Results for diffusion-weighted imaging with a fourth-channel gradient insert

Diffusion-weighted imaging suffers from motion artifacts and relatively low signal quality due to the long echo times required to permit the diffusion encoding. We investigated the inclusion of a noncylindrical fourth gradient coil, dedicated entirely to diffusion encoding, into the imaging system. Standard three-axis whole body gradients were used during image acquisition, but we designed and constructed an insert coil to perform diffusion encodings. We imaged three phantoms on a 3-T system with a range of diffusion coefficients. Using the insert gradient, we were able to encode b values of greater than 1300 s/mm² with an echo time of just 83 ms. Images obtained using the insert gradient had higher signal to noise ratios than those obtained using the whole body gradient: at 500 s/mm² there was a 18% improvement in signal to noise ratio, at 1000 s/mm² there was a 39% improvement in signal to noise ratio, and at 1350 s/mm² there was a 56% improvement in signal to noise ratio. Using the insert gradient, we were capable of doing diffusion encoding at high b values by using relatively short echo times.