## 3 Experiments
### Used Instrumentation and Recording Arrangement  
#### 3.2.1. Phonation Signal Recording  
In the measurement phases \(MF_{2}\) and \(MF_{3}\), the tested person lay in the scanning area of the open-air, low-field (0.178 T) MRI tomograph Esaote E-scan Opera [36] located at the Institute of Measurement Science, Slovak Academy of Sciences in Bratislava (IMS SAS). In this tomograph, a static magnetic field is formed between two parallel permanent magnets [36]. Parallel to the magnets, there are two internal planar coils of the gradient system used to select slices in three dimensions. In the magnetic field, a tested object is placed together with an external radio frequency receiving/transmitting coil. The whole MRI scanning equipment is placed in a metal cage to suppress high-frequency interference. The cage is made of a 2-mm thick steel plate with 2.5-mm diameter holes spaced periodically in a 5-mm grid to eliminate the propagation of the electromagnetic field to the surrounding space of the control room. For the phonation signal recording inside the shielding metal cage of this device, the pick-up condenser microphone Mic1 (Soundking EC 010 W) was placed on the stand at the distance \(D_{\text{X}}\) = 60 cm from the central point of the scanning area to inhibit any interaction with the MRI's working magnetic field. Its height was 75 cm from the floor (in the middle \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** **No.** & **Phonation Type** & **Weight [-]** & **PPG Type** & **Weight [-]** \\ \hline
1 & \(L_{\text{STRESS}}\) & \(w_{\text{GMM1}}=0.75\) & \(PPG_{\text{RANGE}}\) & \(w_{\text{PPG1}}=0.25\) \\
2 & \(L_{\text{NORMAL}}\) & \(w_{\text{GMM2}}=-0.5\) & \(HP_{\text{RIPP}}\) & \(w_{\text{PPG2}}=0.5\) \\
3 & \(\Delta L_{\text{S-N}}\) & \(w_{\text{GMM3}}=0.25\) & \(HR_{\text{@}}\sigma_{\text{REL}}\) & \(w_{\text{PPG3}}=0.5\) \\
4 & – & – & \(HR_{\text{VAR}}\) & \(w_{\text{PPG4}}=0.75\) \\
5 & – & – & \(ORI_{\text{REL}}\) & \(w_{\text{PPG5}}=-1\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Weight settings for parameters entered to the fusion process. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Parameter/Person** & **M1** & **M2** & **M3** & **M4** & **F1** & **F2** & **F3** & **F4** \\ \hline Age (years) & 59 & 53 & 42 & 36 & 59 & 20 & 30 & 58 \\ BMI (kg/m\({}^{2}\)) & 24.9 & 22.2 & 22.5 & 23.1 & 18.3 & 21.8 & 19.0 & 21.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Age and BMI parameters of the persons included in our study. between both gradient coils) and its orientation was 150 degrees from the left corner near the temperature stabilizer. The Behringer XENYX Q802 USB mixer and a laptop used for recording were located outside the MRI shielding metal cage--see an arrangement photo in Figure 7. Another microphone Mic2 (Behringer TM1) was connected to the second channel of the XENYX Q802 mixer for the phonation signal pick-up in the recording phases \(MF_{1}\) and \(MF_{4}\) with the tested person sitting at the desk in the MRI equipment control room. Both professional studio microphones are based on the electrostatic transducer with a 1-inch diaphragm and they have very similar cardioid directional patterns as well as frequency responses at 1, 2, 4, 8, and 16 kHz. Between the measurement phases \(MF_{2}\) and \(MF_{3}\), the scan sequence 3D-CE (with TE = 30 ms, TR = 40 ms; 3D phases = 8) was run with a total time duration of about 8 min. This type of our most used MR sequence produces a noise with a sound pressure level (SPL) of about 72 dB (C); the background SPL inside the metal shielding cage is produced mainly by the temperature stabilizer and reaches about 55 dB (C) [29]. In this case, the physiological effect of the noise and vibration on the human organism and auditory system is small but still measurable and detectable [30]. During the phonation signal pick-up in the \(MF_{1}\) and \(MF_{4}\) measurement phases, the control room background level was up to 45 dB (C).