gms | German Medical Science

Deep brain stimulation in different targets is successfully used in patients with Parkinsonism, essential tremor or dystonia. The discussion about the safety aspects for patients with implanted electrodes and active stimulation during MRI is still unsolved. An experimental setup using a phantom model with implanted electrodes, connection devices and an extracorporal pulse generator was therefore developed. Electrode temperature and resistance, function of the neurostimulator were also investigated as the image quality. Different MRI sequences for morphologic and functional MRI were used.

A cylindrical glass phantom was filled with isotonic sodium chloride solution and two four contact electrodes (Medtronic Model 3387, Minneapolis, USA) were inserted near the center. The percutaneous lead was connected to an extension wire that led to the stimulator outside the scanner room. Temperature measurements were made with a fluoroptic thermometer at equally spaced positions of the electrodes, cables and inside the phantom near the tip of the electrode. Induced voltage and forces were also measured at the leads outside the scanner room. The parameters of connection or disconnection of the electrode with the stimulator and active and inactive stimulation in different positions in the scanner (1.5 Tesla, Symphony, Siemens, Erlangen) were tested. Stimulation parameters were amplitude of 3 Volt, 210 μsec impulse width and a frequency of 130 Hertz in all examinations.

Induction of voltage and heating of the electrodes and leads was strongly correlated to the direction of the cables in the scanner. The best position of the extension cable is in the z-axis of the scanner. In this position no relevant heating or induced voltage could be monitored in all MRI sequences and parameters. The placing of the cable near the RF antenna or the tunnel wall should be avoided. Image quality was only influenced by local artefacts from the electrode or connection device. In cases of defective electrodes or leads, strong induced voltage and heating could be observed.

In this experimental setup with phantom measurements, it could be shown that MRI and functional MRI with active deep brain stimulation and extended leads are possible. Certain safety aspects and precautions like cable positioning and defects in the electrodes or leads need to be checked. Performing morphological and functional MRI sequences in patients with implanted deep brain stimulation electrodes is safe and practicable if certain precautions are kept in mind.