**1. Introduction**

Sinusitis is a common disease with worldwide prevalence and one of the leading causes of antibiotic prescription [1]. In 2018, 28.9 million people in the United States reported a sinusitis diagnosis in the previous 12-month period, which accounted for 11.6% of the adult population [2]. In Europe, sinusitis affects 10.9% of the population [3]. Delay in diagnosis and treatment of sinusitis may cause serious effects such as immune sensitivities to medication, development of different complications, including intracranial complications (50% of deaths). Therefore, an accurate, painless, and timely diagnosis of maxillary sinus pathology is one of the key problems of modern otolaryngology. Diagnostic imaging techniques, such as radiography, computed tomography, magnetic resonance imaging, ultrasound diagnostics (including assessment of stiffness and echogenicity), and rhinoscopy, are important tools to detect this kind of disorder, but they are not recommended for pregnan<sup>t</sup> women and children due to the use of carcinogenic roentgen radiation during the study, painfulness of the diagnostic procedures, and a high level of false-negative results.

Radiography is based on the high penetrating power of radiation and its absorption ability. It allows assessing the general condition of the paranasal sinuses and makes it possible to detect the presence of liquid content (along with formed cysts or polyps) in them, as well as the changes in the mucous membrane. If there is a pathological change in sinus pneumatization, then the resulting image will show significant darkening along the

**Citation:** Bryanskaya, E.O.; Novikova, I.N.; Dremin, V.V.; Gneushev, R.Y.; Bibikova, O.A.; Dunaev, A.V.; Artyushenko, V.G. Optical Diagnostics of the Maxillary Sinuses by Digital Diaphanoscopy Technology. *Diagnostics* **2021**, *11*, 77. https://doi.org/10.3390/ diagnostics11010077

Received: 19 November 2020 Accepted: 31 December 2020 Published: 6 January 2021

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upper horizontal level, asymmetry of the inflamed sinuses, narrowing of the nasal passages, and mucosal thickening [4]. Despite the advantages of this technique, its application in clinical practice is limited to assessments that help to identify the degree of development of a pathological process which already has pronounced signs to determine further treatment tactics and the need for surgical interventions. It should also be noted that a high dose of radiation exposed to pregnan<sup>t</sup> women raises the risk of hypertension, may slow down the growth of the fetus, and cause the worsening of the health indicators of newborns.

The major contribution of computed tomography (CT) is in providing additional useful information. The CT method, similar to other imaging techniques, uses X-ray radiation and its distribution in tissues depending on their density. CT provides the differentiation of soft tissues and can distinguish between density differences of no more than 0.1%. However, it is also associated with significant radiation exposure [5].

Magnetic resonance imaging (MRI), endoscopy (rhinoscopy), or ultrasound are used as alternative methods. The MRI method consists in registering the excitation of hydrogen atomic nuclei by a certain combination of electromagnetic waves in a constant magnetic field of high intensity [5]. MRI can be useful in assessing lesions in nasal bones, inflammatory processes in the paranasal sinuses, formed cysts or polyps, chronic diseases, and changes in bone structure resulting from injury. However, this method is characterized by a high level of false positive results, poor visualization of bone tissue, and is contraindicated in the presence of implants, prostheses, and obesity. The disadvantages of this method are the cost and high microwave load on the patient.

Rhinoscopy is performed by placing a flexible fiber-optic tube into the nasal passage to assess the color of the mucous membrane, its humidity, the shape of the nasal septum, the caliber of vessels, the condition of the nasal shell, and the size and content of the nasal passages. Although rhinoscopy yields important information and adequate sample collection, it also has some disadvantages which include its high cost and discomfort to the patient.

Ultrasound makes it possible to diagnose inflammatory processes in the sinuses, cysts, polyps, and traumatic damage to the walls of the paranasal sinuses, as well as to detect foreign bodies. Normally, the paranasal sinuses contain air, which serves as an obstacle to the propagation of ultrasonic waves. In the absence of pathological changes, the echo signal from the sinus is not detected due to its complete reflection from the air contained in it. If the walls of the sinuses are thickened, for example, due to edema of the mucosa, or they contain pathological contents, then there occur conditions for the propagation of ultrasound waves. When passing through the sinus, ultrasound waves are reflected from its posterior parts and are fixed by an ultrasound device. The results of ultrasound scanning do not always correspond to reality, which can be attributed to deficiencies in equipment design or incorrect interpretation of the results.

Non-invasive optical technologies are increasingly used in various fields of medicine to diagnose pathological conditions. The digital diaphanoscopy method has the potential to separate normal and pathological conditions (inflammation, cystic, and tumor tissues) of the maxillary sinuses. It is based on the visualization of scattering patterns of lowintensity radiation as it passes through the maxillary sinuses [6–8]. Although the method of diaphanoscopy or transillumination has a long history of usage [9,10], especially in ophthalmology [11] and urology [12], it is of limited use in otolaryngology. First examinations of tissue parameters in the near infrared were performed by Beuthan in 1982. Relying on these tests, infrared transillumination seems to be a promising tool for the rapid diagnosis of sinusitis, but white light spectrum radiation is a limiting factor influencing the application of this approach in otolaryngology [13,14]. White light does not provide a complete diagnostic picture because it is absorbed and dispersed by tissues to a grea<sup>t</sup> extent; no informative features and algorithms capable of separating normal and pathological conditions exist. At present, there are no clinically justified classifying features, developed classification models, and diagnostic criteria that can differentiate pathological changes in the maxillary sinuses (inflammation, cysts, and tumor tissues) by digital diaphanoscopy.

The purpose of this study was to develop a scientific and technical basis for instrument implementation of the technology proposed for diagnosing maxillary sinus pathology, taking into account the anatomical features of the study area (skin structure, bone thickness of the facial part of the skull, sinus size, and asymmetry), its optical properties, and age and gender characteristics.

#### **2. Materials and Methods**

*2.1. Experimental Setup*

For the realization of this approach, the experimental setup was designed and assembled (Figure 1a). Low-intensity radiation of the visible (650 nm) and NIR (850 nm) ranges was used for translucence of the paranasal sinuses. The CMOS-camera was applied to visualize the light scattering pattern [15]. To minimize the external illumination influence, a protective screen was designed which facilitated research under various external conditions. To suppress movement artifacts, the volunteers were asked to place their head on a chin rest.

**Figure 1.** General view of the experimental setup (**a**); the LED applicator (the working part) (**b**); and the position of the applicator during measurement with the propagation of probing rays (3D model) (**c**).

The LED applicator takes into account the anatomical features of the study area, namely, the features of the oral cavity and maxillary sinuses (Figure 1b). During the diagnostic procedure, the applicator was placed in the oral cavity, and then the measurements were performed (Figure 1c). Before each use, the surface of the applicator was cleaned with wipes impregnated with a disinfecting solution. The solution composition included purified water, isopropanol, ethanol, didetsildimetilammonium chloride, and dodecyl dipropylene triamine.

The micro-LEDs OSRAM Opto Semiconductors GmbH (Regensburg, Germany) with wavelengths of 650 (C4L-H12T5) and 850 nm (F3453) and 8 pieces on the right and left sides for each wavelength were used as radiation sources for the applicator. The CMOS-camera UI-3240CP-NIR-GL Rev.2 IDS GmbH (Obersulm, Germany) and the lens Pentax C1614-M (Tokyo, Japan) were applied to register diagnostic information in the prototype device. The camera provides high-speed image acquisition, high quality, and maximum quantum efficiency (light sensitivity) in the selected spectral range. The control unit provides the

LEDs sequential switching on and off at wavelengths of 650 and 850 nm, as well as their performance in the setting mode (LEDs flashing at a wavelength of 650 nm).

The specially designed software assists us in analyzing the obtained scattering pattern. It allows for trial control (selection of a radiation source and a camera operation mode), gathering of personal patient data, and recording of diaphanoscopic images and their quantitative (visualization) and qualitative processing (pseudo-color image segmentation). The software also provides the function of uploading a diaphanoscopic examination report, which contains information about the patient, diaphanoscopic images, diagnostic assessments, and quantitative values (the percentage of light passed through the sinus).

#### *2.2. Study Design*

The study groups were formed taking into account the differences in age, gender parameters, and anatomical features of the study area, as well as the existing pathological changes and inflammatory processes of the maxillary sinuses. Preliminary experimental studies were conducted in 20 conditionally healthy volunteers and 15 patients with suspected maxillary sinus inflammation at the medical diagnostic center "MediScan" (Orel, Russia).

The study was approved by the Ethics committee of the Orel State University (record of meeting No. 15 of 21 February 2019) and carried out in accordance with the 2013 Declaration of Helsinki by the World Medical Association. After receiving the description of the protocol, the volunteers signed an informed consent indicating their voluntary willingness to participate in the study.

The experiments were conducted under established protocols. The subjects were in a sitting position. After the pre-disinfected LED-applicator was inserted into the oral cavity of the subject, the subject head was placed in a precision positioning unit and, then, together with the CMOS-camera, it was covered with a protective screen. To account for the effect of the camera exposure time on the light scattering patterns, images were recorded at 40 different camera exposure times in the range from 0 to 40 ms (increment of 1 ms). In the patient study, the measurement results were additionally compared with the T2 weighted images by MRI studies, which were performed using the 1T MRI Scanner of the Magnetom series, Siemens (Munich, Germany).
