In 2013, an international team including the MagLab initiated Ekosi Tesla, the pursuit of 20 tesla human MRI (ekosi is Greek for 20). Today, standard MRI magnets in clinical use for human imaging operate at 1.5 T; the “high-field” systems operate at 3.0 T. There are a few “ultra-high field” systems operating at 7 T to 10 T, and systems up to 11.75 T are in development. The proposed new system should provide unprecedented resolution and play a significant role in decoding the mysteries of the human brain.
The room-temperature bore of the magnet is planned to be 65 cm, which should provide space for typical human torsos with gradient coils installed around the head. That increase in field strength over what is currently available will translate into images of astounding detail that, among other advances, will provide non-invasive views of how neurons are organized in the cortex and how axons connect different regions of the brain involved in common tasks. Such studies are expected to deepen our knowledge of cognition-related connectivities and brain plasticity in health and disease. The 20 tesla field will also provide a huge boost to novel kinds of MRI, including those targeting carbon and phosphorous atoms; this could lead to new insights into the brain’s energetics and metabolism. Boasting a high homogeneity (1 ppm or better over a 16 cm diameter sphere), the new MRI will also make feasible many new metabolic experiments.
Materials & Magnet Technology
The figure above shows the magnet field and bore of MRI magnets. Those built to date show as black squares and are connected by a black line that denotes the “frontier” in this field.Magnets presently in development are shown as blue squares.
|Room-temperature bore size||
Nb3Sn, NbTi, HTS
Our target of 20 T in a 68 cm bore is indicated in green along with a “stepping-stone” project of 14 T in 68 cm. Higher fields have been attained in magnets with smaller bores. Different bore sizes correspond to different size animals that can be imaged. The 21 T, 10 cm bore magnet is used for rat-brain imaging and is located at the MagLab’s Tallahassee NMR-MRI/S Facility. The magnet was developed in-house by a team led by Denis Markiewicz and Iain Dixon. There are a few magnets with bores of ~20 cm that are used for imaging cats, while the 11.1 tesla 40 cm magnet at the University of Florida in Gainesville is large enough for dogs. Magnets for imaging the human head have bores in the 65 – 70 cm range. Whole body human imaging requires ~90 cm.
All the existing magnets in bores of 65 cm or larger use NbTi as the superconducting material. This material stops superconducting at ~12 T. The higher-field, smaller-bore magnets indicated use a higher-field material: Nb3Sn. Obviously, a 20 T magnet cannot be realized using only NbTi. It will require the higher-field Nb3Sn and, most likely, still higher-field conductors referred to (for historical reasons) as high-temperature superconductors (HTS). Developing a 20 T human-head MRI system will require extending the state of the art in numerous technologies, including DC niobium-titanium and niobium-tin magnets, high-field AC gradients, high-field radio-frequency transmitters and receivers. In addition, no magnets using HTS in significant quantities have been put into operation to date. Developing all these technologies simultaneously would take an excessive amount of time. Hence we intend to first develop a 14 T human head system. This will enable developing most of the technology required for the eventual 20 T system, except large-scale HTS coils. We expect this technology will be developed in parallel, enabling development of a 20 T system to start immediately after the completion of the 14 T system.
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- Field and bore of MRI magnets. Field and bore of MRI magnets.
- Conductors used in superconducting magnets Conductors used in superconducting magnets
- Current density of superconducting wires. Current density of superconducting wires.
- Budinger, T. F., et al, MRI and MRS of the human brain at magnetic fields of 14 T to 20 T: Technical feasibility, safety, and neuroscience horizons (2018)
- Budinger, T. F., et al, Toward 20 T magnetic resonance for human brain studies: opportunities for discovery and neuroscience rationale (2016)
Project manager Mark Bird.