Biomedical subjects

Zhongping Chen

Publications and source records attributed to Zhongping Chen.

36 records · Page 2Linked to original sources

PubMed2004

Dynamic morphology of sutureless cataract wounds--effect of incision angle and location.

OBJECTIVE: Sutureless cataract surgery has been growing in popularity over the last decade. These clear corneal incisions allow for rapid visual recovery after phacoemulsification, but may be associated with an increased risk of endophthalmitis. The purpose of this study was to evaluate the effect of intraocular pressure (IOP), location, and angle of cataract incisions on wound apposition and sealing in postmortem globes. METHODS: This was an ex vivo laboratory investigation of 20 rabbit eyes and 14 human eyes. Self-sealing clear corneal, limbal, and scleral incisions were created and IOP was controlled with an infusion cannula. Incisions were made at a variety of angles. Optical coherence tomography was used to image the incisions in real time as the IOP was varied by raising and lowering the infusion bottle, so as to simulate the variation in IOP occurring with blinking or squeezing of the eye. RESULTS: With each type of incision, optical coherence tomography demonstrated the dynamic nature of cataract wound morphology as IOP was varied. Higher IOPs, in general, were associated with more tightly sealed wounds than lower IOPs, but this varied according to the location and angle of the incisions. More perpendicular incisions, relative to the surface tangent, sealed less well than incisions created at smaller angles at higher levels of IOP; At lower IOPs, the reverse relationship was observed such that more perpendicular incisions sealed less well than smaller incision angles. CONCLUSION: Changes in IOP may result in variable and sometime poor wound apposition in sutureless cataract incisions. The type of incision and angle of the incision may affect the likelihood of inoculation of the aqueous humor with potentially pathogenic bacteria. For each type of incision, there may be a critical angle at which the incision is better able to withstand fluctuations in IOP.

Animals↗

PubMed2003

Ultrahigh-resolution optical coherence tomography by broadband continuum generation from a photonic crystal fiber.

We have developed an ultrahigh-resolution optical coherence tomographic system in which broadband continuum generation from a photonic crystal fiber is used to produce high longitudinal resolution. Longitudinal resolution of 1.3-microm has been achieved in a biological tissue by use of continuum light from 800 to 1400 nm. The system employed a dynamic-focusing tracking method to maintain high lateral resolution over a large imaging depth. Subcellular imaging is demonstrated.

Animals↗

PubMed2003

Dynamic morphology of clear corneal cataract incisions.

OBJECTIVE: Clear corneal cataract incisions without sutures allow for rapid visual rehabilitation after phacoemulsification but might be associated with an increased risk of postoperative infection. The goal of this study was to examine in vitro dynamic changes in unhealed clear corneal cataract incisions that might adversely affect the risk of intraocular infection. DESIGN: Laboratory investigation. METHODS: Self-sealing clear corneal incisions were created in cadaveric human and rabbit eyes, and intraocular pressure was controlled with an infusion cannula. Incisions were imaged in real time using optical coherence tomography as intraocular pressure was varied. Using an artificial anterior chamber, India ink was applied to the surface of cadaveric human corneas with clear corneal incisions to detect possible flow of surface fluid along the incision. Intraocular pressure was varied by raising and lowering the infusion bottle so as to simulate the variation in intraocular pressure that would occur with successive blinks. RESULTS: Optical coherence tomography demonstrated variation of corneal wound morphology in response to changes in intraocular pressure. Higher intraocular pressures were associated with close apposition of the wound edges, with no tendency for wound leakage. At low intraocular pressures, however, wound edges tended to gape, starting at the internal aspect of the wound. One incision opened along the entire length, allowing fluid flow across the cornea. Histologic examination revealed India ink particles in all incisions for up to three fourths of the length of the wound. CONCLUSIONS: Transient reduction of intraocular pressure might result in poor wound apposition in clear corneal incisions, with the potential for fluid flow across the cornea and into the anterior chamber, with the attendant risk of endophthalmitis.

Animals↗

PubMed2003

Enhancing alkylating agent resistance through ERCC2 gene transfection in human glioma cell line.

OBJECTIVE: To confirm the enhancing effect of excision repair cross complementing rodent repair deficiency gene 2 (ERCC2) on alkylating agents resistance. METHODS: The authors constructed a pcDNA3-ERCC2 plasmid. The pcDNA3-ERCC2 was transfected into a selected ERCC2 negative human glioma cell line, SKMG-4, using liposome-mediated transfection. After G418 selection, a stable transfected cell line was obtained and tested for cytotoxicity of several alkylating agents. RESULTS: The stable transfectant was obtained and confirmed by RT-PCR as well as Western blot analysis to be strongly expressing ERCC2 at both mRNA and protein levels. The IC(90) ( micro mol/L) of two alkylating agents, cisplatin and melphalan, increased from 1.0 to 1.75 (75%) and 5.6 to 9.0 (61%), respectively, compared with control cell line. CONCLUSION: The present data provided evidences and confirmed the authors' previous results that ERCC2 contributes, at least partially, to alkylating agent resistance in human glioma cell line.

Antineoplastic Agents, Alkylating↗

PubMed2002

Clinical testing of a photoacoustic probe for port wine stain depth determination.

BACKGROUND AND OBJECTIVE: Successful laser treatment of port wine stain (PWS) birthmarks requires knowledge of lesion geometry. Laser parameters, such as pulse duration, wavelength, and radiant exposure, and other treatment parameters, such as cryogen spurt duration, need to be optimized according to epidermal melanin content and lesion depth. We designed, constructed, and clinically tested a photoacoustic probe for PWS depth determination. STUDY DESIGN/MATERIALS AND METHODS: Energy from a frequency-doubled, Nd:YAG laser (lambda=532 nm, tau(p)=4 nanoseconds) was coupled into two 1,500 mum optical fibers fitted into an acrylic handpiece containing a piezoelectric acoustic detector. Laser light induced photoacoustic waves in tissue phantoms and a patient's PWS. The photoacoustic propagation time was used to calculate the depth of the embedded absorbers and PWS lesion. RESULTS: Calculated chromophore depths in tissue phantoms were within 10% of the actual depths of the phantoms. PWS depths were calculated as the sum of the epidermal thickness, determined by optical coherence tomography (OCT), and the epidermal-to-PWS thickness, determined photoacoustically. PWS depths were all in the range of 310-570 microm. The experimentally determined PWS depths were within 20% of those measured by optical Doppler tomography (ODT). CONCLUSIONS: PWS lesion depth can be determined by a photoacoustic method that utilizes acoustic propagation time.

Dermatology↗

PubMedDate not supplied

In vitro measurement of rabbit corneal epithelial thickness using ultrahigh resolution optical coherence tomography.

The objective of this study was to reproducibly measure corneal epithelial thickness centrally and at the limbus in the rabbit cornea using ultrahigh resolution optical coherence tomography (OCT). Twelve freshly enucleated New Zealand white rabbit eyes were kept in a moist chamber at 4 degrees C. An ultrahigh resolution OCT system with a spatial resolution of 1.3 microm was used to image the cornea and its component layers. The central and peripheral (limbal) regions of all the samples were scanned within 6 h of harvest in order to minimize the post-mortem degradation of the corneal epithelium. The thickness of the corneal epithelium was determined by measuring the pixel equivalents of the obtained image. Unpaired Student's t-test was used to evaluate differences. The epithelial thickness centrally was found to be 45.8 +/- 2.2 microm, and 37.6 +/- 1.4 microm at the limbus (P < 0.001). Rabbit corneal epithelium is thicker centrally than at the limbus when measured by ultrahigh resolution OCT. This technique will aid in delineating the pathophysiology of diseases of the anterior cornea.

Animals↗

PubMedDate not supplied

Determination of burn depth by polarization-sensitive optical coherence tomography.

An assessment of burn depth is a key step in guiding the treatment of patients who have sustained thermal injuries. Polarization-sensitive optical coherence tomography (PS-OCT) might eventually provide the physician with a quantitative estimate of actual burn depth. Burns of various depths were induced by contacting rat skin with a brass rod preheated to 75 degrees C for 5, 15, or 30 s. Thermal injury denatured the collagen in the skin, and PS-OCT imaged the resulting reduction of birefringence through the depth-resolved changes in the polarization state of light propagated and reflected from the sample. Stokes vectors were calculated for each point in the PS-OCT images and the reduction in the rate of phase retardation between two orthogonal polarizations of light (deg/microm) was found to show a consistent trend with burn exposure time. PS-OCT is a noninvasive technique with potential to give the physician the information needed to formulate an optimal treatment plan for burn patients.

Animals↗

PubMedDate not supplied

Fluorescence correlation spectroscopy investigation of a GFP mutant-enhanced cyan fluorescent protein and its tubulin fusion in living cells with two-photon excitation.

This study investigates the feasibility of using the enhanced cyan mutant of green fluorescent protein (ECFP) as a probe for two-photon fluorescence correlation spectroscopy (FCS). Molecular dynamics and other properties of ECFP and an ECFP-tubulin fusion protein were investigated in living Potorous tridactylis (PTK2) cells. ECFP has high molecular brightness in the nucleus (eta=3.3 kcpsm) and in the cytoplasm (3.2 kcpsm) under our experimental conditions. The diffusion constants of ECFP were determined to be 20+/-7 microm(2)/s in the nucleus and 21+/-8 microm(2)/s in the cytoplasm. ECFP has stable molecular characteristics with negligible photobleaching and photodynamic effects in our measurements. At the highest concentration of monomer ECFP (425 nM) the amount of dimer ECFP was estimated to be negligible ( approximately 1.8 nM), consistent with our data analysis using a single species model. ECFP-tubulin has a diffusion constant of 6 microm(2)/s in the living cells. In addition, we demonstrate that analysis of the molecular brightness can provide a new avenue for studying the polymerization state of tubulin. We suggest that the tubulin in the vicinity of the nucleus exists primarily as a heterodimer subunit while those in the area away from the nucleus (d>5 microm) are mostly oligomers. We conclude that ECFP is a useful genetic fluorescent probe for FCS studies of various cellular processes when in fusion to other biomolecules of interest.

Animals↗

PubMedDate not supplied

Imaging wound healing using optical coherence tomography and multiphoton microscopy in an in vitro skin-equivalent tissue model.

Laser thermal injury and subsequent wound healing in organotypic, skin-equivalent tissue models were monitored using optical coherence tomography (OCT), multiphoton microscopy (MPM), and histopathology. The in vitro skin-equivalent raft tissue model was composed of dermis with type I collagen and fibroblast cells and epidermis of differentiated keratinocytes. Noninvasive optical imaging techniques were used for time-dependent, serial measurements of matrix destruction and reconstruction and compared with histopathology. The region of laser thermal injury was clearly delineated in OCT images by low signal intensity. High resolution MPM imaging using second-harmonic generation revealed alterations in collagen microstructure organization with subsequent matrix reconstruction. Fibroblast cell migration in response to injury was monitored by MPM using two-photon excited fluorescence. This study illustrates the complementary features of linear and nonlinear light-tissue interaction in intrinsic signal optical imaging and their use for noninvasive, serial monitoring of wound healing processes in biological tissues.

Burns↗

PubMedDate not supplied

Optical coherence tomography of malignancy in hamster cheek pouches.

Optical coherence tomography (OCT)/optical Doppler tomography (ODT) provides real-time in vivo high-resolution (10-microm) imaging of tissues and real-time spatially resolved blood flow in microvasculature. Hamster cheek pouches with induced dysplasia and malignancies were imaged with OCT/ODT to assess the potential for application to airway malignancy. In 22 Golden Syrian hamsters, 0.5% 9,10-dimethyl-1,2-benzanthracene induces carcinogenesis over 10 weeks in right side cheek pouches; the left side three served as controls. The cheek pouches are imaged in vivo prior to sacrifice, and in vitro after excision, using a prototype 1310-nm broadband superluminescent diode based OCT/ODT device. Images are compared to standard histopathology. OCT imaging offers good resolution of the hamster cheek pouches to depths of 1 to 3 mm and paralleled histologic images. The feasibility of high-resolution functional imaging is demonstrated in this hamster cheek pouch tumor model. ODT accurately detects vascular change associated with carcinogenesis.

9,10-Dimethyl-1,2-benzanthracene↗

PubMedDate not supplied

Accurate measurement of blood vessel depth in port wine stained human skin in vivo using pulsed photothermal radiometry.

We report on application of pulsed photothermal radiometry (PPTR) to determine the depth of port wine stain (PWS) blood vessels in human skin. When blood vessels are deep in the PWS skin (>100 microm), conventional PPTR depth profiling can be used to determine PWS depth with sufficient accuracy. When blood vessels are close or partially overlap the epidermal melanin layer, a modified PPTR technique using two-wavelength (585 and 600 nm) excitation is a superior method to determine PWS depth. A direct difference approach in which PWS depth is determined from a weighted difference of temperature profiles reconstructed independently from two-wavelength excitation is demonstrated to be appropriate for a wider range of PWS patients with various blood volume fractions, blood vessel sizes, and depth distribution. The most superficial PWS depths determined in vivo by PPTR are in good agreement with those measured using optical Doppler tomography (ODT).

Algorithms↗

PubMedDate not supplied

Noninvasive imaging of oral premalignancy and malignancy.

Early detection of cancer and its precursors remains the best way to ensure patient survival and quality of life. Our specific aim is to test a multimodality approach to noninvasive diagnostics of oral premalignancy and malignancy. In the hamster cheek pouch model (120 hamsters), in vivo optical coherence tomography (OCT) and optical Doppler tomography (ODT) map epithelial, subepithelial, and vascular change throughout carcinogenesis. In vivo multiwavelength multiphoton (MPM) and second-harmonic generated (SHG) fluorescence techniques provided parallel data on surface and subsurface tissue structure, specifically collagen presence and structure, cellular presence, and vasculature. Images are diagnosed by two blinded, prestandardized investigators using a scale from 0 to 6 for all modalities. After sacrifice, histopathology is evaluated on a scale of 0 to 6. Imaging data are reproducibly obtained with good accuracy. Carcinogenesis-related structural and vascular changes are clearly visible to tissue depths of 2 mm. Sensitivity (OCT/ODT alone, 71 to 88%; OCT+MPMSHG, 79 to 91%) and specificity (OCT alone, 62 to 83%; OCT+MPMSHG, 67 to 90%) compare well with conventional techniques. Our conclusions are that OCT/ODT and MPM/SHG are promising noninvasive in vivo diagnostic modalities for oral dysplasia and malignancy.

Animals↗

PubMedDate not supplied

Effect of pulse duration on two-photon excited fluorescence and second harmonic generation in nonlinear optical microscopy.

We have developed a multiphoton microscopy (MPM) system using a 12-fs Ti:sapphire laser with adjustable dispersion precompensation in order to examine the impact of pulse duration on nonlinear optical signals. The efficiencies of two-photon-excited fluorescence (TPEF) and second harmonic generation (SHG) were studied for various pulse durations, measured at the sample, ranging from approximately 400 fs to sub-20 fs. Both TPEF and SHG increased proportionally to the inverse of the pulse duration for the entire tested range. Because of improved signal-to-noise ratio, sub-20-fs pulses were used to enhance MPM imaging depth by approximately 160%, compared to 120-fs pulses, in human skin.

Algorithms↗

PubMedDate not supplied

Combined multiphoton microscopy and optical coherence tomography using a 12-fs broadband source.

A 12-fs broadband (100-nm) source is used to combine multiphoton microscopy (MPM) and optical coherence tomography (OCT) in a single platform. An ultrafast Ti:sapphire laser simultaneously provides short pulses necessary for efficient MPM excitation and the broad bandwidth required for high-resolution OCT. Using 0.3-microm microspheres and a 63x, 0.95 numerical aperture objective, we demonstrate that MPM and OCT channels are coregistered with lateral resolution of approximately 0.5 microm and axial resolution of approximately 1.5 microm. Preliminary studies of a 3-D organotypic epithelial tissue model show that multiphoton images of fluorescence and second harmonic signals are derived from cellular and extracellular matrix structures, respectively, while OCT images are generated from scattering interfaces due to tissue variations in refractive index. The combined MPM/OCT microscope is capable of providing simultaneous functional and structural information from cells and extracellular matrix and is potentially a powerful tool for studying biological processes in thick tissues.

Equipment Design↗

PubMedDate not supplied

Office-based optical coherence tomographic imaging of human vocal cords.

Optical coherence tomography (OCT) is an evolving noninvasive imaging modality and has been used to image the larynx during surgical endoscopy. The design of an OCT sampling device capable of capturing images of the human larynx during a typical office based laryngoscopy examination is discussed. Both patient's and physician's movements were addressed. In vivo OCT imaging of the human larynx is demonstrated. Though the long focal length limits the lateral resolution of the image, the basement membrane can still be readily distinguished. Office-based OCT has the potential to guide surgical biopsies, direct therapy, and monitor disease. This is a promising imaging modality to study the larynx.

Equipment Design↗

PubMedDate not supplied

Use of polarization-sensitive optical coherence tomography to determine the directional polarization sensitivity of articular cartilage and meniscus.

The directional polarization sensitivity of articular cartilage and meniscus is investigated by use of polarization-sensitive optical coherence tomography (PS-OCT) by varying the angle of incident illumination. Experimental results show that when the incident light is perpendicular to the tissue surface, normal articular cartilage demonstrates little polarization sensitivity, while meniscus demonstrates strong polarization sensitivity. Differences in optical phase retardation produced by articular cartilage and meniscus are observed when the incident angle of the scanning light beam is adjusted between 0 and 90 deg relative to the tissue surface. Directional polarization sensitivity of articular cartilage and meniscus as obtained by PS-OCT imaging using variations in the angle of incident illumination can be used to assess the orientation and organization of the collagen matrix of these tissues. The polarization sensitivity as evidenced by the Stokes vector and optical phase retardation images can be explained by the orientation of the angle of illumination relative to the unique structural organization of the collagen fibrils and fibers of articular cartilage and meniscus.

Animals↗

PubMedDate not supplied

Evaluation of tracheal imaging by optical coherence tomography.

BACKGROUND: Optical coherence tomography (OCT) is a new technology capable of generating high resolution cross-sectional images of complex tissue in real time. Analogous to ultrasound, OCT measures backscattered light intensity using coherence interferometery to construct topographical images of complex tissue. Since OCT uses infrared light rather than acoustic waves, its spatial resolution is exceptionally high (2-10 microm). Recent advances in data acquisition, analysis, and processing enable real-time imaging, and make OCT a potentially valuable tool for pulmonary airway diagnostic applications, including assisting directed airway biopsies. OBJECTIVE: This study evaluates feasibility of OCT for delineating proximal airway microstructures in various animal as well as human tracheas. METHODS: Excised trachea samples from New Zealand white rabbits, Duroc pigs, and human trachea were imaged using a compact, 1,300-nm broad-band superluminescent-diode-based prototype fiber OCT device we constructed. The resulting structural OCT images were compared to conventional hematoxilin and eosin (HE) stained histological sections from the same samples. RESULTS: OCT was able to delineate microstructures such as the epithelium, mucosa, cartilage, and glands in all samples. CONCLUSION: These findings suggest that integration of OCT with flexible fiberoptic bronchoscopy could enhance pulmonary diagnostic medicine and detection of pathologic tissue changes in various respiratory diseases.

Animals↗

PubMedDate not supplied

In vivo optical coherence tomography of the nasal mucosa.

BACKGROUND: Optical coherence tomography (OCT) is an emerging imaging modality that uses light to produce in vivo high-resolution cross-sectional images (7 microm) of tissues to depths of up to 3 mm. OCT is analogous to ultrasound, but relies on interferometry and low-coherence optical sources to produce images of tissue structure at the histological level. METHODS: In this study, OCT was used to image the mucosa overlying structures in the nasal cavity to obtain information regarding normative in vivo tissue microstructure. An OCT system using a Michaelson interferometer and a 1.3-microm broadband light source was incorporated into a fiber-optic imaging device that was inserted into the nasal cavity. Cross-sectional tomographic images of the anterior and posterior nasal septum, turbinates, and vestibule were acquired in 44 patients in either the office or the operating room during surgical endoscopy. RESULTS: OCT images of the nasal mucosa identified the distinct boundaries between the epithelium, lamina propria, and underlying bone/cartilaginous tissue. Within the lamina propria, features consistent with glands, ducts, and blood vessels were clearly identified. In patients who underwent decongestant therapy, before and after images showed distinct morphological changes in the mucosa. The thickness of the epithelium was tabulated, as well. CONCLUSION: This study establishes the potential of using OCT to produce high-resolution images of the nasal mucosa. As an in vivo tissue microstructural imaging modality, OCT may be valuable in studying the impact of allergic and infectious disease on the nasal mucosa and monitoring its response to pharmacologic therapy.

Adolescent↗