How Coil Design Impacts the Effectiveness of TMS Therapy
If you’re considering TMS therapy in Seattle, it’s helpful to understand the technology behind the treatment—especially the role of TMS coils. The type of coil used can significantly impact how deep and how wide the magnetic stimulation reaches in your brain, which is important when treating complex conditions like depression, anxiety, or OCD.
The Basics of TMS Coil Designs
Early TMS Coils: Circular Design
The earliest TMS devices in the 1980s used a circular coil, but the magnetic fields produced were too shallow to effectively stimulate brain areas related to mood regulation.
Figure-of-Eight Coils: Focused and Widely Used
In 2008, the first FDA-cleared TMS coil for depression therapy was the figure-of-eight coil. This design allows for a more focused and deeper magnetic field compared to circular coils.
- Depth of stimulation: around 1.5–2 cm
- Produces a magnetic field shaped like an upside-down cone
- Commonly used in standard TMS treatments today
However, the figure-of-eight coil has limitations: the field narrows quickly with depth, and it may miss the brain regions it aims to stimulate, especially if anatomical targeting is not precise.
Introducing H-Coils: A Deeper, Broader Reach
In 2013, a new type of coil was FDA-cleared: the Brainsway H1 coil, developed at the National Institute of Mental Health. H coils were designed to overcome the limitations of figure-of-eight coils.
Key Features of H-Coils:
- Greater depth: up to 4–5 cm, reaching deeper brain structures
- Wider stimulation area: covers more brain tissue
- Flexible design: conforms to the shape of your head, improving magnetic connection
- Dual-hemisphere targeting: the H1 coil stimulates both left and right dorsolateral prefrontal cortices
Other FDA-cleared H coils:
- H7 coil: for both OCD and depression
- H4 coil: for smoking cessation
- Off-label uses: alcohol use disorder, PTSD, fatigue in MS, social anxiety in autism
Compared to figure-of-eight coils, H coils stimulate up to 17x more brain volume, making them more effective for patients with brain structure variations or age-related brain thinning.
Why Coil Design Matters for Depression Therapy
Depression isn’t caused by just one part of the brain—it involves widespread decreases in brain activity. A coil that reaches deeper and wider brain regions can offer more comprehensive stimulation, especially for treatment-resistant depression.
Many TMS providers still use the 5 cm rule to find treatment targets, based on measuring from the motor cortex (where thumb twitching is induced). However, this approach can miss the real treatment target up to 66% of the time with figure-of-eight coils. H coils help solve this problem by increasing the likelihood of hitting the right brain areas—even if individual anatomy varies.
TMS in Seattle: Choosing the Right Coil with Clear Path Psychiatry
At Clear Path Psychiatry in Seattle, we use advanced TMS technology, including H coils, to maximize the effectiveness of your treatment. Whether you’re receiving TMS for depression, OCD, or anxiety, coil design can make a major difference in your outcomes.
We tailor each TMS treatment based on your unique needs, brain structure, and clinical response—ensuring the most effective, evidence-based care.
