Robust real‐time robot–world calibration for robotized transcranial magnetic stimulation

Richter, Lars; Ernst, Floris; Schlaefer, Alexander; Schweikard, Achim

doi:10.1002/rcs.411

Cited by 29 publications

(23 citation statements)

References 24 publications

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“…Consequently, since we do not wish to privilege one frame of reference, the average of the errors is used. This, and the way of computing the rotational error, is in line with standard approaches for hand-eye calibration [26][27]. Note that, as the calibration of IMU to FT only consists of a rotational part, no translational error is estimated.…”

Section: Stability Of Calibrationsupporting

confidence: 60%

Calibration of force/torque and acceleration for an independent safety layer in medical robotic systems

Richter¹,

Bruder²,

Schweikard³

2012

Cureus

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Background: Most medical robotic systems require direct interaction with the robot. Force-Torque (FT) sensors can easily be mounted to the robot. However, an accurate FT control requires the current robot position to compute the spatial orientation of the sensor for gravity compensation. Methods: We developed an independent safety system, named FTA sensor, which is based on an FT sensor and an accelerometer. With a calibration of accelerations to the FT coordinate frame, the current spatial orientation of the sensor is computed. Results: We found that the calibration of accelerations into the FT coordinate frame can be performed with a median rotational error of 3.5°. The median error for gravity compensation based on accelerations was 0.3N and 0.04Nm for forces and torques, respectively. Conclusion: By combining accelerations with force-torque readings, the FTA sensor works independently from robot input. Furthermore, the accuracy of the FTA sensor is sufficient for the purpose of medical robotic systems.

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Section: Stability Of Calibrationsupporting

confidence: 60%

Calibration of force/torque and acceleration for an independent safety layer in medical robotic systems

Richter¹,

Bruder²,

Schweikard³

2012

Cureus

Self Cite

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“…For different series it was guaranteed that only the coil orientation was varied. The overall coil positioning accuracy of robotized TMS with this setup is 1.8 mm on average [28].…”

Section: Methodsmentioning

confidence: 96%

Optimal Coil Orientation for Transcranial Magnetic Stimulation

et al. 2013

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We study the impact of coil orientation on the motor threshold (MT) and present an optimal coil orientation for stimulation of the foot. The result can be compared to results of models that predict this orientation from electrodynamic properties of the media in the skull and from orientations of cells, respectively. We used a robotized TMS system for precise coil placement and recorded motor-evoked potentials with surface electrodes on the abductor hallucis muscle of the right foot in 8 healthy control subjects. First, we performed a hot-spot search in standard (lateral) orientation and then rotated the coil in steps of 10° or 20°. At each step we estimated the MT. For navigated stimulation and for correlation with the underlying anatomy a structural MRI scan was obtained. Optimal coil orientation was 33.1±18.3° anteriorly in relation to the standard lateral orientation. In this orientation the threshold was 54±18% in units of maximum stimulator output. There was a significant difference of 8.0±5.9% between the MTs at optimal and at standard orientation. The optimal coil orientations were significantly correlated with the direction perpendicular to the postcentral gyrus (). Robotized TMS facilitates sufficiently precise coil positioning and orientation to study even small variations of the MT with coil orientation. The deviations from standard orientation are more closely matched by models based on field propagation in media than by models based on orientations of pyramidal cells.

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“…This enables a more accurate and comparable stimulation setting in contrast to common hand-held approaches (Richter et al, 2013). An individual three-dimensional (3D) digital contour of the participant's head was constructed before stimulation using a GALAXY3D laser scanning system (LAP, Lu¨neburg, Germany) for head navigation (Richter et al, 2011). A headband with passive marker spheres measured by the tracking system was used for precise head tracking and real-time motion compensation.…”

Section: Methodsmentioning

confidence: 99%

Tracking post-error adaptation in the motor system by transcranial magnetic stimulation

et al. 2013

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Abstract-The commission of an error triggers cognitive control processes dedicated to error correction and prevention. Post-error adjustments leading to response slowing following an error (''post-error slowing''; PES) might be driven by changes in excitability of the motor regions and the corticospinal tract (CST). The time-course of such excitability modulations of the CST leading to PES is largely unknown. To track these presumed excitability changes after an error, single pulse transcranial magnetic stimulation (TMS) was applied to the motor cortex ipsilateral to the responding hand, while participants were performing an Eriksen flanker task. A robotic arm with a movement compensation system was used to maintain the TMS coil in the correct position during the experiment. Magnetic pulses were delivered over the primary motor cortex ipsilateral to the active hand at different intervals (150, 300, 450 ms) after correct and erroneous responses, and the motor-evoked potentials (MEP) of the first dorsal interosseous muscle (FDI) contralateral to the stimulated hemisphere were recorded. MEP amplitude was increased 450 ms after the error. Two additional experiments showed that this increase was neither associated to the correction of the erroneous responses nor to the characteristics of the motor command. To the extent to which the excitability of the motor cortex ipsi-and contralateral to the response hand are inversely related, these results suggest a decrease in the excitability of the active motor cortex after an erroneous response. This modulation of the activity of the CST serves to prevent further premature and erroneous responses. At a more general level, the study shows the power of the TMS technique for the exploration of the temporal evolution of post-error adjustments within the motor system. Ó

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Robust real‐time robot–world calibration for robotized transcranial magnetic stimulation

Abstract: This robust online calibration greatly enhances the system's user-friendliness and safety.

Cited by 29 publications

References 24 publications

Calibration of force/torque and acceleration for an independent safety layer in medical robotic systems

Calibration of force/torque and acceleration for an independent safety layer in medical robotic systems

Optimal Coil Orientation for Transcranial Magnetic Stimulation

Tracking post-error adaptation in the motor system by transcranial magnetic stimulation

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