Imaging of subsquamous Barrett's epithelium with ultrahigh-resolution optical coherence tomography: a histologic correlation study.

BACKGROUND: Optical coherence tomography (OCT) is being developed as a potentially valuable method for high-resolution cross-sectional imaging of the esophageal mucosal and submucosal layers. One potential application of OCT imaging is to identify subsquamous Barrett's epithelium in patients who have undergone ablative therapy, which is not visible on standard endoscopic examination. However, histologic correlation confirming the ability of OCT to image subsquamous Barrett's epithelium has yet to be performed. DESIGN: Histologic correlation study. OBJECTIVE: To perform histologic correlation of ultrahigh-resolution optical coherence tomography (UHR-OCT) imaging for identification of subsquamous Barrett's epithelium. SETTING: Academic Medical Center (University of Washington, Seattle, WA). PATIENTS: Fourteen patients with pathologic biopsy specimens, proven to be high-grade dysplasia or adenocarcinoma underwent esophagectomy. INTERVENTIONS: UHR-OCT imaging was performed on ex vivo esophagectomy specimens immediately after resection. MAIN OUTCOME MEASUREMENTS: Correlation of UHR-OCT images with histologic images. RESULTS: Subsquamous Barrett's epithelium was clearly identified by using UHR-OCT images and was confirmed by corresponding histology. LIMITATIONS: Difficulty distinguishing some subsquamous Barrett's glands from blood vessels in ex vivo tissue (because of the lack of blood flow) in some cases. Imaging was performed with a bench-top system. CONCLUSIONS: Results from this study demonstrate that UHR-OCT imaging is capable of identifying subsquamous Barrett's epithelium.

High-resolution OCT balloon imaging catheter with astigmatism correction.

We report new optics designs for an optical coherence tomography (OCT) balloon imaging catheter to achieve diffraction-limited high resolution at a large working distance and enable the correction of severe astigmatism in the catheter. The designs employed a 1 mm diameter gradient-index lens of a properly chosen pitch number and a glass rod spacer to fully utilize the available NA of the miniature optics. Astigmatism caused by the balloon tubing was analyzed, and a method based on a cylindrical reflector was proposed and demonstrated to compensate the astigmatism. A catheter based on the new designs was successfully developed with a measured diffraction-limited lateral resolution of approximately 21 microm, a working distance of approximately 11-12 mm, and a round-shape beam profile. The performance of the OCT balloon catheter was demonstrated by 3D full-circumferential imaging of a swine esophagus in vivo along with a high-speed, Fourier-domain, mode-locked swept-source OCT system.

Scanning fiber-optic nonlinear endomicroscopy with miniature aspherical compound lens and multimode fiber collector.

A flexible scanning fiber-optic endomicroscope using a miniature compound lens and a multimode-fiber (MMF) collector was developed for two-photon fluorescence (TPF) and second-harmonic generation (SHG) imaging. The compound lens consisted of a pair of aspherical lenses and exhibited reduced chromatic aberration compared with gradient-index lenses, thus increasing the TPF/SHG collection efficiency. The introduction of a short MMF collector at the distal end of the double-clad fiber of the endomicroscope further mitigated the adverse influence of chromatic aberration of the lens and enhanced the TPF/SHG collection efficiency. Both ray-tracing simulations and experiments on TPF imaging of fluorescent beads and SHG imaging of rattail tendon demonstrated approximately nine (approximately four) times improved collection efficiency for TPF (SHG) with the new endomicroscope design that utilized a compound lens and an MMF collector.

Fiber-optic endomicroscopy system for high-resolution nonlinear imaging of biological tissue.

A flexible fiber-optic endomicroscopy system was developed for nonlinear optical imaging of biological samples. Double-clad fiber and photonic bandgap fiber were employed in the endomicroscope for femtosecond pulse delivery, dispersion compensation, nonlinear optical signals collection and fast beam scanning. Three-dimensional imaging of biological tissues based on second harmonic generation and two-photon excited fluorescence was performed with the endomicroscope. The depth-resolved imaging results strongly suggest the potential of this flexible fiber-optic microscope system for real-time assessment of both epithelial and stromal structures in luminal organs.

Flexible miniature compound lens design for high-resolution optical coherence tomography balloon imaging catheter.

We report on a new optics design for an optical coherence tomography (OCT) balloon imaging catheter. The design involves a miniature compound gradient-index (GRIN) rod lens, which consists of a fiber optic mode-field reducer and relay rod lenses to achieve predictable high lateral resolution at a desired large working distance. The compound lens design significantly simplifies the engineering process for an OCT catheter and enables 3-D full circumferential cross sectional imaging of large luminal organs such as human esophagus. An as-designed OCT catheter is developed and demonstrated for real-time in vivo swine esophagus imaging in a 3-D spiral fashion.

Non-invasive imaging of carcinogen-induced early neoplasia using ultrahigh-resolution optical coherence tomography.

BACKGROUND AND OBJECTIVE: Improved diagnostics capable of non-invasive detection of early stage carcinogenesis would benefit basic research, and potentially aid in clinical cancer diagnosis and management. The two-stage carcinogenesis protocol is widely used for studying the multi-stage nature of tumor development in mice and provides insight into tumor development in other animal models and humans. The objective of this study was to investigate the feasibility of non-invasive optical coherence tomography (OCT) for in vivo imaging of microanatomical changes in the epidermis and dermis during early carcinogenesis using a mouse skin model. MATERIALS AND METHODS: 10 NIH mice were treated with DMBA and TPA following the well-established two-stage carcinogenesis protocol. OCT imaging of treated skin from live mice was performed at five time points (Week 4-8) after tumor initiation to reveal the structural changes in the epidermis and dermis associated with the earliest, premalignant stages of tumor development. OCT images were compared with histology findings. In addition, OCT signals were quantitatively analyzed to evaluate tissue optical property changes during early carcinogenesis. RESULTS: Early structural changes in the epidermis, dermis and hair follicles during carcinogenesis were clearly delineated in vivo using OCT. OCT images correlated well with histological findings. Quantitative OCT signal analysis revealed a statistically significant change in the extinction coefficient for untreated (40.5 +/- 17.0 mm(-1)) and treated (9.6 +/- 3.6 mm(-1)) mouse epidermis (P < 0.005). The dermis extinction coefficient for the treated mouse skin (3.7 +/- 0.9 mm(-1)) was lower than the untreated one (4.7 +/- 1.6 mm(-1)), but was not statistically significant (P > 0.10). Furthermore, the papilloma extinction coefficient (2.9 +/- 0.3 mm(-1)) was significantly lower than the extinction coefficient for the treated epidermis (P < 0.005) and dermis (P < 0.01). CONCLUSION: OCT is a viable tool for assessing the earliest stages of carcinogenesis and has potential for early detection of neoplasia in skin, as well as in epithelial linings of other organs.

Real-time in vivo blood-flow imaging by moving-scatterer-sensitive spectral-domain optical Doppler tomography.

We present a moving-scatterer-sensitive optical Doppler tomography (MSS-ODT) technique for in vivo blood flow imaging in real time by using a spectral-domain optical coherence tomography system. In MSS-ODT the influence of stationary scatterers is suppressed by subtracting adjacent complex axial scans before calculating the Doppler frequency shift. We demonstrate that MSS-ODT is a useful technique for accurate determination of blood vessel size by imaging flow in a small capillary tube with a 75 microm inner diameter. The flow profile obtained with MSS-ODT yields a substantially more accurate tube diameter than that obtained with the conventional phase-resolved method, which underestimates the diameter by about 23%. We also demonstrate that MSS-ODT provides improved sensitivity over the conventional phase-resolved method for imaging in vivo blood flow in small vessels in a mouse ear.

Noninvasive assessment of cutaneous wound healing using ultrahigh-resolution optical coherence tomography.

Ultrahigh-resolution optical coherence tomography (OCT) was used for noninvasive in vivo evaluation of the wound healing process. Cutaneous wounds were induced by 2.5-mm diameter full-thickness punch biopsies on the dorsal surface of seven mice. OCT imaging was performed to assess the structural characteristics associated with the healing process. The OCT results were compared to corresponding histology. Two automated quantitative analysis routines were implemented to identify the dermal-epidermal junction and segment the OCT images. Hallmarks of cutaneous wound healing such as wound size, epidermal migration, dermal-epidermal junction formation, and differences in wound composition were readily identified on the OCT images. Blister formation was also observed. Preliminary findings suggest OCT is a viable tool to noninvasively monitor wound healing in vivo.

Continuous focus tracking for real-time optical coherence tomography.

We report an approach to achieving continuous focus tracking and a depth-independent transverse resolution for real-time optical coherence tomography (OCT) imaging. Continuous real-time focus tracking is permitted by use of a lateral-priority image acquisition sequence in which the depth-scanning rate is equivalent to the imaging frame rate. Real-time OCT imaging with continuous focus tracking is performed at 1 frame/s by reciprocal translation of a rapid lateral-scanning miniature imaging probe (e.g., an endoscope). The optical path length in the reference arm is scanned synchronously to ensure that the coherence gate coincides with the imaging beam focus. The image quality improvement is experimentally demonstrated by imaging a tissue phantom embedded with polystyrene microspheres and rabbit esophageal tissues.

Optical coherence tomography imaging of the pancreas: a needle-based approach.

A novel, high-resolution, needle-based optical coherence tomography (OCT) device for improving the ability to detect early epithelial dysplasia in solid tissues/organs in vivo is currently in development. An instrument capable of real-time imaging of tissue microstructures in vivo could improve the ability to detect pathologic conditions such as dysplasia, and consequently improve patient outcomes. OCT is an emerging technology that can perform real-time cross-sectional imaging of tissue structures at micron-scale resolution in vivo. OCT has been shown to be effective in the imaging of luminal epithelium, capable of detecting epithelial dysplasia in Barrett's esophagus, and colonic polyps. However, OCT imaging depth with conventional probes is limited to the luminal surface (approximately 1-2 mm). The development of a technology and device that enables high-resolution, real-time imaging of solid tissues beyond 1- to 2-mm deep at or near the cellular level in vivo could improve the diagnosis of diseases of the pancreas and other solid organs.

Gold nanocages: bioconjugation and their potential use as optical imaging contrast agents.

Gold nanocages of <40 nm in dimension have been synthesized using the galvanic replacement reaction between Ag nanocubes and HAuCl4 in an aqueous solution. By controlling the molar ratio between Ag and HAuCl4, the gold nanocages could be tuned to display surface plasmon resonance peaks around 800 nm, a wavelength commonly used in optical coherence tomography (OCT) imaging. OCT measurements on phantom samples indicate that these gold nanocages have a moderate scattering cross-section of approximately 8.10 x 10(-16) m2 but a very large absorption cross-section of approximately 7.26 x 10(-15) m2, suggesting their potential use as a new class of contrast agents for optical imaging. When bioconjugated with antibodies, the gold nanocages have also been demonstrated for specific targeting of breast cancer cells.

Rapid-scanning forward-imaging miniature endoscope for real-time optical coherence tomography.

We developed a miniature endoscope that is capable of rapid lateral scanning and is suitable for real-time forward-imaging optical coherence tomography (OCT). The endoscope has an outer diameter of 2.4 mm, consisting of a miniature tubular lead zirconate titanate (PZT) actuator, a single-mode fiber-optic cantilever, and a graded-index lens. Rapid lateral scanning at 2.8 kHz is achieved when the fiber-optic cantilever is resonated with the PZT actuator. This allows OCT imaging to be performed by fast lateral beam scanning followed by slow depth scanning, which is different from the conventional OCT imaging sequence. Real-time OCT imaging with the endoscope operated in the new image acquisition sequence at 6 frames/s is demonstrated.

Rapid scanning all-reflective optical delay line for real-time optical coherence tomography.

We describe a dispersion-free high-speed scanning optical delay line that is suitable for real-time optical coherence tomography, in particular, when an ultrabroadband light source is used. The delay line is based on all-reflective optics consisting of two flat and one curved mirrors. We achieve optical path-length scanning by oscillating one of the two flat mirrors with a resonant galvanometer. The delay line is compact and easy to implement. A total scanning depth of 1.50 mm with an 89% duty ratio, a maximal scanning speed of approximately 9.1 m/s, and a 4.1-kHz repetition rate has been demonstrated.