The safety of transcranial magnetic stimulation with deep brain stimulation instruments.
OBJECTIVE
Transcranial magnetic stimulation (TMS) has been employed in patients with an implanted deep brain stimulation (DBS) device. We investigated the safety of TMS using simulation models with an implanted DBS device.


METHODS
The DBS lead was inserted into plastic phantoms filled with dilute gelatin showing impedance similar to that of human brain. TMS was performed with three different types of magnetic coil. During TMS (1) electrode movement, (2) temperature change around the lead, and (3) TMS-induced current in various situations were observed. The amplitude and area of each evoked current were measured to calculate charge density of the evoked current.


RESULTS
There was no movement or temperature increase during 0.2 Hz repetitive TMS with 100% stimulus intensity for 1 h. The size of evoked current linearly increased with TMS intensity. The maximum charge density exceeded the safety limit of 30 muC/cm(2)/phase during stimulation above the loops of the lead with intensity over 50% using a figure-eight coil.


CONCLUSIONS
Strong TMS on the looped DBS leads should not be administered to avoid electrical tissue injury. Subcutaneous lead position should be paid enough attention for forthcoming situations during surgery.
Shimojima
Yoshio
Y
Department of Medicine (Neurology & Rheumatology), Shinshu University School of Medicine, Asahi 3-1-1 Matsumoto 390-8621, Japan.
Morita
Hiroshi
H
Nishikawa
Noriko
N
Kodaira
Minori
M
Hashimoto
Takao
T
Ikeda
Shu-Ichi
S
D001703:Biophysics; D001921:Brain; D046690:Deep Brain Stimulation / Q000295:instrumentation* / Q000379:methods; D004558:Electric Stimulation / Q000379:methods; D004567:Electrodes, Implanted; D019054:Evoked Potentials, Motor / Q000502:physiology*; D006801:Humans; D009068:Movement; D013696:Temperature; D050781:Transcranial Magnetic Stimulation / Q000295:instrumentation* / Q000379:methods*