A comparison of Cunyite and Fosterite NIR tunable laser tissue welding using native collagen fluorescence imaging.

OBJECTIVE: To evaluate the technique of native collagen fluorescence imaging for assessing the extent of welded areas for tissues exposed to different near-infrared (NIR) laser wavelengths. BACKGROUND: Native fluorescence imaging may be used to identify the distribution of collagen and elastin in tissues. Our past work demonstrated that different welding strengths were obtained under the same laser power conditions using different NIR wavelengths. The role of collagen in tissue welding experiments is not well understood. METHODS: Two new NIR tunable lasers were used to weld canine skin. The welded areas on the surface and in cross sections were analyzed by measuring the spatial distribution of native collagen fluorescence at 380 nm excited by 340 nm radiation. RESULTS: The results show that native collagen fluorescence imaging is a useful technique for analyzing the extent of tissue welds produced under a range of laser exposures. Fluorescence imaging reveals the depth of laser interaction with the tissue as well as evaluating collateral damage to the tissue surface. The welded volume obtained in skin using Cunyite laser exposure at 1,430 nm is deeper than that produced with Forsterite laser exposure at 1,250 nm. The post welded tensile strength for the same power density is greater for the Cunyite lasers. Ablated tissue on the surface is more prevalent with Forsterite laser welding at 1,250 nm than with Cunyite at 1,430 nm. CONCLUSION: Native collagen fluorescence can distinguish between tissue welds that have been produced by different NIR wavelengths. Tissue welding using 1,430 nm radiation is more effective than that using 1,250 nm.     

Aorta and skin tissues welded by near-infrared Cr4+:YAG laser

OBJECTIVE: The aim of our study was to explore the wavelength dependence of welding efficacy. Ex vivo samples of human and porcine aorta and skin tissues were investigated using a tunable Cr(4+):yttrium aluminum garnet (YAG) laser. BACKGROUND DATA: Tissue welding is possible using laser light in the NIR spectral range. Collagen bonding in the tissue induced by thermal, photothermal, and photochemical reactions-or a combination of all of these-is thought to be responsible for tissue welding. Laser tissue welding (LTW) has gained success in the laboratory using animal models. Transition from laboratory to clinical application requires the optimization of welding parameters. MATERIALS AND METHODS: A near-infrared (NIR) Cr(4+):YAG laser was used to weld ex vivo samples of human and porcine aorta and skin at wavelengths from 1430 to 1470 nm. Welding efficacy was monitored by measuring the tensile strength of the welded tissue and the extent of collateral tissue damage. Tensile strengths were measured using a digital force gauge. Changes in tissue morphology were evaluated using optical and scanning electron microscope (SEM). Fluorescence imaging of the welded areas was also used to evaluate molecular changes following tissue welding. RESULTS: Full-thickness tissue bonding was observed with porcine aorta samples. No collateral damage of the aorta samples was observed. Tissue denaturation was observed with human aorta, human skin, and porcine skin samples. The optimum tensile strength for porcine and human aorta was 1.33 +/- 0.15 and 1.13 +/- 0.27 kg/cm2, respectively, at 1460 nm, while that for porcine and human skin was 0.94 +/- 0.15 and 1.05 +/- 0.19 kg/cm2, respectively, achieved at 1455 nm. The weld strength as a function of wavelength demonstrated a correlation with the absorption spectrum of water. Fluorescence imaging of welded aorta and skin demonstrated no significant changes in collagen and elastin emission at the weld site. CONCLUSION: The observation that welding strength as a function of wavelength follows the absorption bands of water suggests that absorption of light by water plays a significant role in laser tissue welding.     

Role of basement membrane collagen and elastin in the autofluorescence spectra of the colon.

BACKGROUND: Autofluoresence can be used to detect neoplasia in the colon. Two known fluorophores, collagen and elastin, are probably partly responsible for colonic emission spectra. Their contribution to colonic autofluorescence was investigated. METHODS: Autofluorescence spectra of normal, dysplastic, and malignant colonic tissue were studied by using excitation wavelengths from 280 nm to 350 nm. The wavelengths of peak emission and their widths at half maximum intensity were measured. Similar measurements were performed on collagen types I, III, IV, V, IX, and elastin. Colonic spectra were compared to those of collagen and elastin. Spectral differences between collagen types IV (basement membrane) I, III, V, and IX were studied. RESULTS: Four major emission peaks were noted whose wavelength of peak emission and full widths at half maximum intensity were independent of tissue histology. The emission spectra of type IV collagen differed markedly from that of nonbasement membrane collagens and elastin. CONCLUSIONS: Type IV (basement membrane) collagen is most likely responsible for the emission peak at 365 nm. The spectra of basement membrane collagen and not other types of collagen should be used in studies of epithelial tissue spectra. Elastin did not appear to be responsible for any of the four autofluorescence peaks observed in colonic tissue.     

Laser Induced Fluorescence Identification of Sinoatrial and Atrioventricular Nodal Conduction Tissue

Transcatheter ahlation of nodal tissue is used for the treatment of arrhythmia resistant to medical therapy. We have investigated the use of laser induced fluorescence spectroscopy for the in vitro recognition of nodal conduction tissue. Twelve fresh human necropsy specimens (< 48 hours)were obtained from sinoatrial node and atrioventricular node areas. Spectra were recorded during excitation at 308 nm (XeCl excimer iaser, 1.5–2.0 mJ/puJse, 10 Hz). Each area examined was marked for subsequent histoiogic examination. Four hundred eleven spectra were obtained, of which 37 contained nodai conduction tissue (21 sinoatrial, 16 atrioventricular node). Normalized fluorescence emission intensity from these areas was compared with that of surrounding endomyocardial tissue at 18 wavelengths and 35 ratios of fluorescence intensity at selected wavelengths. Spectra recorded from nodal tissue could be clearly distinguished hy a visible decrease in fluorescence emission intensity at wavelengths from 440 to 500 nm (P < 0.0006 at 450 nm), peak area, and peak width when compared to that of adjacent atrial endomyocardial tissue. Nodal conduction tissue was also distinguished from ventricular endocardium (14 spectra) by an increase in fluorescence emission at 430 to 550 nm (P < 0.0001). The specificity was 73% and 88% and the sensitivity was 73% and 60% for sinus nodal and atrioventricular nodal conduction tissue identification, respectively. A ratio of fluorescence emission intensity > 1.3 for 380/475 nm was able to detect nodal conducfion tissue (P < 0.001). Conclusion. Laser induced fluorescence can differentiate nodal conduction tissue from atrial and ventricular endocardium and may provide a new diagnostic tool for the recognition and subsequent ablation of nodal conduction tissue.     

Development of a nonlinear fiber-optic spectrometer for human lung tissue exploration

Several major lung pathologies are characterized by early modifications of the extracellular matrix (ECM) fibrillar collagen and elastin network. We report here the development of a nonlinear fiber-optic spectrometer, compatible with an endoscopic use, primarily intended for the recording of second-harmonic generation (SHG) signal of collagen and two-photon excited fluorescence (2PEF) of both collagen and elastin. Fiber dispersion is accurately compensated by the use of a specific grism-pair stretcher, allowing laser pulse temporal width around 70 fs and excitation wavelength tunability from 790 to 900 nm. This spectrometer was used to investigate the excitation wavelength dependence (from 800 to 870 nm) of SHG and 2PEF spectra originating from ex vivo human lung tissue samples. The results were compared with spectral responses of collagen gel and elastin powder reference samples and also with data obtained using standard nonlinear microspectroscopy. The excitation-wavelength-tunable nonlinear fiber-optic spectrometer presented in this study allows performing nonlinear spectroscopy of human lung tissue ECM through the elastin 2PEF and the collagen SHG signals. This work opens the way to tunable excitation nonlinear endomicroscopy based on both distal scanning of a single optical fiber and proximal scanning of a fiber-optic bundle.     

Optimizing quantitative in vivo fluorescence imaging with near‐infrared quantum dots

Quantum dots (QDs) are fluorescent nanoparticles with broad excitation and narrow, wavelength‐tunable emission spectra. They are used extensively for in vitro fluorescence imaging studies and more recently for in vivo small animal and pre‐clinical studies. To date there has been little concern about the selection of QD size (and thus emission wavelength peak) and excitation wavelengths, as they have little relevance to the results of in vitro studies. In vivo imaging, however, poses additional constraints, such as the scattering and absorption by tissue, which may influence the signal intensity at the body surface. Here, we demonstrate that longer‐wavelength excitation and emission yield less quantization error in measured relative fluorescence intensity, using three near‐infrared QDs (QD655, QD705 and QD800) applied to in vivo lymphatic imaging, and a range of excitation wavelengths from the blue to the red. Statistically significant differences in quantization error were observed between nearly all pairs of excitation wavelengths (445–490, 503–555, 575–605, 615–665 and 671–705 nm). Similarly, quantization error decreased with longer emission wavelengths (655, 705 and 800 nm). Light absorbance and scattering were demonstrated to be more potent factors than absorbance efficiency of QDs in producing quantization error in the measured fluorescence intensity. As a result, while wavelengths can be adjusted for qualitative experiments, the longest possible wavelengths should be used if quantification is desired during QD imaging experiments. Copyright © 2010 John Wiley & Sons, Ltd.     

Single-laser-based simultaneous four-wavelength excitation source for femtosecond two-photon fluorescence microscopy

Multicolor labeling of biological samples with large volume is required for omic-level of study such as the construction of nervous system connectome. Among the various imaging method, two photon microscope has multiple advantages over traditional single photon microscope for higher resolution and could image large 3D volumes of tissue samples with superior imaging depth. However, the growing number of fluorophores for labeling underlines the urgent need for an ultrafast laser source with the capability of providing simultaneous plural excitation wavelengths for multiple fluorophores. Here, we propose and demonstrate a single-laser-based four-wavelength excitation source for two-photon fluorescence microscopy. Using a sub-100 fs 1,070-nm Yb:fiber laser to pump an ultrashort nonlinear photonic crystal fiber in the low negative dispersion region, we introduced efficient self-phase modulation and acquired a blue-shifted spectrum dual-peaked at 812 and 960 nm with 28.5% wavelength conversion efficiency. By compressing the blue-shift near-IR spectrum to 33 fs to ensure the temporal overlap of the 812 and 960 nm peaks, the so-called sum frequency effect created the third virtual excitation wavelength effectively at 886 nm. Combined with the 1,070 nm laser source as the fourth excitation wavelength, the all-fiber-format four-wavelength excitation source enabled simultaneous four-color two-photon imaging in Brainbow AAV-labeled (TagBFP, mTFP, EYFP, and mCherry) brain samples. With an increased number of excitation wavelengths and improved excitation efficiency than typical commercial femtosecond lasers, our compact four-wavelength excitation approach can provide a versatile, efficient, and easily accessible solution for multiple-color two-photon fluorescence imaging in the field of neuroscience, biomolecular probing, and clinical applications with at least four spectrally-distinct fluorophores.     

Fluorescent substances in uremic and normal serum

We measured the fluorescence, at various excitation (Ex) and emission (Em) wavelengths, of serum ultrafiltrates and fractions of serum resolved by chromatography on Sephadex G15, studying both normal subjects and patients in chronic renal failure requiring hemodialysis. We found hitherto undescribed fluorescence at Ex 380 nm/Em 440 nm and Ex 400 nm/Em 460 nm, the intensity being greatly increased in patients with chronic renal failure in comparison with normal subjects (p less than 0.005). This fluorescence persisted unaltered when serum was filtered through membranes having cutoffs ranging from 10 000 to 500 Da. Each serum fraction resolved by gel chromatography demonstrated a characteristic fluorescence, which was generally much more intense in uremics. The most intense fluorescence (Ex 380 nm/Em 440 nm and Ex 400 nm/Em 460 nm) was emitted in the higher-Mr fractions.     

Tumor Hypoxia Imaging

There is a need to measure tumor hypoxia in assessing the aggressiveness of tumor and predicting the outcome of therapy. A number of invasive and noninvasive techniques have been exploited to measure tumor hypoxia, including polarographic needle electrodes, immunohistochemical staining, radionuclide imaging (positron emission tomography [PET] and single-photon emission computed tomography [SPECT]), magnetic resonance imaging (MRI), optical imaging (bioluminescence and fluorescence), and so on. This review article summarizes and discusses the pros and cons of each currently available method for measuring tissue oxygenation. Special emphasis was placed on noninvasive imaging hypoxia with emerging new agents and new imaging technologies to detect the molecular events that are relevant to tumor hypoxia.     

Highly sensitive detection of cancer cells using femtosecond dual-wavelength near-IR two-photon imaging

We describe novel imaging protocols that allow detection of small cancer cell colonies deep inside tissue phantoms with high sensitivity and specificity. We compare fluorescence excited in Styryl-9M molecules by femtosecond pulses at near IR wavelengths, where Styryl-9M shows the largest dependence of the two-photon absorption (2PA) cross section on the local environment. We show that by calculating the normalized ratio of the two-photon excited fluorescence (2PEF) intensity at 1200 nm and 1100 nm excitation wavelengths we can achieve high sensitivity and specificity for determining the location of cancer cells surrounded by normal cells. The 2PEF results showed a positive correlation with the levels of MDR1 proteins expressed by the cells, and, for high MDR1 expressors, as few as ten cancer cells could be detected. Similar high sensitivity is also demonstrated for tumor colonies induced in mouse external ears. This technique could be useful in early cancer detection, and, perhaps, also in monitoring dormant cancer deposits.     

Combined hemoglobin and fluorescence diffuse optical tomography for breast tumor diagnosis: a pilot study on time-domain methodology

A combined time-domain fluorescence and hemoglobin diffuse optical tomography (DOT) system and the image reconstruction methods are proposed for enhancing the reliability of breast-dedicated optical measurement. The system equipped with two pulsed laser diodes at wavelengths of 780 nm and 830 nm that are specific to the peak excitation and emission of the FDA-approved ICG agent, and works with a 4-channel time-correlated single photon counting device to acquire the time-resolved distributions of the light re-emissions at 32 boundary sites of tissues in a tandem serial-to-parallel mode. The simultaneous reconstruction of the two optical (absorption and scattering) and two fluorescent (yield and lifetime) properties are achieved with the respective featured-data algorithms based on the generalized pulse spectrum technique. The performances of the methodology are experimentally assessed on breast-mimicking phantoms for hemoglobin- and fluorescence-DOT alone, as well as for fluorescence-guided hemoglobin-DOT. The results demonstrate the efficacy of improving the accuracy of hemoglobin-DOT based on a priori fluorescence localization.OCIS codes: (170.3880) Medical and biological imaging, (170.6960) Tomography, (170.6920) Time-resolved imaging, (170.3010) Image reconstruction techniques     

Simultaneous decomposition of multiple hyperspectral data sets: signal recovery of unknown fluorophores in the retinal pigment epithelium

Upon excitation with different wavelengths of light, biological tissues emit distinct but related autofluorescence signals. We used non-negative matrix factorization (NMF) to simultaneously decompose co-registered hyperspectral emission data from human retinal pigment epithelium/Bruch’s membrane specimens illuminated with 436 and 480 nm light. NMF analysis was initialized with Gaussian mixture model fits and constrained to provide identical abundance images for the two excitation wavelengths. Spectra recovered this way were smoother than those obtained separately; fluorophore abundances more clearly localized within tissue compartments. These studies provide evidence that leveraging multiple co-registered hyperspectral emission data sets is preferential for identifying biologically relevant fluorophore information.OCIS codes: (100.2960) Image analysis, (100.4145) Motion, hyperspectral image processing, (110.4234) Multispectral and hyperspectral imaging, (170.4470) Ophthalmology, (170.6280) Spectroscopy, fluorescence and luminescence, (170.6510) Spectroscopy, tissue diagnostics     

Fluoromodule-based reporter/probes designed for in vivo fluorescence imaging

Optical imaging of whole, living animals has proven to be a powerful tool in multiple areas of preclinical research and has allowed noninvasive monitoring of immune responses, tumor and pathogen growth, and treatment responses in longitudinal studies. However, fluorescence-based studies in animals are challenging because tissue absorbs and autofluoresces strongly in the visible light spectrum. These optical properties drive development and use of fluorescent labels that absorb and emit at longer wavelengths. Here, we present a far-red absorbing fluoromodule–based reporter/probe system and show that this system can be used for imaging in living mice. The probe we developed is a fluorogenic dye called SC1 that is dark in solution but highly fluorescent when bound to its cognate reporter, Mars1. The reporter/probe complex, or fluoromodule, produced peak emission near 730 nm. Mars1 was able to bind a variety of structurally similar probes that differ in color and membrane permeability. We demonstrated that a tool kit of multiple probes can be used to label extracellular and intracellular reporter–tagged receptor pools with 2 colors. Imaging studies may benefit from this far-red excited reporter/probe system, which features tight coupling between probe fluorescence and reporter binding and offers the option of using an expandable family of fluorogenic probes with a single reporter gene.     

Standoff detection of biological agents using laser induced fluorescence—a comparison of 294?nm and 355?nm excitation wavelengths

Standoff detection measuring the fluorescence spectra of seven different biological agents excited by 294 nm as well as 355 nm wavelength laser pulses has been undertaken. The biological warfare agent simulants were released in a semi-closed aerosol chamber at 210 m standoff distance and excited by light at either of the two wavelengths using the same instrument. Significant differences in several of the agents’ fluorescence response were seen at the two wavelengths. The anthrax simulants’ fluorescence responses were almost an order of magnitude stronger at the shorter wavelength excitation. However, most importantly, the fluorescence spectra were significantly more dissimilar at 294 nm than at 355 nm excitation with ~7 nm spectral resolution. This indicates that classification of the substances should be possible with a lower error rate for standoff detection using 294 nm rather than 355 nm excitation wavelength, or even better, utilizing both.OCIS codes: (170.6280) Spectroscopy, fluorescence and luminescence; (280.1100) Aerosol detection; (280.1415) Biological sensing and sensors; (280.3640) Lidar; (300.2530) Fluorescence, laser-induced     

In vivo local fluorescence spectroscopy in PDD of superficial bladder cancer

ObjectiveA combination of fluorescence imaging with in vivo local fluorescence spectroscopy (LFS) was used to improve the predictive ability of photodynamic diagnosis (PDD) of superficial bladder cancer after intravesical instillation of Alasense, a 5-aminolevulinic acid (5-ALA)-based agent.Material and methodA total of 62 patients with superficial malignancies of the urinary bladder were included in a preliminary clinical study. Nineteen patients underwent autofluorescence (AF) examination, whereas 43 patients underwent photodynamic diagnosis (PDD) after intravesical instillation of Alasense (NIOPIK, Russia). After visual examination of the urinary bladder wall under white and blue light, fluorescence emission spectra were recorded in vivo under 442 and 532 nm laser excitation within visible red fluorescent zones that had been preliminarily revealed by fluorescence imaging. For spectral data interpretation, a spectral fluorescence parameter was introduced as a ratio of the 5-ALA-induced protoporphyrin IX-emission intensity to that of the AF emission. In the search for a quantitative criterion for this parameter, as well as a diagnostic algorithm to facilitate differentiation between inflammatory and neoplastic tissues, two approaches were tested based on: (1) a posteriori estimation of the threshold values of the spectral fluorescence parameters for inflammation and cancerous tissues, and (2) a posteriori probability of attributing an acquired emission spectrum to a histologically confirmed tissue type.ResultsIn the group of patients without intravesical instillation of Alasense (n=19), LFS showed a dramatic drop (with a factor of 5–20, p<0.0001) in the AF emission intensity of superficial bladder malignancies under 442 and 532 nm laser excitation, although no reliable distinction was revealed in the AF emission intensity between normal urothelium and inflammatory foci. In the group of patients with intravesical instillation of Alasense (n=43), false positive (FP) results were confirmed histologically in 18 of 54 fluorescent foci revealed by fluorescence imaging, and the positive predictive value (PPV) was estimated to be 67%. Correlations of the spectral fluorescence parameter with the histological results were studied and probability distribution functions (PDFs) of this parameter were constructed for normal urothelium (type I), inflammation, papilloma, low-grade dysplasia (type II), as well as high-grade dysplasia, CIS and TCC (type III) at both excitation wavelengths. PDF distributions for “inflammation – neoplasia” were shown to have essential overlaps, causing certain problems in definition of the thresholds of the spectral fluorescence parameters and attribution of the recorded spectra to the three tissue types. Despite this, the threshold-based approach allowed for a reduction in the number of FP cases to 3 and an increase of the PPV to 91%. In another approach, the maximum realization probabilities of the spectral fluorescence parameter were selected as criteria for attribution of the tested tissue to one of the histological tissue types. Estimations based on this approach showed that the probability of FP cases and the PPV could be roughly estimated as 0–0.1 and as 91–100% at λ_ex=442 and 532 nm respectively.ConclusionThis preliminary clinical study shows that both approaches allow for a significant increase in the PPV of PDD of superficial bladder cancer. Therefore the combination of fluorescence imaging with in vivo LFS may be helpful for minimizing false-positive fluorescence and reducing the number of biopsies necessary.     

Label-free diagnostics and cancer surgery Raman spectra guidance for the human colon at different excitation wavelengths

Raman spectroscopy and imaging are highly structure-sensitive methods that allow the characterization of biological samples with minimal impact. In this paper, Raman spectra and imaging of noncancerous and cancerous human colon tissue samples were measured at different excitation wavelengths: 355, 532, and 785 nm. Intra-patient variability in the analyzed spectra showed colon sample heterogeneity for both noncancerous and cancerous human sample types. The lowest inter-patient variability of Raman spectra was observed for the fingerprint region of noncancerous samples for the 532 nm excitation laser line. The bands of principal biochemical constituents (proteins, lipids, nucleic acids) predominate in VIS and NIR-Raman spectra (excitation: 532, 785 nm), with the special role of the bands of intrinsic tissue chromophores—carotenoids for VIS excitation due to resonance enhancement. At 355 nm excitation, high autofluorescence of colon tissues were observed. Our studies proved high potential of Raman spectroscopy and Raman imaging in differentiation of noncancerous and cancerous human colon tissues and that the wavelengths 532 and 785 nm offer wide possibilities for the detection of human colon tissue pathology for ex vivo and in vivo measurements and prevail over 355 nm excitation.

Raman spectroscopy and imaging are highly structure-sensitive methods that allow the characterization of biological samples with minimal impact.     

ARFI Imaging for Noninvasive Material Characterization of Atherosclerosis Part II: Toward In Vivo Characterization

Seventy percent of cardiovascular disease (CVD) deaths are attributed to atherosclerosis. Despite their clinical significance, nonstenotic atherosclerotic plaques are not effectively detected by conventional atherosclerosis imaging methods. Moreover, conventional imaging methods are insufficient for describing plaque composition, which is relevant to cardiovascular risk assessment. Atherosclerosis imaging technologies capable of improving plaque detection and stratifying cardiovascular risk are needed. Acoustic radiation force impulse (ARFI) ultrasound, a novel imaging method for noninvasively differentiating the mechanical properties of tissue, is demonstrated for in vivo detection of nonstenotic plaques and plaque material assessment in this pilot investigation. In vivo ARFI imaging was performed on four iliac arteries: (1) of a normocholesterolemic pig with no atherosclerosis as a control, (2) of a familial hypercholesterolemic pig with diffuse atherosclerosis, (3) of a normocholesterolemic pig fed a high-fat diet with early atherosclerotic plaques and (4) of a familial hypercholesterolemic pig with diffuse atherosclerosis and a small, minimally occlusive plaque. ARFI results were compared with spatially matched immunohistochemistry, showing correlations between elastin and collagen content and ARFI-derived peak displacement and recovery time parameters. Faster recoveries from ARFI-induced peak displacements and smaller peak displacements were observed in areas of higher elastin and collagen content. Importantly, spatial correlations between tissue content and ARFI results were consistent and observable in large and highly evolved as well as small plaques. ARFI imaging successfully distinguished nonstenotic plaques, while conventional B-mode ultrasound did not. This work validates the potential relevance of ARFI imaging as a noninvasive imaging technology for in vivo detection and material assessment of atherosclerotic plaques. (E-mail: russbehler@unc.edu)     

Design of miniaturized illumination for transvaginal co-registered photoacoustic and ultrasound imaging

A novel lens-array based illumination design for a compact co-registered photoacoustic/ultrasound transvaginal probe has been demonstrated. The lens array consists of four cylindrical lenses that couple the laser beams into four 1-mm-core multi-mode optical fibers with optical coupling efficiency of ~87%. The feasibility of our lens array was investigated by simulating the lenses and laser beam profiles using Zemax. The laser fluence on the tissue surface was experimentally measured and was below the American National Standards Institute (ANSI) safety limit. Spatial distribution of hemoglobin oxygen saturation (sO₂) of a mouse tumor was obtained in vivo using photoacoustic measurements at multiple wavelengths. Furthermore, benign and malignant ovaries were imaged ex vivo and evaluated histologically. The co-registered images clearly showed different patterns of blood vasculature. These results highlight the clinical potential of our system for noninvasive photoacoustic and ultrasound imaging of ovarian tissue and cancer detection and diagnosis.OCIS codes: (110.0110) Imaging systems, (170.2945) Illumination design, (170.5120) Photoacoustic imaging, (170.6960) Tomography, (170.7170) Ultrasound     

Methanol immersion reduces spherical aberration of water dipping lenses at long wavelengths used in multi-photon laser scanning microscopy

Dipping objectives were tested for multi-photon laser scanning microscopy, since their large working distances are advantageous for thick specimens and the absence of a coverslip facilitates examination of living material. Images of fluorescent bead specimens, particularly at wavelengths greater than 850 nm showed defects consistent with spherical aberration. Substituting methanol for water as the immersion medium surrounding the beads corrected these defects and produced an increase in fluorescence signal intensity. The same immersion method was applied to two representative biological samples of fixed tissue: mouse brain labeled with FITC for tubulin and mouse gut in which the Peyer’s patches were labeled with Texas Red bilosomes. Tissue morphology was well preserved by methanol immersion of both tissues; the two-photon-excited fluorescence signal was six times higher than in water and the depth of penetration of useful imaging was doubled. No modification of the microscope was needed except the provision of a ring to retain a sufficient depth of methanol for imaging.OCIS codes: (220.1000) Aberration compensation, (180.0180) Microscopy, (180.4315) Nonlinear microscopy, (160.4670) Optical materials     

光学分子影像学技术在肿瘤中的应用进展

分子影像学技术是一种在活体状态下从微观上显示组织、细胞及亚细胞水平的影像技术,具有实时、无创、精准及灵敏等特点,可在细胞和分子水平进行肿瘤早期筛查和诊断。随着生物发光与荧光成像技术的进步,光学分子影像学技术快速发展。本文就光学分子影像学技术在肿瘤中的应用进展进行综述。