In vivo endoscopic optical biopsy with optical coherence tomography

High resolution imaging of endometriosis and ovarian carcinoma with optical coherence tomography: feasibility for laparoscopic-based imaging

High resolution imaging of gynaecological tissue offers the potential for identifying pathological changes at early stages when interventions are more effective. Optical coherence tomography (OCT) is a high resolution high speed optical imaging technology which is analogous to ultrasound B-mode imaging except reflections of light are detected rather than sound. The OCT technology is capable of being integrated with laparoscopy for real-time subsurface imaging. In this report, the feasibility of OCT for differentiating normal and pathologic laparoscopically-accessible gynaecologic tissue is demonstrated. Differentiation is based on architectural changes of in vitro tissue morphology. OCT has the potential to improve conventional laparoscopy by enabling subsurface imaging near the level of histopathology.

Noninvasive imaging of human oral mucosa in vivo by confocal reflectance microscopy

OBJECTIVES/HYPOTHESIS

To study the microscopic anatomy of normal oral tissues in vivo using confocal reflectance microscopy (CRM). This novel and noninvasive imaging modality can define and characterize healthy oral mucosa and thus this work serves as the foundation for studying oral diseases in vivo.

STUDY DESIGN

This was a pilot observational cohort study comparing noninvasive CRM images with histology.

MATERIALS AND METHODS

Lip and tongue mucosa were imaged by CRM in six healthy human subjects. In CRM living tissue is illuminated by a laser source and backscattered (or reflected) light is collected by a detector. Image contrast is determined by natural differences in refractive indices of organelles and other subcellular structures within the tissues. Gray-scale images were displayed in real-time on a video monitor and represented horizontal (en face) optical sections through the tissue. Motion of the oral tissue relative to the objective lens was minimized with a tissue stabilizer. After imaging, biopsies were taken from the same site of lip mucosa to correlate noninvasive confocal images with conventional histology.

RESULTS

Confocal images correlated well with conventional histology, both qualitatively (visual analysis) and quantitatively (stereology). Imaging was possible up to depths of 490 and 250 microm in the lip and tongue, respectively. Cells and organelles including nuclei, circulating blood cells, and extracellular matrix were clearly observed.

CONCLUSION

CRM provides details of normal human oral mucosa at the cellular level without the artifacts of histological processing, and thus has the potential for further development and use in clinical practice as a diagnostic tool for the early detection of oral cancer and precancer.

High resolution in vivo intra-arterial imaging with optical coherence tomography

BACKGROUND

Optical coherence tomography (OCT) is a new method of catheter based micron scale imaging. OCT is analogous to ultrasound, measuring the intensity of backreflected infrared light rather than sound waves.

OBJECTIVE

To demonstrate the ability of OCT to perform high resolution imaging of arterial tissue in vivo.

METHODS

OCT imaging of the abdominal aorta of New Zealand white rabbits was performed using a 2.9 F OCT imaging catheter. Using an ultrashort pulse laser as a light source for imaging, an axial resolution of 10 micrometer was achieved.

RESULTS

Imaging was performed at 4 frames/second and data were saved in either super VHS or digital format. Saline injections were required during imaging because of the signal attenuation caused by blood. Microstructure was sharply defined within the arterial wall and correlated with histology. Some motion artefacts were noted at 4 frames/second.

CONCLUSIONS

In vivo imaging of the rabbit aorta was demonstrated at a source resolution of 10 micrometer, but required the displacement of blood with saline. The high resolution of OCT allows imaging to be performed near the resolution of histopathology, offering the potential to have an impact both on the identification of high risk plaques and the guidance of interventional procedures.

Combined scanning optical coherence and two-photon-excited fluorescence microscopy

We demonstrate simultaneous imaging by optical coherence microscopy (OCM) and two-photon-excited (TPE) fluorescence microscopy. A mode-locked Ti:sapphire laser is focused and scanned in three dimensions through a fixed sample, generating both backscattered light and fluorescence light, which are independently detected. Both imaging modes provide rapid en-face imaging with submicrometer resolution. High-power delivery into the sample yields an OCM sensitivity in excess of 130 dB at 100-kHz pixel rates. Simultaneous imaging of cell nuclei with OCM and TPE is demonstrated in live drosophila embryos.

Polarization Effects in Optical Coherence Tomography of Various Biological Tissues

Polarization sensitive optical coherence tomography (PS-OCT) was used to obtain spatially resolved ex vivo images of polarization changes in skeletal muscle, bone, skin and brain. Through coherent detection of two orthogonal polarization states of the signal formed by interference of light reflected from the biological sample and a mirror in the reference arm of a Michelson interferometer, the depth resolved change in polarization was measured. Inasmuch as any fibrous structure will influence the polarization of light, PS-OCT is a potentially powerful technique investigating tissue structural properties. In addition, the effects of single polarization state detection on OCT image formation is demonstrated.

Polarization Effects in Optical Coherence Tomography of Various Biological Tissues

Polarization sensitive optical coherence tomography (PS-OCT) was used to obtain spatially resolved ex vivo images of polarization changes in skeletal muscle, bone, skin and brain. Through coherent detection of two orthogonal polarization states of the signal formed by interference of light reflected from the biological sample and a mirror in the reference arm of a Michelson interferometer, the depth resolved change in polarization was measured. Inasmuch as any fibrous structure will influence the polarization of light, PS-OCT is a potentially powerful technique investigating tissue structural properties. In addition, the effects of single polarization state detection on OCT image formation is demonstrated.

High-resolution optical coherence tomography-guided laser ablation of surgical tissue

BACKGROUND

Optical coherence tomography (OCT) is a compact high-speed imaging technology which uses infrared light to acquire cross-sectional images of tissue on the micrometer scale. Because OCT images are based on the optical backscattering properties of tissue, changes in tissue optical properties due to surgical laser ablation should be detectable using this technique. In this work, we examine the feasibility of using real-time OCT imaging to guide the placement and observe the dynamics of surgical laser ablation in a variety of tissue types.

MATERIALS AND METHODS

More than 65 sites on five ex vivo rat organ tissue types were imaged at eight frames per second before, during, and after laser ablation. Ablation was performed with a coincident continuous wave argon laser operating at 514-nm wavelength and varying exposure powers and durations. Following imaging, tissue registration was achieved using microinjections of dye followed by routine histologic processing to confirm the morphology of the ablation site.

RESULTS

High-speed OCT imaging at eight frames per second permitted rapid tissue orientation and guided ablation in numerous organ specimens. Acquisition rates were fast enough to capture dynamic changes in optical backscatter which corresponded to thermal tissue damage during laser ablation.

CONCLUSIONS

The ability of high-resolution high-speed OCT to guide laser ablation and image the dynamic changes suggests a role in image-guided surgical procedures, such as the ablation of neoplasms. Future in vivo studies are necessary to demonstrate performance intraoperatively.

In vivo imaging of tumors with protease-activated near-infrared fluorescent probes

We have developed a method to image tumor-associated lysosomal protease activity in a xenograft mouse model in vivo using autoquenched near-infrared fluorescence (NIRF) probes. NIRF probes were bound to a long circulating graft copolymer consisting of poly-L-lysine and methoxypolyethylene glycol succinate. Following intravenous injection, the NIRF probe carrier accumulated in solid tumors due to its long circulation time and leakage through tumor neovasculature. Intratumoral NIRF signal was generated by lysosomal proteases in tumor cells that cleave the macromolecule, thereby releasing previously quenched fluorochrome. In vivo imaging showed a 12-fold increase in NIRF signal, allowing the detection of tumors with submillimeter-sized diameters. This strategy can be used to detect such early stage tumors in vivo and to probe for specific enzyme activity.

Early development of optical low-coherence reflectometry and some recent biomedical applications

This paper explains the term low-coherence interferometry, reviews the early development of optical low-coherence reflectometry, and shows some of the paths that led to the field of biomedical optics. This paper demonstrates that early technical developments in the telecommunications industry resulted in a myriad of technical implementations and applications in biology, medicine, and the explosion of the field in noninvasive biomedical optical techniques. Recent examples of innovative applications of this proliferating technology into the fields of ophthalmology, developmental biology, and endoscopy are described. © 1999 Society of Photo-Optical Instrumentation Engineers.

Early diagnosis of lung cancer

Recent advances in computer-assisted image analysis, tumor biology, PCR-based assays, fluorescence bronchoscopy, spiral CT, endobronchial treatment modalities, and chemoprevention make it possible to re-examine the strategy of early detection in the comprehensive management of lung cancer.

Diode-Pumped Cr:forsterite Laser Mode Locked by a Semiconductor Saturable Absorber

We report the passive mode locking of a diode-pumped Cr:forsterite laser using a semiconductor saturable absorber. The laser generates 10-pJ pulses as short as 1.5 ps in duration with ~650 mW of absorbed pump power. We measured the transient reflectance of the saturable absorber mirror under different incident energy fluences by using a standard pump-probe method. The performance of this laser is also compared with a high-power fiber-laser-pumped femtosecond forsterite laser mode locked with the same absorber.

Optical coherence tomography for neurosurgical imaging of human intracortical melanoma

OBJECTIVE

Intraoperative identification of brain tumors and tumor margins has been limited by either the resolution of the in vivo imaging technique or the time required to obtain histological specimens. Our objective was to evaluate the feasibility of using optical coherence tomography (OCT) as a high-resolution, real-time intraoperative imaging technique to identify an intracortical melanoma.

INSTRUMENTATION

OCT is a new, noncontact, high-speed imaging technology capable of resolutions on the micrometer scale. OCT is analogous to ultrasound B-mode imaging, except that reflections of infrared light, rather than sound, are detected. OCT uses inherent tissue contrast, rather than enhancement with dyes, to differentiate tissue types. The compact, fiberoptic-based design is readily integrated with surgical instruments.

METHODS

A portable handheld OCT surgical imaging probe has been constructed for imaging within the surgical field. Cadaveric human cortex with metastatic melanoma was harvested and imaged in two and three dimensions. Changes in optical backscatter intensity were used to identify regions of tumor and to locate tumor margins. Structures within the optical coherence tomographic images were compared with the histological slides.

RESULTS

Two-dimensional images showed increased optical backscatter from regions of tumor, which was quantitatively used to determine the tumor margin. The images correlated well with the histological findings. Three-dimensional reconstructions revealed regions of tumor penetrating normal cortex and could be resectioned at arbitrary planes. Subsurface cerebral vascular structures could be identified and were therefore avoided.

CONCLUSION

OCT can effectively differentiate normal cortex from intracortical melanoma based on variations in optical backscatter. The high-resolution, high-speed imaging capabilities of OCT may permit the intraoperative identification of tumor and the more precise localization of tumor margins.

In vivo OCT imaging of hard and soft tissue of the oral cavity

We use optical coherence tomography (OCT) to perform a comprehensive program of in vivo and in vitro structural imaging of hard and soft tissues within the oral cavity. We have imaged the different types of healthy oral mucosa as well as normal and abnormal tooth structure. OCT is able to differentiate between the various types of keratinized and non-keratinized mucosa with high resolution. OCT is also able to provide detailed structural information on clinical abnormalities (caries and non-caries lesions) in teeth and provide guidance in dental restorative procedures. Our investigations demonstrate the utility of OCT as a diagnostic imaging modality in clinical and research dentistry.

In vivo video rate optical coherence tomography

An optical coherence tomography system is described which can image up to video rate. The system utilizes a high power broadband source and real time image acquisition hardware and features a high speed scanning delay line in the reference arm based on Fourier-transform pulse shaping technology. The theory of low coherence interferometry with a dispersive delay line, and the operation of the delay line are detailed and the design equations of the system are presented. Real time imaging is demonstrated in vivo in tissues relevant to early human disease diagnosis (skin, eye) and in an important model in developmental biology (Xenopus laevis).

Ice-Front Propagation Monitoring in Tissue by the use of Visible-Light Spectroscopy

For demonstrating that visible-light spectroscopy can be used for ice-front detection within freezing tissue, proton magnetic resonance images were correlated to time-evolving transmittance spectra as an ice front progressed across a tissue sample. The experimental apparatus was designed to be compatible with magnetic resonance imaging, to produce one-dimensional freezing, and to allow both reflectance and transillumination emitter-detector configurations about a normally progressing planar ice front in chicken muscle. This demonstration has potentially important medical applications in cryopreservation (freezing of biological materials for preservation) and cryosurgery (destruction of tissue by freezing).

Two- and three-dimensional high-resolution imaging of the human oviduct with optical coherence tomography

OBJECTIVE

To evaluate the feasibility of optical coherence tomography, a new method of micron-scale imaging, for high-resolution assessment of the oviduct. Optical coherence tomography is analogous to ultrasound except that it measures the backreflection of infrared light rather than acoustical waves.

DESIGN

The ampulla of a human fallopian tube was imaged in vitro using optical coherence tomography. Images were generated in 2 and 3 dimensions.

SETTING

University.

PATIENT(S)

Samples were obtained from women who had undergone hysterectomy for leiomyomatosis.

INTERVENTION(S)

None

MAIN OUTCOME MEASURE(S)

The ability to perform imaging on a micron scale, which is a level of resolution higher than that of any currently available clinical technology.

RESULT(S)

Two- and three-dimensional data sets of the reflectance of a human fallopian tube were acquired. A volume of 5 x 5 x 2.5 mm (length x width x depth) was scanned. The axial resolution was 11 microm, and the lateral resolution at the focus was 20 microm. The data sets showed detailed structures of the fallopian tube.

CONCLUSION(S)

Our ability to obtain micron-scale two- and three-dimensional images of an in vitro oviduct suggests that it may be possible to identify and surgically treat tubal causes of infertility.

High-resolution cross-sectional imaging of the gastrointestinal tract using optical coherence tomography: preliminary results

BACKGROUND

Optical coherence tomography (OCT) is a novel technique for noninvasive cross-sectional imaging with high spatial resolution (10 to 20 microm). OCT is similar to B-mode ultrasound except that it uses infrared light rather than ultrasound. We studied OCT imaging of the gastrointestinal (GI) tract in vitro to analyze the potential of this technique for endoscopic applications.

METHODS

Human gastrointestinal tissues harvested from surgical resection and autopsy specimens were used. Specimens were imaged within 5 hours of resection or snap frozen in liquid nitrogen. After imaging, OCT scan locations were carefully marked using dye microinjections, fixed, and prepared for routine histologic processing. OCT images were then compared and correlated with the histologic sections.

RESULTS

OCT images demonstrated clear delineation of the mucosa and submucosa in most specimens. Furthermore, microscopic structures such as crypts, blood vessels, or esophageal glands in the submucosa and lymphatic nodules were observed.

CONCLUSIONS

The resolution of OCT images of GI wall is sufficient to delineate the microscopic structure of the mucosa and submucosa. Potentially, OCT would allow in vivo imaging at endoscopy of the microstructure of the mucosa and submucosa. This would be particularly useful in the detection and staging of small lesions such as early stage cancers.

Mechanisms of light scattering from biological cells relevant to noninvasive optical-tissue diagnostics

We have studied the optical properties of mammalian cell suspensions to provide a mechanistic basis for interpreting the optical properties of tissues in vivo. Measurements of the wavelength dependence of the reduced scattering coefficient and measurements of the phase function demonstrated that there is a distribution of scatterer sizes. The volumes of the scatterers are equivalent to those of spheres with diameters in the range between ~0.4 and 2.0 mum. Measurements of isolated organelles indicate that mitochondria and other similarly sized organelles are responsible for scattering at large angles, whereas nuclei are responsible for small-angle scattering. Therefore optical diagnostics are expected to be sensitive to organelle morphology but not directly to the size and shape of the cells.

High resolution imaging of the upper respiratory tract with optical coherence tomography: a feasibility study

A need exists in respiratory medicine for a technology capable of identifying airway pathology on a micron scale. This study has demonstrated the feasibility of optical coherence tomography (OCT) for ultrahigh resolution imaging of the upper respiratory tract by in vitro studies of human tissue. OCT is a relatively new technique that can be used to noninvasively collect tomographic images of tissue microstructure with micron-scale resolution. OCT is analogous to ultrasound, measuring the intensity of infrared light rather than acoustical waves. Samples throughout the upper respiratory tract, from the epiglottis to the secondary bronchi, were imaged. The resulting images were compared with histopathology and verified the ability of OCT to delineate relevant structures such as the epithelium, mucosa, cartilage and its sublayers, and glands at a resolution higher than any clinical imaging technology. The ability of OCT to generate image resolution in the range close to that of histopathology in real time, as well as easy integration with small, relatively inexpensive endoscopes, low cost, and lack of a need for a transducing medium, supports the hypothesis that this optical technology could become a powerful modality in the diagnosis and management of a wide range of clinical respiratory pathology.

Optical scattering properties of soft tissue: a discrete particle model

We introduce a micro-optical model of soft biological tissue thatpermits numerical computation of the absolute magnitudes of itsscattering coefficients. A key assumption of the model is that therefractive-index variations caused by microscopic tissue elements canbe treated as particles with sizes distributed according to a skewedlog-normal distribution function. In the limit of an infinitelylarge variance in the particle size, this function has the samepower-law dependence as the volume fractions of the subunits of anideal fractal object. To compute a complete set of opticalcoefficients of a prototypical soft tissue (single-scatteringcoefficient, transport scattering coefficient, backscatteringcoefficient, phase function, and asymmetry parameter), we apply Mietheory to a volume of spheres with sizes distributed according to thetheoretical distribution. A packing factor is included in thecalculation of the optical cross sections to account for correlatedscattering among tightly packed particles. The results suggest thatthe skewed log-normal distribution function, with a shape specified bya limiting fractal dimension of 3.7, is a valid approximation of thesize distribution of scatterers in tissue. In the wavelength range 600 </= lambda </= 1400 nm, the diameters of the scatterers thatcontribute most to backscattering were found to be significantlysmaller (lambda/4-lambda/2) than the diameters of the scatterersthat cause the greatest extinction of forward-scattered light(3-4lambda).

In vivo detection of experimentally induced cortical dysgenesis in the adult rat neocortex using optical coherence tomography

Imaging cerebral structure in vivo can be accomplished by many methods, including MRI, ultrasound, and computed tomography. Each offers advantages and disadvantages with respect to the others, but all are limited in spatial resolution to millimeter-scale features when used in routine applications. Optical coherence tomography (OCT) is a new, high resolution imaging technique which uses light to directly image living tissue. Here, we investigate the potential use of OCT for structural imaging of the fully developed mammalian cerebral cortex. In particular, we show that OCT can perform in vivo detection of neocortex and differentiate normal and abnormal cortical anatomy. We present the results of detailed optical coherence tomographic (OCT) observations of both normal and abnormal rat neocortex obtained in vivo. Comparative histologic analysis shows excellent correlation with the OCT tomograms.

Full-field optical coherence microscopy

We present a new microscopy system for imaging in turbid media that is based on the spatial coherence gate principle and generates in parallel a complete two-dimensional head-on image without scanning. This system has been implemented in a commercial microscope and preserves the lateral resolution of the optics used. With a spatially incoherent source, speckle-free images with diffraction-limited resolution are recorded at successive depths with shot-noise-limited detection. The setup comprises a photoelastic modulator for path difference modulation and a two-dimensional CCD array and uses a multiplexed lock-in detection scheme.

Optical biopsy with optical coherence tomography

A need exists in medicine for a technology capable of 'optical biopsy,' imaging at or near the resolution of histopathology without the need for excisional biopsy. Optical coherence tomography (OCT) is a recently developed imaging technology that uses infrared light to generate cross-sectional images on a micron scale. In this work, the feasibility of OCT for optical biopsy was confirmed with in vitro tissue from the skeletal and male reproductive systems. This work supports the hypothesis that OCT is an attractive technology for in vivo optical biopsy.

Femtosecond Cr:forsterite laser diode pumped by a double-clad fiber

We present a compact, all-solid-state femtosecond Cr:forsterite laser. The laser is pumped by diodes through a double-clad fiber. Kerr-lens mode locking is initiated and stabilized by a semiconductor saturable-absorber mirror with a single InGaAs quantum well. This system generates transform-limited 80-fs pulses near 1.3microm . An average power of 68 mW with fluctuation of much less than 1% is obtained with 3.8 W of absorbed pump power. The stability, efficiency, compactness, and potential for scaling to higher power of this system make it an attractive short-pulse source for applications.

High resolution imaging of in vivo cardiac dynamics using color Doppler optical coherence tomography

Color Doppler optical coherence tomography (CDOCT) is a noninvasive technique for simultaneous high spatial resolution (~20 aem) imaging and high velocity resolution (~500 aem/s) imaging flowmetry in living tissues. In this paper, we demonstrate a reconstruction method which overcomes fundamental limitations on Doppler flow mapping associated with both high- and low-speed imaging. This algorithm is successful in retaining the high velocity resolution of CDOCT while eliminating motion artifact caused by slow image acquisition in samples which exhibit repetitive motion. We demonstrate reconstruction of blood flow throughout a beating Xenopus laevis heart and surrounding vasculature using gated CDOCT reconstruction.

High-speed phase- and group-delay scanning with a grating-based phase control delay line

A rapid-scanning optical delay line that employs phase control has several advantages, including high speed, high duty cycle, phase- and group-delay independence, and group-velocity dispersion compensation, over existing optical delay methods for interferometric optical ranging applications. We discuss the grating-based phase-control delay line and its applications to interferometric optical ranging and measurement techniques such as optical coherence domain reflectometry and optical coherence tomography. The system performs optical ranging over an axial range of 3 mm with a scanning rate of 6m/s and a repetition rate of 2 kHz. The device is especially well suited for applications such as optical coherence tomography that require high-speed, repetitive, linear delay line scanning with a high duty cycle.

Cr:forsterite laser pumped by broad-area laser diodes

We report the demonstration of a Cr:forsterite laser pumped by broad-area laser diodes producing non-diffraction-limited beams. The use of a thin crystal to reduce losses at the lasing wavelength and of short-wavelength pump diodes reduces the lasing threshold to <500 mW .Relatively low output powers (5 mW) are obtained, but prospects for increasing the power and achieving mode-locked operation of this laser are good and are discussed.