The goal of this study was to evaluate the feasibility of active deep brain stimulation (DBS) during the application of standard clinical sequences for functional MRI (fMRI) in phantom measurements. During active DBS, we investigated induced voltage, temperature at the electrode tips and lead, forces on the electrode and lead, consequences of defective leads and loose connections, proper operation of the neurostimulator, and image quality. Sequences for diffusion-and perfusion-weighted imaging, fMRI, and morphologic MRI were used. The DBS electrode and lead were placed in a NaCl solution-filled phantom. Over the past decade, deep brain stimulation (DBS) has become an established technique in the neurosurgical treatment of patients suffering from medically intractable, chronic pain, Parkinson's disease, or seizures. However, about 30% of the patients in whom electrodes were implanted did not improve clinically (1,2).MRI examinations to map activity, perfusion, and cellular integrity in the human brain (e.g., fMRI, perfusionweighted imaging, and diffusion-weighted imaging) have become an integral part of clinical radiodiagnostics. If these techniques were also feasible in patients undergoing DBS, they could be used as powerful tools to distinguish between responders and nonresponders to DBS, and to investigate possible causes of treatment success or failure (3). During fMRI, a periodic switching between active and inactive DBS can serve as a stimulation paradigm to map brain activity and assess therapeutic effects.Recent studies (3-7) have suggested that in patients undergoing examination with inactive or disconnected implanted neurostimulators, MRI does not appear to be hazardous because the induced voltage is in the range of a few volts. Given the high frequency of the sinusoidal induced voltage, it was assumed that an action potential could not be evoked in neurons. The temperature increase at the electrodes and the implanted pulse generator (IPG) did not exceed 3.7°C for commonly used positioning and specific absorption rate (SAR) values (4). When the stimulators were switched off during imaging, they worked properly after they were switched on again. Imaging was not affected by the electrodes, except for an MR signal loss near the electrode due to susceptibility artifacts.The results obtained with inactive IPGs and disconnected electrodes cannot be applied to the setup required for fMRI, where the electrodes are connected to an active extracorporeal pulse generator that is switched on and off during the examination. The aim of this study was to investigate the feasibility of fMRI techniques using such an experimental setup. We focused on the question of whether the safety and feasibility of MRI are influenced by 1) the sequences used for the examinations (i.e., diffusionweighted spin-echo EPI, T* 2 gradient-echo EPI for perfusion MRI, and BOLD imaging); 2) the periodic switching (on/off) of the pulse generator during measurements; and 3) the localization of the pulse generator outside the scanning room. THEOR...

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Until suggestions can be made concerning the exposure of hydrocephalic patients to 3.0 T-MRI, further testing is necessary.