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外2013手持和机器人经颅磁刺激的刺激强度。
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Stimulus Intensity for Hand Held and Robotic Transcranial Magnetic Stimulation Lars Richter a,b,*, Peter Trillenberg c, Achim Schweikard a, Alexander Schlaefer a,b,d a Institute for Robotics and Cognitive Systems, University of Lübeck, 23562 Lübeck, Germany b Graduate School for Computing in Medicine and Life Sciences, University of Lübeck, 23562 Lübeck, Germany c Department of Neurology, University Hospital of Schleswig-Holstein, 23538 Lübeck, Germany d Medical Robotics Group, University of Lübeck, 23562 Lübeck, Germany a r t i c l e i n f o Article history: Received 20 March 2012 Received in revised form 1 June 2012 Accepted 3 June 2012 Available online 29 June 2012 Key words: Transcranial magnetic stimulation Induced electric field Motion compensation Robotized TMS Head rest a b s t r a c t Background: Transcranial Magnetic Stimulation (TMS) is based on a changing magnetic field inducing an electric field in the brain. Conventionally, the TMS coil is mounted to a static holder and the subject is asked to avoid head motion. Additionally, head resting frames have been used. In contrast, our robotized TMS system employs active motion compensation (MC) to maintain the correct coil position. Objective/hypothesis: We study the effect of patient motion on TMS. In particular, we compare different coil positioning techniques with respect to the induced electric field. Methods: We recorded head motion for six subjects in three scenarios: (a) avoiding head motion, (b) using a head rest, and (c) moving the head freely. Subsequently, the motion traces were replayed using a second robot to move a sensor to measure the electric field in the target region. These head movements were combined with 2 types of coil positioning: (1) using a coil holder and (2) using robotized TMS with MC. Results: After 30 min the induced electric field was reduced by 32.0% and 19.7% for scenarios (1a) and (1b), respectively. For scenarios (2a)e(2c) it was reduced by only 4.9%, 1.4% and 2.0%, respectively, which is a significant improvement (P < 0.05). Furthermore, the orientation of the induced field changed by 5.5, 7.6, 0.4, 0.2, 0.2 for scenarios (1a)e(2c). Conclusion: While none of the scenarios required rigid head fixation, using a simple holder to position a coil during TMS can lead to substantial deviations in the induced electric field. In contrast, robotic motion compensation results in clinically acceptable positioning throughout treatment. 2013 Elsevier Inc. All rights reserved. Introduction Based on the principle of electromagnetic induction, Trans- cranial Magnetic Stimulation (TMS) is used for noninvasive stimu- lation of the brain [1]. Typically, a TMS coil is placed on the patient’s head such that the maximum magnetic field covers the target region. Particularly, repetitive transcranial magnetic stimulation (rTMS) has become a promising tool for treatment of a variety of medication resistant neurological and psychiatric conditions. Clin- ical trials have proven effects, e.g., for depression [2], chronic tinnitus [3] or chronic pain [4]. Typically, rTMS is applied for 15e30 min for each single treatment session. Even more important is single-pulse TMS for brain research and cognitive neuroscience [5e7]. To locate the stimulation target and to position the coil, different approaches exist. In its simplest way, localization is based on external anatomical landmarks, e.g., midline or ear-to-ear-line. Another way is to take advantage of the 1020 system of elec- trode placement for electroencephalogram (EEG) recordings [8]. The TMS coil can be placed relative to these electrode positions. A recent technique for coil positioning and target localization is the application of neuro-navigation [9]. Neuro-navigation combines a three-dimensional (3D) scan of the patient’s head with a realtime tracking system. After registration and with tracking of coil and head, the TMS coil can be positioned based on the 3D head scan. Hence, neuro-navigated TMS is the state-of-the- art tool for precise target localization [10,11]. As holding the coil by hand for a stimulation sequence of up to 30 min is an exhausting task, commonly a rigid holder or This work was partially supported by the Graduate School for Computing in Medicine and Life Sciences funded by Germany’s Excellence Initiative [DFG GSC 235/1]. All authors reported no biomedical financial interests or potential conflicts of interest. * Corresponding author. Institute for Robotics and Cognitive Systems, University of Lübeck, Ratzeburger Allee 160, 23562 Lübeck, Germany. Tel.: 49 451 5005207; fax: 49 451 5005202. E-mail address: richter@rob.uni-luebeck.de (L. Richter). Contents lists available at SciVerse ScienceDirect Brain Stimulation journal homepage: www.brainstimjrnl.com 1935-861X/$ e see front matter 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.brs.2012.06.002 Brain Stimulation 6 (2013) 315e321

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