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Patterson EA, Whelan MP, Worth AP. The role of validation in establishing the scientific credibility of predictive toxicology approaches intended for regulatory application. ACTA ACUST UNITED AC 2021; 17:100144. [PMID: 33681540 PMCID: PMC7903516 DOI: 10.1016/j.comtox.2020.100144] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Revised: 09/15/2020] [Accepted: 11/04/2020] [Indexed: 12/14/2022]
Abstract
The role of validation in establishing the credibility of predictive methods is discussed. Various assessment frameworks for predictive methods have evolved independently, being developed by different communities. A set of seven credibility factors is proposed as a method-agnostic means of comparing the various assessment frameworks. It is hoped this will facilitate communication and cross-disciplinary collaboration between method developers and users.
New approaches in toxicology based on in vitro methods and computational modelling offer considerable potential to improve the efficiency and effectiveness of chemical hazard and risk assessment in a variety of regulatory contexts. However, this presents challenges both for developers and regulatory assessors because often these two communities do not share the same level of confidence in a new approach. To address this challenge, various assessment frameworks have been developed over the past 20 years with the aim of creating harmonised and systematic approaches for evaluating new methods. These frameworks typically focus on specific methodologies and technologies, which has proven useful for establishing the validity and credibility of individual methods. However, given the increasing need to compare methods and combine their use in integrated assessment strategies, the multiplicity of frameworks is arguably becoming a barrier to their acceptance. In this commentary, we explore the concepts of model validity and credibility, and we illustrate how a set of seven credibility factors provides a method-agnostic means of comparing different kinds of predictive toxicology approaches. It is hoped that this will facilitate communication and cross-disciplinarity among method developers and users, with the ultimate aim of increasing the acceptance and use of predictive approaches in toxicology.
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Affiliation(s)
| | | | - Andrew P Worth
- European Commission, Joint Research Centre (JRC), Ispra, Italy
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2
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Patterson EA, Whelan MP. A framework to establish credibility of computational models in biology. Progress in Biophysics and Molecular Biology 2017; 129:13-19. [DOI: 10.1016/j.pbiomolbio.2016.08.007] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2016] [Revised: 07/18/2016] [Accepted: 08/01/2016] [Indexed: 10/20/2022]
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3
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Whelan MP. S5-1: Validation—An intrinsic part of safety assessment science. Reprod Toxicol 2013. [DOI: 10.1016/j.reprotox.2013.06.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Thomas RS, Philbert MA, Auerbach SS, Wetmore BA, Devito MJ, Cote I, Rowlands JC, Whelan MP, Hays SM, Andersen ME, Meek MEB, Reiter LW, Lambert JC, Clewell HJ, Stephens ML, Zhao QJ, Wesselkamper SC, Flowers L, Carney EW, Pastoor TP, Petersen DD, Yauk CL, Nong A. Incorporating new technologies into toxicity testing and risk assessment: moving from 21st century vision to a data-driven framework. Toxicol Sci 2013; 136:4-18. [PMID: 23958734 PMCID: PMC3829570 DOI: 10.1093/toxsci/kft178] [Citation(s) in RCA: 190] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Based on existing data and previous work, a series of studies is proposed as a basis toward a pragmatic early step in transforming toxicity testing. These studies were assembled into a data-driven framework that invokes successive tiers of testing with margin of exposure (MOE) as the primary metric. The first tier of the framework integrates data from high-throughput in vitro assays, in vitro-to-in vivo extrapolation (IVIVE) pharmacokinetic modeling, and exposure modeling. The in vitro assays are used to separate chemicals based on their relative selectivity in interacting with biological targets and identify the concentration at which these interactions occur. The IVIVE modeling converts in vitro concentrations into external dose for calculation of the point of departure (POD) and comparisons to human exposure estimates to yield a MOE. The second tier involves short-term in vivo studies, expanded pharmacokinetic evaluations, and refined human exposure estimates. The results from the second tier studies provide more accurate estimates of the POD and the MOE. The third tier contains the traditional animal studies currently used to assess chemical safety. In each tier, the POD for selective chemicals is based primarily on endpoints associated with a proposed mode of action, whereas the POD for nonselective chemicals is based on potential biological perturbation. Based on the MOE, a significant percentage of chemicals evaluated in the first 2 tiers could be eliminated from further testing. The framework provides a risk-based and animal-sparing approach to evaluate chemical safety, drawing broadly from previous experience but incorporating technological advances to increase efficiency.
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Affiliation(s)
- Russell S Thomas
- * The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina 27709
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Rodrigues RM, Bouhifd M, Bories G, Sacco MG, Gribaldo L, Fabbri M, Coecke S, Whelan MP. Assessment of an automated in vitro basal cytotoxicity test system based on metabolically-competent cells. Toxicol In Vitro 2012; 27:760-7. [PMID: 23261643 DOI: 10.1016/j.tiv.2012.12.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2012] [Revised: 11/15/2012] [Accepted: 12/07/2012] [Indexed: 11/17/2022]
Abstract
When in vitro test systems are evaluated for assessment of the toxicity of chemical compounds, particular efforts are made to mimic the in vivo reality as close as possible. Cellular models with appropriate metabolic competence, i.e. with the potency to biotransform chemical compounds, are considered crucial since some metabolites have a different toxicity than their parent compounds. In this study a cell based in vitro test system is proposed to investigate the basal cytotoxicity of several reference chemicals. Both metabolic competent HepaRG cells and cells with no or low hepatic enzyme activity (undifferentiated HepaRG and proliferating HepG2) were used. The classic Neutral Red Uptake (NRU) assay proved to be robust and reliable to be applied as viability assay. The test was performed on a robotic platform, which enabled fully automated and simultaneous screening of the compounds. The outcome of these tests grouped the tested compounds in three categories following their detoxification effect (benzo(a)pyrene, valproic acid), their bio-activation effect (aflatoxin B1) and their specific effect on inhibition of cell proliferation (cycloheximide, sodium lauryl sulphate, atropine sulphate monohydrate, acetylsalicylic acid).
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Affiliation(s)
- Robim M Rodrigues
- Institute for Health and Consumer Protection, European Commission Joint Research Centre, 21027 Ispra (VA), Italy.
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Bouhifd M, Bories G, Casado J, Coecke S, Norlén H, Parissis N, Rodrigues RM, Whelan MP. Automation of an in vitro cytotoxicity assay used to estimate starting doses in acute oral systemic toxicity tests. Food Chem Toxicol 2012; 50:2084-96. [PMID: 22465836 DOI: 10.1016/j.fct.2012.03.046] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2011] [Revised: 02/23/2012] [Accepted: 03/09/2012] [Indexed: 11/27/2022]
Abstract
Application of High Throughput Screening (HTS) to the regulatory safety assessment of chemicals is still in its infancy but shows great promise in terms of facilitating better understanding of toxicological modes-of-action, reducing the reliance on animal testing, and allowing more data-poor chemicals to be assessed at a reasonable cost. To promote the uptake and acceptance of HTS approaches, we describe in a stepwise manner how a well known cytotoxicity assay can be automated to increase throughput while maintaining reliability. Results generated with selected reference chemicals compared very favourably with data obtained from a previous international validation study concerning the prediction of acute systemic toxicity in rodents. The automated assay was then included in a formal ECVAM validation study to determine if the assay could be used for binary classification of chemicals with respect to their acute oral toxicity, using a threshold equivalent to a dose of 2000 mg/kg b.w. in a rodent bioassay (LD50). This involved the blind-testing of 56 reference chemicals on the HTS platform to produce concentration-response and IC50 data. Finally, the assay was adapted to a format more suited to higher throughput testing without compromising the quality of the data obtained.
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Affiliation(s)
- Mounir Bouhifd
- Institute for Health and Consumer Protection, European Commission Joint Research Centre, 21027 Ispra (VA), Italy
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Bednarkiewicz A, Rodrigues RM, Whelan MP. Non-invasive monitoring of cytotoxicity based on kinetic changes of cellular autofluorescence. Toxicol In Vitro 2011; 25:2088-94. [PMID: 21959354 DOI: 10.1016/j.tiv.2011.09.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Revised: 07/22/2011] [Accepted: 09/12/2011] [Indexed: 11/25/2022]
Abstract
A quantitative, non-destructive cellular autofluorescence based in vitro imaging assay has been developed and applied to study the cytotoxicity of Sodium Lauryl Sulfate (SLS) and HgCl2 on Balb/c 3T3 cells. A phenomenological double logistic model was proposed to quantify and relate the observed kinetic changes of fluorescence to the toxic potency of chemical compounds. This work forms the basis for cellular autofluorescence measurements in in vitro toxicity screening assays.
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Affiliation(s)
- Artur Bednarkiewicz
- Institute for Health and Customer Protection, European Commission Joint Research Centre, 21-027 Ispra (VA), Italy.
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Rodrigues RM, Macko P, Palosaari T, Whelan MP. Autofluorescence microscopy: a non-destructive tool to monitor mitochondrial toxicity. Toxicol Lett 2011; 206:281-8. [PMID: 21864658 DOI: 10.1016/j.toxlet.2011.06.025] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2010] [Revised: 06/08/2011] [Accepted: 06/18/2011] [Indexed: 01/22/2023]
Abstract
Visualization of NADH by fluorescence microscopy makes it possible to distinguish mitochondria inside living cells, allowing structure analysis of these organelles in a non-invasive way. Mitochondrial morphology is determined by the occurrence of mitochondrial fission and fusion. During normal cell function mitochondria appear as elongated tubular structures. However, cellular malfunction induces mitochondria to fragment into punctiform, vesicular structures. This change in morphology is associated with the generation of reactive oxygen species (ROS) and early apoptosis. The aim of this study is to demonstrate that autofluorescence imaging of mitochondria in living eukaryotic cells provides structural and morphological information that can be used to assess mitochondrial health. We firstly established the illumination conditions that do not affect mitochondrial structure and calculated the maximum safe light dose to which the cells can be exposed. Subsequently, sequential recording of mitochondrial fluorescence was performed and changes in mitochondrial morphology were monitored in a continuous non-destructive way. This approach was then used to assess mitochondrial toxicity induced by potential toxicants exposed to mammalian cells. Both mouse and human cells were used to evaluate mitochondrial toxicity of different compounds with different toxicities. This technique constitutes a novel and promising approach to explore chemical induced toxicity because of its reliability to monitor mitochondrial morphology changes and corresponding toxicity in a non-invasive way.
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Affiliation(s)
- Robim M Rodrigues
- European Commission Joint Research Centre, Institute for Health and Customer Protection, Via E. Fermi 2749, 21027 Ispra (Varese), Italy.
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Abstract
The forward scattering of light in a conventional inverted optical microscope by nanoparticles ranging in diameter from 10 to 50nm has been used to automatically and quantitatively identify and track their location in three-dimensions with a temporal resolution of 200ms. The standard deviation of the location of nominally stationary 50-nm-diameter nanoparticles was found to be about 50nm along the light path and about 5nm in the plane perpendicular to the light path. The method is based on oscillating the microscope objective along the light path using a piezo actuator and acquiring images with the condenser aperture closed to a minimum to enhance the effects of diffraction. Data processing in the time and spatial domains allowed the location of particles to be obtained automatically so that the technique has potential applications both in the processing of nanoparticles and in their use in a variety of fields including nanobiotechnology, pharmaceuticals and food processing where a simple optical microscope maybe preferred for a variety of reasons.
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Affiliation(s)
- J-M Gineste
- Systems Toxicology Unit, Institute for Health and Consumer Protection, European Commission DG Joint Research Centre, Italy
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10
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Bednarkiewicz A, Rodrigues RM, Whelan MP. Enrichment of hepatocytes in a HepaRG culture using spatially selective photodynamic treatment. J Biomed Opt 2010; 15:028002. [PMID: 20459292 DOI: 10.1117/1.3369000] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The human hepatoma HepaRG cell line is an in vitro cell model that is becoming an important tool in drug metabolism, hepatotoxicity, genotoxicity, and enzyme induction studies. The cells are highly proliferative during their undifferentiated state but once committed, they differentiate into two distinctly different cell types, namely, hepatocyte-like and biliary epithelial-like cells. The presence of the latter in the cell culture is considered to be a drawback of the cell model. Since the proliferating undifferentiated HepaRG cells have a bipotent character, the only way to improve the content ratio of hepatic versus biliary cells of differentiated HepaRG cells is to eradicate biliary cells in situ, in a way that free surface space does not become available and thus no transdifferentiation can occur. Spatially selective photodynamic therapy has proven to be effective for that purpose. First, all the cells were administered aminolevulinic acid (delta-ALA) to stimulate the synthesis of protoporphyrin IX (PpIX), a naturally occurring photosensitizer. Then, the biliary cells were automatically identified and outlined by bright-field image processing. Last, UV light patterns were projected onto the epithelial cells alone by a spatial light modulation device connected to an optical microscope; therefore, only these cells were destroyed by photodynamic therapy.
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Affiliation(s)
- Artur Bednarkiewicz
- European Commission, Institute of Health and Customer Protection, Via Enrico Fermi 1, Ispra, 21020 Italy.
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11
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Macko P, Whelan MP. Aberration-free lithography setup for fabrication of holographic diffractive optical elements. Opt Lett 2009; 34:3006-3008. [PMID: 19794797 DOI: 10.1364/ol.34.003006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
A holographic optical lithography setup with extremely small longitudinal spherical aberration is described. The setup is used for the fabrication of holographic diffractive optical elements intended to collect light emitted from a fluorescence spot located on a biochip surface. A key feature of the optical setup is its ability to simulate a point-source-like fluorescence spot. A detailed description of the setup together with its optical properties are provided. The fluorescence light collection efficiency of the holographic diffractive optical elements produced using this setup is demonstrated.
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Affiliation(s)
- Peter Macko
- Systems Toxicology Unit, Institute for Health and Consumer Protection, European Commission-DG Joint Research Centre, I-21027 Ispra (VA), Italy.
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12
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Macko P, Whelan MP. Fabrication of holographic diffractive optical elements for enhancing light collection from fluorescence-based biochips. Opt Lett 2008; 33:2614-2616. [PMID: 19015685 DOI: 10.1364/ol.33.002614] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
An approach to enhancing the light collection from fluorescence emitters bound on the surface of a biochip is presented. It is based on the integration of diffractive optical elements on the underside of the chip that are essentially thick volume holograms written into a layer of photopolymer recording material. The high diffractive efficiency and angular selectivity of these types of diffractive elements make them very effective collectors of the spatially anisotropic light emitted by surface-bound fluorophores. The holographic lithography setup used to fabricate the diffractive elements is described. Results obtained using both a focused laser and light from a fluorescence spot to characterize the performance of the diffractive optical elements are presented.
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Affiliation(s)
- Peter Macko
- Nanotechnology and Molecular Imaging Unit, Institute for Health and Consumer Protection, European Commission-DG Joint Research Centre, Ispra, Italy.
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13
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Affiliation(s)
- Eann A Patterson
- Department of Mechanical Engineering, Michigan State University, East Lansing, MI 48824, USA.
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14
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Bednarkiewicz A, Whelan MP. Global analysis of microscopic fluorescence lifetime images using spectral segmentation and a digital micromirror spatial illuminator. J Biomed Opt 2008; 13:041316. [PMID: 19021324 DOI: 10.1117/1.2950308] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Fluorescence lifetime imaging (FLIM) is very demanding from a technical and computational perspective, and the output is usually a compromise between acquisition/processing time and data accuracy and precision. We present a new approach to acquisition, analysis, and reconstruction of microscopic FLIM images by employing a digital micromirror device (DMD) as a spatial illuminator. In the first step, the whole field fluorescence image is collected by a color charge-coupled device (CCD) camera. Further qualitative spectral analysis and sample segmentation are performed to spatially distinguish between spectrally different regions on the sample. Next, the fluorescence of the sample is excited segment by segment, and fluorescence lifetimes are acquired with a photon counting technique. FLIM image reconstruction is performed by either raster scanning the sample or by directly accessing specific regions of interest. The unique features of the DMD illuminator allow the rapid on-line measurement of global good initial parameters (GIP), which are supplied to the first iteration of the fitting algorithm. As a consequence, a decrease of the computation time required to obtain a satisfactory quality-of-fit is achieved without compromising the accuracy and precision of the lifetime measurements.
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Affiliation(s)
- Artur Bednarkiewicz
- European Commission Joint Research Center, Institute of Health and Customer Protection, T.P.202 Via E. Fermi 2749, I-21027 Ispra (VA), Italy.
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15
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Stummann TC, Wronski M, Sobanski T, Kumpfmueller B, Hareng L, Bremer S, Whelan MP. Digital Movie Analysis for Quantification of Beating Frequencies, Chronotropic Effects, and Beating Areas in Cardiomyocyte Cultures. Assay Drug Dev Technol 2008; 6:375-85. [DOI: 10.1089/adt.2008.129] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Tina C. Stummann
- European Centre for the Validation of Alternative Methods, Institute for Health and Consumer Protection, Joint Research Centre, European Commission, Ispra (VA), Italy
| | - Mateusz Wronski
- Faculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Wroclaw, Poland
| | - Tomasz Sobanski
- Nanotechnology and Molecular Imaging Unit, Institute for Health and Consumer Protection, Joint Research Centre, European Commission, Ispra (VA), Italy
| | - Benjamin Kumpfmueller
- European Centre for the Validation of Alternative Methods, Institute for Health and Consumer Protection, Joint Research Centre, European Commission, Ispra (VA), Italy
| | - Lars Hareng
- European Centre for the Validation of Alternative Methods, Institute for Health and Consumer Protection, Joint Research Centre, European Commission, Ispra (VA), Italy
| | - Susanne Bremer
- European Centre for the Validation of Alternative Methods, Institute for Health and Consumer Protection, Joint Research Centre, European Commission, Ispra (VA), Italy
| | - Maurice P. Whelan
- Nanotechnology and Molecular Imaging Unit, Institute for Health and Consumer Protection, Joint Research Centre, European Commission, Ispra (VA), Italy
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16
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Bednarkiewicz A, Bouhifd M, Whelan MP. Digital micromirror device as a spatial illuminator for fluorescence lifetime and hyperspectral imaging. Appl Opt 2008; 47:1193-1199. [PMID: 18709064 DOI: 10.1364/ao.47.001193] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Time-domain fluorescence lifetime imaging (FLIM) and hyper-spectral imaging (HSI) are two advanced microscopy techniques widely used in biological studies. Typically both FLIM and HSI are performed with either a whole-field or raster-scanning approach, which often prove to be technically complex and expensive, requiring the user to accept a compromise among precision, speed, and spatial resolution. We propose the use of a digital micromirror device (DMD) as a spatial illuminator for time-domain FLIM and HSI with a laser diode excitation source. The rather unique features of the DMD allow both random and parallel access to regions of interest (ROIs) on the sample, in a very rapid and repeatable fashion. As a consequence both spectral and lifetime images can be acquired with a precision normally associated with single-point systems but with a high degree of flexibility in their spatial construction. In addition, the DMD system offers a very efficient way of implementing a global analysis approach for FLIM, where average fluorescence decay parameters are first acquired for a ROI and then used as initial estimates in determining their spatial distribution within the ROI. Experimental results obtained on phantoms employing fluorescent dyes clearly show how the DMD method supports both spectral and temporal separation for target identification in HSI and FLIM, respectively.
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Affiliation(s)
- Artur Bednarkiewicz
- Nanotechnology and Molecular Imaging Unit, Institute for Health and Consumer Protection, European Commission Joint Research Centre, Via E. Fermi 1, 21020 Ispra, Varese, Italy.
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Abstract
An elegant method is proposed and demonstrated for tracking the location and movement of nanoparticles in an optical microscope using the optical phenomenon of caustics. A simple and reversible adjustment to the microscope generates caustics several orders of magnitude larger than the particles. The method offers a simple and relatively inexpensive method for visualizing such phenomena as the formation of self-assembled monolayers and the interaction of nanoparticles with chemically functionalized surfaces.
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Affiliation(s)
- Eann A Patterson
- Department of Mechanical Engineering, Michigan State University, East Lansing, MI 48824, USA
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18
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Connelly MJ, Szecówka PM, Jallapuram R, Martin S, Toal V, Whelan MP. Multipoint laser Doppler vibrometry using holographic optical elements and a CMOS digital camera. Opt Lett 2008; 33:330-332. [PMID: 18278100 DOI: 10.1364/ol.33.000330] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
A laser Doppler vibrometer (LDV) is described in which holographic optical elements are used to provide the interferometer reference and object illumination beams. A complementary metal-oxide semiconductor camera, incorporating a digital signal processor, is used to carry out real-time signal processing of the interferometer output to allow multipoint LDV to be implemented.
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Affiliation(s)
- Michael J Connelly
- Department of Electronic and Computer Engineering, Optical Communications Research Group, University of Limerick, Limerick, Ireland.
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19
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Egan P, Connelly MJ, Lakestani F, Whelan MP. Random depth access full-field heterodyne low-coherence interferometry utilizing acousto-optic modulation and a complementary metaloxide semiconductor camera. Opt Lett 2006; 31:912-4. [PMID: 16599209 DOI: 10.1364/ol.31.000912] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
With analog scanning, time-domain low-coherence interferometry lacks precise depth information, and optical carrier generation demands a linear scanning speed. Full-field heterodyne low-coherence interferometry that uses a logarithmic complementary metal-oxide semiconductor camera, acousto-optic modulation, and digital depth stepping is reported, with which random regions of interest, lateral and axial, can be accessed. Furthermore, nanometer profilometry is possible through heterodyne phase retrieval of the interference signal. The approach demonstrates inexpensive yet high-precision functional machine vision offering true digital random access in three dimensions.
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Affiliation(s)
- Patrick Egan
- Optical Communications Research Group, University of Limerick, Castletroy, County Limerick, Ireland.
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20
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Aguanno MV, Lakestani F, Whelan MP, Connelly MJ. Single-pixel carrier-based approach for full-field laser interferometry using a CMOS-DSP camera. ACTA ACUST UNITED AC 2004. [DOI: 10.1117/12.532651] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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Casagrande F, Crespi P, Grassi AM, Lulli A, Kenny RP, Whelan MP. From the reflected spectrum to the properties of a fiber Bragg grating: a genetic algorithm approach with application to distributed strain sensing. Appl Opt 2002; 41:5238-5244. [PMID: 12211548 DOI: 10.1364/ao.41.005238] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We describe a genetic algorithm approach to solve an inverse problem in optics, which determines the characteristics of a fiber Bragg grating from its reflected spectrum. The validity of the proposed method is demonstrated by use of a Bragg sensor for the measurement of nonlinear strain acting on a uniaxial aluminum test specimen.
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Affiliation(s)
- Federico Casagrande
- Dipartimento di Fisica dell'Universita di Milano, Istituto Nazionale di Fisica della Materia, Milan, Italy.
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23
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Abstract
Finite element methods have been applied extensively and with much success in the analysis of orthopaedic hip and knee implants. Very recently a burgeoning interest has developed, in the finite element community, in how numerical models can be constructed for the solution of problems in contact mechanics. New developments in this area are of paramount importance in the design of implants for orthopaedic surgery. Modern techniques are described for finite element contact analysis and applied to two problems of stress analysis in a plastic tibial component. In the former, results are compared with a previous finite element analysis and with Hertzian solutions. In the latter, an estimate of the extent of convergence of the finite element solutions is provided.
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Affiliation(s)
- J E Mottershead
- Department of Mechanical Engineering, University of Liverpool
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