An Improved 28 Channel Coil Array for Optic Nerve Imaging

Methods: The Optic Nerve (ON) coil was constructed using two fiberglass formers that fit together to surround the entire head. The anterior former supports 26 overlapping coil elements in a mask arrangement as shown in Fig. 1. The posterior former supports the neck and head and houses two additional overlapped coil elements, totaling to 28 elements. In this design, the two formers can slide over each other to accommodate any arbitrary head size, while maintaining close coupling near the eyes and around the head in general. This design eliminates the air void regions that occur between the coil elements and the forehead when smaller heads are imaged in one-piece, non-adjustable coil formers. The elements were placed using a soccer ball layout [2]. In addition, the coil elements were designed and placed to optimize parallel imaging along the optic nerve from the orbit to the chiasm. Elements were circular in shape and constructed from 14-gauge wire to minimize any flux shielding effect that might occur when using dense arrays of etched copper loops [3]. Phantom studies were performed using a homemade fiberglass, CuSO4 solution head phantom in a Siemens 3T TIM Trio MRI scanner (Siemens Medical Solutions). Phantom images were used to assess and compare the relative SNR (rSNR) and inverse g-factor maps of the two coils.