Henning Wisweh

CLINICAL VALUE OF OPTICAL COHERENCE TOMOGRAPHY IN LARYNGOLOGY

Optical coherence tomography (OCT) is a new, noninvasive imaging technology for the evaluation of superficial lesions. The objective of this study is to evaluate microlaryngoscopy in combination with OCT compared with microlaryngoscopy alone (ie, without OCT) in supplying a specific diagnosis, predicting invasive tumor growth and epithelial dysplasia in the larynx.

[Optical coherence tomography : significance of a new method for assessing unclear laryngeal pathologies].

BACKGROUND Optical coherence tomography (OCT) is a new imaging technology of as yet unknown significance in laryngology. The objective of this study was to evaluate the ability of this noninvasive method to reliably predict diagnosis and possible malignancy in laryngeal disease. PATIENTS AND METHODS In a prospective study, a total of 225 laryngeal lesions in 201 consecutive patients were examined during elective microlaryngoscopy. Clinical assessment under the operating microscope with and without OCT was compared with conventional histopathology. RESULTS For all cases, diagnosis gained by OCT was significantly superior to microlaryngoscopy alone. In particular, the exact grade of dysplasia could be better determined with the help of OCT, whereas statistical significance was just barely missed for the prediction of benign lesions. Additionally, OCT proved to be a very helpful method for identifying malignant tumors of the larynx. CONCLUSIONS OCT is a simple, rapid, and reliable aid in the diagnostic investigation of unclear laryngeal pathologies, especially of laryngeal cancer and its precursor lesions.

Optical coherence tomography monitoring of vocal fold femtosecond laser microsurgery

Surgery of benign pathological alterations of the vocal folds results in permanent disphonia if the bounderies of the vocal fold layers are disregarded. Precise cutting with a femtosecond laser (fs-laser) combined with simultanous imaging of the layered structure enables accurate resections with respect to the layer boundaries. Earlier works demonstrated the capability of optical coherence tomography (OCT) for utilization on vocal folds. The layered structure can be imaged with a spatial resolution of 10-20&mgr;m up to a depth of 1.5mm. The performance of fs-laser cutting was analyzed on extracted porcine vocal folds with OCT monitoring. Histopathological sections of the same processed samples could be well correlated with the OCT images. With adequate laser parameters thermal effects induced only negligable damage to the processed tissue. The dimensions of the thermal necrosis were determined to be smaller than 1&mgr;m. OCT contolled fs-laser cutting of porcine vocal fold tissue in the &mgr;m range with minimal tissue damage is presented.

Optical characterization of vocal folds by OCT-based laryngoscopy

Optical coherence tomography (OCT) is a new non-invasive method to investigate biological tissue. It is particularly suitable for examination of human vocal folds due to its optical penetration depth of around 1.5mm. We developed a modified laryngoscope with an integrated OCT beam path for non-contact imaging of human vocal folds. In vivo studies on awake patients show that synchronous OCT and conventional laryngoscopy works well. For enabling the choice of the appropriate OCT encoding technique for OCT-based laryngoscopy measurements on simulated vibrations were performed with time domain (TD) and fourier domain (FD) OCT devices. The results show that TD-OCT is much more suitable for non-contact imaging than FD-OCT. In studies on porcine and monkey vocal folds the performance of femtosecond laser tissue ablation was analyzed with OCT monitoring. Histopathological sections could be well correlated with the OCT images. In future applications a combined system that uses one femtosecond laser as light source for tissue ablation as well as for OCT imaging is conceivable. In conclusion, OCT can be used as a pre-, intra- and post-operative diagnostic instrument for analysing the vocal fold structure down to the vocalis muscle allowing a more precise indication for potential subsequent invasive procedures. We suggest that OCT should be used in addition to established examination methods for diagnostic evaluation of vocal fold malignancies and functional alterations.

Automatic segmentation of clinical OCT images for the determination of epithelial thickness changes in laryngeal lesions

Automated classification of laryngeal lesions using optical coherence tomography data can be helpful in making a faster and safer diagnosis. A change in the epithelial layer thickness seems to be an effective indicator for laryngeal cancer and its precursors. Lesions with different grades of malignancy were scanned with a time domain OCT system during microlaryngoscopy. Every diagnosis was confirmed by performing a biopsy. Each OCT image was separately segmented, manually by an expert and automatically by a segmentation algorithm. Values for the maximal and average epithelial thickness as well as the standard deviations were compared for both segmentations. The results show a thickening of the epithelium from normal over dysplastic to cancerous tissue. The values for the automatic segmentation are in good agreement with expert segmentation. In conclusion, automatic segmentation can be used for epithelial thickness measurements as a promising indicator for laryngeal cancer. It would also be possible to extract other characteristics like standard deviation or signal attenuation within the segments. Thus, we laid the foundation for computer-aided diagnosis of laryngeal lesions.

[Morphologic classification of Reinke's edema through optical coherence tomography].

OBJECTIVE Several classification systems for Reinkes edema have been proposed in the past, which are somewhat less than morphologically ideal. The objective of the present study is to evaluate the ability of optical coherence tomography (OCT) to attain a reproducible graduation of Reinkes edema. MATERIAL AND METHODS In a prospective study, 30 consecutive patients underwent endolaryngeal, microsurgical resection of their Reinkes edema. Graduation was performed through OCT based on morphologic criteria, where each result was compared with that of other classification systems. RESULTS In Reinkes edema grade I according to Glanz, a feathered pattern is found, while Reinkes edema grade II demonstrates a lacunar and Reinkes edema grade III a confluent pattern. Correlation between the different classification systems was uniformly weak and not significant. CONCLUSIONS Due to the three different recognizable patterns, OCT qualifies as an objective and reproducible aid for the graduation of Reinkes edema and gives certain insights in its pathogenesis.

A laryngoscope for office-based imaging of human vocal folds using OCT

We developed a laryngoscope with an integrated OCT beam path for office-based non-contact imaging of human vocal folds. In combination with conventional videolaryngoscopy superficial and subsurface lesions can be detected. For error-free interpretation of OCT images obtained in office-based examination motion artifacts have to be considered. To demonstrate the implications on OCT images we simulated probe and patient movements for different commercial systems representing the three OCT modalities and analyzed the OCT data. Our results show that time domain and fourier domain OCT with a swept light source are probably better suited for noncontact imaging of awake patients than the current generation of fourier domain OCT engines with spectrometer design.

OCT-aided femtosecond laser micromachining device

Fs-lasers are widely used for microsurgery and micromachining. Due to nonlinear interaction of ultrashort pulses with tissue or matter precisions of a few μm can be achieved. But particularly in the field of surgery this precision can not be obtained as the devices for diagnostics and treatment have to be changed due to separate systems. We show a combined system of a fs-laser and a Fourier-Domain optical coherence tomography (FD-OCT) enabling to cut and image the region of interest alternately. The FD-OCT offers non-invasive imaging at an axial resolution of 6, 2 μm and a transverse resolution of 3 μm in air which is comparable to the interaction zone of the fslaser-pulses. OCT-aided subsurface cutting is successfully demonstrated on biological ex-vito samples of porcine cornea and larynx. Furthermore it appeared that in situ OCT imaging enables to monitor cuts produced with pulse energies close to the energy threshold. In conclusion, this setup demonstrates the potential of a system combining cutting and OCT imaging within the same optical setup without the need of changing devices.

Significance of optical coherence tomography in the assessment of laryngeal lesions

Optical coherence tomography (OCT) is a new promising imaging modality in laryngology as yet of undetermined value. The objective of the present study was to evaluate the ability of this noninvasive method to make a reliable prediction of diagnosis in laryngeal disease. In a prospective study, 225 benign and malignant laryngeal lesions were examined with a fiber-based OCT system in contact mode during elective microlaryngoscopy. Intraoperative OCT findings were compared to conventional histopathology supplying a correct specific diagnosis in about 90% of cases. With increasing experience, a reliable prediction of invasive tumor growth and often the exact grade of dysplasia were possible. Due to the current spatial resolution of OCT, microinvasive cancer could not be safely delineated from severe dysplasia or carcinoma in situ. In contrast, benign lesions made no essential diagnostic difficulties due to their characteristic OCT image. In conclusion, OCT has proved to be very useful in the diagnostic investigation and the intraoperative monitoring of laryngeal disease.