Constraint free Magnetic Resonance Imaging of patients with deep brain stimulation devices

Deep brain stimulation (DBS) is now a standard of care therapeutic intervention in which electrodes are implanted deep into a patient’s brain so that an electrical stimulus can be applied to precisely targeted nuclei for neurological conditions and movement disorders including Parkinson disease, essential tremor, dystonia, epilepsy, and obsessive-compulsive disorder; DBS treatment of numerous other neurological and neuropsychiatric illnesses are under active investigation. More than 160,000 DBS implants had been performed worldwide, as of 2019, and this patient population, which includes people at all stages of life, including children, is rapidly growing. Although the mechanisms underlying DBS are not yet fully understood, it is becoming increasingly apparent that DBS results in widespread changes in structure and function of the brain. Magnetic Resonance Imaging (MRI) is the standard of care modality for anatomical brain imaging, can provide radiation free functional brain imaging, and is regarded as a primary modality for clinical assessments as well being a powerful neuroscience research tool. During imaging, MRI scanners generate (transmit) radiofrequency (RF) magnetic fields to excite signals and then detect very weak RF echoes. Optimal imaging requires both intense excitation fields and deployment of sophisticated array receivers for signal detection– 32-channel receiver arrays are the gold standard. Unfortunately, RF excitation fields can cause currents to flow in DBS devices creating risk of focal heating, potentially damaging tissue. For this reason, DBS devices (as well as many other common devices, such a cardiac pacemakers) are classified as MR conditional, with specified constraints that must be applied to the MRI RF transmit system during imaging to ensure safety. Parallel Transmit (pTx) is a platform technology that enables much greater control of generated RF excitation fields during MRI. pTx systems with 8 or 16 channels are common in ultra-high field (7T) MRI scanners, but for mainstream clinical neuroimaging with MRI at 3T, systems with only 1 or 2 channels are used. We have shown in simulations, in test objects and in animal studies that 8- or 16-channel pTx can fully control risk from implanted electrodes in clinical scanners, while equalling and even surpassing the performance of conventional RF systems operating without constraints. This has potential to provide significant gains in clinical care for patients with DBS electrodes and we wish to initiate clinical studies to test this. However, to prove genuine clinical utility and demonstrate imaging performance superior to current systems in conditional mode, requires a level playing field for signal reception. Although 32-channel receivers are common in clinical practice, no commercially available devices are compatible with high channel count pTx transmit systems at 3T. Thus, clinical studies of DBS patients can have optimal receive and constrained transmit, or optimal transmit but inferior receive. It is perfectly feasible to achieve optimal transit and optimal receive for prospective clinical trials, but the cost of putting in place a receiver array unbalances grant proposals, and the delay and project risk in building or procuring one as a lead-in item creates a failure point in any rational project plan. This proposal seeks to fill this “gap” by building a 32-channel receiver array to be used in prospective clinical trials of pTx for safe implant imaging. Our primary target is to enhance MRI for DBS patients, but the resulting device would allow testing of pTx methods for other kinds of electrodes too.