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Frequency domain photon migration in the δ−P1 approximation: Analysis of ballistic, transport, and diffuse regimes

Physical Review E 2005年第2期72卷 021903-021903页

作者： J. S. You C. K. Hayakawa V. Venugopalan Department of Biomedical Engineering University of California Irvine Irvine California 92697-2715 USA Laser Microbeam and Medical Program Beckman Laser Institute University of California Irvine Irvine California 92697-3010 USA Department of Chemical Engineering and Materials Science University of California Irvine Irvine California 92697-2575 USA

The standard diffusion approximation (SDA) to the Boltzmann transport equation (BTE) is commonly used to describe radiative transport for biomedical applications of frequency-domain diffuse optical imaging and spectroscopy. Unfortunately, the SDA is unable to provide accurate radiative transport predictions on spatial scales comparable to the transport mean free path and for media in which optical scattering is not dominant over absorption. Here, we develop and demonstrate the use of the δ−P1 approximation to provide improved radiative transport estimates in the frequency domain via the addition of a Dirac δ function to both radiance and phase function approximations. Specifically, we consider photon density wave propagation resulting from the illumination of an infinite turbid medium with an embedded, intensity-modulated, spherical light source. We examine the accuracy of the standard diffusion and δ−P1 approximations relative to Monte Carlo simulations that provide exact solutions to the BTE. This comparison establishes the superior accuracy of the δ−P1 approximation relative to the SDA that is most notable at distances less than 3 transport mean free paths from the source. In addition, we demonstrate that the differences in photon density wave propagation in a highly forward scattering medium (g1=0.95) vs an isotropically scattering medium (g1=0) provides a basis to define three spatial regimes where the light field is dominated by (a) unscattered/ballistic light, (b) minimally scattered light, and (c) diffusely scattered light. We examine the impact of optical properties, source modulation frequency, and numerical aperture of detection on the spatial extent and location of these regimes.

关键词： TURBID MEDIA IN-VIVO DENSITY WAVES STEADY-STATE OPTICAL TOMOGRAPHY LIGHTDOSIMETRY RADIATIVE TRANSPORT SCATTERING MEDIA TISSUE SPECTROSCOPY

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A three-week hands-on introduction to biotransport & drug delivery for first-year engineering students

A three-week hands-on introduction to biotransport & drug de...

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ASEE 2004 Annual Conference and Exposition, "engineering Researchs New Heights"

作者： Cavanagh, Daniel P. Wagner, John J. Biomedical Engineering Program Department of Chemical Engineering Bucknell University Lewisburg PA

An seminar on biotransport and drug delivery course for the first year engineering students of Bucknell University was discussed. The goal of the seminar was to expose the students to the fundamental concepts associated with drug delivery and to provide the opportunity to implement these concepts in a hands-on environment. The seminar consisted of ten lectures and three labs sessions in which the early lectures focused on possible routes of entry of a drug into the body. Other lectures focused on simple diffusion in order to describe the transport of drug from the stomach into the bloodstream.

关键词： engineering education

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Biodegradable, multireservoir microdevice for drug delivery

Biodegradable, multireservoir microdevice for drug delivery

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2003 MRS Fall Meeting

作者： Kim, Grace Y. Richards Grayson, Amy C. Cima, Michael J. Langer, Robert Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA Harvard-MIT Division of Health Sciences and Technology Massachusetts Institute of Technology Cambridge MA School of Chemical and Biomolecular Engineering Biomedical Engineering Program Cornell University Ithaca NY Department of Chemical Engineering Massachusetts Institute of Technology Cambridge MA

Drugs have been released from an array of reservoirs in a biodegradable, polymeric microdevice. The reservoirs are formed in a polylactic acid (PLA) substrate and covered with a thin polymer membrane of a faster degrading polymer such as poly(lactic-co-glycolic) acid (PLGA) or a polyanhydride (PA). It is hypothesized that the release characteristics are a result of the drug-membrane interaction, chemical degradation of the membrane, and mechanical rupture of the membrane. This drug delivery platform features an entirely passive mechanism, the ability to simultaneously deliver multiple drugs with different release profiles, and independent drug formulation of the various drug payloads, which is not possible with other drug delivery technologies such as hydrogels or microspheres. The polymer microdevice is now being developed to deliver interleukin-2, followed by the chemotherapeutic carmustine (BCNU) for in vivo experiments. The combination of these two agents has been show to have a synergistic effect in prolonging survival after an intercranial 9L gliosarcoma challenge in a rat model. © 2004 Materials Research Society.

关键词： Drug dosage

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A BioMEMS review: MEMS technology for physiologically integrated devices

A BioMEMS review: MEMS technology for physiologically integr...

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作者： Grayson, Amy C. Richards Shawgo, Rebecca S. Johnson, Audrey M. Flynn, Nolan T. Li, Yawen Cima, Michael J. Langer, Robert School of Chemical and Biomolecular Engineering Biomedical Engineering Program Cornell University Ithaca NY 14853 United States Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA 02139 United States Department of Chemical Engineering Massachusetts Institute of Technology Cambridge MA 02139 United States Department of Chemistry Wellesley College Wellesley MA 02481 United States

MEMS devices are manufactured using similar microfabrication techniques as those used to create integrated circuits. They often, however, have moving components that allow physical or analytical functions to be performed by the device. Although MEMS can be aseptically fabricated and hermetically sealed, biocompatibility of the component materials is a key issue for MEMS used in vivo. Interest in MEMS for biological applications (BioMEMS) is growing rapidly, with opportunities in areas such as biosensors, pacemakers, immunoisolation capsules, and drug delivery. The key to many of these applications lies in the leveraging of features unique to MEMS (for example, analyte sensitivity, electrical responsiveness, temporal control, and feature sizes similar to cells and organelles) for maximum impact. In this paper. we focus on how the biological integration of MEMS and other tmplantable devices can be improved through the application of microfabrication technology and concepts. Innovative approaches for improved physical and chemical integration of systems with the body are reviewed. An untapped potential for MEMS may lie in the area of nervous and endocrine system actuation, whereby the ability of MEMS to deliver potent drugs or hormones, combined with their precise temporal control, may provide new treatments for disorders of these systems. © 2004 IEEE.

关键词： Microelectromechanical devices

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Use of the delta-P1 approximation and Monte Carlo simulations to examine the transition from ballistic to diffuse propagation in frequency-domain photon migration

Use of the delta-P1 approximation and Monte Carlo simulation...

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Frontiers in Optics, FiO-2004

作者： You, Joon S. Hayakawa, Carole K. Spanier, Jerome Venugopalan, Vasan Department of Biomedical Engineering University of California IrvineCA92697 United States Laser Microbeam and Medical Program Beckman Laser Institute University of California IrvineCA92697 United States Department of Chemical Engineering and Materials Science University of California IrvineCA92697 United States

ISBN: (纸本)1557527792

We develop the delta-P1 approximation for frequency-domain radiative transport predictions. Comparison with Monte Carlo simulations establishes superior accuracy of the delta-P1 approximation relative to the standard diffusion approximation. We demonstrate the identification of three spatial regimes where the light field is dominated by ballistic photons, multiply-scattered photons;and diffusely-scattered photons. © 2004 OSA/FIO 2004

关键词： Ballistics

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Optoacoustic imaging via the interferometric measurement of surface displacement

Optoacoustic imaging via the interferometric measurement of ...

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Frontiers in Optics, FiO-2004

作者： Carp, Stefan A. Guerra, Arnold Duque, Samuel Q. Venugopalan, Vasan Department of Chemical Engineering & Materials Science University of California IrvineCA92697 United States Laser Microbeam and Medical Program Beckman Laser Institute University of California IrvineCA92697 United States Department of Biomedical Engineering University of California IrvineCA92697 United States

ISBN: (纸本)1557527792

A modified Mach Zehnder interferometer system has been developed to measure surface motion with 4 ns temporal resolution and 0.2 nm displacement sensitivity. We discuss its use to measure the optical properties of homogeneous turbid media and image heterogeneous volumes to depths of 1 cm with 200 micrometer resolution. © 2004 OSA/FIO 2004

关键词： Optical properties

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Forming 3D scaffolds of hydroxyapatite-gelatin nano-composites using mechanical method and selective solid etching method

Forming 3D scaffolds of hydroxyapatite-gelatin nano-composit...

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Transactions - 7th World Biomaterials Congress

作者： Ko, C.C. Douglas, W.H. Chu, T.-M. Chang, M.C. Narayanan, R.A. Hu, W.-S. Minnesota Dent. Res. Ctr. B./B. Univ. of Minnesota Minneapolis MN 55455 United States Biomedical Engineering Program Indiana Univ. Purdue Univ. Indianapolis IN 46202 United States Department of Chemical Engineering University of Minnesota Minneapolis MN 55455 United States

ISBN: (纸本)1877040193

Direct mechanical approaches and selective solid etching methods were developed to create a 3D porous scaffold of hydroxyapatite-gelatin (HAP-GEL) nanocomposites. The mechanical method creates a regular array of pores but with limited architectures. The selective solid etching using computer aided design (CAD) can create controlled pore structures, but with shrinkage cracks. It has been possible to eliminate cracks using hydraulic pressure for dehydration;this technique in combination with the selective solid etching method is currently under developing.

关键词： Nanostructured materials

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Sampling tissue volumes using frequency-domain photon migration

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Physical Review E 2004年第5期69卷 051908-051908页

作者： Frédéric Bevilacqua Joon S. You Carole K. Hayakawa Vasan Venugopalan Laser Microbeam and Medical Program Beckman Laser Institute 1002 Health Sciences Road East Irvine California 92612 USA Department of Biomedical Engineering Univeristy of California–Irvine Irvine Calfornia 92697 USA Department of Chemical Engineering and Materials Science University of California–Irvine Irvine California 92697 USA

We demonstrate the use of Monte Carlo simulations to generate photon scattering density functions (PSDFs) that represent the tissue volume sampled by steady-state and frequency-domain photon migration. We use these results to illustrate how scaling laws can be developed to determine the mean sampling depth of the multiply scattered photons detected by photon migration methods that remain valid outside the bounds of the standard diffusion approximation, i.e., at small source-detector separations and in media where the optical absorption is significant relative to scattering. Using both the PSDF computation and the newly formulated scaling laws, we focus on a comprehensive description of the effects of source modulation frequency, optical absorption, and source-detector separation on the depth of the sampled tissue volume as well as the sensitivity of frequency-domain photon migration measurements to the presence of a localized absorption heterogeneity.

关键词： Tissue

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Effective laboratory exercises for an introduction to biomedical engineering course

Effective laboratory exercises for an introduction to biomed...

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2003 ASEE Annual Conference and Exposition: Staying in Tune with engineering Education

作者： Cavanagh, Daniel P. Herbertson, Luke H. Biomedical Engineering Program Chemical Engineering Department Bucknell University Lewisburg PA

The application of two experimental laboratory exercises to provide students with hands-on experiences in the areas of biotransport and biomaterials is discussed. A hemodialysis simulation unit implemented for biomedical laboratory consists of recirculationmg blood side, commercial hemodialyzers and various pressure and flow transducers. The material testing exercise also help student to design constraints for the development of artificail skin and tissue engineering. It also helps to demonstrate the similarities and differences between the two materials.

关键词： biomedical engineering

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A Microsensor Based on a Microcantilever Patterned with an Environmentally Sensitive Hydrogel

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MRS Online Proceedings Library 2003年第1期729卷 481-486页

作者： Zachary Hilt, J. Gupta, Amit K. Bashir, Rashid Peppas, Nicholas A. NSF Program on Therapeutic and Diagnostic Devices Purdue University West Lafayette USA Biomaterials and Drug Delivery Laboratories School of Chemical Engineering Purdue University West Lafayette USA Department of Electrical and Computer Engineering Purdue University West Lafayette USA Department of Biomedical Engineering Purdue University West Lafayette USA

A process was developed for patterning thin films of environmentally sensitive hydrogels onto silicon microcantilevers. Microcantilevers have been shown to be ultra-sensitive transducers for chemical, physical, and biological microsensors. By patterning environmentally sensitive hydrogels onto silicon microcantilevers, novel microsensors were prepared for MEMS and BioMEMS applications. Specifically, a cross-linked poly(methacrylic acid) (PMAA) network containing significant amounts of poly(ethylene glycol) dimethacrylate (PEGDMA) was studied. This hydrogel exhibits a swelling dependence on pH. By increasing the environmental pH above the pKa of PMAA to cause ionization of the carboxylic acid groups, electrostatic repulsion is produced along the main polymer chain causing the polymer network to expand and swell. Therefore, a pH change induces swelling or shrinking of the polymer network and creates stress on the microcantilever surface causing it to bend. In this study, silicon microcantilevers were fabricated on p-type (100) SOI wafers. Covalent adhesion was gained between the polymer and the silicon surface through the modification of the silicon surface with ?-methacryloxypropyl trimethoxysilane. Hydrogels were patterned onto the silicon microcantilevers utilizing a mask aligner to allow for precise positioning. The micropatterned hydrogels were analyzed using optical microscopy and profilometry. The bending response of patterned cantilevers with a change in environmental pH was observed, providing proof-of-concept for a MEMS/BioMEMS sensor based on microcantilevers patterned with environmentally sensitive hydrogels.

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