Cooldown and Ramp Test of a Low-Cryogen, Lightweight, Head-Only 7T MRI Magnet

A compact 7.0 T MRI system (C7T) has been successfully constructed, cooled down, and ramped (energized) to 7.01 T at GE HealthCare Technology and Innovation Center. The C7T magnet is designed for a B0-field homogeneity of <1.0 ppm over a 26-cm field-of-view, dedicated for MRI brain imaging. The C7T magnet applies a fully closed-loop cryogenic cooling system which condenses only 12 liters of liquid helium at 4.2 K from high pressure helium gas charged at room temperature. The helium is permanently sealed inside the cooling system even after a quench. This newly developed 7.0 T MRI has similar size and stray magnetic field as a clinical whole-body 3.0 T MRI magnet, it can be easily installed in a 3T scanner bay. This C7T MRI system can greatly improve the access to high performance 7T brain imaging for more patients. The cooldown, ramp and quench protection performance of the compact 7T MRI magnet prototype is reported in this paper.