Optical coherence tomography in otolaryngology: current opportunities and perspectives for use

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The main challenge in modern ENT practice is the specialist's strong reliance on the results of visual examination, including endoscopy, as the physician can only assess superficial tissue changes, which is quite subjectively. Significant advantages in treatment strategy selection would be provided by additional information on the condition of ENT tissues at the cellular and tissue levels, as it would allow for more precise characterization of pathomorphological changes, as well as for assessing the response to treatment.

Structural changes in various organs and tissues accompany virtually any disease occurring in the organism. Studying the nature of these transformations is often fundamental both for establishing a diagnosis and for selecting a treatment method and monitoring its efficacy. Histological examination, while remaining the "gold standard," has a number of limitations related to its invasiveness, the risk of sampling errors, and the impossibility of in vivo dynamic observations. This creates a demand for techniques of in vivo morphological diagnostics [1–6].

Widely used techniques of biological tissue imaging, namely high-frequency ultrasound, computed tomography, and magnetic resonance imaging, despite their obvious advantages, lack sufficient resolution. This significantly limits their feasibility and applicability, especially concerning the early detection of neoplastic processes [7, 8].

This underscores the need for the development and implementation of tissue imaging technologies that combine high informational value, safety, and accessibility for use in real clinical practice – all characteristics successfully combined in the optical coherence tomography (OCT) technique.

The potential of OCT was first demonstrated in 1991 by the group of J.G. Fujimoto [9]. The technique is based on low-coherence interferometry, which allows for recording the depth-resolved intensity distribution of backscattered radiation, while transverse scanning enables the acquisition of two- or three-dimensional images. Since biological tissues possess different scattering properties, they exhibit contrast in the resulting OCT images.

Initially, a time-domain OCT (TD-OCT) modification was proposed, where depth scanning was performed using a moving mirror within the interferometer. However, the imaging speed was later significantly improved with the spectral-domain OCT (SD-OCT) modification [10, 11], where the mirror is stationary and signal registration is performed using a spectrometer.

Tissue probing is performed using near-infrared light sources with a power of up to 1.5 mW, which ensures the non-invasiveness of the diagnostics. Standard, real-time OCT images provide information about tissue structure to a depth of up to 2 mm: this is adequate for assessing the condition of surface (epithelial) structures.

A distinctive feature of OCT compared to other tomographic methods (X-ray, magnetic resonance, ultrasound) is its high resolution, ranging from 1 to 15 µm [12–14]. Owing to this significant advantage, OCT has found widespread application in various fields of clinical medicine: primarily in ophthalmology, where the new technique has gained the greatest popularity, as well as in gynecology, urology, dermatology, oncology, and otorhinolaryngology [15–20].

Separately, several pioneering Russian papers should be noted, in which various designs of optical coherence tomography systems were tested, demonstrating the fundamental feasibility and diagnostic value of OCT in both fundamental research and clinical practice [21–25].

However, comprehensive works that summarize global experience in the application of OCT in otorhinolaryngology, enabling an assessment of this method's role in solving a wide range of clinical tasks, are currently lacking. A critical analysis of the accumulated experience could serve as a starting point for the systematic introduction of OCT into ENT practice and for the development of new treatment protocols, including those embodying the principles of personalized medicine.

The objective of this review is to summarize and critically analyze contemporary data on the application of the OCT method across various subspecialties of otorhinolaryngology, aiming to determine its current role and future potential in diagnosing and monitoring conditions of the ENT organs.

We conducted a search and analysis of English- and Russian-language papers dedicated to OCT and its potential applications in otorhinolaryngology. These works were sourced from freely accessible platforms including Scopus, PubMed, Google Scholar, eLibrary.Ru, CyberLeninka, websites of open-access publishers, and other open internet resources. The search was performed using the following keywords: optical coherence tomography / оптическая когерентная томография, otorhinolaryngology / оториноларингология, mucous membrane / слизистая оболочка, epithelium / эпителий, lamina propria / собственная пластинка, chronic diseases of ENT organs / хронические заболевания ЛОР-органов.

The review of the OCT technqiue application is structured into three main domains: laryngology [23, 26–43] (Table 1), otology [44–64] (Table 2), and rhinology [65–77] (Table 3).

 

Table 1. Comparative characteristics of optical coherence tomography application in laryngology

First Author, Reference	Year	Clinical Objective	Number of Patients	Information Obtained via OCT	OCT System Parameters
A.M. Sergeev [26]	1997	Feasibility of OCT for assessing hollow organ mucosa in normal and pathological states	15 (larynx studied in 4)	Normal mucosa shows a layered structure with clear stratification; tumor pathology appears unstructured. Potential of OCT for early tumor diagnosis and precise excisional biopsy guidance	TD-OCT; 2 mm probe integrated into endoscope biopsy channel; resolution 10–15 µm; imaging depth 1.5–2 mm
F.I. Feldchtein [27]	1998	Study of hollow organ mucosa microstructure in norm and pathology; correlation with morphometry	124 (larynx studied in 15)	Endoscopic OCT effectively visualizes organs covered by epithelium separated from underlying stroma by a smooth basement membrane (e.g., bladder, larynx, cervix). Capabilities and limitations regarding diagnostic value were defined. First demonstration of laparoscopic OCT efficacy	TD-OCT; 2 mm probe integrated into endoscope biopsy channel and rigid laparoscope; resolution 10–15 µm; imaging depth 1.5–2 mm
A. Shakhov [23]	1999	Differential diagnosis of tumorous, tumor-like, and inflammatory laryngeal pathology; tumor border definition	> 40	OCT signs of vocal fold nodules/cysts, malignant tumor changes, tumor/normal tissue borders, and radiation mucositis were identified. Correlation with histology	TD-OCT; 2 mm probe inserted via laryngoscope; resolution 10–15 µm; imaging depth 1.5–2 mm
A.V. Shakhov [28]	2001	Intraoperative monitoring of laser surgery for laryngeal cancer	26	Monitoring microstructural changes in collateral tissues during laser exposure enables control of laser parameters	TD-OCT; 2 mm probe inserted via laryngoscope; resolution 10–15 µm; imaging depth 1.5–2 mm
В.Е. Bouma [29]	2002	Overview of OCT capabilities in clinical medicine	> 100	Detailed description of differential diagnostic signs for tumorous, tumor-like, and chronic inflammatory laryngeal pathology. Proven diagnostic value of OCT in detecting severe dysplasia/carcinoma in situ	TD-OCT; 2 mm probe inserted via laryngoscope or endoscope biopsy channel; resolution 10–15 µm; imaging depth 1.5–2 mm
W.B. Armstrong [30]	2006	Study of laryngeal mucosa microstructure changes in cancer	22	Disruption of basement membrane in laryngeal cancer; transition zones at tumor border. Limitation of OCT application in exophytic lesions	TD-OCT; 2 mm probe inserted via laryngoscope with visual control or with microscope; resolution 10 µm; imaging depth 1.6 mm
M. Kraft [31]	2008	Evaluation of OCT microlaryngoscopy efficacy in determining dysplasia grade and invasion depth	193	Epithelial thickness measurement by OCT allows determination of dysplasia grade. Limitation of OCT in pronounced hyperkeratosis	TD-OCT; 2 mm probe inserted via laryngoscope with visual control or with microscope; resolution 10–15 µm; imaging depth 1.5–2 mm
J.M. Ridgway [32]	2008	Visualization of neonatal airways	12	Superficial epithelium, underlying lamina propria, and basement membrane in larynx and trachea were visualized. OCT signal changes detected post-intubation	TD-OCT; 2 mm probe inside endotracheal tube; custom flexible/rigid OCT probes designed considering anatomy and tube specifics; resolution ~7 µm; imaging depth up to 1.6 mm
B. Wong [33]	2009	Study of laryngeal mucosa microstructure in norm and benign pathology	82	Microstructural features (blood vessels, gland ducts, fluid accumulation, epithelium type) were described. Epithelial thickness in different laryngeal zones was measured and mean values calculated	TD-OCT; 2 mm probe inserted via laryngoscope or endoscope biopsy channel; resolution 15 µm; imaging depth up to 2 mm
L. Yu [34]	2009	Feasibility of OCT examination of the larynx during indirect laryngoscopy in awake patients	N/A	Clear OCT images of the larynx were obtained without motion artifacts	SD-OCT; probe combined with endoscope (separate optical channels); manual focusing
T. Just [35]	2010	Comparison of OCT images of benign and dysplastic laryngeal lesions with histology	61	OCT criteria for benign and dysplastic processes, including basement membrane assessment. Improved biopsy precision	Two modifications: 1) TD-OCT, 3 mm probe integrated into endoscope, resolution 15 µm, imaging depth up to 2.5 mm; 2) SD-OCT, 3 mm probe integrated into microscope, resolution 12 µm, imaging depth 1–2 mm
T. Just [36]	2011	Improving visualization of the basement membrane and image quality of laryngeal mucosa	N/A	PS-OCT improves visualization of the basement membrane, especially in healthy mucosa. Breach of basement membrane integrity indicates tumor invasion into the lamina propria. Confocal endoscopy visualizes epithelium but not the basement membrane. Combining OCT with PS-OCT and confocal endoscopy increases diagnostic accuracy	Two modifications: 1) TD-OCT, 3 mm probe integrated into endoscope, resolution 15 µm, imaging depth up to 2.5 mm; 2) SD-OCT with PS-OCT, 3 mm probe integrated into microscope, resolution 12 µm, imaging depth 1–2 mm, combined with confocal endoscopy
J.A. Burns [37]	2011	Improving differential diagnosis of malignant and benign laryngeal lesions using PS-OCT	23	Clearer definition of tumor borders and invasion depth; differentiation of healthy tissue from scar	Two TD-OCT modifications (standard and PS), 2 mm probe; resolution 15 µm; imaging depth up to 2 mm
G.K. Sharma [38]	2015	Visualization of microstructural and wall thickness changes in neonatal airways post-intubation	72	Correlation between intubation duration and changes in airway wall thickness/microstructure. Tissue detection may predict laryngeal stenosis risk	SD-OCT with long-focus transducer; 0.7 mm probe with circumferential rotation inside endotracheal tube; resolution 10 µm; imaging depth up to 1.6 mm
V. Volgger [39]	2015	Visualization of the subglottic space in intubated children	46	Assessed layered microanatomy of laryngeal mucosa and performed 3D-OCT reconstruction of the subglottic space to predict post-intubation stenosis risk	SD-OCT with long-focus transducer; 0.7 and 1.2 mm probes with circumferential rotation inside endotracheal tube; resolution 10 µm; imaging depth 1.5–2 mm
S. Donner [40]	2015	Feasibility of OCT examination of the larynx during indirect laryngoscopy in awake patients with assessment of vocal fold vibratory function	7 volunteers	Clear OCT images of the larynx without motion artifacts, obtained during phonation	SD-OCT; probe integrated into rigid endolarynscope (single optical channel); autofocus
J.A. Garcia [41]	2016	Development of an algorithm for assessing vocal fold maturity	10	Relative OCT signal attenuation coefficients at different points of the vocal folds in patients of various ages were obtained	TD-OCT; 3.7 mm probe; resolution 12 µm; imaging depth up to 2 mm
Z. Xin [42]	2021	Non-invasive assessment of laryngeal tumor invasion depth ex vivo	12 larynges	Decrease in birefringence depending on tumor stage; correlation with histology	PS-OCT; resolution 8.1 µm; imaging depth up to 2 mm
X. Li [43]	2025	Intraoperative differential diagnosis of laryngeal leukoplakia and cancer	12	Numerical characteristics of leukoplakia features were obtained	SD-OCT; 3 mm probe; axial resolution 16.24 µm; imaging depth 2.12 ± 0.43 mm

N/A, data is not available; OCT, optical coherence tomography; PS-OCT, polarization-sensitive OCT; SD-OCT, spectral-domain OCT; TD-OCT, time-domain OCT

 

Table 2. Comparative characteristics of optical coherence tomography application in otology

First Author, Reference	Year	Clinical Objective	Number of Patients/Specimens	Information Obtained via OCT	OCT System Parameters
C. Pitris [44]	2001	Investigation of middle ear tissue and ossicle microstructure ex vivo	Ex vivo specimen	Demonstrated feasibility of visualizing middle ear structures	TD-OCT, 1300 nm, fiber optic probe; resolution 15 µm; imaging depth 2–3 mm
T. Just [45]	2009	Characterization of the oval window niche	5 ex vivo, 8 in vivo	Diagnosis of otosclerosis, tympanosclerosis; monitoring of tympanoplasty results	TD-OCT, 840 nm; resolution 24 µm
H.R. Djalilian [46]	2010	Diagnosis of cholesteatoma	10	Visualization of cholesteatoma; determination of boundaries between cholesteatoma and surrounding tissues	TD-OCT, 1300 nm; fiber optic probe, diameter 2.7 mm; resolution 10–20 µm; imaging depth 1.5 mm
C.T. Nguyen [47]	2012	Detection of biofilms in the middle ear in chronic otitis media	20 (4 healthy, 16 patients)	Demonstrated presence of biofilms in the middle ear of patients with chronic otitis media and their absence in healthy individuals	TD-OCT, 830 nm; resolution 3 µm
N.H. Cho [48]	2015	Diagnosis and differential diagnosis of otitis media	45 (6 healthy, 39 patients)	Defined morphological features of the tympanic membrane (TM) in normal and pathological states. Demonstrated feasibility of OCT visualization of TM perforation	SD-OCT, 870 nm; resolution 6 µm
G.L. Monroy [49]	2015	Differential diagnosis of otitis media	34	TM thickness was determined, and the presence of biofilms/middle ear effusion was assessed	TD-OCT, 830 nm; resolution 4 µm
Z. Hubler [50]	2015	Diagnosis and differential diagnosis of otitis media	N/A	TM thickness was determined via OCT image segmentation; biofilms/effusion behind the TM were detected	SD-OCT, 860 nm; resolution 2.4 µm
E. Guder [51]	2015	Diagnosis of chronic myringitis	36	TM thickness was determined, morphological changes were detected; differences in TM thickness were shown between normal, myringitis, atrophy, and myringosclerosis	OCT camera integrated with surgical microscope; resolution 7.5 µm; imaging depth 5–30 mm
P. Pande [52]	2016	Comprehensive characterization of the tympanic membrane	6	Spatial distribution of TM thickness was determined; in vivo reconstruction of TM surface topography was performed	SD-OCT, 940 nm; resolution 2.4 µm
G.L. Monroy [53]	2017	Monitoring results of surgical treatment for chronic otitis media	25	Visualization of TM structures and biofilms; assessment of surgical outcomes	SD-OCT, 860 nm; resolution 2.4 µm
G.L. Monroy [54]	2017	Diagnosis and differential diagnosis of otitis media	2	TM thickness was determined, biofilms in the middle ear were detected, and effusion viscosity index was determined	SD-OCT, 860 nm; resolution 2.4 µm
G.L. Monroy [55]	2018	Diagnosis and differential diagnosis of otitis	38	Direct analysis of bacterial aggregates and biofilms adherent to the TM	SD-OCT; resolution 2.4 µm; imaging depth 3 mm
K. Park [56]	2018	Assessment of TM structure in various conditions	120	Evaluation of perforation edges, degree of TM retraction, healing process after tympanoplasty	SD-OCT; resolution 15 µm; imaging depth up to 2 mm
G.L. Monroy [57]	2019	Diagnosis and differential diagnosis of otitis media	58	Automated differentiation between normal, biofilm presence, and effusion	SD-OCT, 860 nm; resolution 2.4 µm
D. MacDougall [58]	2019	Diagnosis of hearing disorders	55	Assessment of TM vibrations in normal and otosclerotic ears	SD-OCT, Doppler-modification integrated with a microscope
W. Kim [59]	2019	Assessment of middle/inner ear structures; functional assessment of auditory chain mobility	2	Images of middle ear structures were obtained; vibrational sensitivity was assessed	SD-OCT integrated with a microscope; resolution 10 µm
D. Preciado [60]	2020	Diagnosis and differential diagnosis of otitis media with effusion (OME)	70	Presence and characteristics of effusion behind the TM	SD-OCT, 860 nm; resolution 2.4 µm
A. Novozhilov [61]	2020	Diagnosis and differential diagnosis of OME	24	Presence and type of effusion (liquid/viscous) in middle ear spaces	SD-OCT; imaging depth 15–25 mm
T. Abubakirov [62]	2021	Diagnosis of paraganglioma	1	Visualization of paraganglioma	SD-OCT; imaging depth 15–25 mm
J. Wang [63]	2022	Visualization of cochlear implant	1	Visualization of the electrode and its features	Custom developed SD-OCT system for the middle ear with a swept source, wavelength 1550 nm
D.W. Pan [64]	2025	Assessment of the tympanic membrane and tympanic cavity contents	20	TM, ossicles, chorda tympani, promontory were visualized. Tympanic cavity masses were detected; precise assessment of vascularization degree was performed	SD-OCT and OCT angiography; probe combined with a video camera; resolution ~30 µm

N/A, data is not available; OCT, optical coherence tomography; SD-OCT, spectral-domain OCT; TD-OCT, time-domain OCT

 

Table 3. Comparative characteristics of optical coherence tomography application in rhinology

First Author, Reference	Year	Clinical Objective	Number of Patients/Specimens	Information Obtained via OCT	OCT System Parameters
U. Mahmood [65]	2006	Assessment of nasal mucosa microstructure in normal conditions and after long-term decongestant use	44	OCT images of epithelium, lamina propria, bony-cartilaginous framework, blood vessels, and gland ducts were obtained; morphometry was performed; morphological mucosal changes due to long-term decongestant use were identified	SD-OCT, wavelength 1.3 µm; probe integrated into endoscope; resolution 8–10 µm; imaging depth 1.5–2 mm
J. Jing [66]	2012	Acquisition of structural and anatomical data of the upper airways	5	OCT images of upper airway structures were correlated with endoscopic video for subsequent 3D reconstruction	SD-OCT with long-focus transducer; non-contact imaging, circumferential scanning; 1 mm probe attached to endoscope; resolution 10 µm; imaging depth up to 1.5–2 mm
L. Tóth [67]	2013	Detection of biofilms in patients with chronic polypous rhinosinusitis	27	Biofilm layer, respiratory epithelium, and subepithelial layer were visualized with OCT; a correlation with histopathology data was found	SD-OCT; resolution 10–20 µm; imaging depth up to 2 mm
U. Oltmanns [68]	2016	Assessment of nasal mucosa microstructure in patients with cystic fibrosis	25	Nasal mucosal microstructures in healthy individuals and cystic fibrosis patients were visualized and differences were described. Mucosal changes during antibiotic treatment were identified	SD-OCT; resolution 15 µm; imaging depth 1.4 mm; 2.5 mm probe
H. Schulz-Hildebrandt [69]	2018	Assessment of inferior turbinate epithelium in normal state and in chronic rhinitis	Several ex vivo, 1 in vivo	Cellular structure of inferior turbinate epithelium and ciliary motion were visualized; mucociliary transport velocity was determined	Micro-OCT; 2.75 mm probe; resolution 1.25 µm
T. Ueda [70]	2019	Assessment of olfactory epithelium status ex vivo	48 mice	Microstructural features of olfactory and respiratory epithelium were described; epithelial thickness was measured. Correlation with histology was shown	SD-OCT; resolution 9 µm; imaging depth 1.5–2 mm.
M.A. Shakhova [71]	2019	Differential diagnosis of various forms of chronic rhinitis	51	OCT signs characteristic of different forms of chronic rhinitis were described	SD-OCT; resolution 15 µm; depth 1.4 mm; 2.4 mm probe
H.M. Leung [72]	2019	Assessment of upper airway epithelium status in cystic fibrosis	20	Reduced mucociliary transport velocity, depleted periciliary layer, ciliary loss	Micro-OCT; 2.4 mm probe; resolution 1.3 µm
N. Soloviev [73]	2020	Improving objectivity of OCT diagnostics	78	Results of comparative analysis of several machine learning methods were presented. Methods with advantages were highlighted	SD-OCT; resolution 15 µm; depth 1.4 mm; 2.4 mm probe
A.A. Hakimi [74]	2021	Dynamic assessment of internal nasal valve (INV) changes	8	INV cross-sectional area was measured via OCT, correlated with intraluminal pressure, and a correlation was identified	SD-OCT with long-focus transducer; non-contact imaging, spiral scanning; 1 mm probe attached to endoscope; resolution 13 µm; imaging depth up to 1.5–2 mm
C.M. Waters [75]	2022	Assessment of INV status under different surgical scenarios ex vivo	4 post-mortem specimens	OCT data were comparable to CT images for obtaining information for hydrodynamic computational analysis	SD-OCT with long-focus transducer; non-contact imaging; resolution 10 µm; imaging depth up to 1.6 mm
T.T. Pham [76]	2022	Visualization and assessment of olfactory epithelium, olfactory cleft, and cribriform plate ex vivo with 3D reconstruction	4 rabbits	OCT images of olfactory epithelium, lamina propria, cribriform plate were obtained; morphometry was performed. OCT images correlated with histology. OCT criteria for epithelial damage and regeneration were described	SD-OCT, 2 modifications (wavelengths 1.3 and 1.7 µm); probe integrated into microscope; resolution 8 µm; imaging depth 1.5–2 mm
K. Vijaykumar [77]	2023	Assessment of upper airway epithelium status during viral infection (COVID-19)	13	A significant reduction in functional cilia count, decreased ciliary beat frequency, and abnormal ciliary activity were found	Micro-OCT; probe 2.3 mm; resolution 1.1 µm

CT, computed tomography; OCT, optical coherence tomography; SD-OCT, spectral-domain OCT

 

Optical Coherence Tomography in Laryngology

Studies dedicated to the theoretical rationale and practical application of OCT imaging of the larynx in normal and various pathological states were first conducted worldwide in 1997. In the work by A.M. Sergeev et al. [26], OCT was used to study the mucous membranes of hollow organs, including the larynx, in vivo. This became possible due to the development of a novel endoscopic OCT system (EOCT), which integrated a fiber optic interferometer into a standard endoscope, utilizing its biopsy channel to deliver low-coherence radiation to the biological tissue. The size of the developed forward-viewing OCT probe corresponded to the dimensions of the biopsy channel. Images of tumor tissues were obtained and analyzed in comparison with healthy ones. For the first time, it was demonstrated that OCT images of the laryngeal mucosa in normal and pathological conditions possess entirely different characteristics, which reliably correlated with histological findings. Although the study included only 15 patients, of whom only 4 underwent laryngeal OCT, these data suggested the potential of OCT for early tumor diagnosis and targeted biopsy, laying the groundwork for subsequent research.

Thus, in study [27], the capabilities of EOCT for laryngeal visualization were studied in 15 patients with various pathologies of the vocal folds. OCT features of vocal fold nodules and cysts were identified. In cases of malignant pathology, not only were OCT features typical for tumor changes described, but the ability of OCT to detect the tumor/normal tissue boundary was also demonstrated. Furthermore, to determine the in vivo effects of ionizing radiation on laryngeal tissues, in vivo EOCT monitoring of the vocal fold mucosa was performed during γ-ray therapy for cancer. A correlation was noted between EOCT images and known information about the morphological responses of tissues to radiation.

In papers [23, 29, 78], OCT data were used to detail the key differential diagnostic features of tumorous, tumor-like, and chronic inflammatory pathology of the larynx. Most importantly, these studies proved the diagnostic value of OCT examination in detecting severe dysplasia and carcinoma in situ with high sensitivity and specificity. B. Wong et al. later described the OCT characteristics of the microstructure of various laryngeal zones in healthy subjects and in several types of benign pathology, providing numerical characterization by performing optical micrometry [33].

The studies cited above demonstrated the benefit of OCT in the differential diagnosis of tumorous and non-tumorous laryngeal pathology. However, they did not address the method's drawbacks and limitations.

Subsequent research dedicated to the differential diagnosis of benign and malignant laryngeal neoplasms based on OCT image analysis has been conducted multiple times. W.B. Armstrong et al. [30] succeeded in clearly identifying disruption of the basement membrane in laryngeal cancer, as well as transition zones at the tumor boundary. However, the disappearance of the basement membrane can also be observed in other conditions, such as radiation mucositis. The authors emphasize the need for ultra-high-resolution OCT devices, which would allow for distinguishing subcellular details to differentiate reactive or hyperplastic lesions from dysplasia and carcinoma in situ.

Another limitation of OCT application, according to W.B. Armstrong et al., is associated with extensive exophytic lesions. In such cases, increased backscattering at the surface occurs, and light penetration into deeper tissue layers is limited. This indicates the advisability of using OCT for evaluating subtle lesions with minimal invasion depth.

A similar conclusion was reached by M. Kraft et al. [31], who state that in cases of pronounced hyperkeratosis, visualization of the basement membrane is impossible due to strong absorption of the probing radiation. Consequently, during an OCT examination, invasive cancer cannot be ruled out, and an ulcerative lesion of the laryngeal mucosa could be mistakenly interpreted as cancer due to the absence of a basement membrane. Furthermore, the authors question the advantages of OCT over other known methods in the differential diagnosis of malignant neoplasms and epithelial dysplasia, considering these conditions clinically apparent. They suggest using OCT only for determining the degree of dysplasia by measuring epithelial thickness.

In the study by T. Just et al. [35], a comparative assessment of benign and dysplastic changes in the larynx was conducted. The measurement of the epithelial layer served as the primary criterion for determining the degree of dysplasia, utilizing two OCT system modifications: a time-domain (TD-OCT) endoscopic setup and a spectral-domain (SD-OCT) modification integrated into an operating microscope.

It was demonstrated that intraoperative OCT enhances biopsy accuracy, thereby improving diagnostic quality. When using the spectral-domain setup, imaging speed, image quality, and processing improved; however, probing depth decreased due to the technical features of the microscope.

The main drawback of this technique is the "manual" selection of imaging points, which may result in missing crucial areas of examination. Scanning the entire volume of the vocal fold would help to avoid this limitation.

A study examining the intraoperative application of OCT as a tool to enhance the efficacy and precision of microsurgical treatment for laryngeal diseases is of particular interest [28]. In this work, OCT was utilized for intraoperative monitoring during laser surgery for laryngeal cancer. The information about structural changes in the laryngeal mucosa, obtained via OCT, allowed for not only precise tumor margin delineation but also real-time monitoring of laser effects, thereby preventing excessive tissue damage.

In turn, such precise control over the surgical treatment of laryngeal cancer significantly improves the functional outcomes of these interventions [36].

By visualizing microstructural changes in the larynx during or after various interventions, it is possible to assess the risk of complications such as chondroperichondritis, cicatricial deformations, and post-intubation granuloma. Study [32] demonstrated the potential of OCT in evaluating the airways of newborns. In intubated patients, a decrease in the OCT signal level from laryngeal and tracheal structures was observed, with progressive changes noted at different time points of intubation compared to non-intubated newborns. According to the authors, such information could be valuable in the care of patients requiring prolonged intubation. The examination was performed via a laryngoscope or an endotracheal tube; however, it is important to note that visual assessment of the internal airway surface and, consequently, correlation between endoscopic and OCT images was only possible in the former case. The relatively low imaging speed and radial scanning mode complicated the examination. Furthermore, the relatively small number of patients (n = 12) does not allow for a definitive determination of OCT's diagnostic value, although the method's potential is demonstrated. G.K. Sharma et al. examined 72 intubated newborns [38]. Using OCT with a long-focus transducer, it was possible to identify and quantitatively assess the condition of the mucous membrane and submucosal layer of the airway wall, establishing a correlation between the severity of these changes and the duration of intubation. The device developed by this group of authors offered several advantages over earlier modifications: non-contact operation, high speed, and the capability for 360° circumferential scanning. This justified the feasibility of using long-focus OCT for monitoring airway status during intubation to reduce complication risks. Optimizing the examination time could be achieved through automated tissue recognition and measurement during airway scanning. A drawback of the method was the relatively large volume of image sets excluded from the study (almost 30%) due to insufficient probing depth or motion artifacts. This is likely related to obtaining OCT images through the endotracheal tube and probe wear during high-speed rotation.

Almost simultaneously, a similar study was conducted by another group of authors [39]. OCT examination of the airways using a long-focus instrument modification was performed on 46 children who had undergone intubation. In this case, over 50% of the image sets were deemed unsuitable for inclusion in the study.

Motion artifacts, which hinder OCT performance in anesthetized patients, rendered this procedure nearly impractical in awake patients. However, L. Yu et al. [34] increased the imaging acquisition rate to 40 frames per second, utilized dynamic focusing and a swept light source, and successfully obtained OCT images during indirect laryngoscopy in awake patients, both during inspiration and phonation. It should be noted, however, that this was a two-channel endoscope with manual focus adjustment. S. Donner combined the optical pathways of two devices, integrating OCT into an endolaryngoscope, and compensated for motion through automatic adjustment of the scanning range and autofocusing [40].

The use of polarization-sensitive OCT (PS-OCT), based on the birefringence effect in collagen-containing tissues, provides additional information. Alterations in collagen fibers within the vocal folds, which occur in both tumorous and non-tumorous pathologies, disrupt the characteristic pattern in polarization-sensitive images. An in vivo study [37] demonstrated that employing PS-OCT for the differential diagnosis of benign and malignant neoplasms, in conjunction with standard OCT, does not yield fundamentally new information regarding the morphological characterization of the lesion itself. However, it aids in more clearly delineating the linear tumor/normal tissue boundaries, and the method may be useful in determining the degree of tumor invasion. The enhancement of the birefringence signal allowed for differentiation between healthy tissue and areas of scar changes, making PS-OCT promising for diagnosing this pathology. Nevertheless, the correlation between signal intensity and direct collagen content remains unstudied.

PS-OCT could be used to monitor the correction of laryngeal scar changes, for instance, for more precise injection of biomaterials into the vocal fold. The fundamental feasibility of using standard OCT to monitor implants in the vocal fold ex vivo and in vivo in animals is demonstrated in study [79].

Attempts have been made to study age-related features and identify markers of vocal fold development using OCT [41]. However, the small sample size (n = 20), scanning of specific areas rather than the entire vocal fold, and the use of only standard OCT modification prevented reliable conclusions from being drawn.

In recent years, research on the application of OCT in laryngology has focused on improving the quality of differential diagnosis of precancerous and early-stage tumor pathology. This is pursued by leveraging additional information obtained through OCT technology modifications (particularly PS-OCT with numerical processing) and machine learning [42, 43].

In summary, at present, various OCT modifications in laryngology can be most successfully used for the differential diagnosis of malignant and benign pathology, determination of linear malignant tumor margins, biopsy guidance, monitoring of laser effects during surgery, and detection of scar changes in the vocal folds. The potential for OCT monitoring of post-traumatic and scar changes in the larynx, as well as their correction, is promising but awaits further investigation. The OCT assessment of age-related developmental features of the larynx currently remains at the pilot experimental stage.

Optical Coherence Tomography in Otology

Research dedicated to exploring the fundamental and applied aspects of OCT in otology is extensive. One of the earliest studies investigating the potential of OCT as a method for imaging the anatomical structures of the middle ear was conducted by C. Pitris et al. in 2001 using ex vivo material [44]. This work first succeeded in obtaining high-quality images of the intact tympanic membrane and the structures immediately behind it: the ossicular chain, middle ear muscle tendons, and the medial wall of the tympanic cavity. Subsequent research focused on integrating and adapting OCT technology for practical otology.

Once compact OCT probes became available, the utility of the method was demonstrated in detecting biofilms forming on the inner surface of the tympanic membrane in patients with various forms of middle ear inflammation [47]. Later, an original method for the differential diagnosis of acute and chronic otitis media was proposed, based on measuring tympanic membrane thickness on OCT images [48–50, 52].

In such studies, the measured tympanic membrane thickness was considered a cumulative value reflecting the thickness of the membrane itself plus any material adhered to its inner surface, such as bacterial agglomerations or biofilms. It has been shown that patients with acute otitis media exhibit thickening of the tympanic membrane itself, whereas patients with chronic otitis media do not show such changes in the membrane itself. However, the total measured thickness in chronic cases significantly exceeds that in acute processes, presumably due to the proliferation of biofilms under conditions of chronic inflammation.

Continuing the discussion on the significance of OCT in diagnosing chronic inflammatory diseases of the middle ear, it is important to highlight the study by H.R. Djalilian et al. [46], which described the differences between cholesteatoma and normal/inflamed mucosa. Furthermore, this work was the first to demonstrate the feasibility of integrating OCT into an operating microscope system.

In later studies utilizing this technique, the microarchitecture of the tympanic membrane under conditions of chronic inflammation (so-called chronic myringitis) was detailed, and the layers of the tympanic membrane were clearly differentiated from each other [51, 59, 80].

K. Park et al. [56] used OCT to visualize the characteristics of microstructural changes in the tympanic membrane in various pathological states. The authors were able to measure the thickness of perforation edges, obtained a precise assessment of the degree of tympanic membrane retraction, and managed to track the postoperative healing process of the tympanic membrane.

Studies evaluating the role of OCT in diagnosing otitis media with effusion (OME) are of particular interest. Among the numerous publications on this topic, the works by G.L. Monroy et al. [53–55, 57] stand out, providing a detailed description of the OCT imaging findings of changes within the tympanic cavity in the presence of non-purulent fluid accumulation. In patients with OME, OCT typically reveals numerous inclusions behind the tympanic membrane. Based on their quantity and size, one can infer the viscosity and nature of the effusion, which is fundamentally important for determining the treatment approach for this pathology.

A. Novozhilov et al. [61] also proposed introducing a numerical criterion to objectify the assessment of OCT images of effusion.

The use of OCT has enabled the development of original algorithms for diagnosing and classifying otitis media. Within the framework of study [60], the authors demonstrated high sensitivity (91%) and specificity (90%) of OCT examination in diagnosing OME, despite a certain degree of subjectivity inherent in the method.

The application of OCT has been also studied for diagnosing a number of other non-suppurative middle ear diseases. Specifically, the work by T. Just et al. describes an OCT study of the oval window niche in normal and pathological conditions. In patients with otosclerosis and tympanosclerosis, heterogeneous thickening of the stapes footplate was identified [45].

The integration of OCT into the operating microscope has expanded the method's capabilities. For instance, in the surgical treatment of otosclerosis, OCT can be used to visualize the oval window area, assess the annular ligament, calculate prosthesis length, and monitor its positioning [81–85].

The complementary use of OCT and vibrometry allows for the assessment of not only anatomy but also the function of the sound conduction system. This is achieved by measuring the motion of middle ear structures (tympanic membrane and ossicles) and determining the efficiency of sound vibration transfer to the cochlea. This was demonstrated in a laboratory animal experiment by W. Dong et al. [86], while research groups led by D. MacDougall [58] and W. Kim [59] have explored the use of OCT vibrometry in clinical practice.

It should be noted that the method may have certain limitations depending on the technical specifications of the OCT system, as involuntary patient motion, chest movement, and cardiac rhythm can distort the results.

In the study by T.E. Abubakirov et al., OCT served as an auxiliary diagnostic method for a glomus tumor of the middle ear [62]. However, the researchers employed a standard OCT modification, which only allows for the detection of the presence of biotissue masses in the middle ear but cannot verify the specific nature of the formation. The application of OCT angiography (OCTA) would enable more accurate diagnosis of a glomus tumor by revealing a high density of the vascular network [64].

Studies dedicated to detailed OCT imaging of the inner ear structures currently remain more experimental than applied. For instance, experiments have successfully obtained OCT images of the inner ear in rats and correlated these findings with histological sections of microspecimens [87–89]. Technical limitations of non-invasive in vivo human cochlear imaging currently prevent the translation of the method into real clinical practice. Nevertheless, recent studies have attempted not only to detect inner ear structures but also to monitor the advancement and positioning of implants during cochlear implantation [69, 90].

Thus, in otological practice, OCT examination can be most useful for diagnosing tympanic cavity effusion, assessing its viscosity to determine surgical indications, and studying the structural features of the tympanic membrane in various pathological states and after surgical intervention. The complementary application of other techniques, such as OCT angiography and vibrometry, will expand the indications for OCT use in ear pathology.

Optical Coherence Tomography in Rhinology

Publications dedicated to various aspects of OCT application in rhinological practice are limited. Based on the results of a study conducted by U. Mahmood et al., the OCT-specific features of nasal cavity mucosal morphology in normal conditions and in patients who had used decongestants long-term were detailed [65]. This work suggests that OCT can be considered a promising method not only for the non-invasive study of the mucosa but also for the dynamic assessment of changes occurring in nasal tissues due to various pathologies and as a result of therapy.

Of interest are studies where OCT is used for anatomical imaging of the upper airways followed by the creation of volumetric models. This can assist surgeons in identifying and evaluating zones of obstruction and rationally selecting a correction method. For example, J. Jing et al., using a functional endoscopic OCT system, obtained in vivo images of the upper airways from the nasal cavity to the cricoid cartilage with their three-dimensional transformation [66]. However, to obtain quantitative information, numerical modeling methods need to be employed.

C.M. Waters et al. used OCT on post mortem specimens followed by 3D reconstruction and correlation with computed tomography to objectively assess the condition of the internal nasal valve (INV) [75], specifically to obtain data on its geometry and area during breathing. However, the small number of specimens (n = 4), technical difficulties that prevented complete reconstruction of the INV area, and an extremely lengthy computer modeling process hinder the translation of this experience into clinical practice.

Another group of authors [74] conducted a dynamic assessment of the INV condition in 8 volunteers. A correlation was found between its internal cross-sectional area and intraluminal pressure indicators. According to the researchers, surgeons, by determining the functional significance of INV narrowing, will be able to optimize surgical strategy. However, like previous work in this field, this method also requires further validation. Specifically, to understand which indicators should be considered pathological, it is advisable to obtain values for the INV area in norm using OCT.

Another potential application of OCT in rhinology is the non-invasive, in vivo assessment of the olfactory epithelium, which would be valuable for diagnosing neurological disorders and neurodegenerative diseases. T. Ueda et al. used OCT to study the morphology of the olfactory epithelium in mice [70], and T.T. Pham et al. obtained OCT images of the olfactory epithelium and cribriform plate and performed 3D OCT reconstruction in rabbits ex vivo [76]. However, replicating these studies in clinical practice has not yet been achieved.

M.A. Shakhova et al. demonstrated the potential of OCT in the differential diagnosis of various forms of chronic rhinitis [71]. It was established that OCT allows not only for the assessment of the layered structure of the inferior nasal turbinate mucosa but also for distinguishing the pathomorphological features of different forms of chronic rhinitis. To objectify the information, the authors proposed using numerical image processing, which improved the method's sensitivity [73]. Incorporating OCT into the standard diagnostic workup for chronic rhinitis would improve the differential diagnosis of its various forms, thereby optimizing treatment strategy.

L. Tóth et al. used OCT to detect bacterial and fungal biofilms in patients with chronic polypous rhinosinusitis [67]. U. Oltmanns et al., based on OCT data, described morphological changes in the nasal cavity mucosa in cystic fibrosis [68]. Information about the state and function of ciliated epithelium cilia and the number of seromucinous glands could contribute significantly to the treatment of such patients. However, the described OCT technique does not allow for obtaining this information. Study [69] presented an endomicroscopic OCT system with a resolution of up to 1.25 µm, which was used to examine the mucosa of the inferior nasal turbinates, obtaining data at the cellular level and tracking mucus transport dynamics. The authors noted that distinguishing individual cells was not always possible due to difficulties in positioning the endoscope. Current research on OCT application in rhinology is precisely focused on increasing the method's resolution [72, 77].

The limitations of using OCT in this area of rhinology include the complex architecture and relatively small volume of the nasal cavity, which complicate the manipulation of the optical probe during OCT examination. In this regard, non-contact techniques with circumferential scanning hold an advantage. Furthermore, increasing the resolution of OCT systems will enable the assessment of mucosal condition at the cellular level, helping to define the endotype of sinonasal pathology and personalize treatment.

Prospective Applications of Optical Coherence Tomography in Otorhinolaryngology

Recent advancements involve the implementation of multimodal OCT technqiues, which enable the simultaneous acquisition of both morphological and functional information about the biological tissue under study. Particular emphasis should be placed on OCT angiography (OCTA), which, in parallel with the standard OCT image, can provide a map of the active microcirculatory bed within the tissue [91]. Since OCT image formation is based on interferometry principles, the presence of moving objects (erythrocytes and other blood cells) in the examined tissue causes local dynamic changes in the image's speckle pattern. Therefore, analyzing speckle dynamics allows for the identification of areas with blood flow.

The OCTA method holds high potential in ENT applications, as analyzing microcirculatory bed activity can aid both in studying the fundamental pathophysiology of ENT organs and in addressing diagnostic and differential diagnostic challenges, as well as assessing tissue condition during or following treatment. For example, since the classical signs of inflammation in the development of rhinosinusitis, otitis, tonsillopharyngitis, and other ENT diseases are manifestations of microcirculation disturbances, monitoring the development of capillary permeability, vascular stasis, and exudation would allow for assessing the severity of inflammation and, if necessary, treatment efficacy. The exceptional sensitivity of the cochleovestibular analyzer to ischemia, which underlies the vascular theory of acute sensorineural hearing loss, Meniere's disease, and other cochleovestibulopathies, necessitates the use of methods capable of detecting thrombosis or spasm of the labyrinthine arteries, and disturbances in the microcirculation of the stria vascularis. This would enable monitoring of hair cell hypoxia and prevention of their death. Additionally, assessing microcirculation in the postoperative period following tympanoplasty, rhinoplasty, or septoplasty would enable the prediction of risks for necrosis, graft rejection, and allow for treatment strategy adjustments. However, implementing this approach necessitates the development of specialized probes, including endoscopic ones, as such diagnostics would be impossible without them.

Separate emphasis should be placed on the application of machine learning methods for interpreting OCT images, which are becoming increasingly widespread. These approaches are widely used to solve two main classes of tasks in OCT applications: 1) Segmentation of OCT images, involving the automatic delineation of structural elements and their characterization and 2) classification, involving the automated determination of the presence of a specific pathology based on a diagnostic OCT image.

Both tasks have been addressed in ophthalmology studies [92], where images are easiest to analyze due to weak scattering in tissues, and in dermatology [93–95], where multiple scattering in the skin leads to significant OCT signal attenuation with depth and limits probing depth.

The works most relevant to ENT applications are those where OCT is used to examine mucous membranes [96–98]. The application of such approaches in otorhinolaryngology is currently limited [43, 57, 71, 73] but appears promising.

Conclusion

This review demonstrates that OCT is a highly informative, non-invasive technique capable of real-time assessment of the condition of the pharyngeal and laryngeal mucosa, nasal cavity, and middle ear structures. It provides the ability to differentiate the pathomorphological features of ENT diseases.

Supplementing standard diagnostic procedures with OCT examination will enhance the diagnosis of inflammatory ENT pathology by identifying its pathomorphological variants, including latent forms. It will also improve the informativeness of diagnosing early-stage oncological diseases. Furthermore, the ability to monitor ongoing treatment will contribute to its optimization.

However, it should be noted that the results of OCT examination significantly depend on a number of factors. The experience and qualifications of the examiner are of key importance: like most other imaging techniques, the use of OCT requires knowledge of anatomy and morphology, as well as extensive practical experience in the specific application of the method. The technical parameters of OCT systems (time-domain/spectral-domain modifications, resolution, probe type, integration into an endoscope or microscope) are equally important.

The work of a multidisciplinary team of specialists, the implementation of automated image analysis, technical innovations, and the standardization of examination protocols will undoubtedly enhance the value of OCT in clinical practice, including in otorhinolaryngology.

Additional information

Funding

The study was performed under the grant from the Russian Research Foundation # 24-15-00175 (https://rscf.ru/project/24-15-00175/).

Conflict of interests

The authors declare no conflict of interests regarding this article.

Authors' contribution

M.A. Shakhova, the study concept and design, literature search and analysis, text writing; V.A. Fokeev, literature search and analysis in laryngology, text writing; A.E. Meller, literature search and analysis in rhinology, text editing; A.B. Terentyeva, literature search and analysis in otology, text editing; M.Yu. Kirillin, the study concept and design, literature search and analysis of the application and processing of OCT modifications, text writing, approval of the final version of the manuscript; A.V. Shakhov, the paper concept and design, text editing, approval of the final version of the manuscript. All the authors have read and approved the final version of the manuscript before submission, agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

About the authors

Mariia A. Shakhova

Privolzhsky Research Medical University; Federal Research Center A.V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences;

Author for correspondence.
Email: shahova_m@pimunn.net
ORCID iD: 0000-0002-5377-8858
SPIN-code: 3133-5958
Scopus Author ID: 25646831000

MD, PhD, Associate Professor, Head of the Department of Ear, Throat, and Nose Diseases named after Professor V.Yu. Shakhov; Research Fellow, Laboratory of Biophotonics

Russian Federation, ploshchad Minina i Pozharskogo 10–1, Nizhny Novgorod, 603005; ul. Ulyanova 46, Nizhny Novgorod, 603950

Vyacheslav A. Fokeev

Privolzhsky Research Medical University; Federal Research Center A.V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences

Email: s.fokeev1994@yandex.ru
ORCID iD: 0009-0005-4651-0828

Postgraduate Student, Department of Ear, Throat, and Nose Diseases named after Professor V.Yu. Shakhov; Junior Research Fellow, Laboratory of Biophotonics

Russian Federation, ploshchad Minina i Pozharskogo 10–1, Nizhny Novgorod, 603005; ul. Ulyanova 46, Nizhny Novgorod, 603950

Alina E. Meller

Privolzhsky Research Medical University

Email: mellalina@mail.ru
ORCID iD: 0000-0001-7169-5266

Senior Teacher, Department of Ear, Throat, and Nose Diseases named after Professor V.Yu. Shakhov

Russian Federation, ploshchad Minina i Pozharskogo 10–1, Nizhny Novgorod, 603005

Anna B. Terentyeva

Privolzhsky Research Medical University

Email: anna-t-nn@mail.ru
ORCID iD: 0000-0002-8375-4064

MD, PhD, Associate Professor, Department of Ear, Throat, and Nose Diseases named after Professor V.Yu. Shakhov

Russian Federation, ploshchad Minina i Pozharskogo 10–1, Nizhny Novgorod, 603005

Mikhail Y. Kirillin

Federal Research Center A.V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences

Email: kirillin@ipfran.ru
ORCID iD: 0000-0002-6804-6369

PhD (in Phys.-Math.), Senior Research Fellow, Laboratory of Biophotonics

Russian Federation, ul. Ulyanova 46, Nizhny Novgorod, 603950

Andrei V. Shakhov

Privolzhsky Research Medical University

Email: shakhovav54@yandex.ru
ORCID iD: 0000-0002-5969-8066

MD, PhD, Associate Professor, Professor of the Department of Ear, Throat, and Nose Diseases named after Professor V.Yu. Shakhov

Russian Federation, ploshchad Minina i Pozharskogo 10–1, Nizhny Novgorod, 603005

References

Supplementary files