Having set up the TMS coil using BrainSight it would be useful to verify the TMS position on the head at the end of the session, in case of large movement. There's likely no fix, but it would be a way to determine why some experiments might be giving lousy data. A typical approach is to place MR visible markers on the TMS coil. These come in various forms, but the approach is common: to acquire a 3D scan of the coil markers and head/brain in the same volume.
As a single channel coil the birdcage coil doesn't permit parallel imaging, so a scan like MP-RAGE would be very slow, or low resolution to compensate for the slow acquisition. An alternative would be to set up a multislice 2D GRE scan and aim to get sufficient contrast of the markers and brain for localizing. We might get a full scan in something like 2 min with acceptable contrast.
Or, don't use MRI at all. Justin informs me that it's routine to loosen the head band worn by the subject to hold the reflective balls in place for use with the BrainSight camera. Apparently it's very uncomfortable. So using the BrainSight likely isn't an option to reference the TMS coil back to the subject. It would in any case be very slow because the equipment would have to be brought back into the room.
So, perhaps we might set up an alternative form of optical location tracking to augment the BrainSight initial positioning. It might be a two-step procedure, the first step being capture of a reference position just before the subject is inserted into the magnet. (The BrainSight positioning proceeds as now.) Then the second step is performed the moment the subject comes out of the scanner. The two images, or whatever, are assessed for differences.
Photography is one form of optical tracking, and we have cameras that work in the stray field of the magnet. But the camera location would have to be held constant (or reproduced accurately at the end of the experiment) and the patient bed retracted to precisely the same location in order for this to work. A better option might be to mount a dedicated tracking camera on the bed or the RF coil somehow, and triangulate the TMS coil position and the head position separately to determine their relative locations. The ideal method would take seconds to capture the TMS coil and subject head position. Accuracy is t.b.d.
Having set up the TMS coil using BrainSight it would be useful to verify the TMS position on the head at the end of the session, in case of large movement. There's likely no fix, but it would be a way to determine why some experiments might be giving lousy data. A typical approach is to place MR visible markers on the TMS coil. These come in various forms, but the approach is common: to acquire a 3D scan of the coil markers and head/brain in the same volume.
As a single channel coil the birdcage coil doesn't permit parallel imaging, so a scan like MP-RAGE would be very slow, or low resolution to compensate for the slow acquisition. An alternative would be to set up a multislice 2D GRE scan and aim to get sufficient contrast of the markers and brain for localizing. We might get a full scan in something like 2 min with acceptable contrast.
Or, don't use MRI at all. Justin informs me that it's routine to loosen the head band worn by the subject to hold the reflective balls in place for use with the BrainSight camera. Apparently it's very uncomfortable. So using the BrainSight likely isn't an option to reference the TMS coil back to the subject. It would in any case be very slow because the equipment would have to be brought back into the room.
So, perhaps we might set up an alternative form of optical location tracking to augment the BrainSight initial positioning. It might be a two-step procedure, the first step being capture of a reference position just before the subject is inserted into the magnet. (The BrainSight positioning proceeds as now.) Then the second step is performed the moment the subject comes out of the scanner. The two images, or whatever, are assessed for differences.
Photography is one form of optical tracking, and we have cameras that work in the stray field of the magnet. But the camera location would have to be held constant (or reproduced accurately at the end of the experiment) and the patient bed retracted to precisely the same location in order for this to work. A better option might be to mount a dedicated tracking camera on the bed or the RF coil somehow, and triangulate the TMS coil position and the head position separately to determine their relative locations. The ideal method would take seconds to capture the TMS coil and subject head position. Accuracy is t.b.d.