Check of Oct 2015 results when TMS pulses are applied during fatsat and slice excitation. TMS amplitude 70%, TMS pulses start at the last 1/3 of slice 6, then proceeds for 36.4 ms. For a slice duration of approx 2000/36 = 55.56 ms, this means we're covering the last 17.56 ms of slice 6 (in its k-space readout) and then the first 18.84 ms of slice 7. This is a direct repeat of the results shown in issue #11.
TMS coil positioned on FBIRN gel phantom as shown in these photos:
First run: flip angle set at 60 deg (vs only 30 deg in tests of #11) to accentuate the shape of the excitation. 386 volumes acquired.
Second run: FA still at 60 deg, same position of TMS pulse. Acquisition terminated after 200 volumes, since we only want to see the effects during the RF pulses of slice 7. File name erroneously appended with FA30.
Third run: FA set at 30 deg, same position of TMS pulses. Acquisition set at 200 volumes to match second run.
Fourth run: FA set at 60 deg, but TMS coil position moved so that the plane of the coil was more perpendicular to the magnet axis.
In all four cases, the trace through the RF pulses is not as symmetric as we saw previously. TMS coil position? Perhaps the location of the TMS coil near to the "fat"end ring of the birdcage? Are we whacking the birdcage coil electronics differently this time? Or is it a combined effect of RF shielding and the direction of the TMS pulsed field, effects that would vary with relative position of TMS coil to phantom but not TMS coil to birdcage coil? Most likely explanation is that we are seeing a different degree of coupling of the TMS field to the RF coil, causing a far greater disruption of k-space as previously.
Inspecting the time series (videos are on my laptop) we clearly see the effects of the TMS pulse on the fat sat pulse on the target slice, but also on many images collected after it. This is expected. Then we see a subtle degradation during the slice-selective excitation, perhaps suggesting that the TMS pulse is performing as a reasonably well-balanced gradient echo. And finally we see the total loss of target slice signal as the TMS pulse hits the in-plane pre-phasing gradients and the readout period. There is RF interference visible in slice 6 early, and slice 7 late, confirming TMS pulse to RF coil electronics coupling.
Check of Oct 2015 results when TMS pulses are applied during fatsat and slice excitation. TMS amplitude 70%, TMS pulses start at the last 1/3 of slice 6, then proceeds for 36.4 ms. For a slice duration of approx 2000/36 = 55.56 ms, this means we're covering the last 17.56 ms of slice 6 (in its k-space readout) and then the first 18.84 ms of slice 7. This is a direct repeat of the results shown in issue #11.
TMS coil positioned on FBIRN gel phantom as shown in these photos:
First run: flip angle set at 60 deg (vs only 30 deg in tests of #11) to accentuate the shape of the excitation. 386 volumes acquired.
Second run: FA still at 60 deg, same position of TMS pulse. Acquisition terminated after 200 volumes, since we only want to see the effects during the RF pulses of slice 7. File name erroneously appended with FA30.
Third run: FA set at 30 deg, same position of TMS pulses. Acquisition set at 200 volumes to match second run.
Fourth run: FA set at 60 deg, but TMS coil position moved so that the plane of the coil was more perpendicular to the magnet axis.
In all four cases, the trace through the RF pulses is not as symmetric as we saw previously. TMS coil position? Perhaps the location of the TMS coil near to the "fat"end ring of the birdcage? Are we whacking the birdcage coil electronics differently this time? Or is it a combined effect of RF shielding and the direction of the TMS pulsed field, effects that would vary with relative position of TMS coil to phantom but not TMS coil to birdcage coil? Most likely explanation is that we are seeing a different degree of coupling of the TMS field to the RF coil, causing a far greater disruption of k-space as previously.
Inspecting the time series (videos are on my laptop) we clearly see the effects of the TMS pulse on the fat sat pulse on the target slice, but also on many images collected after it. This is expected. Then we see a subtle degradation during the slice-selective excitation, perhaps suggesting that the TMS pulse is performing as a reasonably well-balanced gradient echo. And finally we see the total loss of target slice signal as the TMS pulse hits the in-plane pre-phasing gradients and the readout period. There is RF interference visible in slice 6 early, and slice 7 late, confirming TMS pulse to RF coil electronics coupling.