FL Citation: A volume birdcage coil with an adjustable sliding tuner ring for neuroimaging in high field vertical magnets: Ex and in vivo applications at 21.1 T, Qian, C., Masad, I.S., Rosenberg, J.T., Elumalai, M., Brey, W.W., Grant, S.C. and Gor'kov, P.L., J. Magn. Reson., 221, (2012). Figure 1. Expanded view of coil assembly. Major components include: 1. copper legs and static rings of the birdcage that generate the B 1 field; 2. gears and shuttles that tune the birdcage circuit by positioning the copper sliding ring; 3. Faraday shield to isolate the coil from external RF interference; and 4. anesthesia & vacuum lines for animal maintenance. Figure 2. MR images using the sliding-ring coil for samples representing widely different RF loads: (a) in vivo rat brain, (b) multiple ex vivo mouse brains, and (c) a human brain section from an Alzheimer’s patient. (a) (b) 1 cm (c) 1 cm

While present day medical MRI’s use magnetic fields up to 3-T, researchers visiting the NHMFL can now do MRI research at 21-T in the unique 900-MHz ultra-wide-bore (105mm) vertical magnet. There are several recognized challenges to performing research using MRI in very-high-field vertical bore magnets: vertical-bore magnets are thought to be less conducive to maintaining the animal in a low-stress environment. typical bore sizes for high-field magnets are often too small to house the specimen along with the complex electrical circuitry necessary to generate B 1 - the radio-frequency (RF) magnetic field necessary to form the MR image. MRI instrumentation for research must accommodate changes in RF tuning that result from different-sized samples with widely varying dielectric properties. Each of these challenges is addressed by a tunable 900-MHz transmit/receive volume coil recently constructed for 1 H MR imaging. To accommodate a diverse range of specimens and RF loads at such a high frequency, a sliding-ring adaptation of a low- pass birdcage was implemented. This large volume (33-mm ID) coil can be impedance matched under a variety of loading conditions without sacrificing B 1 homogeneity, maintained by the simultaneous alteration of the distributed capacitance between the sliding copper tuner ring and conductive legs. The sliding ring coil displays good homogeneity and sufficient tuning range for high-resolution images of samples of various dimensions representing a large span of RF loads. An adjustable sliding ring coil for neuroimaging in vertical high fields: ex vivo and in vivo applications at 21.1 T Chunqi Qian 1,3,*, Ihssan S. Masad 1,2,4, Jens T. Rosenberg 1,2, Malathy Elumalai 1, William W. Brey 1, Samuel C. Grant 1,2 and Peter L. Gor’kov 1 1. National High Magnetic Field Laboratory, 2. Florida State University, 3. National Institutes of Health, 4. King Faisal University Funding Grants: G.S. Boebinger (NSF DMR ); S.C. Grant (NSF-NHMFL User Collaboration Grants Program) Facilities: 900-MHz Widebore NMR Magnet, Tallahassee, FL Citation: A volume birdcage coil with an adjustable sliding tuner ring for neuroimaging in high field vertical magnets: Ex and in vivo applications at 21.1 T, Qian, C., Masad, I.S., Rosenberg, J.T., Elumalai, M., Brey, W.W.,Grant, S.C. and Gor'kov, P.L., J. Magn. Reson., 221, (2012). Figure 1. Expanded view of coil assembly. Major components include: 1. conductive legs of the bird cage coil that generates the radio frequency magnetic field necessary for imaging; 2. components that enable tuning of the bird cage circuit, including the gears that position the sliding copper tuner ring; 3. Faraday shield cover to isolate the bird cage from outside interference; and 4. anesthesia and vacuum tubing for animal handling. Figure 2. MR images using the sliding-ring bird cage coil for specimens representing widely different RF loads: (a) in vivo rat brain, (b) multiple ex vivo mouse brains, and (c) an Alzheimer’s human brain section (a) (b) 1 cm (c) 1 cm

A tunable 900-MHz transmit/receive volume coil was constructed for 1 H MR imaging of biological samples in a 21.1-T vertical bore magnet. To accommodate a diverse range of specimen and RF loads at such a high frequency, a sliding-ring adaptation of a low-pass birdcage was implemented. This large volume (33- mm ID) coil can be impedance matched under a variety of loading conditions without sacrificing B 1 homogeneity, which is maintained by the simultaneous alteration of the distributed capacitance between the tuner ring and conductive legs. The configuration permits for the design of a birdcage coil with a large number of conductive legs that can be tuned simultaneously. To make efficient use of the constrained space inside the vertical bore, a modular probe design was implemented with bottom-adjustable tuning and matching apparatus. The sliding ring coil displays good homogeneity and sufficient tuning range for different samples of various dimensions representing large span of RF loads. High resolution in vivo and ex vivo images of large rats (up to 350 g), mice and human postmortem tissues were obtained to demonstrate coil functionality and to provide examples of potential applications at 21.1 T and other vertical high fields. An adjustable sliding ring coil for neuroimaging in vertical high fields: ex and in vivo applications at 21.1 T Chunqi Qian 1,3,*, Ihssan S. Masad 1,2,4, Jens T. Rosenberg 1,2, Malathy Elumalai 1, William W. Brey 1, Samuel C. Grant 1,2 and Peter L. Gor’kov 1 1. National High Magnetic Field Laboratory, 2. Florida State University, 3. National Institutes of Health, 4. King Faisal University Funding Grants: G.S. Boebinger (NSF DMR ); S.C. Grant (NSF-NHMFL User Collaboration Grants Program) Facilities: 900-MHz Widebore NMR Magnet, Tallahassee, FL Citation: A volume birdcage coil with an adjustable sliding tuner ring for neuroimaging in high field vertical magnets: Ex and in vivo applications at 21.1 T, Qian, C., Masad, I.S., Rosenberg, J.T., Elumalai, M., Brey, W.W.,Grant, S.C. and Gor'kov, P.L., J. Magn. Reson., 221, (2012). Figure 1. Coil assembly, expanded view. 1: coil former; 2: conductive legs pattern; 3 and 4: bottom and top static end rings; 5 and 6: Teflon layers; 7: sliding copper ring; 8: threaded tuner tube; 9: Faraday shield cover; 10: gearbox flange; 11: large spur gear; 12: pinion gear; 13: tuning shaft with screwdriver jack; 14: gearbox cover; 15: BeCu grounding finger; 16: match trimmer; 17: MCX RF connectors; 18: anesthesia and vacuum tubing. Figure 2. MRI with the sliding ring showing in vivo rat brain, multiple ex vivo mouse brains & an Alzheimer’s human brain section.

An adjustable sliding ring coil for neuroimaging in vertical high fields: ex and in vivo applications at 21.1 T Chunqi Qian 1,3,*, Ihssan S. Masad 1,2,4, Jens T. Rosenberg 1,2, Malathy Elumalai 1, William W. Brey 1, Samuel C. Grant 1,2 and Peter L. Gor’kov 1 1. National High Magnetic Field Laboratory, 2. Florida State University, 3. National Institutes of Health, 4. King Faisal University Funding Grants: G.S. Boebinger (NSF DMR ); S.C. Grant (NSF-NHMFL User Collaboration Grants Program) Note: The “bad” Jet Li (in black) escapes from this situation after his gun is pulled into the field by punching the magnet to quench it. I have not yet tried this method of bringing down a magnet.