Transcranial Magnetic Stimulation (TMS) is a form of non-invasive brain stimulation therapy. Coils are placed near the scalp and deliver pulses of magnetic energy to stimulate targeted regions. What many people don’t know is that there are actually different coil shapes and types. Each type has a specific use. Some target certain areas of the brain better while others can stimulate deeper brain tissue. These are the most commonly used coil types.
Round or circular, coils are the original type of coil used for TMS therapy. Standard TMS using round coils is effective at treating depression, however, it’s not able to penetrate the brain as deeply therefore while it is effective at treating treatment-resistant depression it’s not often used as there are coils that can reach a much greater depth and increase the antidepressant effect. Round coils are good for superficial TMS, but further coils have now been developed that are more suitable for dTMS.
A figure eight coil, also called a butterfly coil, looks just how the name implies, with two circles connected creating the shape of the number eight. It doesn’t target as deeply as some other coils, but it produces a stronger and more targeted magnetic field. This makes it the perfect coil to use if you’re trying to stimulate a specific area of the brain.
The double-cone coil has two wings that are fixed at an angle creating a sort of cup for which the head fits nicely into. It can stimulate deeper regions of the brain, and can even activate lower limb motor responses. The double-cone coil is often used for deep transcranial magnetic stimulation.
H coil is now the most commonly used type of coil in TMS and it’s also the newest. The H coil looks complicated, but it has a base portion that runs along the scalp and a return portion above the head. The complicated shape was designed to generate a larger electrical field that targets specific regions deep within the brain.
There is also the Halo coil (HCA coil), which is a large circular coil that places around the heave to target deep brain tissue. It’s often used in tangent with regular round coils placed on top of the head. This type of coil is able to stimulate deep within the brain and has greater flexibility than a conventional circular coil.
The four-leaf coil, which got its name because it’s four circles connected in the middle looking like a four leaf clover, was specifically designed to stimulate peripheral nerves. It’s not as commonly used, but for specific cases, it’s the best.
The coil shape used during TMS therapy can impact how effective the treatment is. Scientists are continuously exploring which shapes are best at treating which ailments, and are still developing new coils based on the research. Your doctor might use a few different coil types or might switch until they find the right one. If you have any questions or think TMS therapy is right for you, feel free to contact us!