Light experiment comparing NIRSport and Octamon

1 min read

This is a guest post by Andrew Gundran and Paul Mazaika, both working with NIRS in Stanford University. They did an interesting experiment comparing the light power between NIRSport and Octamon.

Paul Mazaika
Paul Mazaika
Andrew Gundran
Andrew Gundran

We ran experiments to compare the emission signal strengths of the NIRsport and Octomon. Since these systems run in the Near IR, we experimented with some non-standard test equipment.

It was a fun experiment.

The NIRsport uses LED wavelengths of 760 nm and 850 nm. A typical spectral spread shows that only a few percent of total power is emitted more than 50 nm away from the spectral peak (Fig. 1). Since the upper end of visible light to the eye is 700 nm, the eye can see some of the light from the 760 nm LED, thus the system looks red when it is turned on. By far, most of the power is in the infrared and invisible to the eye.

A camera has red, green, and blue sensors. Usually the red sensor will also detect IR, unless there is a good-quality IR filter in front of the lens. So poor quality cameras may be better to detect near IR, and then IR sources may show up brighter in the camera image. Using an iPhone camera, the Octamon lights are much brighter than a red object (Figure 2), although the lights and camera look similarly colored red to the human eye. Thus, a phone camera detects some infrared.

Using the camera phone, the NIRsport emitter looks much brighter than the Octamon emitters, suggesting NIRsport puts out more IR power than the Octamon (Fig. 3).

More light power (the power is mostly in IR) may provoke more heating at the LED emitter, since there is some energy absorption when crossing the boundary from fiber to air. A thermal image (8000-14000 nm) shows that the NIRsport emitter generates more heat than the Octomon emitters (Fig. 4), suggesting that NIRsport is emitting more IR power.

Hmmm, makes you wonder if the Hitachi emitters start getting hot after 10 minutes?

Cross-checking with the actual NIRS equipment is better since they use real IR detectors. To check signal strength: put a finger in front of the Octamon detector, point a NIRsport or Octamon emitter through the finger to see which generates a higher response on the same detector. Possibly will find out that quality of contact is the most important factor.

NIRS light experiment
NIRS light experiment


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8 Replies to “Light experiment comparing NIRSport and Octamon”

  1. A colleague and I have been trying to decide which NIRS system to purchase. We have no experience with NIRS and have lots of ideas for how it may be used in our psychology/behavioral neuroscience department (we are not purchasing it for one particular research goal). We’d like to be able to record from any area of cortex (not just prefrontal) and we’d like something flexible and modular so that we can scale up when we get more funds. Assuming we have 75 – 100k to work with, what would you suggest? We’d need good support and we do not know if we will have money for software updates. Any advice would be appreciated. I have found your blog extremely helpful, Xu. Thank you.

  2. @Katherine Hooper
    Hi Katherine,

    TechEn is a leading developer of fNIRS continuous wave systems. We have been developing and commercializing systems for over 12 years. We collaborate with Dr. David Boas at MGH-Harvard.

    We have a new compact system that will meet your budget.
    Please email me some details on your potential studies.
    I will configure a system and provide a quote.

    Thank you for your interest in fNIRS technology.

    Best regards,
    Buzz DiMartino
    508-478-0042

  3. @Katherine Hooper
    Great to hear that, Katherine. NIRS has opened a new door to a lot of nice applications and I am sure you will find it very productive. I personally used Hitachi’s ETG 4000 but the price is way beyond $100K. Our lab also has NIRx products – I can connect you to the people who actually use it to get their suggestion. Other manufactures, e.g. TechEn, shimadzu, bio-pac, obelab, artinis etc probably have products in the price range but unfortunately we do not have first hand experience.

  4. @Katherine Hooper
    Hi Katherine,

    Happy to see that you want to explore new ideas with new technology! At Artinis we are always happy to work with you to reach your scientific goals. Our equipment allows you to measure anywhere you like, in any way you like. Our equipment is very modular and can even be used as several independent smaller systems. It is really designed to be easy to use, as well as fit every researchers specific needs! The system is also very competitively priced. For your price range we can offer a large multi-channel system, which can still be upgraded in the future. If you need any further information, please feel free to contact me at marco@artinis.com.

    Best regards,

    Marco

  5. Hello Dr. Hooper,

    Thank you for your interest in fNIRS neuroimaging. NIRx does offer some of the most versatile and effective fNIRS platforms out there with portable measurement devices (NIRSport), multi-modal compatibility (EEG, fMRI, et al.) and high-level scientific support from actual fNIRS researchers included with every system. All our systems are highly-configurable and may be used as separate independent systems or combined in a ‘tandem’ configuration.

    We have an extensive network of end-users and company offices and encourage you to check out our system either at one of the labs using our equipment or from a demonstration performed by one of our technical experts.

    Please take some time to check out our website and get in touch if you would like more information: http://www.nirx.net.

    Sincerely,

    Thomas

  6. @Katherine Hooper
    Hi Katherine,

    we use NIRSport by NIRx and PortaLite by Artinis. They are being used in different situations and work excellent in their own way. PortaLite can be used prefrontally and on muscles. While NIRSport is a wearable system for the whole head. So with NIRSport you can basically measure activity anywhere you want. We use it for motor and prefrontal cortex while the test subject is walking. The portaLite is a wireless system, and setup is easy (no need for prepping the subject, or calibration). We currently use it on subjects doing strength training. I think both companies have good support, and they are very interested in talking with and meeting their customers. I would recommend reading a review on fNIRS systems called “A review on continuous wave functional near-infrared spectroscopy and imaging instrumentation and methodology”, by Felix Scholkmann et al.

    hope that helps!

    With regards,

    Evin

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