Method and apparatus for focused neuromagnetic stimulation and detection

DETAILED DESCRIPTION OF THE INVENTION 1.
Prior Art FIG.
1 illustrates conventional coils that are horizontally (coil 11 in FIG.
1a) or vertically (coil 12 in FIG.
1b) positioned in air 100 over semi-infinite planar tissue 110.
The tissue 110 has a surface 120.
The highest tissue currents 13 induced by current I.
sub.
H (or detected in the horizontal coil 11) can be found in tissue 110 underneath the coil 11, roughly along the circumference of the coil 11 near the surface 120.
With increasing tissue depth the diameter D of these current rings 13 increases and the current intensity decreases (I.
sub.
2 <I.
sub.
1).
As FIG.
1b illustrates, this is also true for the current rings 14, 15 induced in the tissue 110 by the current I.
sub.
V of the vertical coil 12 (or biomagnetically detected in it.
) These current rings are two side-by-side current loops 14 and 15.
They are joined at location 16 which exhibits a relatively high concentration of current intensity (I.
sub.
3 +I.
sub.
3) because of the geometrical superposition of the two current rings 14 and 15.
This location 16 underneath the vertical coil 12 therefore serves as the focality region for stimulation (or detection) because of its field concentrating characteristics.
The horizontal coil 11, however, produces larger absolute current densities in deeper tissues than the vertical coil 12, indicating that horizontal coils can more effectively stimulate deeper neuronal tissues (or biomagnetically detect signals therefrom.
) It is to be understood that the actual design of the physical coils 11 and 12 for stimulation is different than that for detection as pointed out above in the Background section.
The function, however, is the same.
Nerve currents in the region of I.
sub.
1 and I.
sub.
2 produce a current I.
sub.
H in coil 11 and nerve currents in the region of I.
sub.
14 and I.
sub.
15 produce a current I.
sub.
V in coil 12.
These detected nerve currents are much weaker than the induced nerve currents.
The above prior art coil configurations utilizing a Butterfly, Double D, sharp corners, or slinky design produce higher concentrations of current intensity although only for relatively shallow tissue depths