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Background: Volumetric laser endomicroscopy (VLE) allows for near-microscopic imaging of the superficial esophageal wall and may improve detection of early neoplasia in Barrett's esophagus (BE). Interpretation of a 6-cm long, circumferential VLE "full scan" may however be challenging for endoscopists. We aimed to evaluate the accuracy of VLE experts in correctly diagnosing VLE full scans of early neoplasia and non-dysplastic BE (NDBE).Methods: 29 VLE full scan videos (15 neoplastic and 14 NDBE) were randomly evaluated by 12 VLE experts using a web-based module. Experts were blinded to the endoscopic BE images and histology. The 15 neoplastic cases contained a subtle endoscopically visible lesion, which on endoscopic resection showed high grade dysplasia or cancer. NDBE cases had no visible lesions and an absence of dysplasia in all biopsies. VLE videos were first scored as "neoplastic" or "NDBE." If neoplastic, assessors located the area most suspicious for neoplasia. Primary outcome was the performance of VLE experts in differentiating between non-dysplastic and neoplastic full scan videos, calculated by accuracy, sensitivity, and specificity. Secondary outcomes included correct location of neoplasia, interobserver agreement, and level of confidence.Results: VLE experts correctly labelled 73 % (95 % confidence interval [CI] 67 % - 79 %) of neoplastic VLE videos. In 54 % (range 27 % - 66 %) both neoplastic diagnosis and lesion location were correct. NDBE videos were consistent with endoscopic biopsies in 52 % (95 %CI 46 % - 57 %). Interobserver agreement was fair (kappa 0.28). High level of confidence was associated with a higher rate of correct neoplastic diagnosis (81 %) and lesion location (73 %).Conclusions: Identification of subtle neoplastic lesions in VLE full scans by experts was disappointing. Future studies should focus on improving methodologies for reviewing full scans, development of refined VLE criteria for neoplasia, and computer-aided diagnosis of VLE scans. [ABSTRACT FROM AUTHOR]

Volumetric laser endomicroscopy (VLE) has been shown to improve detection of early neoplasia in Barrett's esophagus (BE). However, diagnostic performance using histopathology-correlated VLE regions of interest (ROIs) has not been adequately studied. We evaluated the diagnostic accuracy of VLE assessors for identification of early BE neoplasia in histopathology-correlated VLE ROIs. In total, 191 ROIs (120 nondysplastic and 71 neoplastic) from 50 BE patients were evaluated in a random order using a web-based module. All ROIs contained histopathology correlations enabled by VLE laser marking. Assessors were blinded to endoscopic BE images and histology. ROIs were first scored as nondysplastic or neoplastic. Level of confidence was assigned to the predicted diagnosis. Outcome measures were: (i) diagnostic performance of VLE assessors for identification of BE neoplasia in all VLE ROIs, defined as accuracy, sensitivity, and specificity; (ii) diagnostic performance of VLE assessors for only high level of confidence predictions; and (iii) interobserver agreement. Accuracy, sensitivity, and specificity for BE neoplasia identification were 79% (confidence interval [CI], 75–83), 75% (CI, 71–79), and 81% (CI, 76–86), respectively. When neoplasia was identified with a high level of confidence, accuracy, sensitivity, and specificity were 88%, 83%, and 90%, respectively. The overall strength of interobserver agreement was fair (k  = 0.29). VLE assessors can identify BE neoplasia with reasonable diagnostic accuracy in histopathology-correlated VLE ROIs, and accuracy is enhanced when BE neoplasia is identified with high level of confidence. Future work should focus on renewed VLE image reviewing criteria and real-time automatic assessment of VLE scans. [ABSTRACT FROM AUTHOR]

Background: Successful surgical management of primary hyperparathyroidism requires an understanding of the underlying pathological diagnosis. Various methods have been employed to distinguish normal from hyperfunctional diseased glands. Confocal reflectance microscopy (CRM) is a novel optical method of imaging tissue non-invasively without the need for fixation, sectioning and staining as in standard histopathology. Gray-scale images are displayed in real time on a monitor, and represent horizontal (en face) optical sections through the tissue. Using CRM, the goal of this study was to delineate histological features characteristic of the parathyroid gland, and to determine if confocal imaging could distinguish normal from adenomatous parathyroid tissue. Methods: In this pilot observational cohort study, a total of 18 parathyroid glands was imaged using CRM immediately after excision in eight patients undergoing surgery for primary hyperparathyroidism. Confocal images were compared with corresponding permanent, haematoxylin and eosin-stained sections obtained from the same gland. For each patient, the percentage area occupied by fat cells was calculated in ten independent images (593 μm × 509 μm) of both normal and diseased glands. Results: Characteristic histological features of the parathyroid gland were readily discernible by CRM and correlated well with permanent, haematoxylin and eosin-stained sections. The fat content of both normal and diseased glands could be determined easily. The percentage area occupied by fat cells was distinctly different in normal (mean(s.d.) 21·8(5·3) per cent) and diseased (0·9(2·4) per cent) parathyroid glands. Conclusion: CRM rapidly revealed histological features of the parathyroid gland without histological processing. This new, simple, rapid and non-invasive technique has the potential for use as an adjunct to frozen-section analysis in intraoperative consultation during parathyroide... [ABSTRACT FROM AUTHOR]

Objectives: Optical coherence tomography (OCT) is a new technique for performing high-resolution, cross-sectional tomographic imaging in human tissue. OCT is somewhat analogous to ultrasound B mode imaging except that it uses light rather than acoustical waves. OCT has over 10 times the resolution of currently available clinical high-resolution imaging technologies. In this work, we investigate the capability of OCT to differentiate the architectural morphology of gastrointestinal tissue with the long-term objective of extending OCT to endoscopic based diagnostics. Methods: Normal and diseased gastrointestinal tissues were taken postmortem and imaged using OCT. Images were compared with corresponding histology to confirm tissue identity and suggest the mechanisms that produce tissue contrast Results: Microstructure was delineated in different tissues, including the esophagus and colon, at 16 ± 1 µm resolution, higher than any clinically available cross-sectional imaging technology. Differentiation of tissue layers, such as the mucosa, submucosa, and muscularis were achieved because of their different optical properties. Conclusions: The ability of OCT to provide high-resolution in situ imaging of gastrointestinal microstructure, without the need for excisional biopsy. suggests the feasibility of using OCT as a powerful diagnostic imaging technology, which can be integrated with conventional endoscopy. [ABSTRACT FROM AUTHOR]

We demonstrate a linear laser resonator incorporating a semiconductor optical amplifier and scanning filter for high repetition rate, broad wavelength, unidirectional scanning. The laser operates at up to 115 kHz repetition rates and demonstrates a tuning-speed-independent power of >30 mW. We apply this laser to enable ultrahigh-speed optical frequency domain imaging of the dynamics of laser ablation of biological tissue. The imaging system acquires single longitudinal scans (A-lines) in 8.7 μs and complete cross-sectional images comprising 575 A-lines at a rate of 200 frames per second. [ABSTRACT FROM AUTHOR]

A novel heterodyne Doppler interferometer method for compensating motion artifacts caused by cardiac motion in intracoronary optical frequency domain imaging (OFDI) is demonstrated. To track the relative motion of a catheter with regard to the vessel, a motion tracking system is incorporated with a standard OFDI system by using wavelength division multiplexing (WDM) techniques. Without affecting the imaging beam, dual WDM monochromatic beams are utilized for tracking the relative radial and longitudinal velocities of a catheter-based fiber probe. Our results demonstrate that tracking instantaneous velocity can be used to compensate for distortion in the images due to motion artifacts, thus leading to accurate reconstruction and volumetric measurements with catheter-based imaging.

Understanding pediatric voice development and laryngeal pathology is predicated on a detailed knowledge of the microanatomy of the layered structure of the vocal fold. Our current knowledge of this microanatomy and its temporal evolution is limited by the lack of pediatric specimen availability. By providing the capability to image pediatric vocal folds in vivo, a noninvasive microscopy technique could greatly expand the existing database of pediatric laryngeal microanatomy and could furthermore make longitudinal studies possible. A variety of natural-contrast optical imaging technologies, including optical frequency domain imaging (OFDI), full-field optical coherence microscopy (FF-OCM), and spectrally encoded confocal microscopy (SECM) have been recently developed for noninvasive diagnosis in adult patients. In this paper, we demonstrate the potential of these three techniques for laryngeal investigation by obtaining images of excised porcine vocal fold samples. In our study, OFDI allowed visualization of the vocal fold architecture deep within the tissue, from the superficial mucosa to the vocalis muscle. The micron-level resolution of SECM allowed investigation of cells and extracellular matrix fibrils from the superficial mucosa to the intermediate layer of the lamina propria (LP) (350 microm penetration depth). The large field of view (up to 700 microm), penetration depth (up to 500 microm), and resolution (2x2x1microm [XxYxZ]) of FF-OCM enabled comprehensive three-dimensional evaluation of the layered structure of the LP. Our results suggest that these techniques provide important and complementary cellular and structural information, which may be useful for investigating pediatric vocal fold maturation in vivo.

Spectral-domain optical coherence phase microscopy (SD-OCPM) measures minute phase changes in transparent biological specimens using a common path interferometer and a spectrometer based optical coherence tomography system. The Fourier transform of the acquired interference spectrum in spectral-domain optical coherence tomography (SD-OCT) is complex and the phase is affected by contributions from inherent random noise. To reduce this phase noise, knowledge of the probability density function (PDF) of data becomes essential. In the present work, the intensity and phase PDFs of the complex interference signal are theoretically derived and the optical path length (OPL) PDF is experimentally validated. The full knowledge of the PDFs is exploited for optimal estimation (Maximum Likelihood estimation) of the intensity, phase, and signal-to-noise ratio (SNR) in SD-OCPM. Maximum likelihood (ML) estimates of the intensity, SNR, and OPL images are presented for two different scan modes using Bovine Pulmonary Artery Endothelial (BPAE) cells. To investigate the phase accuracy of SD-OCPM, we experimentally calculate and compare the cumulative distribution functions (CDFs) of the OPL standard deviation and the square root of the Cramér-Rao lower bound (1/ square root 2SNR ) over 100 BPAE images for two different scan modes. The correction to the OPL measurement by applying ML estimation to SD-OCPM for BPAE cells is demonstrated.

The capability to image tissue motion such as blood flow through an endoscope could have many applications in medicine. Spectrally encoded endoscopy (SEE) is a recently introduced technique that utilizes a single optical fiber and miniature diffractive optics to obtain endoscopic images through small diameter probes. Using spectral-domain interferometry, SEE is furthermore capable of three-dimensional volume imaging at video rates. Here we show that by measuring relative spectral phases, this technology can additionally measure Doppler shifts. Doppler SEE is demonstrated in flowing Intralipid phantoms and vibrating middle ear ossicles.

Endoscopic imaging below tissue surfaces and through turbid media may provide improved diagnostic capabilities and visibility in surgical settings. Spectrally encoded endoscopy (SEE) is a recently developed method that utilizes a single optical fiber, miniature optics and a diffractive grating for high-speed imaging through small diameter, flexible endoscopic probes. SEE has also been shown to provide three-dimensional topological imaging capabilities. In this paper, we have configured SEE to additionally image beneath tissue surfaces, by increasing the system's sensitivity and acquiring the complex spectral density for each spectrally resolved point on the sample. In order to demonstrate the capability of SEE to obtain subsurface information, we have utilized the system to image a resolution target through intralipid solution, and conduct volumetric imaging of a mouse embryo and excised human middle-ear ossicles. Our results demonstrate that real-time subsurface imaging is possible with this miniature endoscopy technique.

Polarization sensitive optical coherence tomography (PS-OCT) provides a cross-sectional image of birefringence in biological samples that is complementary in many applications to the standard reflectance-based image. Recent ex vivo studies have demonstrated that birefringence mapping enables the characterization of collagen and smooth muscle concentration and distribution in vascular tissues. Instruments capable of applying these measurements percutaneously in vivo may provide new insights into coronary atherosclerosis and acute myocardial infarction. We have developed a polarization sensitive optical frequency domain imaging (PS-OFDI) system that enables high-speed intravascular birefringence imaging through a fiber-optic catheter. The novel design of this system utilizes frequency multiplexing to simultaneously measure reflectance of two incident polarization states, overcoming concerns regarding temporal variations of the catheter fiber birefringence and spatial variations in the birefringence of the sample. We demonstrate circular cross-sectional birefringence imaging of a human coronary artery ex vivo through a flexible fiber-optic catheter with an A-line rate of 62 kHz and a ranging depth of 6.2 mm.

We present a novel method for rapidly acquiring optical coherence tomography (OCT) images at multiple backscattering angles. By angularly compounding these images, high levels of speckle reduction were achieved. Signal-to-noise ratio (SNR) improvements of 3.4 dB were obtained from a homogeneous tissue phantom, which was in good agreement with the predictions of a statistical model of speckle that incorporated the optical parameters of the imaging system. In addition, the fast acquisition rate of the system (10 kHz A-line repetition rate) allowed angular compounding to be performed in vivo without significant motion artifacts. Speckle-reduced OCT images of human dermis show greatly improved delineation of tissue microstructure.

Recently, we have experimentally demonstrated a new form of cross-sectional, coherence-gated fluorescence imaging referred to as SD-FCT ('spectral-domain fluorescence coherence tomography'). Imaging in SD-FCT is accomplished by spectrally detecting self-interference of the spontaneous emission of fluorophores, thereby providing depth-resolved information on the axial positions of fluorescent probes. Here, we present a theoretical investigation of the factors affecting the detected SD-FCT signal through scattering media. An imaging equation for SD-FCT is derived that includes the effects of defocusing, numerical-aperture, and the optical properties of the medium. A comparison between the optical sectioning capabilities of SD-FCT and confocal microscopy is also presented. Our results suggest that coherence gating in fluorescence imaging may provide an improved approach for depth-resolved imaging of fluorescently labeled samples; high axial resolution (a few microns) can be achieved with low numerical apertures (NA<0.09) while maintaining a large depth of field (a few hundreds of microns) in a relatively low scattering medium (6 mean free paths), whereas moderate NA's can be used to enhance depth selectivity in more highly scattering biological samples.

Full-field optical coherence microscopy (FFOCM) utilizes coherence gating to obtain high-resolution optical sections in thick tissues. FFOCM is an attractive technology for endoscopic microscopy at the cellular level since it does not require a high NA objective lens or beam scanning and is therefore particularly amenable to miniaturization. In this manuscript, we present a novel scheme for conducting FFOCM that utilizes spectrally modulated, spatially incoherent illumination and a static Linnik interferometer. This approach is advantageous for endoscopic microscopy since it allows FFOCM to be conducted through a single multimode fiber optic imaging bundle and does not require moving parts in the endoscope probe. Images acquired from biological samples in free space demonstrate that this new method provides the same detailed microscopic structure as that of conventional FFOCM. High-resolution images were also obtained through a multimode fiber bundle, further supporting the potential of this method for endoscopic microscopy.

Speckle noise significantly limits the information content provided by coherent optical imaging methods such as optical coherence tomography and its recent derivative, optical frequency-domain imaging (OFDI). In this paper, we demonstrate a novel OFDI system that simultaneously acquires hundreds of angularly resolved images, which can be compounded to reduce speckle noise. The system comprises an InGaAs line-scan camera and an interferometer, configured so that the elements of the detector array simultaneously capture light spanning a backscattering angular range of 32 degrees. On successive read-outs of the array, the wavelength of the laser source was stepped through a range of 130 nm centered at 1295 nm to concurrently generate 400 angle-resolved OFDI images. A theory of angle-resolved OFDI and the design equations of the system are presented. Incoherent averaging of the angle-resolved data is shown to yield substantial speckle reduction (as high as an 8 dB SNR improvement) in images of a tissue phantom and esophageal tissue ex vivo.

Full-field optical coherence microscopy (FFOCM) is an interferometric technique for obtaining wide-field microscopic images deep within scattering biological samples. FFOCM has primarily been implemented in the 0.8 mum wavelength range with silicon-based cameras, which may limit penetration when imaging human tissue. In this paper, we demonstrate FFOCM at the wavelength range of 0.9 - 1.4 mum, where optical penetration into tissue is presumably greater owing to decreased scattering. Our FFOCM system, comprising a broadband spatially incoherent light source, a Linnik interferometer, and an InGaAs area scan camera, provided a detection sensitivity of 86 dB for a 2 sec imaging time and an axial resolution of 1.9 mum in water. Images of phantoms, tissue samples, and Xenopus Laevis embryos were obtained using InGaAs and silicon camera FFOCM systems, demonstrating enhanced imaging penetration at longer wavelengths.