NAVIGATED TMS THERAPY

In this article, we will talk about Navigated TMS Therapy. What it is, how it is used, what it’s used for, and the advantages of navigated TMS over regular [blind] TMS. At the end of the article, I will mention the different types of navigated TMS therapy. This includes structural-MRI-guided navigated TMS, functional-MRI-guided navigated TMS, and non-MRI-guided navigated TMS.

Learn more about TMS therapy pros & cons

Overview

TMS therapy is Transcranial Magnetic Stimulation. The word transcranial means that the magnetic field can pass through the skull to the brain treatment target. Magnetic Stimulation means that we activate certain areas of the brain with a magnetic pulse which would improve the interconnections between brain cells. To enhance the efficacy and tolerability of TMS, we can work on two things.

The characteristics of the magnetic pulse (intensity, frequency, depth).

The target location of the magnetic pulse (location, accuracy, consistency).

Navigated TMS tries to work on the 2nd aspect of TMS to improve the quality and outcome but better location targeting. But how could we do that? Well, I will try to make a complicated thing as simple as possible.

How does Navigated TMS work?

Navigated Transcranial Magnetic Stimulation of the brain is a noninvasive method used to stimulate activity in specific areas of the cortex. Electricity is sent through a coil, generating an electromagnetic field directed through their head by the device sitting on top. An electromagnetic field is unimpeded by the scalp, skull, and cerebrospinal fluid, enabling precise stimulation pulses to be delivered from external sources. When paired with a frameless stereotactic navigational system, magnetic pulses can be provided at highly accurate locations within the brain. This is called Navigated TMS.

How does TMS work? Click here to learn more.

Navigated Transcranial Magnetic Stimulation system uses 3D spatial cameras to locate the location of the treatment coil in real-time in relation to the location of the patient’s head. To achieve this task, you need the following essential variables.

Location of the patient’s head. This is achieved by putting a “head tracker” on the patient’s head. Typically it is the forehead. This is executed by a 3D reflective balls module that sticks using EEG electrodes stickers on the patient’s head [StimGuide by MagStim]. Or by using a headband with the tracker attached to it. Some manufacturers even use a disposable head tracker [Nexstim SmartFocus].

Location of the mapping and treatment coil. This is achieved by the same method of a reflective balls tracker on the casing of the TMS coil.

Anatomical landmarks of the skull. People have different skull shapes. For a frameless spatial camera to render a 3D input of data, we need to tell the software about the shape and size of the skull we are dealing with. A landmark pointer achieves this. Some navigation software may require more data points than others.

Brain imaging. Or an AI software that assumes a standardized brain structure. That part is tricky to understand for now. But basically, a more accurate navigated TMS would require an individualized MRI input to calculate treatment location more accurately. Less accurate navigated TMS systems can just standardize the dimensions based on the skull size and shape.

Navigated TMS for pre-surgical brain mapping

When it comes to surgery, pre-op mapping is a valuable practice that helps surgeons map out the eloquent areas before going in for the big snip.

Brain tumors are physically and functionally destructive, so surgeons must map the brain to preserve its function after removing the tumor. Mapping is considered to be most accurately achieved with a technique called direct cortical stimulation (DCS), which is performed intraoperatively. The gold standard of preoperative assessment for brain surgery is direct cortical stimulation with intracranial EEG, a method requiring craniotomy and implantation of electrodes to deliver electric pulses.

Learn about TMS for anxiety

Navigated transcranial magnetic stimulation (nTMS) is a noninvasive imaging method used in individuals with brain lesions to reduce damage to verbal and motor functions during surgery. Despite its promise in helping neurosurgeons map the brain before surgery, DCS is still the gold standard in brain mapping for brain surgery.

Navigated TMS for better depression treatment

Now we know that we can use Transcranial Magnetic Stimulation to activate brain circuits in depressed brains. What if we can use a navigation system similar to what neurosurgeons tried to utilize before brain surgery. Still, this time the goal is to increase the accuracy of TMS treatment targeting depression. The results are encouraging.

Advantages of Navigated TMS Therapy

Navigated TMS treatments have been designed to be customized for your brain’s anatomy and alertness level, to offer you:

An accurate and individualized dose of TMS
An unmatched level of accuracy
You have personalized treatment sessions for you and your brain.
Enhanced safety and comfort

Types of Navigated TMS Therapy for depression

There are three types of navigated TMS. Well, maybe more if we count in EEG-based navigated TMS. But that is a topic for another article that I will post in the future.

#1 Non-MRI Navigated TMS Therapy

This one doesn’t require an MRI to do the software calculation for mapping and treatment target. Instead, it calculates the treatment target based on the 5.5 cm rule. This is less accurate than the following two methods mentioned below. But it is more convenient, no need to get an MRI, and less costly. StimGuide from Magstim is FDA approved non-MRI neuronavigation TMS therapy system.

#2 Structural-MRI Navigated TMS Therapy

This one will require the input of a structural MRI and a radiologist reading of where the anatomical target F3. The system will guide the operator to target this particular location. This is more accurate structurally compared to the non-MRI navigation system. But it is less accurate than the functional connectivity MRI navigated TMS. The cost of an MRI is usually not covered by insurance, and brain imaging is not indicated for diagnosing depression. SmartFocus from Nextsim is FDA approved MRI Neuronavigation TMS therapy system.

#3 Functional-MRI Navigated TMS Therapy

This has the most potential to revolutionize the practice of TMS as we know it today. You see, the structural anatomy of the rain doesn’t always reflect the functional anatomy of the brain. So instead of targeting an anatomical landmark in a one size fits all assumption, we do individualized functional MRI for each individual to decide exactly where this particular patient functional DL-PFC is located. This is what Nolan Williams used in his breakthrough SAINT-TRD protocol. The problem, though, is the complicated method we do functional MRI and the reproducibility of it.

Unlike structural MRI, functional MRI requires patients to lie very still for long periods to assess motor and language functions. This makes it impractical for people who are claustrophobic or have difficulty lying still. In these cases, a non-MRI-based navigation system can be a good alternative.

Interpretation of functional connectivity MRI can be challenging. It requires a certain level of expertise from a neuroradiologist. Also, it might be challenging to reproduce the same reading of a functional MRI.

Navigated Transcranial Magnetic Stimulation Is Advancing Mental Health Care

With more accurate TMS treatment, we can do more. We can identify our treatment targets better. We can be consistent in stimulating these targets. We can avoid side effects associated with stimulating unwanted targets [I’m looking at you, Brainsway!]. I am very excited about the future of navigated TMS, and I think you should be too!