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EM pulse coil = small-scale model of a Transcranial Magnetic Stimulator (TMS)

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Milarepa108

Sat Jan 15 2011, 05:19PM

Registered Member #3620 Joined: Sat Jan 15 2011, 04:16PM
Location:
Posts: 11

Hi guys

Here at my University we work with this utterly fascinating technology called transcranial magnetic stimulation. (TMS on wikipedia) It's a relatively simple device: A capacitor bank switched my a microprocessor stores the energy delivered over a cable to a special coil you can hold in your hand and position over the participants head. The magnetic pulse induces a small current in the tissue, just large enough to change the neural activity of the brain at this particular location. This in turn leads to behavioral or perceptual changes we can measure in the laboratory. (We do a lot of research on the visual system with this device but it has been applied to a lot of other stuff, see google scholar. If you want more info, just ask.) As a researcher planning an experiment you'll have to choose some key variables: Field strength (measured in arbitrary units), Pulse frequency (in Hz) or Single Pulse and which coil you want to use. Field strength is pretty self-explanatory: The higher the field strength, the more current is induced, the more noise is induced into the system. Pulse frequency is a more difficult parameter to choose, because different pulse frequencies have been shown to produce very different changes in neural activity. While some frequencies might activate a given area, others might suppress its activity. This is not too important here because only single pulse will be implemented. The coil is also important: While a standard round coil tends to produce stronger fields in general, a double-8 wound coil tends to be more focal, which can be very important, depending on what you are interested in. While other coils are available, we use these two, mostly the latter. There are also differences between manufacturers. (Here an article on that.)
Last year, in order to explain the device and the differences in the magnetic coils to some other students, I attempted to built a model. What I wanted the model to show was primarily how the circuitry works and how the magnetic field differs depending on the shape of the coil. For the electronics, I used the transformer and capacitor circuitry from a disposable camera. I connected two AA batteries to the transformer which gave me a an unknown voltage (didn't measure). The capacitor and some switches were used to that I could use a key-switch to load the capacitor and a pushbutton to fire the coil. I hand-wound the coils to mimic X-ray photographs I have from the manufacturers coils. I connected them to the capacitor via some speaker-cable and also allowed for them to be connected directly to the battery. For the demonstration I wanted to use a small jar filled with oil and iron filings. I hoped to get a gel-like consistence with iron filings equally distributed with in the oil but couldn't get a substance that fit the purpose. In the end, I didn't even get proper iron filings but had to use abuse some iron-wool sponges.
It didn't work out too well: The capacitors charge was not large enough to make the filings noticably change position within the oil. So all that was left was to show the circuit and the magnetic field which was evident when the batteries were directly attached to the coil. Still, the students were very interested and engaged.

Now, I want to build a better version. My objectives:
- The coil should be able to flip a coin when fired. Or some similarly obvious way to show that there's a magnetic pulse.
- The ability to demonstrate the magnetic field on a device (such as the proposed container with oil & iron filings) so that the magnetic field can be visualized.
- The coils should be able to be switched on continuously without me being afraid of exploding batteries, so that the magnetic field can be looked at more closely.
- A microcontroller (probably just an Arduino) will be implemented to measure the voltage on the caps and to fire the coil via a thyristor, connecting to a PC via serial port and a small Processing or Matlab script providing feedback and control.
- The whole project build must of course be a bit visually pleasing. The observer must be able to see the differences between the control circuitry, the caps, the thyristor and the transformer.
- The coils will be encased in epoxy resin to avoid the risk of an electric shock.

I will continue to post my progress.
So far, I have bought a thyristor. I also have the microcontroller (ATMega8/328), some flash capacitors & transformers and some bits and pieces I might include as I go along such as a bunch of displays, cool looking key switches, RGB LEDs and such.

I also have about fourty 6400 pf, 1.2kV foil caps. Are they any good or should I stick to Elkos?

Does anyone have an idea about how much energy I should use? I don't need too much, just so that I get a visible or measurable effect.

I don't think I will implement anything more then single pulse and continuously on mode. I suspect that this would make the project more complicated then it needs to be.

Any other ideas, suggestions are welcome!
Next time, I might also post some pictures of the coils that are used and my previous attempt.

Thanks!
Greetings
Milarepa

Mattski

Sat Jan 15 2011, 07:01PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

wrote ...
- The coil should be able to flip a coin when fired. Or some similarly obvious way to show that there's a magnetic pulse.
- The ability to demonstrate the magnetic field on a device (such as the proposed container with oil & iron filings) so that the magnetic field can be visualized.

What about putting some compasses around the work coil? Just get a bunch of the cheap ones that are a few cm in diameter, they will be pretty sensitive and for a continuously on field you can directly view the field pattern (as long as it's strong compared to earth's magnetic field, which I assume it is). Or you could buy some of these to acquire numeric data on the field pattern (you'll have to check that they have a high enough field capacity and sampling time for your application).

Have you conducted any simulations on the field pattern? I'd be curious to know how much the head affects the field given that it is probably non-magnetic but will be carrying a bit of induced current.

Carbon_Rod

Sun Jan 16 2011, 01:28AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Use a Quantitative Quality Indicator (QQI) or Artificial Flaw Standard

In my opinion... TMS is just a modern day form of Trepanning

Milarepa108

Sun Jan 16 2011, 06:36PM

Registered Member #3620 Joined: Sat Jan 15 2011, 04:16PM
Location:
Posts: 11

@Mattski

What about putting some compasses around the work coil?

That seems like a good idea to me. I'll check if I can get some small ones cheap off ebay!

Or you could buy some of these to acquire numeric data on the field pattern

I though about that too and I might add something like this later on, but for now, it's too complicated.
Also, I haven't made any simulations simply because I haven't discovered an easy way to do so. If anyone could help out though, that would be great.

Also, I remember that unitednuclear.com carried a special foil for a while that would change color depending on the magnetic field. Has anyone come across something like this lately, or can tell me the name of that product?

@Carbon_Rod

TMS is just a modern day form of Trepanning.

How would you get to this preposterous hypothesis? TMS is not a treatment for anything, it's a tool of the cognitive neuroscientist and among scientists there is not really any about it's validity. Sometimes it's used for diagnostic purposes, but that's about it. Are you sure you're not talking about something else?

QQIs seem interesting but a bit overkill for my purposes.

Wolfram

Sun Jan 16 2011, 07:11PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Milarepa108 wrote ...

Also, I remember that unitednuclear.com carried a special foil for a while that would change color depending on the magnetic field. Has anyone come across something like this lately, or can tell me the name of that product?

Something like this

Milarepa108

Sun Jan 16 2011, 07:20PM

Registered Member #3620 Joined: Sat Jan 15 2011, 04:16PM
Location:
Posts: 11

Something like this ?

Yeah, exactly, thanks!
Did you ever seen this stuff 'in action'?

Proud Mary

Sun Jan 16 2011, 07:32PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Milarepa108 wrote ...

@Carbon_Rod

TMS is just a modern day form of Trepanning.

Not so fast, Boy Wonder! Here's a sample of three recent peer-reviewed papers, which must stand in for the dozens to be found in five minutes in a MEDLINE search that all say you're talking bollocks. So who's preposterous now?

Expert Rev Med Devices. 2011 Jan;8(1):85-95.

The effects of repetitive transcranial magnetic stimulation in the treatment of depression.

Fitzgerald PB, Daskalakis ZJ.

Monash Alfred Psychiatry Research Centre, The Alfred and Monash University School of Psychology and Psychiatry, First Floor Old Baker Building, Commercial Road Melbourne, 3004, Victoria 3181 Australia.

Abstract

Repetitive transcranial magnetic stimulation (rTMS) is currently emerging as one of the first fundamentally new treatments in psychiatric practice for a considerable number of years. Research into the use of rTMS for the treatment of patients with depression has now been conducted for over 15 years. The aim of this article was to review the development of rTMS treatment for depression and the current state of evidence supporting its use. The vast majority of the trials conducted on the technique have evaluated the efficacy of high-frequency rTMS applied to the left dorsolateral prefrontal cortex using a set of parameters very similar to those originally described in the mid-1990s. This 'standard' form of rTMS clearly appears to have antidepressant efficacy, and its effects have now been confirmed in several large-scale clinical trials and a number of meta-analyses: response is better than that of sham stimulation, although the number of responders to treatment is relatively modest. A wide range of alternative forms of rTMS have been, or are currently being, evaluated. Low-frequency stimulation applied to the right prefrontal cortex appears to have similar efficacy to standard treatment and it is possible that the bilateral approaches may prove more effective. Novel methods of stimulation, such as priming stimulation, theta-burst stimulation and deep TMS, appear to be promising although require further evaluation. Significant benefit appears likely to accumulate through the use of methods that involve a more reliable targeting of prefrontal brain regions. Research is also required to evaluate the long-term effects of rTMS treatment, its use as a maintenance therapy and to establish reliable predictors of response to treatment.

______________________________________ __________________________________________________ _______________________________

Ann Clin Psychiatry. 2010 Nov;22(4 Suppl 2):S4-11.

Transcranial magnetic stimulation for major depressive disorder: a pragmatic approach to implementing TMS in a clinical practice.

Derstine T, Lanocha K, Wahlstrom C, Hutton TM.

SunPointe Health, State College, PA, USA.

Abstract

Another option for managing major depressive disorder (MDD) became available in October 2008 with the Food and Drug Administration's (FDA) market clearance of NeuroStar TMS (transcranial magnetic stimulation) Therapy System. A panel of psychiatrists who have been treating patients with NeuroStar TMS Therapy in their clinics assembled for a virtual roundtable discussion regarding their experiences. In this supplement, the panel addresses the following issues: the FDA-cleared indication for use of NeuroStar TMS Therapy; logistic and staffing considerations in the outpatient setting; selecting the right patient for TMS Therapy; talking with patients and family about TMS Therapy. To give the overview a meaningful context, each panelist shares a personal account of a patient case, describing the treatment course and outcomes achieved with TMS Therapy.

________________________________________ __________________________________________________ ____________________________

Vertex. 2010 Sep;XXI(93):330-338.

[Transcranial Magnetic Stimulation (TMS) and its contributions to Psychiatrics.]

[Article in Spanish]

Barel MV.

Abstract

Transcranial Magnetic Stimulation (TMS) is a non-invasive and safe procedure with few adverse effects. TMS stimulates the cerebral cortex and makes changes in different psychiatric disorders. Most of the research done has highlighted its antidepressive efficiency in patients suffering resistant depressions. What's more, TMS has been recently approved by the Food and Drug Administration and its analysis and benefits have been extended to other clinical entities, making it possible to consider TMS a possible and promising alternative for the treatment of psychiatric disorders. The aim of the current review is to know and update the possible benefits published so far and to analyze the impact of this new method in Psychiatrics.

Milarepa108

Sun Jan 16 2011, 07:55PM

Registered Member #3620 Joined: Sat Jan 15 2011, 04:16PM
Location:
Posts: 11

Very Proud Mary what's your point? Where am I talking bollocks? I know all these papers... Sure, there are some promising projects also in areas of neurorehabilitation, treatment of traumatic brain injury and so forth. None of those methods are in widespread use or without controversy.
Just stating they prove I'm wrong is not really a valid argument. Besides, it's also a bit offtopic.
I'm thankful for any advice on the project!

Proud Mary

Sun Jan 16 2011, 08:03PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Milarepa108 wrote ...

Proud Mary what's your point? Where am I talking bollocks? I know all these papers...
Just stating they prove I'm wrong is not really a valid argument. Besides, it's also a bit offtopic.
I'm thankful for any advice on the project!

You most clearly wrote "TMS is not a treatment for anything"

But it is - or at least many psychiatrists believe it so.

Ed: What's more, in 2008 the U.S. Food and Drug Administration (FDA) cleared the "NeuroStar TMS (Transcranial Magnetic Stimulation) Therapy" system for the treatment of Major Depressive Disorder in adults. See:

Milarepa108

Sun Jan 16 2011, 08:17PM

Registered Member #3620 Joined: Sat Jan 15 2011, 04:16PM
Location:
Posts: 11

Proud Mary wrote ...

You most clearly wrote "TMS is not a treatment for anything"

But it is - or at least many psychiatrists believe it so.

Sure and they might even be right and one day TMS will actually be used in the standard repertoire of psychiatrists and not only in pilot projects of enthusiastic researchers.... I sure would like to see that!
Nonetheless, you are actually helping my point that comparing TMS to trepanation is a preposterous hypothesis. :)

So, any help on my project?

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