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Results for “reflection”

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At least 757 records · Page 42Linked to original sources

PubMed2005

Adrenomedullin reflects cardiac dysfunction, excessive blood volume, and inflammation in hemodialysis patients.

BACKGROUND: Plasma adrenomedullin (AM) reflects cardiac dysfunction and predicts survival after myocardial infarction. The present study was designed to investigate whether the mature AM (mAM) reflects status of cardiac function, systemic blood volume, or inflammation in hemodialysis patients with cardiovascular disease, and whether mortality and additional cardiovascular morbidity can be predicted by mAM. METHODS: Plasma levels of mAM, atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), norepinephrine (NE), and C-reactive protein (CRP) before hemodialysis were measured in 67 chronic hemodialysis patients with cardiovascular disease, along with 2-dimensional and Doppler echocardiographic variables. RESULTS: By univariate regression analysis, mAM correlated negatively with pulmonary venous flow velocity ratio and left ventricular (LV) ejection fraction and positively with LV inflow velocity ratio, LV end-diastolic, end-systolic volume indexes, plasma CRP level, and removal fluid volume by ultrafiltration. Multivariate stepwise regression analysis revealed that mAM reflected all variables better than log [ANP], log [BNP], and log [NE]. During a 1-year follow-up period, 7 patients died and 8 had additional cardiovascular events. Event-free Kaplan-Meier curves based on the median mAM (4.55 pmol/L) showed that patients with high plasma mAM levels had higher mortality and morbidity than those with low plasma mAM levels (P = 0.0056). By Cox multivariate proportional hazard analysis, mAM was related to mortality and morbidity [hazard ratio (HR) 4.55, 95% CI 1.2-16.8, P= 0.023). CONCLUSION: Plasma mAM reflects cardiac dysfunction, excessive blood volume, and inflammation better than ANP, BNP, and NE, resulting in a predictor of mortality and cardiovascular morbidity in hemodialysis patients with cardiovascular disease.

Adrenomedullin↗

PubMed1993

Duplex scanning and light reflection rheography in the assessment of the severity of short saphenous vein incompetence.

BACKGROUND: Duplex ultrasound assessment of veins in the popliteal fossa is an accepted alternative to venography. Light reflection rheography provides additional quantitative information on venous reflux in chronic venous insufficiency. OBJECTIVE: To use duplex ultrasound and light reflection rheography to study the venous reflux patterns in the popliteal fossa in a group of patients. METHODS: Duplex ultrasound examination and light reflection rheography were used in the assessment of the severity of short saphenous vein incompetence. RESULTS: The study revealed that any associated deep venous reflux which was detectable beyond the saphenopopliteal junction represented a more advanced stage of superficial venous insufficiency. CONCLUSIONS: Light reflection rheography, as a semiquantitative test, provided useful additional information to duplex scan findings in assessing venous reflux of the popliteal fossa. Short saphenous vein reflux with functional deep venous incompetence was associated with shorter venous refilling times and clinically represented a more advanced stage of primary varicose vein disease.

Edema↗

PubMed2006

Tutor perceptions of the use of a reflective portfolio within a pastoral tutor system to facilitate undergraduate personal development planning.

All Higher Education Institutions in the UK are now required to provide transcripts of student activity and outcomes of summative assessments. In addition, the student should be able to reflect on their learning and plan their own development. This article reports on the staff evaluation of the use of a reflective portfolio facilitating the production of highly individualised personal development plans within an existing tutor system. A number of significant issues are highlighted; tutor systems adopting this approach must maintain flexibility for managing student crises when they arise, the difference between appraisal and assessment needs clear definition for both students and tutors, training in basic mentoring skills should be provided for all tutors, tutors should be aware of the difficulties many students experience with reflection and also be alert to the over reflective learner.

Documentation↗

PubMed1995

A transmission electron microscopic (TEM) method for determining structural colors reflected by lizard iridophores.

Iridescent tissue colors are thought to be produced by iridophores through the optical phenomenon of thin-layer interference. Land and others have shown that structural features, predominantly reflecting platelet width and the cytoplasmic spacing between layers of platelets, determine the wavelength of light maximally reflected by this mechanism in iridophores. Some researchers have used interference microscopy to estimate these structural parameters, but the most direct measurement technique should be transmission electron microscopy (TEM). Transmission electron microscopy (TEM) has associated processing artifacts (particularly cytoplasmic shrinkage) that preclude direct measurement of ultrastructure, but if a number of assumptions are made, reflected wavelengths can be predicted. A thin-layer interference model and its associated assumptions were tested using TEM measurements of iridophores from several brightly colored tissues of each of three lizards (Sceloporus jarrovi, S. undulatus erythrocheilus, and S. magister). In all the instances examined when the contribution of the pigments present were accounted for, tissue color corresponded with predicted iridophore reflectances from the model. Finally, if the model and its assumptions are assumed to be correct, the amount of iridophore cytoplasmic shrinkage as a result of TEM processing can be calculated.

Animals↗

PubMed1996

Detection of pulse in oral mucosa and dental pulp by means of optical reflection method.

This paper describes a new system in which optical reflectance is used to test the pulse and vitality of oral mucosa or dental pulp. Radiation at red (660 nm) and near infra-red (850 nm) wavelengths are directed through a thin probe. The beam is directed into tissue and reflected back. Plethysmography is used to measure the pulse rate from the right forefinger. Reflected radiation is related to plethysmogram using a computer. Preliminary findings relating to the lips and gingiva in 9 healthy volunteers were promising. Preliminary tests showed that vital and nonvital pulps reflected the radiation differently. Pulpal pulse did not always correspond to plethysmogram from the right forefinger.

Adult↗

PubMedDate not supplied

Noninvasive determination of the location and distribution of DNAPL using advanced seismic reflection techniques.

Recent advances in seismic reflection amplitude analysis (e.g., amplitude versus offset-AVO, bright spot mapping) technology to directly detect the presence of subsurface DNAPL (e.g., CCl4) were applied to 216-Z-9 crib, 200 West Area, DOE Hanford Site, Washington. Modeling to determine what type of anomaly might be present was performed. Model results were incorporated in the interpretation of the seismic data to determine the location of any seismic amplitude anomalies associated with the presence of high concentrations of CCl4. Seismic reflection profiles were collected and analyzed for the presence of DNAPL. Structure contour maps of the contact between the Hanford fine unit and the Plio/Pleistocene unit and between the Plio/Pleistocene unit and the caliche layer were interpreted to determine potential DNAPL flow direction. Models indicate that the contact between the Plio/Pleistocene unit and the caliche should have a positive reflection coefficient. When high concentrations of CCl4 are present, the reflection coefficient of this interface displays a noticeable positive increase in the seismic amplitude (i.e., bright spot). Amplitude data contoured on the Plio/Pleistocene-caliche boundary display high values indicating the presence of DNAPL to the north and east of the crib area. The seismic data agree well with the well control in areas of high concentrations of CCl4.

Carbon Tetrachloride↗

PubMed1991

In vivo spectrophotometric evaluation of neoplastic and non-neoplastic skin pigmented lesions--I. Reflectance measurements.

Reflectance spectrophotometry from 400 to 800 nm on different cutaneous pigmented lesions, including primary and metastatic malignant melanoma, pigmented nevi, lentigo and seborrhoeic keratosis, has been performed by using an external integrating sphere coupled to a spectrophotometer. Measurements show that reflectance spectra of the different lesions manifest dissimilar patterns, particularly in the near IR region. Comparison of reflectance of nevi with that of malignant melanomas results in a highly significant difference (P less than 10(-6)) between the two samples. Though interpretation of the spectra remains difficult as a result of the complexity of the optical processes of scattering and absorption, our results suggest that a detailed analysis of the reflectance spectrum may give clinically useful information, and could be utilized as an aid in clinical diagnosis of cutaneous pigmented lesions, especially where malignant melanoma is concerned.

Humans↗

PubMedDate not supplied

Pulse pressure method and the area method for the estimation of total arterial compliance in dogs: sensitivity to wave reflection intensity.

We estimated total arterial compliance (C) in eight anesthetized mongrel dogs with (i) the area method (AM), (ii) the pulse pressure method (PPM), and (iii) the stroke volume-to-pulse pressure ratio (SV/PP). Average compliance was C(AM)=1.1+/-0.73 ml mm Hg(-1) using AM; C(PPM)=0.60+/-0.31 ml mm Hg(-1) using PPM and C(SV/PP)=0.87+/-0.49 ml mm Hg(-1) using SV/PP. Mean aortic pressure was 64+/-23 mm Hg. The overall agreement between C(AM) and C(PPM) was relatively poor (C(AM)=0.15+/-1.61 C(PPM); r2=0.48), with a consistent overestimation of the area method with respect to the pulse pressure method. There was a significant correlation (r=-0.78) between the relative difference between PPM and AM, and the modulus of the first harmonic of the wave reflection coefficient [gamma] which was low in our dog population (0.37+/-0.18). SV/PP overestimated PPM, but both methods were highly correlated (C(SV/PP)=0.06+/-1.60C(PPM); r2=0.97). C(SV/PP) and C(AM) were similar only for [gamma]>0.4. The effect of isolated changes of [gamma] on PPM, AM, and SV/PP was studied using the linear wave separation technique. The area method appeared very sensitive to the wave reflection intensity. For low reflection coefficients, the diastolic wave profile was flattened and compliance was overestimated. PPM and SV/PP were relatively independent of [gamma] and remained even applicable for [gamma]=0. We believe that the pulse pressure method is the most consistent method for the estimation of total arterial compliance in hemodynamic conditions characterized by a low wave reflection intensity.

Animals↗

PubMed2000

Physiological relevance of uniform elastic tube-models to infer descending aortic wave reflection: a problem of identifiability.

A uniform, frictional elastic tube terminating in a pure resistor (model A), was compared with a uniform, frictionless elastic tube, terminating in a first-order low-pass filter load (model B). The aim was to address an identifiability problem in uniqueness of parameter estimates and to evaluate the physiological meaning of tube-length estimates obtained from these models applied to the descending aortic circulation. Measurements of high descending aortic pressure and flow were taken from three anaesthetized, open-chest dogs and used to estimate the model parameters. A simultaneous measurement of terminal aortic pressure was used to estimate the foot-to-foot pulse wave velocity. A flow-fitting procedure yielded a multiplicity of equivalent solutions for the wave transit time across the transmission tubes (tau(ai), for model A and tau(bi) for model B, i=0,1,2,...,N,...) and the related tube-lengths d(ai) and d(bi), respectively. The tube length represents the distance to an effective reflection site (effective length) of the descending aortic circulation. Assuming that this length should be no longer than the dimensions of the body, the lowest estimates (i=0) of wave transit time and tube length (average +/- SE: tau(ao)=85.7+/-10.8 ms and d(ao)=53.4+/-3.7 cm for model A; tau(bo)=46.6+/-6.7 ms and d(bo)= 29.1+/-3.5 cm for model B) were identifiable as unique and acceptable solutions. Model A located the effective reflection site a few centimeters below the terminal aortic region. This location is inconsistent with the use of a pure resistor as a tube's terminal load. Further, relatively high estimates of longitudinal frictional losses violated the assumption of small losses across the transmission path and yielded an unphysiological mean-pressure drop of 7.1+/-2.3 mmHg. The estimates of d(bo) provided by model B located the effective reflection site near the origin of the renal arteries. The model-predicted pressure wave at this location approximated the measured pressure. Thus, model B represents a significant improvement over model A as a tool to infer wave travel and reflection in the descending aortic circulation.

Animals↗

PubMedDate not supplied

Optical reflectance assay for the detection of biofilm formation.

We describe the protocol for an inexpensive and nondestructive optical reflectance assay for the measurement of biofilm formation. Reflectance data are obtained using an Ocean Optics (Dunedin, Florida) USB 2000 spectrometer with a polychromatic light source. A fiber optic cable is used both for illumination and collection, and Ocean Optics OOIBase32 Platinum software is used for preliminary processing of the data. Differences in reflectance data collected at times ranging from 2 to 24 h distinguish between cell attachment and volume growth for two strains of Enterococci. Confocal scanning laser microscopy imaging is used to confirm these results. Phase contrast microscopy images are also obtained in conjunction with reflectance measurements for several different biofilm specimens. The experiments consider biofilm formation on glass and polystyrene substrata, but the method can be used for many other abiotic substrata of interest, both opaque and nonopaque.

Biofilms↗

PubMedDate not supplied

In vivo assessment and evaluation of lung tissue morphologic and physiological changes from non-contact endoscopic reflectance spectroscopy for improving lung cancer detection.

We present a method for lung cancer detection exploiting reflectance spectra measured in vivo during endoscopic imaging of the lung. The measured reflectance spectra were analyzed using a specially developed light-transport model to obtain quantitative information about cancer-related, physiological, and morphologic changes in the superficial bronchial mucosa layers. The light-transport model allowed us to obtain the absorption coefficient (mua) and further to derive the micro-vascular blood volume fraction in tissue and the tissue blood oxygen saturation. The model also allowed us to obtain the scattering coefficient (mus) and the anisotropy coefficient (g) and further to derive the tissue scattering micro-particle volume fraction and size distribution. The specular component of the reflectance signal and the instrument response were accounted for during the analysis. The method was validated using 100 reflectance spectra measured in vivo in a noncontact fashion from 22 lung patients (50 normal tissue/benign lesion sites and 50 malignant lesion sites). The classification between normal tissue/benign lesions and malignant lesions was further investigated using the derived quantitative parameters and discriminant function analysis. The results demonstrated significant differences between the normal tissue/benign lesions and the malignant lesions in terms of tissue blood volume fraction, blood oxygen saturation, tissue scatterer volume fractions, and size distribution. The results also showed that the malignant lung lesions can be differentiated from normal tissue/benign lesions with both diagnostic sensitivity and specificity of better than 80%.

Algorithms↗

PubMed2004

Elimination of ghost markers during dual sensor-based infrared tracking of multiple individual reflective markers.

The accuracy of dose delivery in radiotherapy is affected by the uncertainty in tumor localization. Motion of internal anatomy due to physiological processes such as respiration may lead to significant displacements which compromise tumor coverage and generate irradiation of healthy tissue. Real-time tracking with infrared-based systems is often used for tracking thoracic motion in radiation therapy. We studied the origin of ghost markers ("crosstalk") which may appear during dual sensor-based infrared tracking of independent reflective markers. Ghost markers occur when two or more reflective markers are coplanar with each other and with the sensors of the two camera-based infrared tracking system. Analysis shows that sensors are not points but they have a finite extent and this extent determines for each marker a "ghost volume." If one reflective marker enters the ghost volume of another marker, ghost markers will be reported by the tracking system; if the reflective markers belong to a surface their "ghost volume" is reduced to a "ghost surface" (ghost zone). Appearance of ghost markers is predicted for markers taped on the torso of an anthropomorphic phantom. This study illustrates the dependence of the shape, extent, and location of the ghost zones on the shape of the anthropomorphic phantom, the angle of view of the tracking system, and the distance between the tracking system and the anthropomorphic phantom. It is concluded that the appearance of ghost markers can be avoided by positioning the markers outside the ghost zones of the other markers. However, if this is not possible and the initial marker configuration is ghost marker-free, ghost markers can be eliminated during real-time tracking by virtue of the fact that they appear in the coordinate data sequence only temporarily.

Algorithms↗

PubMed2005

Volume concentration and size dependence of diffuse reflectance in a fractal soft tissue model.

Employing a fractal model for the particle size distribution, we examine the possibility of relating the size/volume concentration changes in the tissue to its diffuse reflectance. It is noted that for the practically interesting range of fractal dimension values alpha, the curves depicting the variation of diffuse reflectance (the ratio of diffuse reflectance at two suitably chosen source detector separations) with alpha at fixed volume concentration Tv, are single valued. The same is true if alpha is fixed and Tv is varied. This crucial observation shows that it should be possible to identify changes in the size/volume concentration of the tissue from the diffuse reflectance measurement at two source detector separations when either alpha or Tv is a priori known. Similar results have been obtained for ratio of fluence measured at two suitably chosen depths within the tissue.

Algorithms↗

PubMed2002

Judgments of noticeable differences in sound fields of concert halls caused by intensity variations in early reflections.

In concert halls early reflections combine with the direct sound and with reverberation to determine the subjective rating of a room's acoustics. Of interest is how variations in the amplitudes of these early reflections are related to the subjectively just-noticeable differences (jnd) in several important acoustical parameters for their wide range encountered in existing halls. Investigated were four subjective parameters, apparent source width (ASW), loudness, intimacy and clarity, which are related to the physical measurements, [1-IACC(E3)], G, ITDG, and C80, defined mathematically in Beranek [Concert and Opera Halls: How They Sound (Acoustical Society of America, New York, 1996)]. Forty-eight types of sound fields were chosen in which to make variations in the amplitudes of early reflections and were reproduced electro-acoustically by multiple loudspeakers in an anechoic chamber. The results indicate that ASW and loudness are more sensitive to changes in the levels of early reflections, and were the primary parameters investigated. Although the number of subjects available with enough experience in listening classical music is limited and the measured jnd is an initial estimation, the jnd of [1-IACC(E3)] is measured as 0.065+/-0.015 in variations of sound field structures and the jnd of G was measured as 0.25+/-0.15 dB, which is consistent with the results of previous studies.

Acoustics↗

PubMed2002

Acoustic intensity, impedance and reflection coefficient in the human ear canal.

The sound power per unit cross-sectional area was determined in human ear canals using a new method based on measuring the pressure distribution (P) along the length of variable cross-section acoustic waveguides. The technique provides the pressure/power reflection coefficients (R/R) as well as the acoustic intensity of the nonplanar incident wave (I+, the acoustic input to the ear) and the nonplanar outgoing wave (I-, the acoustic output of the ear). Results were compared to the classical acoustic impedance (Z) and associated plane-wave power reflection coefficient (R(Z)). Performance of the method was investigated theoretically using horn equation simulations and evaluated experimentally using pressure data recorded in nonuniform waveguides. The method was applied in normal-hearing young adults to determine ear-canal position- and frequency-dependence of I(+/-), R, and R(Z) using random phase broadband stimuli (1-15 kHz; approximately 75 dB SPL). Reflection coefficient (R) measurements at two different locations within individual human ear canals exhibited a position dependence averaging deltaR approximately 0.1 (over 6 mm distance)--a difference consistent with predictions of inviscid acoustics in nonuniform waveguides. Since this position dependence was relatively small, an "optimized" position-independent reflection coefficient was defined to facilitate practical application and intersubject comparisons.

Acoustic Impedance Tests↗

PubMed2002

Normal incidence reflection loss from a sandy sediment.

Acoustic reflection loss at normal incidence from a sandy sediment, in the Biodola Gulf on the north side of the island of Elba, Italy, was measured in the frequency band 8-17 kHz, using a self-calibrating method. The water depth was approximately 11 m. The mean and standard deviation of the sand grain diameter were 2.25 (0.21 mm) and 0.6 phi, respectively. The reflection loss was measured using an acoustic intensity integral method, which is insensitive to roughness effects within the selected frequency band. The measured value of reflection loss was 11 dB, +/- 2 dB. The result is consistent with previous measurements in the published literature. The computed reflection loss for a flat interface between water and a uniform fluid or visco-elastic medium with the same properties is 8 dB, +/- 1 dB. The theoretical and experimental values do not significantly overlap, which leads to the conclusion that the visco-elastic model is inappropriate. The Biot model is suggested as a better alternative but more work is needed to ascertain the appropriate parameter values.

Acoustics↗

PubMed2003

The reflection of bounded inhomogeneous waves on a liquid/solid interface.

Fourier analysis and normal mode theory are used to describe the reflection of bounded inhomogeneous waves on a liquid/solid interface. Nonspecular reflection phenomena in the Rayleigh angle are studied in detail. In this way, an explanation is given for the Rayleigh dip phenomenon for positive inhomogeneity factors and the related result of a reflection coefficient larger than unity when the sign of the inhomogeneity factor is reversed. In the limit of large beamwidths, the reflection coefficient predicted by the infinite plane inhomogeneous wave theory is obtained. These results are entirely consistent with the experimental work published by Deschamps [J. Acoust. Soc. Am. 96, 2841-2848 (1994)]. The energy efficiency of Rayleigh wave excitation is investigated as well. It is shown that for large beamwidths, the energy efficiency for bounded inhomogeneous waves is considerably higher in comparison with Gaussian and square-profiled beams.

Journal Article↗

PubMed2003

Stimulus-frequency-emission group delay: a test of coherent reflection filtering and a window on cochlear tuning.

This paper tests and applies a key prediction of the theory of coherent reflection filtering for the generation of reflection-source otoacoustic emissions. The theory predicts that reflection-source-emission group delay is determined by the group delay of the basilar-membrane (BM) transfer function at its peak. This prediction is tested over a seven-octave frequency range in cats and guinea pigs using measurements of stimulus-frequency-emission (SFOAE) group delay. A comparison with group delays calculated from published measurements of BM mechanical transfer functions supports the theory at the basal end of the cochlea. A comparison across the whole frequency range based on variations in the sharpness of neural tuning with characteristic frequency (CF) suggests that the predicted relation holds in the basal-most 60% of the cochlea. At the apical end of the cochlea, however, the measurements disagree with neural and mechanical group delays. This disagreement suggests that there are important differences in cochlear mechanics and/or mechanisms of emission generation between the base and apex of the cochlea. Measurements in humans over a four-octave range indicate that human SFOAE group delays are roughly a factor of 3 longer than their counterparts in cat and guinea pig but manifest similar trends across CF. The measurements thus reveal global deviations from scaling whose form appears quantitatively similar in all three species. Interpreted using the theory of coherent reflection filtering, the group delay measurements indicate that the wavelength at the peak of the traveling wave decreases with increasing CF at a rate of roughly 25% per octave in the base of the cochlea. The measurements and analysis reported here illustrate the rich potential inherent in OAE measurements for obtaining valuable information about basic cochlear properties such as tuning.

Animals↗