A Nonlinear Single Channel Gradient Insert for Prostate Diffusion Imaging

This paper reports on the technical performance of a nonlinear "inside-out" gradient and its feasibility and safety for diffusion encoding in humans. The tested hardware is a solenoidal coil with a 10 cm diameter, positioned at the isocenter of the magnet bore, designed to generate strong gradients within the surrounding volume.

Various methods were used to characterize the spatial, temporal, mechanical, and acoustic properties of the gradient coil. ADC mapping studies show the feasibility of diffusion-weighted imaging and ADC mapping in phantoms and humans.

The hardware was found to generate high gradient strengths (> 200 mT/m) for expected prostate regions whilst heating, noise, and eddy currents remained within acceptable limits for human scanning. Despite its unconventional geometry and compact form factor, standard calibration methods were effective, enabling accurate ADC mapping in both phantoms and human subjects. No peripheral nerve stimulation (PNS) was reported, even at maximum slew rates and gradient amplitudes.

Inside-out nonlinear gradients can be calibrated with conventional techniques, and the hardware can provide a more convenient approach to strong diffusion weighting of targeted organs.