Auditory cortex stimulation might be efficacious in a subgroup of tinnitus patients.

cancellation is nearly complete in certain symmetric positions of the TMS coil relative to the MRI bore, such as configurations Fringe-V, B0-V, and B0-H in Fig. 2 as well as i and iv in Fig. 3 by Yau et al. On the other hand, configurations Fringe-H in Fig. 2 and ii, iii, and v in Fig. 3 have different coupling between each of the two windings of the TMS coil and the MRI scanner magnet. Therefore, we would expect stronger TMS field reduction effect in the latter compared to the former, as is indeed observed. Since the effect depends on differential coupling of the two TMS coil loops, it is understandable why the effect strength correlates with the magnetic field spatial gradient (Fig. 4 of Yau et al.): High spatial gradient of the static magnetic field reveals, via reciprocity, high spatial gradient in the electromagnetic coupling to the superconducting coil. Thus, the two TMS coil loops are more likely to have different coupling to the scanner where the static field gradient is high. Indeed, the strongest effect in configuration iii among the conditions in Fig. 3 is expected, since the plane of the TMS coil is parallel to theMRI superconducting coils, enabling strong coupling, and one of the TMS coil loops is more offset from the scanner z-axis, resulting in differential coupling for the two loops. While the analysis above is only qualitative, it does lend support to the hypothesis that the TMS field reduction results from electromagnetic coupling between the TMS coil and theMRI superconducting magnet. This coupling is not related to the direct current in the MRI magnet that generates the static field in the scannerethe TMS field reduction effect should persist even if the static field of the scanner were turned down to zero. An important implication of the explanatory framework proposed here is that there may be TMS coil placements inside the scanner bore that have stronger coupling to the superconductingmagnet than the symmetric configurations tested in the B0 field in Fig. 2, and hencemay result inmore substantial TMS field suppression effects. This possibility amplifies the concern of Yau et al. about an impact on TMS dosing, and warrants further characterization of the TMSfield reduction effect, especially inside the scanner bore. A practical approach to mitigate this issue could be to incorporate a small search coil with the TMS coil that would allow monitoring of the induced electric field as well as adjustments of the stimulator output to compensate for the pulse reduction effect. More broadly, the observations of Yau et al. remind us once again that the manufacturers of TMS equipment as well as the researchers and clinicians using it should be aware of the various possible electromagnetic interactions between TMS devices and other electronic equipment including imaging systems.