76
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Islam MF, Alsayed AM, Dogic Z, Zhang J, Lubensky TC, Yodh AG. Nematic nanotube gels. PHYSICAL REVIEW LETTERS 2004; 92:088303. [PMID: 14995821 DOI: 10.1103/physrevlett.92.088303] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2003] [Indexed: 05/24/2023]
Abstract
We report the creation of nematic nanotube gels containing large domains of isolated, oriented, half-micron-long, single-wall carbon nanotubes (SWNTs). We make them by homogeneously dispersing surfactant coated SWNTs at low concentration in an N-isopropyl acrylamide gel and then inducing a volume-compression transition. These gels exhibit hallmark properties of a nematic: birefrigence, anisotropy in optical absorption, and disclination defects. We also investigate the isotropic-to-nematic transition of these gels, and we describe the physical properties of their ensuing nematic state, including a novel buckling of sample walls. Finally, we provide a simple model to explain our observations.
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77
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Sapienza R, Mujumdar S, Cheung C, Yodh AG, Wiersma D. Anisotropic weak localization of light. PHYSICAL REVIEW LETTERS 2004; 92:033903. [PMID: 14753877 DOI: 10.1103/physrevlett.92.033903] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2003] [Indexed: 05/20/2023]
Abstract
We have observed angular anisotropy in weak localization of light from highly scattering, orientationally ordered, nematic liquid crystals. This demonstration of angular anisotropy in a multiple-scattering interference phenomenon was facilitated by a light scattering instrument with extraordinary angular resolution. The measured anisotropies were consistent with a simple model of coherent backscattering generalized for propagation-direction dependent mean free paths.
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78
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Culver JP, Durduran T, Cheung C, Furuya D, Greenberg JH, Yodh AG. Diffuse optical measurement of hemoglobin and cerebral blood flow in rat brain during hypercapnia, hypoxia and cardiac arrest. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 510:293-7. [PMID: 12580443 DOI: 10.1007/978-1-4615-0205-0_48] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/22/2023]
Abstract
We have demonstrated the ability to concurrently measure relative changes in cerebral blood flow, hemoglobin concentration, and hemoglobin oxygenation with a single non-contact, non-invasive instrument. Our measurements from rat hypercapnia, hypoxia and cardiac arrest models are in reasonable agreement with the literature, and offer the possibility for further growth and quantification. The optical techniques used in this study are attractive also because they enable experimenters to measure vascular response of deep tissues. The new instrument and concept may also be applicable to human studies especially in infants and neonates permitting noninvasive monitoring of cerebral hemodynamics and oxygen (see [4] and [2] for examples of NIR spectroscopy).
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79
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Culver JP, Durduran T, Furuya D, Cheung C, Greenberg JH, Yodh AG. Diffuse optical tomography of cerebral blood flow, oxygenation, and metabolism in rat during focal ischemia. J Cereb Blood Flow Metab 2003; 23:911-24. [PMID: 12902835 DOI: 10.1097/01.wcb.0000076703.71231.bb] [Citation(s) in RCA: 245] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Diffuse optical tomography (DOT) is an attractive approach for evaluating stroke physiology. It provides hemodynamic and metabolic imaging with unique potential for continuous noninvasive bedside imaging in humans. To date there have been few quantitative spatial-temporal studies of stroke pathophysiology based on diffuse optical signatures. The authors report DOT images of hemodynamic and metabolic contrasts using a rat middle cerebral artery occlusion (MCAO) stroke model. This study used a novel DOT device that concurrently obtains coregistered images of relative cerebral blood volume (rCBV), tissue-averaged hemoglobin oxygen saturation (Sto(2)), and relative cerebral blood flow (rCBF). The authors demonstrate how these hemodynamic measures can be synthesized to calculate an index of the oxygen extraction fraction (OEF) and the cerebral metabolic rate of oxygen consumption (CMRo(2)). Temporary (60-minute) MCAO was performed on five rats. Ischemic changes, averaged over the 60 minutes of occlusion, were as follows: rCBF = 0.42 +/- 0.04, rCBV = 1.02 +/- 0.04, DeltaSto(2) = -11 +/- 2%, rOEF = 1.39 +/- 0.06 and rCMRo(2) = 0.59 +/- 0.07. Although rOEF increased in response to decreased blood flow, rCMRo(2) decreased. The sensitivity of this method of DOT analysis is discussed in terms of assumptions about baseline physiology, and the diffuse optical results are compared with positron emission tomography, magnetic resonance imaging, and histology observations in the literature.
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80
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Intes X, Ripoll J, Chen Y, Nioka S, Yodh AG, Chance B. In vivo continuous-wave optical breast imaging enhanced with Indocyanine Green. Med Phys 2003; 30:1039-47. [PMID: 12852527 DOI: 10.1118/1.1573791] [Citation(s) in RCA: 200] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
We investigate the uptake of a nontargeted contrast agent by breast tumors using a continuous wave diffuse optical tomography apparatus. The instrument operates in the near-infrared spectral window and employs 16 sources and 16 detectors to collect light in parallel on the surface of the tumor-bearing breast (coronal geometry). In our protocol an extrinsic contrast agent, Indocyanine Green (ICG), was injected by bolus. Three clinical scenarios with three different pathologies were investigated. A two-compartment model was used to analyze the pharmacokinetics of ICG and preprocess the data, and diffuse optical tomography was used for imaging. Localization and delineation of the tumor was achieved in good agreement with a priori information. Moreover, different dynamical features were observed for differing pathologies. The malignant cases exhibited slower rate constants (uptake and outflow) compared to healthy tissue. These results provide further evidence that in vivo pharmacokinetics of ICG in breast tumors may be a useful diagnostic tool for differentiation of benign and malignant pathologies.
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81
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Chen DT, Weeks ER, Crocker JC, Islam MF, Verma R, Gruber J, Levine AJ, Lubensky TC, Yodh AG. Rheological microscopy: local mechanical properties from microrheology. PHYSICAL REVIEW LETTERS 2003; 90:108301. [PMID: 12689039 DOI: 10.1103/physrevlett.90.108301] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2002] [Indexed: 05/24/2023]
Abstract
We demonstrate how tracer microrheology methods can be extended to study submicron scale variations in the viscoelastic response of soft materials; in particular, a semidilute solution of lambda-DNA. The polymer concentration is depleted near the surfaces of the tracer particles, within a distance comparable to the polymer correlation length. The rheology of this microscopic layer alters the tracers' motion and can be precisely quantified using one- and two-point microrheology. Interestingly, we found this mechanically distinct layer to be twice as thick as the layer of depleted concentration, likely due to solvent drainage through the locally perturbed polymer structure.
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82
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Islam MF, Lin KH, Lacoste D, Lubensky TC, Yodh AG. Field-induced structures in miscible ferrofluid suspensions with and without latex spheres. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 67:021402. [PMID: 12636674 DOI: 10.1103/physreve.67.021402] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2002] [Indexed: 05/24/2023]
Abstract
We explore magnetic-field-induced ordering and microphase separation of aqueous ferrofluid and of aqueous mixtures of ferrofluid with nonmagnetic latex spheres. The ferrofluid is a surfactant stabilized aqueous suspension of magnetite (Fe3O4) particles with average diameter 20 nm (including the approximately 2.5-nm thick surfactant layer); the nonmagnetic latex spheres are charge stabilized polymethylmethacrylate (PMMA) particles with diameters of 42 nm, 108 nm, and 220 nm. In the presence of a uniform magnetic field, needlelike ferrofluid droplets formed that eventually grew to sample-traversing columns at fields of approximately 600 G; the two-dimensional structure of these columns was, however, glassy rather than hexagonal. In higher fields, approximately 1000 G, the columns stretched and coalesced into sheetlike striped liquids, but a true lamellar phase was not observed. The addition of nonmagnetic latex spheres to the ferrofluid suspension lowered substantially the critical field for the formation of columns, and induced lamellar (stripe) phases at relatively low applied fields. Image analysis was used to determine the spatial correlation functions, the average needle or column spacing, and the average lamellae spacing of these samples as a function of latex sphere size and concentration.
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83
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Culver JP, Choe R, Holboke MJ, Zubkov L, Durduran T, Slemp A, Ntziachristos V, Chance B, Yodh AG. Three-dimensional diffuse optical tomography in the parallel plane transmission geometry: evaluation of a hybrid frequency domain/continuous wave clinical system for breast imaging. Med Phys 2003; 30:235-47. [PMID: 12607841 DOI: 10.1118/1.1534109] [Citation(s) in RCA: 164] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Three-dimensional diffuse optical tomography (DOT) of breast requires large data sets for even modest resolution (1 cm). We present a hybrid DOT system that combines a limited number of frequency domain (FD) measurements with a large set of continuous wave (cw) measurements. The FD measurements are used to quantitatively determine tissue averaged absorption and scattering coefficients. The larger cw data sets (10(5) measurements) collected with a lens coupled CCD, permit 3D DOT reconstructions of a 1-liter tissue volume. To address the computational complexity of large data sets and 3D volumes we employ finite difference based reconstructions computed in parallel. Tissue phantom measurements evaluate imaging performance. The tests include the following: point spread function measures of resolution, characterization of the size and contrast of single objects, field of view measurements and spectral characterization of constituent concentrations. We also report in vivo measurements. Average tissue optical properties of a healthy breast are used to deduce oxy- and deoxy-hemoglobin concentrations. Differential imaging with a tumor simulating target adhered to the surface of a healthy breast evaluates the influence of physiologic fluctuations on image noise. This tomography system provides robust, quantitative, full 3D image reconstructions with the advantages of high data throughput, single detector-tissue coupling path, and large (1L) imaging domains. In addition, we find that point spread function measurements provide a useful and comprehensive representation of system performance.
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84
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Durduran T, Choe R, Culver JP, Zubkov L, Holboke MJ, Giammarco J, Chance B, Yodh AG. Bulk optical properties of healthy female breast tissue. Phys Med Biol 2002; 47:2847-61. [PMID: 12222850 DOI: 10.1088/0031-9155/47/16/302] [Citation(s) in RCA: 168] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We have measured the bulk optical properties of healthy female breast tissues in vivo in the parallel plate, transmission geometry. Fifty-two volunteers were measured. Blood volume and blood oxygen saturation were derived from the optical property data using a novel method that employed a priori spectral information to overcome limitations associated with simple homogeneous tissue models. The measurements provide an estimate of the variation of normal breast tissue optical properties in a fairly large population. The mean blood volume was 34 +/- 9 microM and the mean blood oxygen saturation was 68 +/- 8%. We also investigated the correlation of these optical properties with demographic factors such as body mass index (BMI) and age. We observed a weak correlation of blood volume and reduced scattering coefficient with BMI: correlation with age, however, was not evident within the statistical error of these experiments. The new information on healthy breast tissue provides insight about the potential contrasts available for diffuse optical tomography of breast tumours.
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85
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Lau AWC, Lin KH, Yodh AG. Entropic interactions in suspensions of semiflexible rods: short-range effects of flexibility. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 66:020401. [PMID: 12241139 DOI: 10.1103/physreve.66.020401] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2002] [Indexed: 05/23/2023]
Abstract
We compute the entropic interactions between two colloidal spheres immersed in a dilute suspension of semiflexible rods. Our model treats the semiflexible rod as a bent rod at fixed angle, set by the rod contour and persistence lengths. The entropic forces arising from this additional rotational degree of freedom are captured quantitatively by the model, and account for observations at short range in a recent experiment. Global fits to the interaction potential data suggest the persistence length of the fd virus is about two to three times smaller than the commonly used value of 2.2 microm.
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86
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Ntziachristos V, Yodh AG, Schnall MD, Chance B. MRI-guided diffuse optical spectroscopy of malignant and benign breast lesions. Neoplasia 2002; 4:347-54. [PMID: 12082551 PMCID: PMC1661680 DOI: 10.1038/sj.neo.7900244] [Citation(s) in RCA: 252] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2001] [Accepted: 01/21/2002] [Indexed: 01/29/2023]
Abstract
We present the clinical implementation of a novel hybrid system that combines magnetic resonance imaging (MRI) and near-infrared (NIR) optical measurements for the noninvasive study of breast cancer in vivo. Fourteen patients were studied with a MR-NIR prototype imager and spectrometer. A diffuse optical tomographic scheme employed the MR images as a priori information to implement an image-guided NIR localized spectroscopic scheme. All patients who entered the study also underwent gadolinium-enhanced MRI and biopsy so that the optical findings were cross-validated with MR readings and histopathology. The technique quantified the oxy- and deoxyhemoglobin of five malignant and nine benign breast lesions in vivo. Breast cancers were found with decreased oxygen saturation and higher blood concentration than most benign lesions. The average hemoglobin concentration ([H]) of cancers was 0.130+/-0.100 mM, and the average hemoglobin saturation (Y) was 60+/-9% compared to [H]=0.018+/-0.005 mM and Y=69+/-6% of background tissue. Fibroadenomas exhibited high hemoglobin concentration [H]=0.060+/-0.010 mM and mild decrease in oxygen saturation Y=67+/-2%. Cysts and other normal lesions were easily differentiated based on intrinsic contrast information. This novel optical technology can be a significant add-on in MR examinations and can be used to characterize functional parameters of cancers with diagnostic and treatment prognosis potential. It is foreseen that the technique can play a major role in functional activation studies of brain and muscle as well.
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MESH Headings
- Biopsy
- Breast/chemistry
- Breast/pathology
- Breast Diseases/diagnosis
- Breast Diseases/metabolism
- Breast Diseases/pathology
- Breast Neoplasms/blood supply
- Breast Neoplasms/chemistry
- Breast Neoplasms/diagnosis
- Breast Neoplasms/pathology
- Carcinoma, Ductal, Breast/blood supply
- Carcinoma, Ductal, Breast/chemistry
- Carcinoma, Ductal, Breast/diagnosis
- Carcinoma, Ductal, Breast/pathology
- Carcinoma, Intraductal, Noninfiltrating/chemistry
- Carcinoma, Intraductal, Noninfiltrating/diagnosis
- Carcinoma, Intraductal, Noninfiltrating/pathology
- Contrast Media
- Cysts/blood supply
- Cysts/chemistry
- Cysts/diagnosis
- Cysts/pathology
- Diagnosis, Differential
- Female
- Fibroadenoma/blood supply
- Fibroadenoma/chemistry
- Fibroadenoma/diagnosis
- Fibroadenoma/pathology
- Fibrocystic Breast Disease/diagnosis
- Fibrocystic Breast Disease/metabolism
- Fibrocystic Breast Disease/pathology
- Gadolinium
- Hemoglobins/analysis
- Humans
- Hyperplasia
- Magnetic Resonance Imaging
- Magnetic Resonance Spectroscopy
- Oxygen/analysis
- Oxyhemoglobins/analysis
- Tomography/methods
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87
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Solonenko M, Cheung R, Busch TM, Kachur A, Griffin GM, Vulcan T, Zhu TC, Wang HW, Hahn SM, Yodh AG. In vivo reflectance measurement of optical properties, blood oxygenation and motexafin lutetium uptake in canine large bowels, kidneys and prostates. Phys Med Biol 2002; 47:857-73. [PMID: 11936174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
Motexafin lutetium (MLu) is a second-generation photosensitizer for photodynamic therapy (PDT) of cancer. We have developed and applied a diffuse optical reflectance spectrometer for in vivo measurement of MLu uptake, optical properties, haemoglobin concentration and haemoglobin oxygen saturation in normal canine large bowels, kidneys and prostates. The probe consists of a broadband fibre-optic-coupled light source and detector fibres placed at various distances from the source fibre to collect reflected light. An analysis based on the diffusion approximation of the photon transport equation was used to recover tissue optical properties from the reflectance measurements. The instrumentation and analysis methods were validated using measurements from homogeneous, highly scattering phantoms with known MLu concentrations. The same techniques were then used to estimate chromophore concentrations of normal canine large bowels, kidneys and prostates. We estimated (mean (standard deviation)) total haemoglobin concentrations of 119 (25), 340 (92) and 51 (11) microM in the large bowels, kidneys and prostates of four dogs, respectively; tissue blood oxygen saturations in these same organs were 75 (15), 76 (21) and 74 (16) per cent, respectively. Tissue MLu concentrations (mg l(-1)) were estimated from data taken 3.5 h after injection of a 2 mg kg(-1) injected dose; data from three dogs gave concentrations of 2.4 (0.4) in large bowels, 6.8 (1.3) in kidneys and 2.2 (1.1) in prostates. The reduced scattering coefficients, mu's, estimated for large bowels, kidneys and prostates at 730 nm were, respectively: 10.1 (1.3), 19.6 (4.0) and 12.7 (0.6) cm(-1). We observed significant variability in MLu uptake, tissue scattering and haemoglobin concentration between organs and even between the same organ in different dogs. This class of in situ optical property measurement may be desirable to individualize PDT drug and light delivery.
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88
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Mach P, Wiltzius P, Megens M, Weitz DA, Lin Kh KH, Lubensky TC, Yodh AG. Electro-optic response and switchable Bragg diffraction for liquid crystals in colloid-templated materials. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 65:031720. [PMID: 11909094 DOI: 10.1103/physreve.65.031720] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2001] [Indexed: 05/23/2023]
Abstract
We report optical switching studies on nematic liquid crystal incorporated into structures based on self-assembled colloids. We compare the electro-optic responses of liquid crystal imbibed into colloid-templated polymers, liquid crystal imbibed in the interstitial space of colloid crystals, and conventional polymer-dispersed liquid crystals. We characterize the Bragg diffraction of our templated liquid-crystal/polymer composites as a function of electric field and measure switching times. The response of liquid crystal in connected networks differs qualitatively from that of liquid crystal in isolated cavities.
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89
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Yang N, Angerer WE, Yodh AG. Angle-resolved second-harmonic light scattering from colloidal particles. PHYSICAL REVIEW LETTERS 2001; 87:103902. [PMID: 11531479 DOI: 10.1103/physrevlett.87.103902] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2001] [Indexed: 05/23/2023]
Abstract
We report angle-resolved second-harmonic generation (SHG) measurements from suspensions of centrosymmetric micron-size polystyrene spheres with surface-adsorbed dye (malachite green). The second-harmonic scattering profiles differ qualitatively from linear light scattering profiles of the same particles. We investigated these radiation patterns using several polarization configurations and particle diameters. We introduce a simple Rayleigh-Gans-Debye model to account for the SHG scattering anisotropy. The model compares favorably with our experimental data. Our measurements suggest scattering anisotropy may be used to isolate particle nonlinear optics from other bulk nonlinear optical effects in suspension.
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90
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Lin K, Crocker JC, Zeri AC, Yodh AG. Colloidal interactions in suspensions of rods. PHYSICAL REVIEW LETTERS 2001; 87:088301. [PMID: 11497987 DOI: 10.1103/physrevlett.87.088301] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2001] [Indexed: 05/23/2023]
Abstract
We report direct measurements of entropic interactions of colloidal spheres in suspensions of rodlike fd bacteriophage. We investigate the influence of sphere size, rod concentration, and ionic strength on these interactions. Although the results compare favorably with a recent calculation, small discrepancies reveal entropic effects due to rod flexibility. At high salt concentrations, the potential turns repulsive as a result of viral adsorption on the spheres and viral bridging between the spheres.
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91
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Cheung C, Culver JP, Takahashi K, Greenberg JH, Yodh AG. In vivo cerebrovascular measurement combining diffuse near-infrared absorption and correlation spectroscopies. Phys Med Biol 2001; 46:2053-65. [PMID: 11512610 DOI: 10.1088/0031-9155/46/8/302] [Citation(s) in RCA: 155] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We combine two near-infrared diffuse optical techniques to study variations of blood flow, haemoglobin concentration, and blood oxygen saturation in the functioning rat brain. Diffuse correlation spectroscopy (or flowmetry) monitors changes in the cerebral blood flow, without the use of the principles of tracer clearance, by measuring the optical phase-shifts caused by moving blood cells. Near-infrared absorption spectroscopy concurrently measures tissue absorption at two wavelengths to determine haemoglobin concentration and blood oxygen saturation in this same tissue volume. This optical probe is non-invasive and was employed through the intact skull. The utility of the technique is demonstrated in vivo by measuring the temporal changes in the regional vascular dynamics of rat brain during hypercapnia. Temporal and spatial variations of cerebral blood flow, haemoglobin concentration and blood oxygen saturation during hypercapnia are compared with other measurements in the literature, and a quantitative analysis demonstrating the self-consistency of our combined observations of vascular response is presented.
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92
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Owen RJ, Crocker JC, Verma R, Yodh AG. Measurement of long-range steric repulsions between microspheres due to an adsorbed polymer. PHYSICAL REVIEW E 2001; 64:011401. [PMID: 11461251 DOI: 10.1103/physreve.64.011401] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2000] [Indexed: 11/07/2022]
Abstract
We have measured the interparticle potential between pairs of micron-sized silica spheres induced by adsorbed polyethylene oxide polymer using a line-scanned optical tweezer. We found this long-range steric repulsion to be exponential over the range of energies (0.1k(B)T-5k(B)T) and polymer molecular weights (452,000-1,580,000) studied, and that the potential scaled with the polymer's radius of gyration R(G). The potential's exponential decay length was about 0.6R(G) and its range was about 4R(G), although both parameters varied significantly from one pair of spheres to another. The potential's exponential prefactor was greater than mean-field predictions.
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93
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Ntziachristos V, Hielscher AH, Yodh AG, Chance B. Diffuse optical tomography of highly heterogeneous media. IEEE TRANSACTIONS ON MEDICAL IMAGING 2001; 20:470-8. [PMID: 11437107 DOI: 10.1109/42.929613] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
We investigate the performance of diffuse optical tomography to image highly heterogeneous media, such as breast tissue, as a function of background heterogeneity. To model the background heterogeneity, we have employed the functional information derived from Gadolinium-enhanced magnetic resonance images of the breast. We demonstrate that overall image quality and quantification accuracy worsens as the background heterogeneity increases. Furthermore we confirm the appearance of characteristic artifacts at the boundaries that scale with background heterogeneity. These artifacts are very similar to the ones seen in clinical examinations and can be misinterpreted as actual objects if not accounted for. To eliminate the artifacts and improve the overall image reconstruction, we apply a data-correction algorithm that yields superior reconstruction results and is virtually independent of the degree of the background heterogeneity.
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94
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Culver JP, Ntziachristos V, Holboke MJ, Yodh AG. Optimization of optode arrangements for diffuse optical tomography: A singular-value analysis. OPTICS LETTERS 2001; 26:701-3. [PMID: 18040425 DOI: 10.1364/ol.26.000701] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
We develope a method to optimize the resolution of diffuse optical tomographic instruments. Singular-value analysis of the tomographic weight matrix associated with specific data types, geometries, and optode arrangements is shown to provide a measure of image resolution. We achieve optimization of device configuration by monitoring the resolution measure described. We introduce this idea and demonstrate its utility by optimizing the spatial sampling interval and field-of-view parameters in the parallel-plane transmission geometry employed for diffuse optical breast imaging. We also compare resolution in transmission and remission geometries.
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95
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Ripoll J, Ntziachristos V, Culver JP, Pattanayak DN, Yodh AG, Nieto-Vesperinas M. Recovery of optical parameters in multiple-layered diffusive media: theory and experiments. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2001; 18:821-830. [PMID: 11318332 DOI: 10.1364/josaa.18.000821] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Diffuse photon density waves have lately been used both to characterize diffusive media and to locate and characterize hidden objects, such as tumors, in soft tissue. In practice, most biological media of medical interest consist of various layers with different optical properties, such as the fat layer in the breast or the different layers present in the skin. Also, most experimental setups consist of a multilayered system, where the medium to be characterized (i.e., the patient's organ) is usually bounded by optically diffusive plates. Incorrect modeling of interfaces may induce errors comparable to the weak signals obtained from tumors embedded deep in highly heterogeneous tissue and lead to significant reconstruction artifacts. To provide a means to analyze the data acquired in these configurations, the basic expressions for the reflection and transmission coefficients for diffusive-diffusive and diffusive-nondiffusive interfaces are presented. A comparison is made between a diffusive slab and an ordinary dielectric slab, thus establishing the limiting distance between the two interfaces of the slab for multiple reflections between them to be considered important. A rigorous formulation for multiple-layered (M-layered) diffusive media is put forward, and a method for solving any M-layered medium is shown. The theory presented is used to characterize a two-layered medium from transmission measurements, showing that the coefficients of scattering, mu'(s) , and absorption, mu(a) , are retrieved with great accuracy. Finally, we demonstrate the simultaneous retrieval of both mu;(s) and mu(a).
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96
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Griffin GM, Zhu T, Solonenko M, Del Piero F, Kapakin A, Busch TM, Yodh A, Polin G, Bauer T, Fraker D, Hahn SM. Preclinical evaluation of motexafin lutetium-mediated intraperitoneal photodynamic therapy in a canine model. Clin Cancer Res 2001; 7:374-81. [PMID: 11234893] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
Abstract
Intraperitoneal photodynamic therapy (IP PDT) is an experimental cancer treatment in clinical development for the treatment of peritoneal carcinomatosis and sarcomatosis. A canine study of motexafin lutetium (Lu-Tex)-mediated IP PDT was performed to evaluate normal tissue toxicities of this treatment in the presence and absence of a bowel resection and to assess the feasibility of measuring Lu-Tex fluorescence in abdominal tissues. Thirteen dogs were treated with Lu-Tex (0.2-2 mg/kg) i.v. 3 h before laparotomy and 730-nm light delivery (fluences, 0.5-2.0 J/cm2; average fluence rate <150 mW/cm2). Laparoscopy was performed 7-10 days after the procedure to assess acute toxicities. In situ fluorescence spectra were obtained from various abdominal tissues before and after light delivery using a fiber array probe with fixed-source detector distances. Lu-Tex-mediated IP PDT was well tolerated at the doses of drug and light studied. Bowel toxicity was not observed in animals treated with a bowel resection before PDT. Mild transient liver function test abnormalities without associated clinical sequelae were observed. No gross PDT-related abnormalities were observed at laparoscopy or necropsy; however, thickening in the glomerular capillary wall and the mesangium were noted microscopically in the kidneys of seven dogs. No renal function abnormalities were found. Analysis of the fluorescence spectra from intra-abdominal tissues suggests that measurements of Lu-Tex in situ are feasible and may provide a way of assessing photosensitizer concentration in vivo without the need for a biopsy. These results support the continued development of Lu-Tex as a candidate photosensitizer for IP PDT.
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97
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Intes X, Chance B, Holboke M, Yodh A. Interfering diffusive photon-density waves with an absorbing-fluorescent inhomogeneity. OPTICS EXPRESS 2001; 8:223-31. [PMID: 19417808 DOI: 10.1364/oe.8.000223] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
This work reports an investigation of the fluorescent field re-emitted by an object embedded in a highly scattering media illuminated by two-interfering sources. Simulations in the frequency domain with a finite difference method solving the diffusion equation were performed. The media considered had features typical of a soft-compressed breast. An absorbing-fluorescent inhomogeneity was embedded in the center of the slab. A qualitative study of the re-emitted field was achieved. The re-emitted field was found to possess unique features characteristic of the two-interfering sources excitation, i.e. null intensity when the object was between the two sources and a 180 degrees transition crossing this position. Those features, when performing a scan of the two sources, permitted accurate localization of the inhomogeneity. Moreover, even when the detector was not placed on the mid-plane of the two sources, the re-emitted field still exhibited the interfering characteristic pattern, which was not seen at the excitation wavelength. Thus, for such configurations, the re-emitted field still possessed the specific sensitivity of phased array emission conversely to the excitation wavelength.
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98
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Lin K, Crocker JC, Prasad V, Schofield A, Weitz DA, Lubensky TC, Yodh AG. Entropically driven colloidal crystallization on patterned surfaces. PHYSICAL REVIEW LETTERS 2000; 85:1770-1773. [PMID: 10970610 DOI: 10.1103/physrevlett.85.1770] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2000] [Indexed: 05/23/2023]
Abstract
We investigate the self-assembly of colloidal spheres on periodically patterned templates. The surface potentials and the surface phases are induced entropically by the presence of dissolved, nonadsorbing polymers. A rich variety of two-dimensional fluidlike and solidlike phases was observed to form on template potentials with both one- and two-dimensional symmetry. The same methodology was then used to nucleate an oriented single fcc crystal more than 30 layers thick. The general approach provides a new route for directed self-assembly of novel mesoscopic structures.
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99
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Crocker JC, Valentine MT, Weeks ER, Gisler T, Kaplan PD, Yodh AG, Weitz DA. Two-point microrheology of inhomogeneous soft materials. PHYSICAL REVIEW LETTERS 2000; 85:888-91. [PMID: 10991424 DOI: 10.1103/physrevlett.85.888] [Citation(s) in RCA: 366] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/1999] [Indexed: 05/18/2023]
Abstract
We demonstrate a novel method for measuring the microrheology of soft viscoelastic media, based on cross correlating the thermal motion of pairs of embedded tracer particles. The method does not depend on the exact nature of the coupling between the tracers and the medium, and yields accurate rheological data for highly inhomogeneous materials. We demonstrate the accuracy of this method with a guar solution, for which other microscopic methods fail due to the polymer's mesoscopic inhomogeneity. Measurements in an F-actin solution suggest conventional microrheology measurements may not reflect the true bulk behavior.
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100
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Vulcan TG, Zhu TC, Rodriguez CE, Hsi A, Fraker DL, Baas P, Murrer LH, Star WM, Glatstein E, Yodh AG, Hahn SM. Comparison between isotropic and nonisotropic dosimetry systems during intraperitoneal photodynamic therapy. Lasers Surg Med 2000; 26:292-301. [PMID: 10738292 DOI: 10.1002/(sici)1096-9101(2000)26:3<292::aid-lsm7>3.0.co;2-t] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
BACKGROUND AND OBJECTIVE On-line monitoring of light fluence during intraperitoneal photodynamic therapy (IP PDT) is crucial for safe light delivery. A flat photodiode-based dosimetry system is compared with an isotropic detector-based system in patients undergoing IP PDT. STUDY DESIGN/MATERIALS AND METHODS Flat photodiodes and spherical detectors were placed side by side in the abdomen, for simultaneous light dosimetry in 19 patients. Tissue phantom experiments were performed to provide a preliminary estimate of the tissue optical properties of the peritoneum. RESULTS The conversion factor between systems for 630-nm light was found to be 1.7 +/- 0.12. The mu(eff) of the tissues in the abdomen is estimated to vary between 0.5 cm(-1) to 1.4 cm(-1) assuming a mu(s)' = 7 cm(-1). CONCLUSIONS The measured conversion factor should allow for comparison of light fluences with future clinical protocols that use an isotropic-based detector system. Differences in the optical properties of the underlying tissues may contribute to the variability in light measurements.
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