Magnet driver for producing ultra-high gradient magnetic fields for magnetic resonance imaging

Pulsed gradient magnetic fields are required for magnetic resonance imaging (MRI). Many imaging sequences (e.g., echo planar imaging, diffusion tensor imaging) could be improved with shorter gradient pulses. MRI systems currently available typically require ramp times of hundreds of microseconds. The goal of the work described here is to achieve very high gradient fields, with very short rise times to peak gradient strength, in order to improve MRI studies while avoiding neuronal stimulation. The magnet driver is capable of generating unipolar and bipolar pulses in a 100μH resistive electromagnet. Pulse rise-times, determined by the value of the initial storage capacitance, as short as 3.5μs and 13μs, with peak currents as high as 700A, have been achieved. The driver operates at up to 9kV and uses an array of opening and closing switches to determine the pulse shape, polarity and magnitude. When generating bipolar pulses, >;85% energy in the magnetic field is recovered and reused on the following pulse, significantly reducing operational costs.