MRI Powered and Triggered Current Stimulator for Concurrent Stimulation and MRI

Abstract

Bioelectric stimulation during concurrent magnetic resonance imaging (MRI) is of interest to basic and translational studies. However, existing stimulation systems often interfere with MRI, are difficult to use or scale up, have limited efficacy, or cause safety concerns. To address these issues, we present a novel device capable of supplying current stimulation synchronized with MRI while being wirelessly powered by the MRI gradient fields. Results from testing it with phantoms and live animals in a 7 Tesla small-animal MRI system suggest that the device is able to harvest up to 72 (or 18) mW power during typical echo-planar imaging (or fast low angle shot imaging) and usable for stimulating peripheral muscle or nerve to modulate the brain or the gut, with minimal effects on MRI image quality. As a compact and standalone system, the plug-and-play device is suitable for animal research and merits further development for human applications. Introduction:Neurostimulation, e.g. Deep Brain Stimulation (DBS), Vagal Nerve Stimulation (VNS), Spinal Cord Stimulation (SCS), has been widely used to treat Parkinson's disease [1], dystonia [2], [3], epilepsy [4], [5], and intractable pain syndrome [6], [7], to name a few examples. It has also been increasingly recognized that magnetic resonance imaging (MRI) can guide neuromodulation and improve its efficacy, especially if neural stimulation and imaging are performed simultaneously [8]-[12]. However, concurrent stimulation and MRI is non-trivial. A conventional stimulation device may jeopardize patient safety and degrade imaging quality [13], while MRI may interfere with the device and corrupt its function [14]-[16], due to the strong and varying magnetic fields during MRI [17]. In addition, a device often requires long cables to connect to a power source or receive external triggers, where-as such cables may perturb the magnetic fields and degrade image acquisition [18], [19]. Widely used methods for simultaneous MRI and neuromodulation involve non-MR-safe stimulators, which are placed outside the MRI room and connected to the subject using long twisted cables [20]-[23]. The longer stimulation cables sometime pick up fast gradient magnetic fields and lead to unwanted electrical stimulation [24][25]. Few studies include conditionally MRsafe stimulators placed near the MRI bore with shorter cables and RF filtering [26]-[28][29].However, such setups are difficult to scale up, since more stimulation channels would require more cables and RF filtering circuits and amount to an increasingly bulky and complex system.The system also causes patient discomfort, prolongs preparation time, affects imaging quality, especially at a high field (7 Tesla or above) [30].