# Feasibility of Magneto-Encephulography Scan under Color-Tailored Illumination
## 3 Results
### Data Analysis  
Measured MEG sensor data were uploaded into Matlab data format, with each data set around 0.5 GB in size. These data were first plotted onto a color map based on its amplitude to make it easier to compare with each data set. A Matlab command was used to plot the color map of the data. In some cases, it was necessary to omit some sensors due to faulty values, e.g., sensor 29 had too large of values compared to other sensor channels. After removed outliers, data were mapped into Matlab surf plot and can be used for qualitative analysis (Figure 3). No brain function is analysed in this current study, but rather, technical capability to use MEG scanner in the shielded room and USB controlled LED lamp is used.  
Since colors are produced using different pigments and intensities in LEDs, it was necessary to compare MEG equipment response under different LED colors. Figure 4 shows a summary of results for the RGB+amber single colors (no person in a MEG seat). Apparently, there was approximately \(\sim\)10 s higher readout currents in half of the sensors for the blue illumination. This can be taken into account in real settings, when experiments usually start even after a longer delay. The background signal of sensors was fluctuating at 1-10 fT level, while 1-10 pT are usually measured under on-off color stimulations in similar MEG experiments [14].  
The MEG operates in a very low frequency range. Therefore, the noise levels in a low-frequency domain up to 50 Hz were checked. Experimental data in the time domain (Figures 3 and 4) were converted to the frequency domain by using fast Fourier transform (FFT) in Matlab and were plotted as color maps. The absolute value was plotted, which is calculated from a complex number FFT result (amplitude and phase), as shown in Figure 5. The amplitude values on the linear scale are shown in insets for an empty room and a person in the MEG scanner without LED lights (top row in Figure 5). This corresponds to the standard operation conditions and related noise levels. The test of the empty room (no person in MEG) with operated LED lamp via USB link showed the acceptable level of noise (bottom row in Figure 5) for real MEG scans under different color settings.  
Figure 3: Raw experimental data. Magneto-encephalography (MEG) setup test with and without LED-lamp and person in the MEG scanner; LED-lamp is set for the candle light 1500 K color temperature. Scanner No. 29 is excluded from the plot due to erroneous data. Data color-maps are plotted on the same intensity scale.  
Brain activity is most pronounced at frequencies < 5 Hz, as evident for most of MEG scanners (Figure 5), especially in linear intensity scale (insets). Most of the background signal is expected from the blue component of the LED lamp channel. The frequency response due to usage of the blue channel was expanding to higher frequencies that are stronger as compared to amber, red, and green (Figure 5). Timing protocols of color changes in actual MEG experiments need to take into account the frequency of the illumination change, reaction time, and neural activities.  
Figure 4: Magneto-encephalography (MEG) setup test with LED-lamp at different color illumination RGB+amber. Data color-maps are plotted on the same intensity scale.  
Figure 5: Magneto-encephalography (MEG) sensor frequency response. The top row shows Figure 3. The top row measurement is an absolute value of fast Fourier transform (FFT) filtered data at 1 Hz sampling step; insets show the same plots in linear intensity scale. The bottom row is a MEG setup response to the RGB+amber illumination (Figure 4) without a person in the MEG seat. Note that the MEG room’s shielding was effective by design against 50 Hz power supply noise.