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Neuronavigation-guided Repetitive Transcranial Magnetic Stimulation for Aphasia
Chapters
Summary May 6th, 2016
This study is designed to test the hypothesis that neuronavigational system-guided transcranial magnetic stimulation has higher accuracy for targeting the intended target as demonstrated by eliciting a greater degree of virtual aphasia in healthy subjects, measured by delay in reaction time to picture naming.
Transcript
The overall goal of this procedure, is to introduce a more precise and effective repetitive transcranial magnetic stimulation method, using a neuro-navigational system, targeting the Brocha's area, for patients with post-stroke aphasia. This method can help as a in the field of aphasia and rehabilitation, by showing that delivery of all TMS, using a neuro-navigational system, is superior to using a 10/20 easy system. The main advantage of this technique is that our TMS can be delivered to the optimal target in the brain, in order to maximize this effect.
Though this method can provide insight into the application of neuro-navigational rTMS on Brocha's area, it can also be applied to the other areas of the brain, such as M1, for motor weakness, or posterior parietal cortex for neolect following stroke. We first had the idea for this method, when we recognized the errors of the conventional TMS targeting, based on the 10/20 EEG system. To determine the resting motor threshold, first place the active electrode on the left first dorsal interosseous, or FDI, muscle.
Then, deliver ten consecutive stimulations to the right in one area, at a four to six second interstimulus interval, checking the contraction of the left FDI muscle. Determine the subjects resting motor threshold, by using the minimum TMS intensity, at which a peak to peak motor evoked potential, or MEP amplitude, greater than 50 micro volts, is produced nine out of ten times. Next, obtain high resolution T1 weighted magnetic resonance, or MR, anatomical images of the subject, using an MR scanner, for use with the neuro navigational system.
To reconstruct skin structure, obtain the file of the subjects MR image, in standard digital imaging and communications in medicine, or DICOM, format. Transfer the DICOM file to the computer in which the neuro navigation program is installed, then start the navigation program. Next, click Atlas spaces to set the reference point to reconstruct each image.
Find the patients interior com-a-ser of the corpus callosum, just the mid-line of two hemispheres placed in front of the columns of the fornix. Mark the interior com-a-ser on the MR image. Likewise, find the patients posterior com-a-ser, the midland of the two hemispheres in the dorsal aspect of the upper end of the cerebral aqueduct.
Mark the posterior com-a-ser on the MR image. Next, click reconstructions to make this constructure. Include the whole skull, with the nasal tip and both ears, and then display the skin morphology.
Reconstruct the brain curvilinear after skin reconstruction. Configure the landmark in order to match the anatomical point between the patient and the reconstructed skin structure. First, mark the nasion on the computed skin structure, then mark the nasal tip, and each tragus on the skin structure.
Following this, put the head strap with the subjective tracker, on the participants head. Ensure that the navigational camera detects and displays all of the tracking system of the subject, chair, and coil before proceeding Calibrate the coil tracker with the calibration block of the navigational seating system, before every know navigational TMS stimulation. To do this, click TMS Coil Calibration, at the second session, flip the coil name used the first time, and re-calibrate.
Finally, place the TMS coil horizontally on the standard point posterior of the calibration block. Check that the camera is detecting both the calibration block and coil tracker, then begin calibration countdown, and hold the coil still during the five second countdown. To begin, identify the anatomical inferior frontal gyrus, or IFG, based on the surface of the normalized brain.
Register the IFG as the TMS target. Mark the IFG on the window displaying the brain curvilinear. Save the point as trajectory, then register landmarks with the subjects scalp, and create a new session.
Next, click registration, to match the reconstructive brain curvilinear with the subject. Use the previously registered landmark to match the anatomical point with the real anatomical structure. Make sure the camera identifies both the pointer, and the subject tracker, displayed in green color.
Point at the subjects nasion, then to the subjects nasal tip, and sample it. Repeat until all four landmarks are matched. Check the screen to ensure the coil is on the desired target, and is maintained throughout the TMS procedure.
Ensure that the screen displays the subjects brain surface, intended target, and the coil, as well as the arrow range as the coil moves away from the target shown by the bullseye. Use the screen as a reference to adjust the coil on the target, as it is moved away. Then, perform TMS over the registered target.
Ensure the camera identifies both the subject tracker and coil tracker. Finally, make sure that the screen displays the relative distance and angle of the TMS coil from the registered target, the IFG. Note, if the coil moves away from the target, the distance is marked in red, whereas it is marked in green when the coil is within the intended target range.
Obtain the angle between the coil and the target as a bullseye, as much as possible. This protocol demonstrates that navigational TMS produced a higher accuracy for targeting the intended brain area, than conventional TMS. By eliciting a greater degree of virtual aphasia in healthy subjects during the picture naming task, here navigational TMS induced a significant delay in reaction time, compared with base line.
And a greater consistency of localization of stimulation with the target. Furthermore, the distance from the actual stimulation site relative to the target, is closer with the navigational TMS, than conventional TMS. Thus the arrow range is narrower for navigational TMS compared to conventional TMS.
After watching this video, you should have a good understanding of how to perform neuro-navigation to rTMS, to specific target areas over the brain. Once mastered, this technique can be performed within 30 minutes, if it is done properly. While attempting this procedure, it's important to know exactly where you want to stimulate, and to find the spot on the brain image, in order to set it as the target.
After it's development, this technique paved a way for the researchers in the field of neuromodulation, by exploring benefits of neuronavigation guided rTMS, for treatment of a variety of neurological symptoms from a stroke, a post stroke neuro rehabilitation. Following this procedure, neuro navigational rTMS on other area of brain, such as for motor weakness, or intellect symptoms of stroke, can be performed. Don't forget that working with TMS can be contraindicated in some cases, and precautions should always be taken while performing this procedure, to avoid instances of headache, hearing loss, and even seizures.
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