Design and assembly of an 8 tesla whole-body MR scanner

Abstract

Purpose: The purpose of this report is to describe the design and construction of an 8 T/80 cm whole-body MRI system operating at 340 MHz.

Method: The 8 T/80 cm magnet was constructed from 414 km of niobium titanium superconducting wire. The winding of this wire on four aluminum formers resulted in a total inductance of 4,155 H. Gradient subsystems included either a body gradient or a head gradient along with a removable shim insert. The magnet and gradient subsystems were interfaced to two spectrometers. These provided the control of the gradient amplifiers and the two sets of four RF power amplifiers. The latter provide in excess of 8 kW of RF power from 10 to 140 MHz and 10 kW of RF power from 245 to 345 MHz. A dedicated computer-controlled patient table was designed and assembled. The entire system is located in a clinical setting, facilitating patient-based studies.

Results: The 8 T/80 cm magnet was energized without complication and achieved persistent operation using 198.9 A of current, thereby storing 81.5 MJ of magnetic energy. Exceptional performance was observed for nearly all components both in isolation and when combined within the complete system.

Conclusion: An 8 T/80 cm MRI system has been assembled. The magnet subsystem is extremely stable and is characterized by good homogeneity and acceptable boil-off rates.