Beyond the Iseult magnet 11.74 T (500 MHz): preliminary design of two whole body MRI magnets, 14.09 T (600 MHz) and 16.44 T (700 MHz)

Rationale Magnetic field intensity is a main characteristic of MRI machines. Most of about 50,000 installed ones worldwide make use of 1.5T or 3T magnets. Even if dedicated machines work with a much lower field like 64 mT of the Hyperfine Swoop permanent magnet, the interest of fields higher than 3T is widely acknowledged, in particular for brain studies. 7T (300 MHz) machines are already in clinical use. The core part of the Iseult MRI at Neurospin is an actively shielded NbTi magnet cooled by a superfluid helium bath at 1.8 K , operated in driven mode, providing a homogeneous field of 11.7 T within a 90 cm warm bore. The first images obtained in September 2021 are a world first making a decisive step in “Ultra-High-Field MRI”. Two European initiatives have already got funding for a 14.09 T (600 MHz) whole body MRI project with various options for building the magnet. This paper presents alternative preliminary designs for such a magnet together with an even further step at 16.44T (700 MH).