Frequently asked questions

NIRS is based on absorption of light by certain chromophores. When NIRS is used on biological tissue the main absorbing chromophores are hemoglobin and myoglobin. Both these chromophores have similar absorption spectra and cannot be distinguished using NIRS. However, most important for NIRS are the changes in oxygen binding to these chromophores. Very often only hemoglobin is used to refer to both chromophores, as also by us. Hemoglobin mainly exists in two forms, oxy- and deoxyhemoglobin.
The NIRS device measures changes in light absorption and uses the modified Lambert Beer law to calculate changes in hemoglobin concentrations.
Our NIRS devices also have the possibility to calculate absolute concentrations using spatially resolved spectroscopy (SRS).
For more information you are referred to the manual.

To start with, the changes in concentration of oxy- and deoxyhemoglobin. If you add these up you will have the change in concentration of total hemoglobin. Total hemoglobin can be used to calculate local blood volume and blood flow if the concentration of hemoglobin in blood is known. With the high sampling frequency of our devices you can accurately measure response time. Standard on the PortaMon and PortaLite and as an option on the Oxymon, Tissue Saturation Index (TSI) is possible. TSI gives you an absolute percentage of oxygenated hemoglobin. It is also possible to have different wavelength (optional) so you can measure other chromophores.

General assumption is made based on Monte Carlo models that the measurement depth is roughly half the distance between the receiver and transmitter optode (Cui, 1991). It mainly depends on the tissue, power settings and the fibers (split/unsplit, length, fiber end) what the maximum distance is. With ideal fibers (unsplit fibers with straight ends), the maximum separation distance is approximately 5.5 cm for the Oxymon. For the PortaMon and PortaLite the maximum distance is 4 cm. We also have special fibers for the Oxymon which can measure at very short distances of ~1cm. The minimum distance of the PortaMon and PortaLite is 3 cm.

Choose your DPF according to literature. The DPF can be changed in your measurement properties, also after the data has been recorded. It will adjust the graphical data representation of the concentration changes. Some reference values can be found in the NIRS manual (table 2). For brain applications we suggest to use the software calculation button, DPF= 4.99 + 0.067(Age^0.814).
This formula is valid for ages 17-50 and derived from data of Duncan et al.: Duncan A, Meek J H, Clemence M, Elwell C E, Fallon P, Tyszczuk L, Cope M, Delpy D T, 1996. Measurement of cranial optical pathlength as a function of age using phase resolved near infrared spectroscopy. Pediatr. Res. 39, 889–894.

Yes. Especially the Oxymon, as it uses optical fibers (no electrical signals) to transport the signal from the subject to the device. For the Oxymon we have optional extra-long fibers, with plastic ends so that you can measure inside an MRI scanner or together with MEG, TMS and tDCS. Because we use light all our systems can be combined with modalities as EEG, ECG, EMG, plethysmography, gas exchange analysis, laser Doppler. Only modalities using (near) infrared light can cause artefacts on the NIRS signal. For example eye or motion tracking, which use infrared emitting cameras. This can be solved by carefully covering the area measured by NIRS with a black cloth so no external light can enter the sampled tissue. We offer several solutions for synchronizing the NIRS data with other modalities.

Sometimes fibers are ‘split’, meaning that they have two ends on one end (the subject end) of the fiber. With this fiber one receiver or transmitter unit can measure at two independent areas (e.g. left and right arm) at the same time. Please do notice that these endings do need to make different combinations with the other transmitters/receivers (for example: R1a-T1 and R1b-T2). The advantage of splitting fibers is that you can have more channels without adding receivers or transmitters. The disadvantage of splitting fibers is a small loss of light intensity, resulting in a smaller maximum distance between receiver and transmitter (~0.5cm).

PortaMon and PortaLite always have the same type of sensor. There you always use the same template. For the Oxymon can choose many from the preset template as long as you have the correct type of fibers and enough receivers and transmitters. It is even possible to create your own template! You can do this in the optodetemplate.xml file in your Oxysoft folder. Follow the instructions given with the first template. If you are uncertain about your new template you can always contact us for help.

- Acute Care, Ischemia
- ALS
- Animal Imaging
- Autism
- Behavioral studies
- Brain-Computer Interface (BCI) - Neurofeedback
- Child studies
- Elite sports training
- Hypoxia research
- Language, Cognition
- Learning, Memory
- Motor-control and movement-related studies
- Multi-modal studies (NIRS used simultaneously with EEG, TMS, eye-tracking, tDCS, and other modalities).
- Neonatal monitoring
- Sensory, Motor, Visual
- Sports performance studies
- Traumatic Brain Injury (TBI) Studies