Hequn Wang

University of Washington Seattle, Seattle, Washington, United States

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Publications (22)45.39 Total impact

  • Journal of Biomedical Optics 10/2014; 19(10):106011. · 2.75 Impact Factor
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    ABSTRACT: Characterization of the relationship between external pressure and blood flow is important in the examination of pressure-induced disturbance in tissue microcirculation. Optical coherence tomography (OCT)-based microangiography is a promising imaging technique, capable of providing the noninvasive extraction of functional vessels within the skin tissue with capillary-scale resolution. Here, we present a feasibility study of OCT microangiography (OMAG) to evaluate changes in blood perfusion in response to externally applied pressure on human skin tissue in vivo. External force is loaded normal to the tissue surface at the nailfold region of a healthy human volunteer. An incremental force is applied step by step and then followed by an immediate release. Skin perfusion events including baseline are continuously imaged by OMAG, allowing for visualization and quantification of the capillary perfusion in the nailfold tissue. The tissue strain maps are simultaneously evaluated through the available OCT structural images to assess the relationship of the microcirculation response to the applied pressure. The results indicate that the perfusion progressively decreases with the constant increase of pressure. Reactive hyperemia occurs right after the removal of the pressure. The perfusion returns to the baseline level after a few minutes. These findings suggest that OMAG may have great potential for quantitatively assessing tissue microcirculation in the locally pressed tissue in vivo.
    Journal of Biomedical Optics 05/2014; 19(5):56003. · 2.75 Impact Factor
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    ABSTRACT: Background and Objective Faster and better wound healing is a longstanding goal. Blood flow, angiogenesis, and tissue oxygenation are important parameters in evaluating the healing process. Optical microangiography (OMAG) allows 3D imaging of tissue vasculature and can provide quantitative blood flow information down to the capillary level of resolution. Dual wavelength laser speckle imaging (DW-LSI) can measure tissue oxygenation status.Materials and Methods Cutaneous wound healing of a mouse ear model using a multimodal imaging system that combines OMAG with DWLSI was studied.ResultsA complete microvasculature map of the ear in vivo was obtained. The imaging system revealed both hemodynamic and metabolic changes during acute stage wound healing. Blood flow velocity, blood flow direction, as well as changes in concentration of oxygenated hemoglobin (ΔHbO) and deoxygenated hemoglobin (ΔHb) were measured and quantified. In addition, capillary recruitment and angiogenesis were visualized during the chronic stage of repairing.Conclusions The combination of DW-LSI and OMAG imaging technique may be a powerful tool to visualize and understand microvascular, hemodynamic, and metabolic changes during cutaneous wound healing. Lasers Surg. Med. © 2014 Wiley Periodicals, Inc.
    Lasers in Surgery and Medicine 04/2014; · 2.61 Impact Factor
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    ABSTRACT: Vasculature response is a hallmark for most inflammatory skin disorders. Tape stripping on human skin causes a minor inflammation which leads to changes in microvasculature. In this study, optical microangiography (OMAG), noninvasive volumetric microvasculature in vivo imaging method, has been used to track the vascular responses after tape stripping. Vessel density has been quantified and used to correlate with the degree of skin irritation. The proved capability of OMAG technique in visualizing the microvasculature network under inflamed skin condition can play an important role in clinical trials of treatment and diagnosis of inflammatory skin disorders. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Journal of Biophotonics 03/2014; · 3.86 Impact Factor
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    ABSTRACT: Evaluation of spatiotemporal hemodynamic and metabolic responses during neural activation is crucial in studying brain function. We explore the use of a noninvasive multifunctional optical imaging system to measure these responses in a mouse brain upon electrically stimulated neural activation, with the cranium left intact. The system is developed by integrating an optical microangiography (OMAG) imaging system with a dual-wavelength laser speckle imaging (DW-LSI) system. The DW-LSI, running at an image acquisition speed of ∼100 Hz, is used to extract the large-scale two-dimensional map, revealing the localized response of blood flow, hemoglobin concentration, and metabolic rate of oxygen change. Guided by DW-LSI, the OMAG is, however, used to image the response of individual blood vessels with its unique depth-resolved capability. We show that the integrated system is capable of investigating neural activation, thus is potentially valuable in the preclinical study of the mechanism of neurovascular coupling.
    Journal of Biomedical Optics 02/2014; 19(2):26013. · 2.75 Impact Factor
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    ABSTRACT: The movement from the subjects during in vivo confocal Raman spectral measurements could change the measurement volume, leading to non-specific signals and inaccurate interpretation of the acquired spectrum. Here we introduce a generally applicable method that includes (1) developing a multimodal system to achieve real-time monitoring of every spectral measurement with reflectance confocal microscopy (RCM) and multiphoton microscopy (MPM) imaging; (2) performing region-of-interest measurement by scanning an area of the tissue during spectral acquisition. The developed method has been validated by measuring different micro-structures of in vivo human skin. Our results demonstrated great consistency between RCM images and confocal Raman spectra. The superior quality of the images and spectra allows us to derive blood flow velocity and blood glucose level. We believe this method is valuable for realizing accurate microscopic spectral measurement and have great potential to be adapted into clinic to achieve non-invasive measurement of important biological parameters.
    Scientific Reports 05/2013; 3:1890. · 5.08 Impact Factor
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    ABSTRACT: One-photon absorption based traditional laser treatment may not necessarily be selective at the microscopic level, thus could result in un-intended tissue damage. Our objective is to test whether two-photon absorption (TPA) could provide highly targeted tissue alteration of specific region of interest without damaging surrounding tissues. TPA based laser treatments (785 nm, 140 fs pulse width, 90 MHz) were performed on ex vivo mouse skin using different average power levels and irradiation times. Reflectance confocal microscopy (RCM) and combined second-harmonic-generation (SHG) and two-photon fluorescence (TPF) imaging channels were used to image before, during, and after each laser treatment. The skin was fixed, sectioned and H & E stained after each experiment for histological assessment of tissue alterations and for comparison with the non-invasive imaging assessments. Localized destruction of dermal fibers was observed without discernible epidermal damage on both RCM and SHG + TPF images for all the experiments. RCM and SHG + TPF images correlated well with conventional histological examination. This work demonstrated that TPA-based light treatment provides highly localized intradermal tissue alteration. With further studies on optimizing laser treatment parameters, this two-photon absorption photothermolysis method could potentially be applied in clinical dermatology. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).
    Journal of Biophotonics 03/2013; · 3.86 Impact Factor
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    ABSTRACT: Here we present a method for improving Raman spectroscopy signal-to-noise ratio (SNR) based on fluorescence photobleaching. Good SNR is essential to obtain biochemical information about biological tissues. Subtracting high levels of tissue autofluorescence background is a major challenge in extracting weak Raman signals. We found that pre-exposure to laser light significantly reduces tissue autofluorescence, but minimally affects Raman signals, allowing subsequent acquisition of high-SNR Raman spectra. We demonstrated this method with in vivo Raman spectral measurements of human skin. This method will benefit clinical skin Raman measurements of body sites with high autofluorescence background such as the forehead and nose.
    Photodiagnosis and photodynamic therapy 12/2012; 9(4):299-302.
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    ABSTRACT: We present a multimodal in vivo skin imaging instrument that is capable of simultaneously acquiring multiphoton and reflectance confocal images at up to 27 frames per second with 256 × 256 pixel resolution without the use of exogenous contrast agents. A single femtosecond laser excitation source is used for all channels ensuring perfect image registration between the two-photon fluorescence (TPF), second harmonic generation (SHG), and reflectance confocal microscopy (RCM) images. Images and videos acquired with the system show that the three imaging channels provide complementary information in in vivo human skin measurements. In the epidermis, cell boundaries are clearly seen in the RCM channel, while cytoplasm is better seen in the TPF imaging channel, whereas in the dermis, SHG and TPF channels show collagen bundles and elastin fibers, respectively. The demonstrated fast imaging speed and multimodal imaging capabilities of this MPM/RCM instrument are essential features for future clinical application of this technique. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).
    Journal of Biophotonics 07/2012; · 3.86 Impact Factor
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    ABSTRACT: There are increased interests on using multiphoton imaging and spectroscopy for skin tissue characterization and diagnosis. However, most studies have been done with just a few excitation wavelengths. Our objective is to perform a systematic study of the two-photon fluorescence (TPF) properties of skin fluorophores, normal skin, and diseased skin tissues. A nonlinear excitation-emission-matrix (EEM) spectroscopy system with multiphoton imaging guidance was constructed. A tunable femtosecond laser was used to vary excitation wavelengths from 730 to 920 nm for EEM data acquisition. EEM measurements were performed on excised fresh normal skin tissues, seborrheic keratosis tissue samples, and skin fluorophores including: NADH, FAD, keratin, melanin, collagen, and elastin. We found that in the stratum corneum and upper epidermis of normal skin, the cells have large sizes and the TPF originates from keratin. In the lower epidermis, cells are smaller and TPF is dominated by NADH contributions. In the dermis, TPF is dominated by elastin components. The depth resolved EEM measurements also demonstrated that keratin structure has intruded into the middle sublayers of the epidermal part of the seborrheic keratosis lesion. These results suggest that the imaging guided TPF EEM spectroscopy provides useful information for the development of multiphoton clinical devices for skin disease diagnosis.
    Journal of Biomedical Optics 07/2012; 17(7):077004. · 2.75 Impact Factor
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    ABSTRACT: Skin cancer is the most common type of cancer in humans. Current techniques for identifying normal and neoplastic tissues are either destructive or not sensitive and specific enough. Raman spectroscopy and confocal imaging may obviate many limitations of existing methods by providing noninvasive, high-resolution, and real-time morphological and biochemical analysis of living tissues and cells. We conducted micro-Raman spectroscopy studies on HaCaT cells, melanocytes (MC) and their malignant counterparts squamous cell carcinoma (SCC) and melanoma (MM) cells, respectively. Reflectance confocal imaging is used as guidance for the spectral measurements. Significant differences were found between the spectra of HaCaT cells and SCC cells, MC cells and MM cells, as well as all normal cells (HaCaT and MC) and all tumor cells (SCC and MM). Approximately 90% sensitivity and specificity was achieved for all the separations that we performed. Our results demonstrated the robust capability of confocal Raman spectroscopy in separating different cell lines. The acquired Raman spectra of major types of skin cells and their malignant counterparts will be useful for the interpretation of Raman spectra from in vivo skin. We believe it will eventually help diagnosis of skin cancer and other skin disease in clinical dermatology.
    Photodermatology Photoimmunology and Photomedicine 06/2012; 28(3):147-52. · 1.52 Impact Factor
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    ABSTRACT: The spectral dependence of SHG intensity in biological tissues is an optical property that is not fully understood so far. In this paper, we will investigate this problem in detail through experiments. Through examining different biology tissues, it is found that SHG intensity drops down from shorter to longer wavelength from 375 nm to 460 nm. By comparing these curves with 1/λn dependence, the n is found to vary from 4.5 to 8.5. These patterns can not be fully explained by scattering properties of collagen. Other factors such as direct generation of SHG may have contribution to these wavelength dependence patterns, which needs further investigation.
    Proc SPIE 02/2012;
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    ABSTRACT: Raman spectroscopy is a minimally-invasive optical technique with great potential for in vivo cancer detection and disease diagnosis. However, there is no systematic study of the Raman spectra from different organs to date. We measured and characterized the Raman spectra eighteen naïve mouse organs in a broad frequency range of 700 to 3100 cm⁻¹. The peaks of generic proteins and lipids appeared in Raman spectra of all organs. Some organs like bone, teeth, brain and lung had unique Raman peaks. The autofluorescence was strong in liver, spleen, heart, and kidney. These results suggest that organ specific Raman probe design and specific data processing strategies are required in order to get the most useful information.
    Optics Express 11/2011; 19(23):22892-909. · 3.53 Impact Factor
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    ABSTRACT: We present a multiphoton microscopy instrument specially designed for in vivo dermatological use that is capable of imaging human skin at 27 frames per second with 256 pixels × 256 pixels resolution without the use of exogenous contrast agents. Imaging at fast frame rates is critical to reducing image blurring due to patient motion and to providing practically short clinical measurement times. Second harmonic generation and two-photon fluorescence images and videos acquired at optimized wavelengths are presented showing cellular and tissue structures from the skin surface down to the reticular dermis.
    Optics Letters 08/2011; 36(15):2865-7. · 3.39 Impact Factor
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    ABSTRACT: There has been a dramatic increase in photothermal therapy as a minimally invasive treatment modality for cancer treatment due to the development of novel nanomaterials as the light absorption agents. Single-wall carbon nanotubes (SWNTs) with strong optical absorption in the broad visible and near IR offer unique advantages for photothermal cancer therapy. A broad range of wavelengths can be used for the treatment with SWNTs, whereas conventional photothermal therapeutic agent is designed to absorb light only near one selected wavelength. The objective of this study is to validate the hypothesis that intratumoral injected SWNTs can absorb 785 nm near IR laser light and generate significant local hyperthermia to destroy tumors. SCCVII tumor in C3H/HeN mice was exposed to 785-nm laser after intratumoral injection of SWNTs with different light and SWNTs dose combinations. The temperatures of the tumor with laser irradiation were monitored. In vivo and ex vivo Raman spectra in different organs were obtained with a rapid Raman system. Tumor responses (tumor volume and mouse survival) were documented daily after treatment up to day 45 to assess the effectiveness of the treatment. The temperature within the tumors increased in a light- and SWNTs-dose dependent manner. Squamous cell carcinomas can be eradicated at a moderate light irradiance and fluence (200 mW/cm² and 120 J/cm²). This light dose is also comparable to those used with photodynamic therapy. Tissue Raman spectroscopy measurements revealed that SWNTs remained localized in the tumor even 3 months after injection but was not found in other organs. This animal study represents a significant step forward towards the goal of advancing SWNTs based photothermal cancer therapy into clinical applications.
    Lasers in Surgery and Medicine 11/2010; 42(9):638-48. · 2.61 Impact Factor
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    ABSTRACT: We have developed a micro-Raman spectrometer system for use to differentiate tumor lesions from normal skin using an in vivo animal model. A study of 494 Raman spectra from 24 mice revealed different spectral patterns at different depths and between normal and tumor-bearing skin sites. A peak at 899 cm−1 (possibly from proline or fatty acids) and one with higher intensity in the 1325–1330 cm−1 range (assigned to nucleic acids) were correlated with the presence of tumors, which can potentially be used as biomarkers for skin cancer detection. Spectral diagnosis performed on the murine tumor model achieved a diagnostic sensitivity of 95.8% and specificity of 93.8%. These results encourage us to develop further the use of confocal Raman spectroscopy as a clinical tool for noninvasive human skin biochemical analysis, particularly in relation to skin cancer. Copyright © 2010 John Wiley & Sons, Ltd.
    Journal of Raman Spectroscopy 05/2010; 42(2):160 - 166. · 2.68 Impact Factor
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    ABSTRACT: We present the construction of a new multimodal, multiphoton spectroscopic and imaging instrument for in vivo patient use. Utilizing a tunable femtosecond laser, we are able to simultaneously acquire two-photon excited fluorescence, second harmonic generation, and confocal reflectance images at half video rate, while concurrently acquiring two-photon excited fluorescence and second harmonic generation spectra.
    Proc SPIE 02/2010;
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    ABSTRACT: Single-wall carbon nanotubes (SWNTs) are a new type of nanomaterial with strong optical absorption. SWNTs also have intense Raman signals that facilitate convenient monitoring of their location within tissue thereby enabling noninvasive pharmacokinetic study. We hypothesize that SWNTs can absorb 785-nm laser light and generate significant local hyperthermia to destroy cancer cells and eradicate tumors. In this study a 785-nm diode laser is used for both Raman excitation and photothermal therapy. SWNTs are made water-soluble by functionalizing with polyethylene glycol (PEG) and administrated by intratumoral injection. C3H/HeN mice were injected subcutaneously with 2 million mouse squamous cell carcinoma (SCCVII) cells to create the tumor model. We conducted experiments with 100 mice divided into 10 different groups: control, SWNT only, 100 mW/cm2 laser irradiation only, 200 mW/cm2 laser irradiation only, and 6 treatment groups with different drug and light dose combinations (SWNTs 0.1, 0.5. 1 mg/ml, laser 100 and 200 mW/cm2). The treatment time was 10 minutes. The temperatures of the tumors irradiated by laser were monitored by an IR thermometer. Mice survival was observed for 45 days. The study revealed that the temperature within the tumors increased in a light- and drug-dose dependent manner. The optimized light and drug dose combinations (1 mg/ml + 120 J/cm2) resulted in tumor temperature elevation of 18.5°C and successful eradication of the tumors. This light dose is moderate and is as low as 1/10 of other published studies using nanomaterials. The Raman spectroscopy measurements suggest that SWNTs persisted within the tumor tissue for months.
    Proc SPIE 02/2010;
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    ABSTRACT: We report various technologies developed in our lab for in vivo Raman spectroscopy and related clinical applications. This includes macroscopic probes and endoscopy catheters that interrogate millimeter-scale tissue volumes for skin and lung cancer detection and a confocal microscopy system for depth-resolved Raman measurements of the skin in vivo.
    11/2009;
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    ABSTRACT: Ten groups of mice were exposed to 785 nm laser after intratumoral injection of single-wall carbon nanotubes (SWNTs). The temperature within the tumors increased in light- and drug-dose dependent manner; optimized light and drug dose combinations resulted in eradication of skin tumors. SWNTs persisted within the tumor tissue for months.
    11/2009;

Publication Stats

71 Citations
45.39 Total Impact Points

Institutions

  • 2014
    • University of Washington Seattle
      • Department of Bioengineering
      Seattle, Washington, United States
  • 2009–2013
    • University of British Columbia - Vancouver
      • Department of Dermatology and Skin Science
      Vancouver, British Columbia, Canada
  • 2012
    • BC Cancer Research Centre
      Vancouver, British Columbia, Canada
  • 2010
    • Chinese PLA General Hospital (301 Hospital)
      Peping, Beijing, China