KEYWORDS: Oxygen, Photoacoustic spectroscopy, Echocardiography, In vivo imaging, Arteries, Acoustics, Lithium, Picture Archiving and Communication System, Oximetry
Mixed venous oxygen saturation (SvO2), measured from pulmonary arteries, is a gold-standard measure of the dynamic balance between the oxygen supply and demand in the body. In critical care, continuous monitoring of SvO2 plays a vital role in early detection of circulatory shock and guiding goal-oriented resuscitation. In current clinical practice, SvO2 is measured by invasive pulmonary artery catheters (PAC), which are associated with a 10% risk of severe complications. To address the unmet clinical need for a non-invasive SvO2 monitor, we are developing a new technology termed photoacoustic transesophageal echocardiography (PA-TEE). PA-TEE integrates transesophageal echocardiography with photoacoustic oximetry, and enables continuous assessment of SvO2 through an esophageal probe that can be inserted into the body in a minimally invasive manner.
We have constructed a clinically translatable PA-TEE prototype, which features a mobile OPO laser, a modified ultrasonography console and a dual-modality esophageal probe. Comprised of a rotatable acoustic array detector, a flexible optical fiber bundle and a light-integrating acoustic lens, the oximetric probe has an outer diameter smaller than 15 mm and will be tolerable for most patients. Through custom-made C++/Qt software, our device acquires and displays ultrasonic and photoacoustic images in real time to guide the deployment of the probe. SvO2 is calculated on-line and updated every second. PA-TEE has now been used to evaluate SvO2 in living swine. Our findings show that changing the fraction of oxygen in the inspired gas modulates SvO2 measured by PA-TEE. Statistic comparison between SvO2 measurements from PA-TEE in vivo the gold-standard laboratorial analysis on blood samples drawn from PACs will be presented.
Excisional biopsy is the current gold standard for disease diagnosis; however, it requires a relatively long processing
time and it may also suffer from unacceptable false negative rates due to sampling errors. Optical coherence tomography
(OCT) is a promising imaging technique that provide real-time, high resolution and three-dimensional (3D) images of
tissue morphology. Optical coherence microscopy (OCM) is an extension of OCT, combining both the coherence gating
and the confocal gating techniques. OCM imaging achieves cellular resolution with deeper imaging depth compared to
confocal microscopy. An integrated OCT/OCM imaging system can provide co-registered multiscale imaging of tissue
morphology. 3D-OCT provides architectural information with a large field of view and can be used to find regions of
interest; while OCM provides high magnification to enable cellular imaging. The integrated OCT/OCM system has an
axial resolution of <4um and transverse resolutions of 14um and <2um for OCT and OCM, respectively. In this study, a
wide range of human pathologic specimens, including colon (58), thyroid (43), breast (34), and kidney (19), were
imaged with OCT and OCM within 2 to 6 hours after excision. The images were compared with H & E histology to
identify characteristic features useful for disease diagnosis. The feasibility of visualizing human pathology using
integrated OCT/OCM was demonstrated in the pathology laboratory settings.
We evaluate the feasibility of optical coherence tomography (OCT) and optical coherence microscopy (OCM)
for imaging of benign and malignant thyroid lesions ex vivo using intrinsic optical contrast. Thirty four
thyroid gland specimens were imaged from 17 patients, covering a spectrum of pathology, ranging from
normal thyroid to neoplasia and benign disease. The integrated OCT and OCM imaging system allows
seamlessly switching between low and high magnifications, in a way similar to traditional microscopy. Good
correspondence was observed between optical images and histological sections. The results provide a basis for
interpretation of future OCT and OCM images of the thyroid tissues and suggest the possibility of future in
vivo evaluation of thyroid pathology.
Optical coherence microscopy (OCM) combines confocal microscopy and optical coherence tomography (OCT) to improve imaging depth and contrast, enabling cellular imaging in human tissues. We aim to investigate OCM for ex vivo imaging of upper and lower gastrointestinal tract tissues, to establish correlations between OCM imaging and histology, and to provide a baseline for future endoscopic studies. Co-registered OCM and OCT imaging were performed on fresh surgical specimens and endoscopic biopsy specimens, and images were correlated with histology. Imaging was performed at 1.06-µm wavelength with <2-µm transverse and <4-µm axial resolution for OCM, and at 14-µm transverse and <3-µm axial resolution for OCT. Multiple sites on 75 tissue samples from 39 patients were imaged. OCM enabled cellular imaging of specimens from the upper and lower gastrointestinal tracts over a smaller field of view compared to OCT. Squamous cells and their nuclei, goblet cells in Barrett's esophagus, gastric pits and colonic crypts, and fine structures in adenocarcinomas were visualized. OCT provided complementary information through assessment of tissue architectural features over a larger field of view. OCM may provide a complementary imaging modality to standard OCT approaches for endoscopic microscopy.
We evaluate the feasibility of optical coherence tomography (OCT) and optical coherence microscopy (OCM) for imaging of benign and malignant thyroid lesions ex vivo using intrinsic optical contrast. 34 thyroid gland specimens are imaged from 17 patients, covering a spectrum of pathology ranging from normal thyroid to benign disease/neoplasms (multinodular colloid goiter, Hashimoto's thyroiditis, and follicular adenoma) and malignant thyroid tumors (papillary carcinoma and medullary carcinoma). Imaging is performed using an integrated OCT and OCM system, with <4 µm axial resolution (OCT and OCM), and 14 µm (OCT) and <2 µm (OCM) transverse resolution. The system allows seamless switching between low and high magnifications in a way similar to traditional microscopy. Good correspondence is observed between optical images and histological sections. Characteristic features that suggest malignant lesions, such as complex papillary architecture, microfollicules, psammomatous calcifications, or replacement of normal follicular architecture with sheets/nests of tumor cells, can be identified from OCT and OCM images and are clearly differentiable from normal or benign thyroid tissues. With further development of needle-based imaging probes, OCT and OCM could be promising techniques to use for the screening of thyroid nodules and to improve the diagnostic specificity of fine needle aspiration evaluation.
We report an imaging study using integrated 3D-OCT and OCM for the assessment of various human thyroid and breast pathologies. The 3D-OCT data sets enable en face projection imaging, which provides large field of view with uniform focus and signal level, while OCM provides high magnification that enables cellular resolution imaging. We have demonstrated that the integrated 3D-OCT and OCM technology provide a substantial improvement over standard OCT for the visualization of tissue pathology and can serve as a useful imaging tool in the clinical settings.
Optical coherence tomography (OCT) is an emerging medical imaging technology that enables high-resolution, noninvasive, cross-sectional imaging of microstructure in biological tissues in situ and in real time. When combined with small-diameter catheters or needle probes, OCT offers a practical tool for the minimally invasive imaging of living tissue morphology. We evaluate the ability of OCT to image normal kidneys and discriminate pathological changes in kidney structure. Both control and experimental preserved rat kidneys were examined ex vivo by using a high-resolution OCT imaging system equipped with a laser light source at 1.3-µm wavelength. This system has a resolution of 3.3 µm (depth) by 6 µm (transverse). OCT imaging produced cross-sectional and en face images that revealed the sizes and shapes of the uriniferous tubules and renal corpuscles. OCT data revealed significant changes in the uriniferous tubules of kidneys preserved following an ischemic or toxic (i.e., mercuric chloride) insult. OCT data was also rendered to produce informative three-dimensional (3-D) images of uriniferous tubules and renal corpuscles. The foregoing observations suggest that OCT can be a useful non-excisional, real-time modality for imaging pathological changes in donor kidney morphology prior to transplantation.
Optical coherence tomography (OCT) is an emerging technology for micrometer-scale, cross-sectional imaging of biological tissue and materials. One of the key limitations to achieving ultrahigh-resolution OCT imaging outside the laboratory setting has been the lack of compact, high-performance broadband light sources with sufficient power and stability to allow practical real-time imaging.
The broad-bandwidth supercontinuum (SC) sources were recently demonstrated with femtosecond lasers in combination with nonlinear fibers. Using SC, we can demonstrate ultrahigh resolution OCT. However, wideband SC generally has large excess noise and significant fine structure. Low noise and smooth spectral shape are desired in the
ideal supercontinnum source. In this paper, we describe recent studies on practical SC generation for ultrahigh-resolution OCT. SC generation is first analyzed both numerically and experimentally in terms of OCT imaging requirements and optimized conditions for
generation are discussed. Supercontinua generated by use of highly nonlinear fiber which have a zero-dispersion wavelength near the pump wavelength, generally result in severe spectral modulation and fluctuating fine structure in the spectra. This spectral modulation produces sidelobes and reduced contrast in the interferometric point-spread function. In contrast, normally dispersive, highly nonlinear fibers (ND-HNFs) can generate smooth and Gaussian shaped supercontinua by the combination of self-phase modulation and normal dispersion. Low noise and wideband SC generation is demonstrated using ND-HNFs. Two colored SC generation is also demonstrated using a photonic crystal fiber which has two close zero dispersion wavelengths. The numerical results are almost in agreement with the
experimental ones. Finally, low noise SC generation is demonstrated in an all fiber system based on an ultrashort pulse fiber laser. Wideband, low noise, near Gaussian shaped, high power SC is generated in the 1.55 μm wavelength region. In vivo, high-speed OCT imaging of human skin with ~5.5 μm resolution and 99 dB sensitivity is demonstrated.
Simultaneous optical coherence tomography (OCT) and video microscopy were performed on the rat somatosensory
cortex through a thinned skull during forepaw stimulation. Fractional change measurements in OCT images reveal a
functional signal timecourse similar to well understood hemodynamic signal timecourses measured with video
microscopy. The precise etiology of the observed OCT functional signal is still under investigation, but these results
suggest that OCT can provide high-resolution cross-sectional images of functional neuro-vascular activation.
Optical coherence tomography (OCT) is an emerging medical imaging technology which can generate high resolution, cross-sectional images of tissue in situ and in real time, without the removal of tissue specimen. Although endoscopic OCT has been used successfully to identify certain pathologies in the gastrointestinal tract, the resolution of current endoscopic OCT systems has been limited to 10-15 um for clinical procedures. In this study, in vivo imaging of the gastrointestinal tract is demonstrated at a three-fold higher axial resolution (<5 um), using a portable, broadband, Cr4+:Forsterite laser as the optical light source. Images acquired from the esophagus and colon on animal model display tissue microstructures and architectural details at ultrahigh resolution, and the features observed in the OCT images are well-matched with histology. The clinical feasibility study is conducted through delivering OCT imaging catheter using the standard endoscope. OCT images of normal esophagus and Barrett's esophagus are demonstrated with distinct features.
This paper reports preliminary results from the development and application of a two-dimensional MEMS endoscopic scanner for OCT imaging. A 1 mm diameter mirror provides high aperture over large scan angle and can scan at rates of hundreds of Hz in both axes. The mirror is integrated with focusing optics and a fiber-optic collimator into a package of ~5 mm diameter. Using a broadband femtosecond laser light source, ultrahigh axial image resolution of < 5 um in tissue is achieved at 1.06 um center wavelength. Ultrahigh resolution cross-sectional and three-dimensional OCT imaging is demonstrated with the endoscope with ~12 um transverse resolution and < 5 um axial resolution.
Three-dimensional imaging is achieved by optical coherence tomography (OCT) integrated with a two-axis MEMS scanner to enable noninvasive volume imaging of biological tissues. The longitudinal scan is obtained by optical coherence interferometry. The transverse scan is obtained by tilting the two-axis MEMS mirror to scan the optical beam across the target. High-resolution OCT imaging has enabled in vivo observation of tissue architectural layers and differentiation of normal from tumor lesions within the human gastrointestinal tract. MEMS scanner based catheters with distal beam scanning can image with higher speed, precision, and repeatability than conventional linear scanning catheters. In this work, a 1-mm diameter MEMS scanning mirror with collimator and focusing optics is integrated into a compact 5-mm diameter package that is compatible with limited space in the endoscope. A large fill factor mirror provides high aperture over large scan angle and frequencies of hundreds of Hz in both axes. Using a broadband femtosecond laser light source, high axial image resolution of ~5 um is achieved at 1.06 um wavelength. Transverse resolution of ~ 12-um is demonstrated for cross-sectional image with the endoscope.
Early detection of gastrointestinal cancer is essential for the patient treatment and medical care. Endoscopically guided biopsy is currently the gold standard for the diagnosis of early esophageal cancer, but can suffer from high false negative rates due to sampling errors. Optical coherence tomography (OCT) is an emerging medical imaging technology which can generate high resolution, cross-sectional images of tissue in situ and in real time, without the removal of tissue specimen. Although endoscopic OCT has been used successfully to identify certain pathologies in the gastrointestinal tract, the resolution of current endoscopic OCT systems has been limited to 10 - 15 m for clinical procedures. In this study, in vivo imaging of the gastrointestinal tract is demonstrated at a three-fold higher resolution (< 5 m), using a portable, broadband, Cr4+:Forsterite laser as the optical light source. Images acquired from the esophagus, gastro-esophageal junction and colon on animal model display tissue microstructures and architectural details at high resolution, and the features observed in the OCT images are well-matched with histology. The clinical feasibility study is conducted through delivering OCT imaging catheter using standard endoscope. OCT images of normal esophagus, Barrett's esophagus, and esophageal cancers are demonstrated with distinct features. The ability of high resolution endoscopic OCT to image tissue morphology at an unprecedented resolution in vivo would facilitate the development of OCT as a potential imaging modality for early detection of neoplastic changes.
We demonstrate methods for achieving high resolution imaging using alternate scanning techniques in optical coherence tomography and optical coherence microscopy. These techniques enable high transverse resolutions and overcome depth of field limitations. Cellular level resolutions in human tissue may be achieved.
KEYWORDS: Optical coherence tomography, In vivo imaging, Image resolution, Imaging systems, Femtosecond phenomena, Neodymium glass lasers, Light sources, Single mode fibers, Skin, Real time imaging
We demonstrate compact ultrahigh resolution OCT systems for in vivo studies, with broadband light sources based on a commercially available Nd:Glass femtosecond laser and nonlinear fiber continuum generation. In vivo OCT images of hamster cheek pouch and human skin acquired at 4 frames per second and with 5.5 μm axial resolution are presented. These systems are robust, compact and portable.
Ultrahigh resolution OCT imaging is demonstrated using compact broadband light sources based on a commercially available Nd:Glass femtosecond laser with nonlinear fiber continuum generation. A tapered single mode fiber is used to generate broadband light centered at 1300 nm. Broadband light near 1064 nm can also be generated using a high numerical aperture single mode germanium doped fiber. These light sources enable ultrahigh resolution OCT imaging with 5-6 μm axial resolution at both 1064 nm and 1300 nm.
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