On the modeling of the electromagnetic fields induced by MRI fields in patients with a retinal implant

In this work, we consider the interaction between MRI fields and a patient with a retinal prosthesis (RP) implant, which is a restorative device being designed to mimic the function of basic photoreceptor cells in patients suffering from outer retinal degeneration caused by age related macular degeneration (AMD) or retinal pigmentosa. This work uses 3D expanding grid finite difference time domain (FDTD) method to calculate the SAR distribution and estimate the thermal elevation when the human head with the implant is exposed to RF magnetic field at 64 MHz. The advantage of using an expanding grid FDTD algorithm is that computer memory requirements are greatly reduced and more accurate modeling of the region of the implant is possible where a finer grid with cell sizes of the order of micrometers is used. This helps to model the RF birdcage coil and the human head with the implant as a single system and simulate the EM interactions of the tissues even at higher frequencies. The power deposition is computed as the average SAR over any 1 g of tissue in the head.