Faculty Bibliography

Multiple scattering in a sample presents a significant limitation to achieve meaningful structural information at deeper penetration depths in optical coherence tomography (OCT). Previous studies suggest that the spectral region around 1.7 microm may exhibit reduced scattering coefficients in biological tissues compared to the widely used wavelengths around 1.3 mum. To investigate this long-wavelength region, we developed a wavelength-swept laser at 1.7 microm wavelength and conducted OCT or optical frequency domain imaging (OFDI) for the first time in this spectral range. The constructed laser is capable of providing a wide tuning range from 1.59 to 1.75 microm over 160 nm. When the laser was operated with a reduced tuning range over 95 nm at a repetition rate of 10.9 kHz and an average output power of 12.3 mW, the OFDI imaging system exhibited a sensitivity of about 100 dB and axial and lateral resolution of 24 mum and 14 mum, respectively. We imaged several phantom and biological samples using 1.3 mum and 1.7 microm OFDI systems and found that the depth-dependent signal decay rate is substantially lower at 1.7 microm wavelength in most, if not all samples. Our results suggest that this imaging window may offer an advantage over shorter wavelengths by increasing the penetration depths as well as enhancing image contrast at deeper penetration depths where otherwise multiple scattered photons dominate over ballistic photons.

OBJECTIVES/HYPOTHESIS/OBJECTIVE:Optical coherence tomography (OCT) can provide high-resolution ( approximately 10-15 microm/pixel) images of vocal fold microanatomy, as demonstrated previously. We explored physiologically triggered Fourier-domain OCT for imaging vocal folds during phonation. The goal is to visualize dynamic histological cross sections and four-dimensional data sets where multiple planes are displayed in synchronized motion. If feasible, this approach could be a useful research tool and spur development of new clinical instrumentation. STUDY DESIGN/METHODS:A Fourier-domain, triggered OCT system was created and tested in experiments on excised calf larynges to obtain preliminary observations and characterize important factors affecting image quality. METHODS:Larynges were imaged during phonation driven by warm, humidified air. A subglottal pressure signal was used to synchronize the OCT system with the phonatory cycle. Image sequences were recorded as functions of anatomical location or subglottal pressure. Implant materials were also imaged during vibration, both in isolation and after injection into a vocal fold. RESULTS:Oscillations of epithelium and lamina propria were observed, and parameters such as shape, amplitude, and velocity of the vocal fold mucosal waves were found to be measurable. Ripples of mucosal wave as small as 100 microm in vertical height were clearly visible. Internal strain was also observed in normal and implanted vocal folds. CONCLUSIONS:Four-dimensional OCT of the vocal fold may help to more directly relate biomechanics to anatomy and disease. It may also be useful for assaying the functional rheology of implants in the context of real tissue. With further development, this technology has potential for clinical endoscopic application.

Quantitative cross-sectional imaging of vocal folds during phonation is potentially useful for diagnosis and treatments of laryngeal disorders. Optical coherence tomography (OCT) is a powerful technique, but its relatively low frame rates makes it challenging to visualize rapidly vibrating tissues. Here, we demonstrate a novel method based on triggered laser scanning to capture 4-dimensional (4D) images of samples in motu at audio frequencies over 100 Hz. As proof-of-concept experiments, we applied this technique to imaging the oscillations of biopolymer gels on acoustic vibrators and aerodynamically driven vibrations of the vocal fold in an ex vivo calf larynx model. Our results suggest that triggered 4D OCT may be useful in understanding and assessing the function of vocal folds and developing novel treatments in research and clinical settings.

The ability to quantify and visualize submicrometer-scale oscillatory motions of objects in three dimensions has a wide range of application in acoustics, materials sciences, and medical imaging. Here we demonstrate that volumetric snapshots of rapid periodic motion can be captured using optical coherence tomography (OCT) with subnanometer-scale motion sensitivity and microsecond-scale temporal resolution. This technique, termed OCT vibrography, was applied to generate time-resolved volumetric vibrographs of a miniature drum driven acoustically at several kilohertz.

Efficient transfer of sound by the middle ear ossicles is essential for hearing. Various pathologies can impede the transmission of sound and thereby cause conductive hearing loss. Differential diagnosis of ossicular disorders can be challenging since the ossicles are normally hidden behind the tympanic membrane (TM). Here we describe the use of a technique termed optical coherence tomography (OCT) vibrography to view the sound-induced motion of the TM and ossicles simultaneously. With this method, we were able to capture three-dimensional motion of the intact TM and ossicles of the chinchilla ear with nanometer-scale sensitivity at sound frequencies from 0.5 to 5 kHz. The vibration patterns of the TM were complex and highly frequency dependent with mean amplitudes of 70-120 nm at 100 dB sound pressure level. The TM motion was only marginally sensitive to stapes fixation and incus-stapes joint interruption; however, when additional information derived from the simultaneous measurement of ossicular motion was added, it was possible to clearly distinguish these different simulated pathologies. The technique may be applicable to clinical diagnosis in Otology and to basic research in audition and acoustics.

We present portable preclinical low-coherence interference (LCI) instrumentation for aiding fine needle aspiration biopsies featuring the second-generation LCI-based biopsy probe and an improved scoring algorithm for tissue differentiation. Our instrument and algorithm were tested on 38 mice with cultured tumor mass and we show the specificity, sensitivity, and positive predictive value of tumor detection of over 0.89, 0.88, and 0.96, respectively.

Optical coherence tomography (OCT) is useful for materials defect analysis and inspection with the additional possibility of quantitative dimensional metrology. Here, we present an automated image-processing algorithm for OCT analysis of roll-to-roll multilayers in 3D manufacturing of advanced ceramics. It has the advantage of avoiding filtering and preset modeling, and will, thus, introduce a simplification. The algorithm is validated for its capability of measuring the thickness of ceramic layers, extracting the boundaries of embedded features with irregular shapes, and detecting the geometric deformations. The accuracy of the algorithm is very high, and the reliability is better than 1 μm when evaluating with the OCT images using the same gauge block step height reference. The method may be suitable for industrial applications to the rapid inspection of manufactured samples with high accuracy and robustness.

This study aimed to evaluate the concept of using high-resolution optical coherence tomography (OCT) imaging to rapidly assess surgical specimens and determine if cancer positive margins were left behind in the surgical bed. A mouse model of breast cancer was used in this study. Surgical specimens from 30 animals were investigated with OCT and automated interpretation of the OCT images was performed and tested against histopathology findings. Specimens from 10 animals were used to build a training set of OCT images, while the remaining 20 specimens were used for a validation set of images. The validation study showed that automated interpretation of OCT images can differentiate tissue types and detect cancer positive margins with at least 81% sensitivity and 89% specificity. The findings of this pilot study suggest that OCT imaging of surgical specimens and automated interpretation of OCT data may enable in the future real-time feedback to the surgeon about margin status in patients with breast cancer, and potentially with other types of cancers. Currently, such feedback is not provided and if positive margins are left behind, patients have to undergo another surgical procedure. Therefore, this approach can have a potentially high impact on breast surgery outcome.

We report the development of a novel otoscopy probe for assessing middle ear anatomy and function. Video imaging and phase-sensitive optical coherence tomography are combined within the same optical path. A sound stimuli channel is incorporated as well to study middle ear function. Thus, besides visualizing the morphology of the middle ear, the vibration amplitude and frequency of the eardrum and ossicles are retrieved as well. Preliminary testing on cadaveric human temporal bone models has demonstrated the capability of this instrument for retrieving middle ear anatomy with micron scale resolution, as well as the vibration of the tympanic membrane and ossicles with sub-nm resolution.