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Biomedical subjects

E N Lewis

Publications and source records attributed to E N Lewis.

15 recordsLinked to original sources
PubMed2001

Imaging of collagen and proteoglycan in cartilage sections using Fourier transform infrared spectral imaging.

OBJECTIVE: To test the hypothesis that Fourier transform infrared (FTIR) spectral imaging, coupled with multivariate data processing techniques, can image the spatial distribution of matrix constituents in native and engineered cartilage samples. METHODS: Tissue sections from native and trypsin-digested bovine nasal cartilage (BNC) and from engineered cartilage, generated by chick sternal chondrocytes grown in a hollow fiber bioreactor, were placed either on calcium fluoride windows for FTIR analysis or gelatinized microscope slides for histologic analysis. Based on the assumption that cartilage is predominantly chondroitin sulfate (CS) and type II collagen, chemical images were extracted from FTIR spectral imaging data sets using 2 multivariate methods: the Euclidean distance algorithm and a least-squares approach. RESULTS: Least-squares analysis of the FTIR data of native BNC yielded a collagen content of 54 +/- 13% and a CS content of 37 +/- 16% (mean +/- SD). Euclidean distance analysis of measurements made on trypsin-digested BNC demonstrated only trace amounts of CS. For engineered cartilage, the CS content was significantly lower (15 +/- 5%), while the collagen content (73 +/- 6%) was significantly higher than biochemically determined values (CS 34%, collagen 5%, protein 61%). These differences are due to the fact that the dimethylmethylene blue assay overestimated the CS content of the tissue because it is not specific for CS, while the FTIR spectral imaging technique overestimated the collagen content because it lacks specificity for different proteins. CONCLUSION: FTIR spectral imaging combines histology-like spatial localization with the quantitative capability of bulk chemical analysis. For molecules with a unique spectral signature, such as CS, the FTIR technique coupled with multivariate analysis can define a unique spatial distribution. However, for some applications, the lack of specificity of this technique for different types of proteins may be a limitation.

Animals↗
PubMed1998

Infrared microspectroscopic imaging of the cerebellum of normal and cytarabine treated rats.

Conventionally, the diagnosis of neuropathology in a subject requires the identification of a behavioral modification, which provides direction for appropriate histological analyses. However, since the ultimate diagnosis of the pathology largely depends on the initial choice of histological tests, the opportunity exists for inaccurate or insensitive results. An innovative approach using Fourier transform infrared (FT-IR) spectroscopic imaging to diagnose neuropathology should prove useful. This novel method monitors and visualizes the underlying chemistry of the tissue, based on hundreds of vibrational absorption bands that are intrinsic to the sample. As such, it makes no prior assumptions as to the type or degree of pathology. Using this technique, we have spectroscopically imaged cerebellar tissue slices from rats [control subjects and subjects treated with the antineoplastic drug, cytarabine (Ara-C)], and have been able to correlate lipid and protein distributions within distinct cell types in the cerebellum. A further benefit of the technique is that it simultaneously records tens of thousands of independent spectra from different spatial locations within the sample. Thus, a variety of statistical and multivariate techniques can be exploited to characterize large sample areas and to provide robust classification of individual spectral signatures. In comparison to standard histological protocols, FT-IR spectroscopic imaging simultaneously analyzes cell layers and identifies subtle structural and biochemical changes within the sample. We suggest that FT-IR spectroscopic imaging should provide a highly reliable, complementary tool for standard histological tier testing.

Animals↗
PubMed1997

Visualization of silicone gel in human breast tissue using new infrared imaging spectroscopy.

Between 1 and 2 million women in the United States have silicone breast implants. Complications include capsular contracture and calcification and possibly connective tissue diseases such as scleroderma and rheumatoid arthritis, a subject of some controversy. In order to accurately assess the role of silicone in any histopathologic change, it is necessary to confirm its presence and to identify other foreign materials in the capsular tissue. Although light microscopy is used to visualize regions of tissue containing foreign inclusions, their chemical identity can only be determined using analytical techniques such as infrared or Raman microscopy. However, these conventional microprobe techniques record spectra only at single points and require an a priori knowledge of the locations of the inclusion to be probed. To significantly extend the capabilities of both infrared spectroscopy and optical microscopy, we have developed a new infrared imaging system that completely integrates these two methods. In this manuscript we highlight the ability of the technique to screen rapidly and to determine accurately the presence, size and chemical composition of silicone gel inclusions in human breast tissue.

Breast↗
PubMed1996

Raman chemical imaging: histopathology of inclusions in human breast tissue.

High-definition Raman chemical imaging microscopy is applied to the histopathological characterization of biopsied human breast tissue containing foreign polymer inclusions. The polymer material is found in a patient with a history of silicone implant breast reconstructive surgery. Silicone implants are, on occasion, anchored to the soft tissues of the chest with polyester patches. In the case studied here, the polyester anchors were incorporated into the patient's fibrous tissue surrounding the implant. High-definition Raman chemical imaging provides molecular-specific image contrast in the complex breast tissue matrix without the use of stains or dyes. This is the first example in which Raman spectroscopic imaging microscopy has been applied to pathology. A goal of this and future studies is to complement traditional histopathologic diagnoses of disease states utilizing vibrational spectroscopic imaging techniques.

Breast↗
PubMed1996

The design and implementation of a high-fidelity Raman imaging microscope.

We describe a Raman imaging microscope that produces high-fidelity, large format Raman images and Raman spectra from samples as small as 1 micron in size. Laser illumination is delivered to the object by means of an infinity corrected microscope objective, either by a galvanometer scanning system or a widefield fibre optic. Wavelength selection of Raman scattered emission is achieved by an acousto-optic tunable filter (AOTF), which maintains image fidelity and provides either continuous or random wavelength selection. The collimated AOTF output is imaged first by a tube lens and then by a projection lens onto a cooled silicon CCD array. Instrument features, including factors that determine the system's spatial and spectral resolution, and design considerations are discussed in detail. Images and spectra of test objects and samples that demonstrate the capability of this imaging spectrometer are presented. The potential of intrinsic chemical imaging is discussed in terms of its use in the analyses of a variety of chemical and biological samples.

Microscopy↗
PubMed1995

Fourier transform spectroscopic imaging using an infrared focal-plane array detector.

A powerful new mid-infrared spectroscopic chemical imaging technique combining step-scan Fourier transform Michelson interferometry with indium antimonide focal-plane array (FPA) image detection is described. The coupling of an infrared focal-plane array detector to an interferometer provides an instrumental multiplex/multichannel advantage. Specifically, the multiple detector elements enable spectra at all pixels to be collected simultaneously, while the interferometer portion of the system allows all the spectral frequencies to be measured concurrently. With this method of mid-infrared spectroscopic imaging, the fidelity of the generated spectral images is limited only by the number of pixels on the FPA detector, and only several seconds of starting time is required for spectral image acquisition. This novel, high-definition technique represents the future of infrared chemical imaging analysis, a new discipline within the chemical and material sciences, which combines the capability of spectroscopy for molecular analysis with the power of visualization. In particular, chemical imaging is broadly applicable for noninvasive, molecular characterization of heterogeneous materials, since all solid-state materials exhibit chemical nonuniformity that exists either by design or by development during the course of material preparation or fabrication. Imaging, employing Raman and infrared spectroscopy, allows the precise characterization of the chemical composition, domain structure, and chemical architecture of a variety of substances. This information is often crucial to a wide range of activities, extending from the fabrication of new materials to a basic understanding of biological samples. In this study, step-scan imaging principles, instrument design details, and infrared chemical imaging results are presented. Since the prospect of performing high-resolution and high-definition mid-infrared chemical imaging very rapidly has been achieved with the step-scan approach, the implications for the chemical analysis of materials are many and varied.

Image Processing, Computer-Assisted↗
PubMed1991

Packing characteristics of highly unsaturated bilayer lipids: Raman spectroscopic studies of multilamellar phosphatidylcholine dispersions.

The thermotropic properties and acyl chain packing characteristics of multilamellar dispersions of highly unsaturated lipids were examined by Raman spectroscopy. Bilayer assemblies were composed of POPC (1-palmitoyl-2-oleoylphosphatidylcholine), PAPC (1-palmitoyl-2-arachidonylphosphatidylcholine), and PDPC (1-palmitoyl-2-docosahexaenoylphosphatidylcholine), lipid systems possessing saturated sn-1 chains and unsaturated sn-2 chains with one, four, and six double bonds, respectively. Raman spectra were recorded in the acyl chain 2800-3100-cm-1 carbon-hydrogen (C-H) stretching and 1100-1200-cm-1 carbon-carbon (C-C) stretching mode regions, spectral intervals reflecting both the inter- and intrachain order/disorder properties of the various lipid dispersions. In order to obtain C-H stretching mode spectra relevant solely to the sn-1 chains of PAPC and PDPC, liquid-phase spectra of arachidonic and docosahexaenoic acid, respectively, were subtracted from the observed phospholipid spectra. The unsaturated sn-2 chains of PAPC and PDPC undergo minimal conformational reorganizations as the bilayers pass from the gel to liquid-crystalline phases. Phase transition temperatures, Tm, derived from statistically fitting the temperature-dependent Raman spectral data are approximately -2.5, -22.5, and -3 degrees C for POPC, PAPC, and PDPC, respectively. As the degree of unsaturation increases from POPC to PAPC and PDPC, the cooperativity of the phase transition, as measured by its breadth, decreases. Estimates of the transition widths from the temperature profiles are approximately 15 degrees C for PAPC and 20 degrees C for PDPC. The behavior of various Raman spectral parameters for the lipid gel phase reflects the formation of lateral microdomains, or clusters, whose packing properties maximize the van der Waals interactions between sn-1 chains.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystallography↗
PubMed1989

Infrared spectroscopic study of ethanol-induced changes in rat liver plasma membrane.

Vibrational infrared spectroscopy, a noninvasive method for probing the structural and dynamic properties of biological membranes, is used to characterize the in vivo and in vitro perturbations of ethanol on various liver plasma membrane preparations derived from alcohol-treated rats. Spectral frequency shifts of the bilayer lipid chain methylene carbon-hydrogen symmetric stretching modes indicate that the adaptive response of the liver plasma membranes of the alcohol-treated animals results in an increase in membrane order on the vibrational time scale. Additional in vitro ethanol treatment of these membrane preparations leads to further significant increases in bilayer order. The observed membrane ordering effects are consistent with a bilayer model of partial interdigitation, or chain overlap, of the opposing membrane monolayers near the bilayer center.

Animals↗
PubMed1986

Methyl group substitution at C(1), C(2) or C(3) of the glycerol backbone of a diether phosphocholine: a comparative study of bilayer chain disorder in the gel and liquid-crystalline phases.

Alterations in the inter- and intramolecular packing characteristics of aqueous dispersions of methyl derivatives of di-O-hexadecylglycerophosphocholine (DHPC), an ether lipid in which the methyl group is substituted at the 1, 2 or 3 position of the glycerol backbone, were monitored by changes in the vibrational frequencies and intensities of selected spectral features by Raman spectroscopy. Temperature profiles constructed from spectra reflecting intermolecular order/disorder rearrangements (C-H stretching mode region) and intramolecular order/disorder processes (C-C stretching mode region) provide insight into several important structural properties of diether lipid bilayers. The introduction of a methyl group into any position of the glycerol backbone alters both the characteristics of the DHPC pretransition and the temperature of the gel to liquid-crystalline phase transition. The main gel to liquid-crystalline phase transitions are 42.8 degrees C in the pure diether lipid, 41.6 degrees C for 3-Me-DHPC, 40.5 degrees C for 2-Me-DHPC and 38.1 degrees C for 1-Me-DHPC. Temperature profiles indicate that the degree of disordering for both the gel and liquid-crystalline states follows the sequence 2-Me-DHPC less than 3-Me-DHPC less than DHPC less than 1-Me-DHPC. Phase transition widths, delta T, determined from the spectroscopic temperature profiles, are discussed in terms of van't Hoff enthalpy functions involving both interchain and trans/gauche effects.

1,2-Dipalmitoylphosphatidylcholine↗
PubMedDate not supplied

Infrared and Raman imaging of biological and biomimetic samples.

Established methods for imaging of biological or biomimetic samples, such as fluorescence and optical microscopy, magnetic resonance imaging (MRI), X-ray tomography or positron emission tomography (PET) are currently complemented by infrared (both near-IR and mid-IR) as well as Raman spectroscopic imaging, whether it be on a microscopic or macroscopic scale. These vibrational spectroscopic techniques provide a wealth of information without a priori knowledge of either the spectral data or the composition of the sample. Infrared radiation does not harm the organism, no electric potential needs to be applied, and the measurements are not influenced by electromagnetic fields. In addition, no extrinsic labeling or staining, which may perturb the system under investigation, has to be added. The immense volume of information contained in spectroscopic images requires multivariate analysis methodologies in order to effectively mine the chemical and spatial information contained within the data as well as to analyze a time-series of images in order to reveal the origin of a chemical or biochemical process. The promise and limitations of this new analytical tool are surveyed in this review.

Animals↗