**3. Results**

#### *3.1. Results of Preliminary Experimental Studies*

The data obtained in trials with healthy volunteers showed that changing the camera exposure time does not significantly affect the diagnostic result. Therefore, further analysis of the experimental data was carried out at the camera exposure time of 20.7 ms.

Figures 2 and 3 present the registered and processed images for two conditionally healthy volunteers (a man and a woman of the same age group) with the same camera exposure time of 20.7 ms for probing radiation wavelengths of 650 nm (a) and 850 nm (b).

Preliminary experimental studies using the relevant method MRI have confirmed the sensitivity of the digital diaphanoscopy method in detecting pathological changes in the maxillary sinuses [6]. Figure 4 gives examples of the T2 weighted MRI images (Figure 4a) and the images registered and processed by diaphanoscopy (Figure 4b).

**Figure 2.** Registered (**top**) and processed (**bottom**) images for a conditionally healthy volunteer 1 (male) at a camera exposure time of 20.7 ms for probing radiation wavelengths of: 650 nm (**a**); and 850 nm (**b**). The red line is the selection of the area for analyzing the transmitted light.

**Figure 3.** Registered (**top**) and processed (**bottom**) images for a conditionally healthy volunteer 2 (female) at a camera exposure time of 20.7 ms for probing radiation wavelengths of: 650 nm (**a**); and 850 nm (**b**).

**Figure 4.** The T2 weighted MRI image (**a**); and the images registered and processed by diaphanoscopy (**b**) for a patient (male) at radiation wavelengths of 650 nm (**top**) and 850 nm (**bottom**).

Analysis of the registered and processed images obtained by digital diaphanoscopy revealed that the cys<sup>t</sup> area is characterized by the lowest intensity compared to other structures, which can be explained by the strong absorbing properties of the cystic fluid in the near-infrared range [6]. The results of digital diaphanoscopy are determined by the optical properties of the study area [16–23] and their changes in various anatomical and gender features [24,25]. In our study, we applied Monte Carlo simulation to take into account the effect of the anatomical and gender characteristics of patients on the scattering pattern of light, to justify the medical and technical requirements for the instrument, and to adjust the parameters of the LED applicator.

#### *3.2. Monte Carlo Simulation*

Since the object of research has a rather complex organization, a simplified model of the maxillary sinus was developed to establish the regularity of the weakening of the probing signal from the anatomical and gender features of the studied area (differences in the skin structure, the thickness of the skull bone tissue, and the size of the sinuses). The Monte Carlo methodology was used for the construction of the 3D model. This method is one of the most effective simulation tools when dealing with biological tissues [26,27]. Figure 5 shows a scheme of the developed model.

**Figure 5.** Full 3D view of the developed model.

In the model, the environment is represented by 8 main layers, as well as by an additional layer in the form of a pathological change (cystic fluid or tumor). The optical characteristics of the biological tissues used in the simulation are presented in Table 1.


**Table 1.** The optical characteristics of biological tissues.

The thickness and size of the layers and their absorption and scattering coefficients were set for both females and males. Since the sizes and thicknesses of the layers depend on gender and age [18,19], the layer thicknesses were averaged within one gender to simplify the developed model. The thicknesses of the simulated layers are given in Table 2.

**Table 2.** The thickness of the simulated layers, mm.


Analysis of the optical properties of the research area indicates high absorbing properties of the hypodermis at the selected wavelengths of probing radiation. In addition, the results of the preliminary experimental studies demonstrate that the changes in the hypodermis thickness strongly affect the diagnostic result.

The Monte Carlo simulation involving a simplified model of the research area was performed for 650 and 850 nm radiation sources in the TracePro software environment (Lambda Research Corporation) [34–36]. The number of simulated photons was 106. The power of probing radiation in the simulation for the wavelengths of 650 and 850 nm was 8 mW.

Figures 6–8 show the simulation results of the probe radiation propagation (the photons path through the biological tissue and the irradiance map) for the maxillary sinus of female (a) and male (b) without pathology (Figure 6), with cystic fluid (Figure 7) and with tumor (Figure 8).

**Figure 6.** Simulation results for the probe radiation propagation through the maxillary sinus of female (**a**) and male (**b**) without pathology at a wavelength of 650 nm (**top**) and 850 nm (**bottom**).

**Figure 7.** Simulation results for the probe radiation propagation through the maxillary sinus of female (**a**) and male (**b**) with cystic fluid at a wavelength of 650 nm (**top**) and 850 nm (**bottom**).

Figure 9 illustrates the difference in radiation power (intensity) reduction in males and females. This decrease has a more pronounced character when the pathology in the sinuses is observed in the NIR range (850 nm) and can be attributed to the optical features of pathological tissues, namely, the high absorption properties at selected wavelength [16,17].

**Figure 8.** Simulation results for the probe radiation propagation through the maxillary sinus of female (**a**) and males (**b**) with tumor at a wavelength of 650 nm (**top**) and 850 nm (**bottom**).

**Figure 9.** Dependence of the change in the total flux (power) of radiation coming to the camera detector on the change in the hypodermis thickness and on the presence of pathology in the sinuses of female (**a**) and males (**b**) for wavelengths of 650 and 850 nm. The following labels are used: "N" for healthy tissues, "C" for tissues with cyst, and "T" for tissues with tumor.

Besides, the results demonstrate a decrease in the intensity of radiation at the detector (radiant power) when it passed through the biological tissues at different values of the bone tissue and skin, the sinus size [22,23].

The revealed regularity confirmed the results of the experimental studies. It was also found that the adjustment of the parameters of the probing and measuring parts of the device for implementation of the proposed technology is necessary to ensure similar scattering light patterns for different patients and their further comparison.

#### *3.3. Upgrade of the Experimental Setup*

Based on the simulation results, the experimental setup was upgraded; the block scheme of the setup is shown in Figure 10.

**Figure 10.** The block scheme of a modernized experimental setup.

A controller of the LED applicator brightness was designed and installed in the setup in addition to the unit controlling the output power of the probing applicator. It is positioned in the gap between the LED control unit of the applicator and the LED applicator itself. To control the operation of the controller of the LED applicator, an additional software has been developed, which allows one to change the voltage supplied to the LEDs, as well as to measure the current flow in real time and to calculate the power consumption. The software makes it possible to save many brightness profiles and switch them immediately before starting the measurements, thereby automatically selecting the desired range of radiation power of the applicator for specific volunteers and patients in accordance with their anatomical features.

The experimental studies, which were conducted using the modernized installation, allowed the detection of changes in the power consumption of the LEDs applicator. To identify the values of power consumption specific to each patient based on their gender and anatomical features, the study involved conditionally healthy volunteers; the power consumption of the LEDs applicator varied from 0 to 750 mW in increments of 50 mW. The camera exposure time remained unchanged. It was established that, in healthy male volunteers, the maximum power consumption of the LEDs applicator was insufficient to obtain an adequate scattering pattern of light passing through the sinuses, which is associated with their anatomical features (bone thickness, skin, and size of the sinuses). In female volunteers, the maxillary sinuses were visualized in the range of LEDs power consumption equal to 300–500 mW.

The ranges of changes in the radiation flux for the two radiation sources were also revealed. Thus, it was found that at 850 nm the radiation flux varies in the range from 0 to 200 mW, whereas for the 650 nm radiation source this parameter changes in the range from 0 to 18 mW.

In the future, the elements of the controller of the LED applicator brightness will be adjusted and replaced, and a new applicator will be designed to increase the radiated light power.

## **4. Discussion**

In this study, we tested a device designed to implement the digital diaphanoscopy technology, which is based on visualization and analysis of the low-intensity radiation scattering pattern in the maxillary sinuses.

The review and analysis of existing methods (CT and MRI) for the diagnosis of inflammatory diseases of maxillary sinuses diseases showed their limitation either for the repeated conduct of studies due to radiation or microwave exposure or for the conduct of studies in general, for example, for pregnan<sup>t</sup> women or children. In otolaryngology, the standard methods for diagnosing such pathologies (ultrasound and rhinoscopy techniques) sometimes yield false positive results due to complexity in interpreting the results, or due to trauma-related aspects. In comparison with the considered methods, the method of digital diaphanoscopy allows one to overcome these drawbacks.

In addition, the review of the literature in the field of non-invasive optical diagnosis of paranasal pathology demonstrates that our technology has the advantage over the previously published results, as it provides a foundation for the assessement of the condition of the sinuses for all categories of patients, based on their anatomical and gender features. For this purpose, we designed the original brightness controller of the LED applicator and developed a specialized adjustment software for the probing mode, which makes it possible to select an effective radiation dose for each patient.

Currently, further experimental studies are being conducted to form an appropriate database and identify diagnostic criteria for various pathological changes, taking into account the range of the optical power of probing radiation, that have the greatest sensitivity to visualization of pathological changes in the maxillary sinuses in different study groups divided by gender.
