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Using a 3D-MRI system for coil positioning in repetitive transcanial stimulation
Book Contribution - Book Chapter Conference Contribution
Introduction:
In the therapy of depression, repetitive transcranial magnetic stimulation (rTMS) of the left dorsolateral prefrontal cortex (DLPFC) has been introduced. Crucial in rTMS-treatment is the accurate positioning of the rTMS-coil over the stimulation area. Standard methods for coil positioning are derived from the Talairach atlas and do not take in account any individual anatomical information. In this study we compared an individualized method based on a 3D MRI of the head, the "3D-MRI system" to the standard method.
Methods:
40 healthy female subjects (25±6 years) who conformed the current guidelines for rTMS and MRI research where included. In the standard method, the "5-cm rule", the DLPFC is defined as 5 cm rostral to a point in the motor cortex identified by stimulating the brain with a Magstim rTMS- stimulator and looking for the maximum response recorded with EMG over the right musculus abductor pollicis brevis. For the 3D-MRI system the subjects underwent a T1-weighted MRI (3D-TFE, 1x1x1 mm resolution) of the head using a Philips 1.5T Intera scanner. All post processing was done on a Philips ViewForum console. We located the DLPFC visually on the 3D surface rendering of the brain based on the known gyral morphology. The
corresponding coil position was found by making the projection on the skin. For an accurate determination of the coil position on a patient's head, we drew an axis from left ear to right ear through the coil position and one from nose to atlas. The crossing of both axes is defined as "top". We measured the distances from top to the coil position, to the right ear and to the nose on the 3D surface rendering of the head. To compare both methods, we measured the distance between both coil positions on the patients head.
Results:
The individual stimulation points were scattered widelly about the 5-cm point. There is an average shift of 27±14 mm between both. In most subjects, the standard method positioned the DLPFC too rostrally.
Conclusions:
We showed that the current positioning method used in rTMS- studies easily fail to target the DLPFC. An inaccurate positioning of the rTMS-coil over the DLPFC can be a reason for the heterogeneous outcome of rTMS-treatments. In order to improve the efficacy of this technique, we should use coil positioning techniques witch take the individual anatomy in account by making the combination with MRI.
References:
[1] Herwig U. (2001): Biol Psychiatry; 50: 58-61
In the therapy of depression, repetitive transcranial magnetic stimulation (rTMS) of the left dorsolateral prefrontal cortex (DLPFC) has been introduced. Crucial in rTMS-treatment is the accurate positioning of the rTMS-coil over the stimulation area. Standard methods for coil positioning are derived from the Talairach atlas and do not take in account any individual anatomical information. In this study we compared an individualized method based on a 3D MRI of the head, the "3D-MRI system" to the standard method.
Methods:
40 healthy female subjects (25±6 years) who conformed the current guidelines for rTMS and MRI research where included. In the standard method, the "5-cm rule", the DLPFC is defined as 5 cm rostral to a point in the motor cortex identified by stimulating the brain with a Magstim rTMS- stimulator and looking for the maximum response recorded with EMG over the right musculus abductor pollicis brevis. For the 3D-MRI system the subjects underwent a T1-weighted MRI (3D-TFE, 1x1x1 mm resolution) of the head using a Philips 1.5T Intera scanner. All post processing was done on a Philips ViewForum console. We located the DLPFC visually on the 3D surface rendering of the brain based on the known gyral morphology. The
corresponding coil position was found by making the projection on the skin. For an accurate determination of the coil position on a patient's head, we drew an axis from left ear to right ear through the coil position and one from nose to atlas. The crossing of both axes is defined as "top". We measured the distances from top to the coil position, to the right ear and to the nose on the 3D surface rendering of the head. To compare both methods, we measured the distance between both coil positions on the patients head.
Results:
The individual stimulation points were scattered widelly about the 5-cm point. There is an average shift of 27±14 mm between both. In most subjects, the standard method positioned the DLPFC too rostrally.
Conclusions:
We showed that the current positioning method used in rTMS- studies easily fail to target the DLPFC. An inaccurate positioning of the rTMS-coil over the DLPFC can be a reason for the heterogeneous outcome of rTMS-treatments. In order to improve the efficacy of this technique, we should use coil positioning techniques witch take the individual anatomy in account by making the combination with MRI.
References:
[1] Herwig U. (2001): Biol Psychiatry; 50: 58-61
Book: Proceedings ESMRMB 2008
Pages: 58-58
Number of pages: 1
Publication year:2008
Keywords:rTMS