Combining the world of NIRS and EEG

Combining the world of NIRS and EEG

EEG and fNIRS are complementary measuring techniques. EEG measures electrophysiological brain activation, that is the electromagnetic field created when neurons in the brain are firing. fNIRS measures the hemodynamic response, that is the change of oxygen in the blood when a brain region becomes active. By combining EEG and fNIRS, a more complete picture of brain activity is obtained: activation of neurons and energy demand of neurons. 

The do's and don'ts of baselines

The do's and don'ts of baselines

A common question we get from our customers is what is a baseline and how to use it. Generally with fNIRS, the absolute values are arbitrary. The period before a stimulus is often referred to as the baseline. In this blog we will describe the do's and don'ts of baselines.

Publication overview 2016

Publication overview 2016

At Artinis we consider ultimate success to be good publications by our customers. To see how we are doing we have systematically searched Google Scholar for NIRS and fNIRS publications.

Finding Prana: An Artist’s Experiment with fNIRS

At Artinis we are regularly surprised with the novel and innovative applications of our fNIRS devices. In this blog we would like to share an example of an unique application by one of our customers.

Helen Collard is an interdisciplinary artist working with yogic pranayama (breathing exercises) and technology. Her most recent project has been working with fNIRS to record the changing levels of oxygenated and deoxygenated hemoglobin whilst performing a sequence of pranayama exercises. In these exercises the breathing is controlled, whilst  the hemodynamic response is sonified in real-time allowing the audience to experience the effects of the pranayama performance on changing hemoglobin levels in an audio form.

Helen has been working in collaboration with by Dr. Philippa Jackson at the Brain Performance and Nutritional Research Center based at Northumbria University, Newcastle, UK. Helen and Philippa used a 2-channel continuous-wave Oxymon system and ran two initial pilot studies to see if the pranayama exercises had significant results to justify creating a sonification system. Once it was established there were clear hemodynamic patterns for each pranayama exercise  Helen began work on making a system to sonify the data in real-time. The system was created by sharing Oxysoft data with programming language Max. The audio is composed to illustrate a sound experience or translation of the body and mind during the pranayama sequence in the audience.

The work is entitled Finding Prana. The title refers to the yoga concept of prana which is a Sanskrit word taken to mean both breath and life and pranayama is the control or regulation of the prana or breath. Finding Prana was most recently performed at the international electronic arts festival ISEA 2017 – the International Symposium of Electronic Arts. Artinis provided a portable Octamon for Helen to make the trip to Colombia and perform at the Manizales Botanical Gardens Auditorium. This year’s symposium and festival attracted an international roster of artists and academics working with technology under the theme of Bio-creation and peace.

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For further information please visit:

Finding Prana: https://helencollardo.com/2016/12/1/fnirs-sonification

ISEA: http://www.isea2017.disenovisual.com/

 

 

Image: Finding Prana ISEA 2017 Photo Credit: Juan Waltero

 
 

How to create the best optode template for your fNIRS setup

You have probably seen that there are many different templates (or as others also call it, layouts or montages) possible for the OxyMon. How do I choose the one best for me?

How many channels can I create?

First you need to know how many receivers and transmitters your system has. The easiest way is to simply count it in the device itself. The receivers (blue sticker) are on the left of the OxyMon and the transmitters (yellow sticker) on the right. Be aware that two lasers form one transmitter. So, if you count the number of connectors here, divide this by two. This can be seen in Figure 1.

Figure 1: OxyMon cabinet, left: two receivers ("Rx") labelled with a blue sticker and right four transmitters ("Tx") labeled with a yellow sticker

The maximum number of channels that could theoretically be formed with your device is the number of receivers * number of transmitters.

However, this assumes that every receiver is near every transmitter. Especially with systems with a large amount of optodes this is not feasible as some transmitters and receivers will have a distance that is not sufficient to get a signal. For example, a receiver on one side of the head and a transmitter on the other side will not be able to form a channel as the distance is too large to get sufficient light.

Split versus unsplit optical fibers

To make optimal use of your number of receivers and transmitters we offer the possibility to split your optical fiber.

What does this mean?

A simple example using a 2 channel system is shown in the figure below. A 2 channel system has 1 receiver and 2 transmitters. In case you use only unsplit fibers you will get the template as shown at the top. The receiver forms a channel with each transmitter. If you would replace the unsplit fiber for the receiver by a split fiber (see Figure 2), which has 2 ends at the subject end, you will be able to use the template shown on the bottom.

 

Figure 2:  Two channels using only unsplit fibers (top) versus two channels using an unsplit receiver fiber (bottom)

The advantage of the template on the top is that you now have two channels which can be placed independently on the body. This enables you to have a large amount of channels without the need to buy many receivers. You are required to not place two receiver ends closer than 50mm from each other as this causes crosstalk. The standard multichannel templates available in our Oxysoft software all fulfil this requirement.

The advantage of using an unsplit fiber is that you will have more light. General rule of thumb is that with a full fiber you can increase the interoptode distance with about 5mm in comparison with a split fiber, enabling you to measure deeper in the brain.

By using split fibers it is easier to have a large number of channels of your system. In general, you can never form more channels than ‘receivers’ x ‘transmitters’. If you developed your own template, and you do have more channels, than you have used a (number of) channel(s) multiple times.

Special intermezzo: We also offer a special receiver fiber which is split 8 times! This this fiber can be used to form shallow (or reference or superficial) channels with a short interoptode distance (usually between 5-15mm). Using this fiber, you only need 1 receiver to form up to 8 reference channels!

Choose your template

In the dropdown menu of the optode-template selection screen you will find many different templates you could use. To select the right one for you, you need to know the number of receivers and transmitters you have and the type of fibers (split vs unsplit) you have to your availability. On the bottom right (Figure 3) of the optode-template selection screen you see how many receivers and transmitters are required and which fibers (either 1-end (=unsplit fiber) or 2-end (=split fiber)).

Depending on the template you chose, the software will show you the corresponding NIRS signals for each channel. Do not worry if you chose a template in the software of which afterwards you found that it did not correspond with the actual template that you used on your subject. Oxysoft stores all data from every possible channel. So, it is possible to change the template in the software after finishing a measurement as well.

Tip: If you find a template which uses 1 split fiber, while you only have unsplit fibers, this 1 receiver with 1 split fiber can be replaced by 2 receivers with 2 unsplit fibers.

Tip: If you only have split fibers and the template of your choice has unsplit fibers, it is possible to use just one end of a split fiber by capping off the unused end.

Knowing all this, you can now select the template for your system. If you wish to use another template that can be made with your system or fibers, you can contact us and we can explain what you need to do to use that template.

Figure 3: Template screen from Oxysoft software, an 8 channel split template is chosen, with 2 unsplit receivers (Rx1 & Rx2), 2 unsplit transmitters (Tx1 & Tx2) and 2 split transmitters (Tx3a, Tx3b, Tx4a, Tx4b)

What if the template I want is not in the list?

You can create one yourself! If you go to the folder where Oxysoft is installed (usually C:\Program Files (x86)\Artinis Medical Systems BV\Oxysoft XXX). Here you will find a file named optodetemplate.xml. This file can be edited with any text editor. It includes templates with descriptions which should help you to get on your way. Before you start editing it, do not forget to make a backup. If you need any help, please contact us and we will gladly help you.

How do I choose the best holder for my optodes?

The OxyMon, the fibers and the holders are all separate items therefore a  system can be configured for any application.

As discussed before, the OxyMon can come in many combinations of number of receivers and transmitters, as well as the optical fibers can come split or unsplit. We also offer many options for the holder.For smaller number of channels we usually recommend to use our hard plastic holders. These do not cover large areas of the subjects’ skin and are therefore comfortable and easily accessible.

For larger number of channels (commonly with brain measurements) we advise to use a headcap. We developed these headcaps for optimal use with NIRS. These caps differ in a number of points compared to standard caps. For example they cover a larger area of the prefrontal cortex, have a better optode to skin contact and more coverage of the brain. These caps come with premade holes or without in case you want to determine the exact locations yourself. These caps can be used to in combination with any of the templates predesigned in the software but are also perfect to use when you want to create your own template.

If you need any assistance in determining the right selection for your specific research, please contact Artinis and we are always happy to help you!