Recently, our lab purchased two MagVenture TMS devices together with the Localite setup for navigation. Both companies are independent, but collaborating strongly. Magventure offers the stimulator, Localite the hardware and software for navigation. The Magventure GUI is very easy to handle and i like how the Localite software allows to use template MRIs. It gives a very streamlined experience and handling is relatively intuitive. Additionally, the whole setup is mobile, so you could even use it on the bedside. I believe that easy handling is a huge advantage, especially when it comes to training students for doing measurements.  Yet, there is one minor disadvantage. Nexstim comes with a built-in amplifier, which can record up to six bipolar channels. MagVenture offers a MEP monitor as additional hardware, which can record a single bipolar channel. So, when you are planning to do multi-channel mapping, you are stuck.

In my opinion, this is not a big issue, for two reasons. First, at least in our lab, we usually record EEG and EMG anyways. We use Brainproducts range of amplifiers and they allow to record triggers. As a first solution, you could simply analyze the MEP with BrainVisionRecorder. Furthermore, we are interested in online control of the stimulation settings. This has several advantages. Not only does it allow for full brain-state dependent stimulation (instead of only brain-state dependent triggering). It also allows to script a stimulation protocol, which again makes training students easier, as the process will be much more standardized. Yet, neither the Nexstim nor the Magventure offer  this feature out of the box. If you want integration with BVR, and as a second step, if you want the MEP readout back into Localite, then some tinkering will become necessary.

In the following, i will describe shortly how the two machines communicate. As you will see, we have one Parallel-Port to BNC to D-Sub 26 pipeline, and one USB to 2x D-Sub 9 Pipeline.

BNC Pipeline

Magventure and Localite are both independent processors (Localite comes on a windows machine, and Magventure uses apparently some embedded processor). The Magventure has a trigger in (to trigger stimulation at the current setting) and sends a trigger out (whenever stimulation is performed). Localite has a trigger in. All these triggers are sent via BNC. BrainProducts offers to record triggers via a parallel D-Sub 26 port in their USB Adapter. So, for recording triggers, we are going to need some circuitry from BNC to D-Sub 26. Furthermore, if you want to trigger via the PC, a parallel-port is the most appropriate solution. It allows you to control 8 bits, and if pushed, even more. This equals independent control over eight BNC connections, i.e. Trigger channels. If you have any measurement PC, it should have a parallel-port. If not, buy one, you can get them for 10 EUR.

RS232 Pipeline

At the same time, both machines communicate their settings based on a Null-Modem connection via a D-SUB 9 port following the RS232 protocoll. The Localite PC asks continually for the current status and the Magventure answers. Additionally Magventure broadcasts its settings whenever the user changes them. If you have the MEP-monitor, it would analyzes the MEP and send information via RS232 to Localite. That means we are going to need some circuitry which mimicks this RS232-protocol, faking to be a Magventure MEP-monitor to Localite and allowing control of Magventures stimulation parameters. Hardware-wise, this  can easily be achieved by a RS232 interface to your control PC. I suggest a USB-Adapter to 2x Serial, as modern PCs offer USB, and you can get them for below 20 EUR.

Put Shortly:  You set the stimulation parameters via RS232 from your PC. You trigger the stimulation via Parallel Port to BNC. MagVenture will send a trig-out via BNC, which you record with the D-Sub 26 of BVR. You analyze the MEP. You send the MEP to Localite via RS232. Problem solved – and multi-channel MEP monitor at your disposal. Well almost, because you’ll need to do some soldering and coding.

 

 

Robert Bauer

Written by Robert Bauer

Agricolab | Descendant of Latin 'agricola', farmer; Lab (colloquial) A laboratory

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