Q2. What future works have the authors mentioned in the paper "A review on continuous wave functional near-infrared spectroscopy and imaging instrumentation and methodology" ?
Consequently, in the future, imaging instrumentationwill be increasingly sophisticated and fNIRI imaging of the brain will provide an increasing spatial and temporal resolution. The future will provide fNIRI instrumentation, which will yield orders of magnitude more information than today. The further development of this approach will be an important topic of research. In the future the scope of applications of fNIRIwill continuously grow, and probably at increasing speed.
Q3. What is the popular method to define the forward model?
Numerical methods based on the local solution of the diffusion equation in a meshed space (Arridge et al., 1993; Dehghani et al., 2009a) such as finite elements method (FEM) have been among the most popular methods to define the forward model due to their inherent flexibility to model irregular spaces and the ability to include prior information from other tomographic sources.
Q4. What is the advantage of the MD fNIRI approach compared to MBLL and?
Since changes in light coupling often occur during movements, the advantage of this approach compared to MBLL and SRS is that the coupling factors cancel out and thus the influence of movement artifacts is much reduced.
Q5. Why do APDs require stabilized power supplies?
Due to the dependency of the internal gain on temperature and bias voltage, APDs require stabilized power supplies and are often cooled (Liu, 2005).
Q6. Why is the noise based on the quantum nature of the photons that enter the detector?
Shot noise is based on the quantum nature of the photons that enter the detector as well as the generated carriers, i.e. due to their stochastic non-uniform temporal distribution (Liu, 2005).
Q7. What is the effect of the randommultiplication effect on the detector?
In devices with internal signal amplification, the excess shot noise describes the fluctuations that are due to the randommultiplication effects inside the detector (Liu, 2005).
Q8. What is the effect of the changes in the contact pressure between the optodes and the scalp?
changes in the contact pressure between optodes and the scalp lead to changes in light coupling and thus may introduce artifacts (Gibson et al., 2005; Wahr et al., 1996).
Q9. What are the three factors that play an important role in the selection of a particular light source?
For miniaturized and/or wearable fNIRI instruments, the three factors size, weight and the power consumption play an important role in the selection of a particular light source.
Q10. How many channels can be used for a 16 emitter and 32 detector system?
If the authors define one channel as one path between one emitter including all its wavelengths and one detector, then the maximum (theoretical) number of channels for a 16 emitter and 32 detector system will be 16 ∗ 32 = 512 channels.
Q11. Why did they prefer the arrangement of sources/detectors in a hexagonal geometry?
They favored the arrangement of sources/detectors in a hexagonal geometry, because it has lower requirements for the dynamic range compared to a rectangular geometry.
Q12. What are the widely used types of light sources used in fNIRI instruments?
Laser diodes (LDs) and light emitting diodes (LEDs) are the most widely used types of light sources that are employed in fNIRI instruments (see Table 1).
Q13. What are the advantages of fNIRI compared to other non-invasive neuroimaging?
The strengths of fNIRI compared to other non-invasive neuroimaging techniques such as EEG, fMRI or MEG include its portability, potential wearability, ease of application, and the low purchase and operation costs (especially when compared to fMRI and MEG), the spatially localized nature of fNIRI in contrast to EEG and the more complete information (O2Hb in addition to HHb) compared to fMRI and its compatibility with other neuroscience techniques.
Q14. What are the disadvantages of the multi-spectral approach?
the multi-spectral approach is associated with two drawbacks, i.e. increased computational complexity and the need for reduced incident light power (compared to a normal fNIRI device) since light with a multi-spectrum has a higher total power than light with a restricted wavelength range.
Q15. What is the advantage of combining neuroimaging modalities?
Combining neuroimaging modalities has the advantage of delivering more comprehensive information, e.g. how electrophysiological and hemodynamic/metabolic signals are correlated.
Q16. Why do the authors expect further developments using SiPMs?
Due to their practical advantages compared to PMTs, which the authors recently also started to discover with own experiments (Zimmermann et al., 2013a), the authors expect further developments employing SiPMs in the field of NIRI instrumentation.
Q17. What is the widely used method to remove the components of fNIRI?
Besides these filtering approaches, probably still the most widely used method to remove the components SC4–6, is ‘conventional averaging’ (CA), an average of segments of the fNIRI signal that are time-locked to the presented stimuli.
Q18. What is the optimal wavelength range for pairing with 830 nm?
Okui and Okada (2005) demonstrated in aMonte Carlo simulation byminimizing the crosstalk between [O2Hb] and [HHb], that the optimal wavelength range for pairing with 830 nm for the dual-wavelength setup is between 690 nm and 750 nm.
Q19. What is the way to minimize shot noise?
Shot noise is unavoidable; however, it can be minimized by carefully shielding the detector from background radiation (opaque cover and/or NIR bandpass filters).
Q20. What is the main difference between fNIRI and other non-invasive neuroimaging techniques?
in combination with imaging in 3D, these methods will become much more powerful and a correct separation of the signal components will lead to more reliable data and thus tremendously facilitate the interpretation of the fNIRI signals.