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At least 379 records · Page 21Linked to original sources
PubMed2004

Detection of lumen-intima interface of posterior wall for measurement of elasticity of the human carotid artery.

In our series of studies on noninvasive assessment of the regional elasticity of the arterial wall, the displacement gradient (change in thickness) of the arterial wall caused by the heartbeat was measured by the phased-tracking method. Because the displacement gradient corresponds to the strain due to the change in blood pressure, the elasticity can be evaluated from the displacement gradient of the arterial wall and the blood pressure, which are noninvasively measured at the upper arm. In the measurement of the elasticity of the arterial wall by our method, the region in which the elastic modulus is estimated must be assigned beforehand; currently, the lumen-intima boundary of the arterial wall is manually determined by the operator. For the real-time measurement of the elasticity of the arterial wall, a fast, automated method is necessary for detection of the boundary. In this paper, a cost function is proposed for differentiation of the arterial wall from the lumen. The proposed cost function was applied to ultrasound data, which were noninvasively obtained for five human carotid arteries. In comparison with the case of detection using only the amplitude of the echo, the root mean square error between the automatically detected lumen-intima boundary and the manually assigned boundary was significantly improved by using the proposed cost function. Furthermore, the lumen-intima boundary was automatically detected in a short period. Such a method is required for real-time measurement of the elasticity of the arterial wall, though detection of the outer boundary of the adventitia, which is not described in this paper, is also necessary to realize real-time elasticity measurement by our method.

Adult↗
PubMed2006

Phase-coupled two-dimensional speckle tracking algorithm.

A new two-dimensional (2-D) speckle tracking method for displacement estimation based on the gradients of the magnitude and phase of 2-D complex correlation in a search region is presented. The novelty of this approach is that it couples the phase and magnitude gradients near the correlation peak to determine its coordinates with sub-sample accuracy in both axial and lateral directions. This is achieved with a minimum level of lateral interpolation determined from the angles between the magnitude and phase gradient vectors on the sampled (laterally interpolated) 2-D cross-correlation grid. The key result behind this algorithm is that the magnitude gradient vectors' final approach to the true peak is orthogonal to the zero-phase contour. This leads to a 2-D robust projection on the zero-phase contour that results in subsample accuracy at interpolation levels well below those needed using previously proposed methods. A full description of the 2-D, phase-coupled approach is given, including two implementations based on a geometric projection and constrained optimization. In addition, a robust fast search algorithm that allows the localization of the true peak without the need for exhaustive search is given. Experimental validation on three data sets from speckle-generating phantoms undergoing uniform diagonal motion, uniform axial deformation, and nonuniform lateral flow is given. It is shown that estimated 2-D displacement fields obtained using the phase-coupled technique display a full range of values covering the dynamic range without evidence of quantization. In comparison, a previously published method using 1-D phase-projection after lateral interpolation produces severely quantized lateral displacement fields (at the same levels of interpolation as the 2-D, phase-coupled method).

Algorithms↗
PubMed1992

Maternal care coordination for migrant farmworker women: program structure and evaluation of effects on use of prenatal care and birth outcome.

Nearly three fourths of the migrant farmworkers in the U.S. are Hispanic. Cultural and social barriers, along with constant travel, make coordination of care a significant concern for migrant health centers providing perinatal services to female farmworkers. As part of a demonstration project, a migrant-specific maternal care coordination program was developed that used bilingual staff, outreach services, lay health advisers, and a multistate tracking system. Following the initiation of the project, first-trimester entry into prenatal care and number of prenatal visits increased over a five-year period among the target population. Successful tracking methods provided outcome data on more than 80 percent of participants during the project period. The results of this study suggest that migrant health centers should focus on employing public health-oriented bilingual or bicultural health professionals and that an outreach strategy must be an integral part of a health care delivery system serving migrant farmworkers. Without these key ingredients, health care services will not be accessible or acceptable for this hard-to-reach population. Collaboration among the National Migrant Resource Program, the Migrant Clinicians Network, and the National Perinatal Association can facilitate development of a regionwide perinatal service system for female migrant farmworkers.

Communication Barriers↗
PubMed1986

Poststenotic flow disturbance in the dog aorta as measured with pulsed Doppler ultrasound.

Blood flow velocity was measured in the dog aorta distal to mechanically induced constrictions of various degrees of severity employing an 8-MHz pulsed Doppler ultrasound velocimeter and a phase-lock loop frequency tracking method for extracting velocity from the Doppler quadrature signals. The data were analyzed to construct ensemble average velocity waveforms and random velocity disturbances. In any individual animal the effect of increasing the degree of stenosis beyond approximately 25 percent area reduction was to produce increasing levels of random velocity disturbance. However, variability among animals was such that the sensitivity of random behavior to the degree of stenosis was degraded to the point that it appears difficult to employ Doppler ultrasound measurements of random disturbances to discriminate among stenoses with area reductions less than approximately 75 percent. On the other hand, coherent vortex structures in velocity waveforms consistently occurred distal to mild constrictions (25-50 percent area reduction). Comparison of the phase-lock loop Doppler ultrasound data with simultaneous measurements using invasive hot-film anemometry, which possesses excellent frequency response, demonstrates that the ultrasound method can reliably detect those flow phenomena in such cases. Thus, the identification of coherent, rather than random, flow disturbances may offer improved diagnostic capability for noninvasively detecting arteriosclerotic plaques at relatively early stages of development.

Animals↗
PubMedDate not supplied

Measuring microlymphatic flow using fast video microscopy.

Despite advances in the measurement of lymphatic function, little is known about the actual velocities of flow in microlymphatic ( approximately 100 mum diam) vessels. In this work, video microscopy and particle tracking methods are adapted and integrated with an ultra-high-speed imaging camera to obtain measurements of lymph velocities throughout the entire lymphatic contraction cycle in the ratmesentery, something that previous systems were incapable of measuring. To determine the system's accuracy, calibration experiments are conducted across the hypothesized physiologically significant range of velocities for microlymphatic flow (up to 15 mmsec). The system shows high accuracy, less than 2% error, when comparing actual with measured velocities. Microspheres flowing through 140-mum-diam tubing are imaged to demonstrate the system's ability to determine flow rates in these small vessels by measuring particle velocities. To demonstrate biological applicability, mesenteric microlymphatics in loops of the small intestine of three male Sprague-Dawley rats are exteriorized and imaged with the high-speed system at a rate of 500 framessec for several contraction sequences. Lymph velocity fluctuates cyclically with the vessel wall contractions, ranging from -1 to 7 mmsec. These rates are higher than would be possible with standard video microscopy (3.75 mmsec maximum).

Animals↗
PubMed1982

Inverse frequency dependence of simultaneous tone-on-tone masking patterns at low levels.

Using the Békésy tracking method, tone-on-tone masking patterns were measured with eight subjects at eight masker frequencies between 250 Hz and 6.03 kHz. Masking patterns were obtained for five masker levels between 20 and 60 dB SPL. Test-tone frequencies were chosen within two critical bands above and below the masker frequency. A level-dependent frequency asymmetry of masking was observed at all masker frequencies except at 250 Hz. At low levels there was a greater spread of masking towards the lower frequencies than toward the higher frequencies, but at high levels there was a greater spread of masking towards the higher frequencies than toward the lower frequencies. Only at masker levels of 40 dB SPL were the masking patterns approximately symmetrical.

Auditory Threshold↗
PubMed1984

Receiving beam patterns and directivity indices of the Atlantic bottlenose dolphin Tursiops truncatus.

The receiving beam patterns of an Atlantic bottlenose dolphin was measured in both the vertical and horizontal planes for frequencies of 30, 60, and 120 kHz. Measurements in the vertical plane were performed by training the dolphin to rotate on its side and station on a vertically oriented biteplate device. A signal source was positioned 3.5 m directly in front of the animal on an arc while the position of a broadband noise source was varied in azimuth along the arc, with the animal stationed at the origin of the arc. Using a go/no-go response procedure, the masked threshold of the dolphin was determined by varying the intensity of the noise source via a tracking method of stimulus presentation, for different azimuth's of the noise source. Measurements in the horizontal plane were obtained with the dolphin stationing on a horizontal biteplate. Two masking noise sources, projecting equal levels of uncorrelated noise, were located at +/- 20 degrees on either side of the arc midpoint. The levels of the noise source were held constant and the masked thresholds determined by varying the level of the signal source while positioned at different azimuths along the arc. Results indicated that maximum sensitivity in the vertical plane (the major axis of the beam) occurred between 5 degrees and 10 degrees above the midline of the animal's mouth and that the beam patterns were not symmetrical about the major axis. The sensitivity dropped off more quickly with increasing angle above the head than below. The beam patterns in the horizontal plane were directed forward and were fairly symmetrical about the midline of the animal's body.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Individual differences in auditory capabilities. I.

Twenty-eight audiometrically normal adult listeners were given a variety of auditory tests, ranging from quiet and masked thresholds through the discrimination of simple and moderately complex temporal patterns. Test-retest reliability was good. Individual differences persisted on a variety of psychoacoustic tasks following a period of training using adaptive threshold-tracking methods, and with trial-by-trial feedback. Large individual differences in performance on temporal-sequence-discrimination tasks suggest that this form of temporal processing may be of clinical significance. In addition, high correlations were obtained within given classes of tests (as, between all tests of frequency discrimination) and between certain classes of tests (as, between tests of frequency discrimination and those of sequence discrimination). Patterns of individual differences were found which support the conclusion that individual differences in auditory performance are, in part, a function of patterns of independent abilities.

Adolescent↗
PubMed1997

The influence of different timbre attributes on the perceptual segregation of complex-tone sequences.

Spectral factors such as differences in harmonic content are powerful cues in the perceptual organization of tone sequences. Temporal features such as rise time, however, have been shown to be poor cues [W. M. Hartmann and D. Johnson, Mus. Perc. 9, 155-184 (1991)]. The relative influence of these timbral features on perceptual segregation was investigated. Complex tones were sequenced in a repeating ABA- "gallop" format, under four conditions in which tones A and B had the same or different timbres as defined by differences in numbers of harmonics and temporal-envelope features. A sequence started with A and B tones at the same F0. The F0 difference between A and B then increased over the course of a trial, until a listener terminated the trial indicating perceptual segregation into sub-sequences comprising A and B tones, respectively. The F0 difference required to reach this crossover point of segregation provided a measure of the efficacy of stimulus features of A and B as cues for perceptual organization. Sequences combining differences in harmonic structure and temporal envelope required the smallest F0 change for segregation. Sequences of tones with the same harmonic structure and temporal envelope required larger changes in F0, while the other conditions fell in the middle of this range. The F0-tracking method used in this study facilitates measurement of the relative contribution of different stimulus features to stream segregation. It also holds potential as a tool using the point of segregation as a measure of the magnitude of timbre differences brought about by different physical features of sounds.

Adult↗
PubMed2006

How and why do insects migrate?

Countless numbers of insects migrate within and between continents every year, and yet we know very little about the ultimate reasons and proximate mechanisms that would explain these mass movements. Here we suggest that perhaps the most important reason for insects to migrate is to hedge their reproductive bets. By spreading their breeding efforts in space and time, insects distribute their offspring over a range of environmental conditions. We show how the study of individual long-distance movements of insects may contribute to a better understanding of migration. In the future, advances in tracking methods may enable the global surveillance of large insects such as desert locusts.

Animal Migration↗
PubMed1995

Tracking the Response of Burkholderia cepacia G4 5223-PR1 in Aquifer Microcosms.

The introduction of bacteria into the environment for bioremediation purposes (bioaugmentation) requires analysis and monitoring of microbial population dynamics to define persistence and activity from both efficacy and risk assessment perspectives. Burkholderia cepacia G4 5223-PR1 is a Tn5 insertion mutant which constitutively expresses a toluene ortho-monooxygenase that degrades trichloroethylene (TCE). This ability of G4 5223-PR1 to degrade TCE without aromatic induction may be useful for bioremediation of TCE-containing aquifers and groundwater. Thus, a simulated aquifer sediment system and groundwater microcosms were used to monitor the survival of G4 5223-PR1. The fate of G4 5223-PR1 in sediment was monitored by indirect immunofluorescence microscopy, a colony blot assay, and growth on selective medium. G4 5223-PR1 was detected immunologically by using a highly specific monoclonal antibody which reacted against the O-specific polysaccharide chain of the lipopolysaccharides of this organism. G4 5223-PR1 survived well in sterilized groundwater, although in nonsterile groundwater microcosms rapid decreases in the G4 5223-PR1 cell population were observed. Ten days after inoculation no G4 5223-PR1 cells could be detected by selective plating or immunofluorescence. G4 5223-PR1 survival was greater in a nonsterile aquifer sediment microcosm, although after 22 days of elution the number of G4 5223-PR1 cells was low. Our results demonstrate the utility of monoclonal antibody tracking methods and the importance of biotic interactions in determining the persistence of introduced microorganisms.

Journal Article↗
PubMed1999

Visualization of alternative Epstein-Barr virus expression programs by fluorescent in situ hybridization at the cell level.

Epstein-Barr virus (EBV) transforms human B lymphocytes into immortalized lymphoblastoid cell lines (LCLs). They regularly express six virally encoded nuclear proteins (EBNA1 to EBNA6) and three membrane proteins (LMP1, LMP2A, and LMP2B). In contrast, EBV-carrying Burkitt lymphoma (BL) cells in vivo and derived type I cell lines that maintain the BL phenotype express only EBNA1. During prolonged in vitro culturing, most EBV-carrying BL lines drift toward a more immunoblastic (type II or III) phenotype. Their viral antigen expression is upregulated in parallel. We have used fluorescent in situ hybridization to visualize viral transcripts in type I and III BL lines and LCLs. In type I cells, EBNA1 is encoded by a monocistronic message that originates from the Qp promoter. In type III cells, the EBNA1 transcript is spliced from a giant polycistronic message that originates from one of several alternative Wp or Cp promoters and encodes all six EBNAs. We have obtained a "track" signal with a BamHI W DNA probe that could hybridize with the polycistronic but not with the monocistronic message in two type III BL lines (Namalwa-Cl8 and MUTU III) and three LCLs (LCL IB4-D, LCL-970402, and IARC-171). A BamHI K probe that can hybridize to both the monocistronic and the polycistronic message visualized the same pattern in the type III BLs and the LCLs as the BamHI W probe. A positive signal was obtained with the BamHI K but not the BamHI W probe in the type I BL lines MUTU I and Rael. The RNA track method can thus distinguish between cells that use a type III and those that use a type I program. The former cells hybridize with both the W and the K probes, but the latter cells hybridize with only the K probe. Our findings may open the way for studies of the important but still unanswered question of whether cells with type I latency arise from immunoblasts with a full type III program or are generated by a separate pathway during primary infection.

Amino Acid Sequence↗
PubMed2005

Does changing the configuration of a motor racing circuit make it safer?

OBJECTIVES: To assess the pattern of injuries presenting to a racing circuit medical centre in two three-year periods before and after two chicanes were built into the track. METHODS: Medical centre records were used to identify all patients assessed during the two time periods. Those referred to hospital were categorised by injury severity into three groups. RESULTS: The proportions of those attending the medical centre that were referred and admitted to hospital were the same in both periods (12-13% and 3% respectively). During the two study periods, the risk of a severe injury for a car driver decreased from 0.1% to 0.03% (p<0.05). For a motorcyclist, similar values were 0% and 0.2% (not significant). CONCLUSIONS: Chicanes have improved the safety of the racing circuit for car drivers, reducing the risk of injury.

Accident Prevention↗
PubMed2004

Measurement of myocardial mechanics in mice before and after infarction using multislice displacement-encoded MRI with 3D motion encoding.

Cardiac MRI is an accurate, noninvasive modality for assessing the structure and function of the murine heart. In addition to conventional imaging, MRI tissue tracking methods can quantify numerous aspects of myocardial mechanics, including intramyocardial displacement, strain, twist, and torsion. In the present study, we developed and applied a novel pulse sequence based on displacement-encoded imaging using stimulated echoes (DENSE) that achieves multislice coverage, high spatial resolution, and three-dimensional (3D) displacement encoding. With the use of this technique, myocardial mechanics of C57Bl/6 mice were measured at baseline and 1 day after experimental myocardial infarction. At baseline, the mean systolic transmural circumferential strain was -0.14 +/- 0.02 and the mean systolic radial strain was 0.30 +/- 0.05. Changes in circumferential and radial strains from the subepicardium to the subendocardium were detected at baseline (P < 0.05). One day after infarction, significantly reduced 3D displacements and strain were detected in infarcted and noninfarcted myocardium. Infarction also reduced normalized systolic torsion from its baseline value of 1.35 +/- 0.27 degrees /mm (R = 0.99) to 0.07 +/- 0.54 degrees /mm (R = 0.96, P < 0.05). DENSE MRI can assess the 3D myocardial mechanics of the murine heart in <1 h of scan time at 4.7 T and may be applied to studies of myocardial mechanics in genetically engineered mice.

Animals↗
PubMedDate not supplied

Lip kinematics for /p/ and /b/ production during whispered and voiced speech.

In the absence of voicing, the discrimination of "voiced" and "voiceless" stop consonants in whispered speech relies on such acoustic cues as burst duration and amplitude, and formant transition characteristics. The articulatory processes that generate these features of whispered speech remain speculative. This preliminary investigation examines the articulatory kinematics differences between whispered /p/ and /b/, which may underlie the acoustic differences previously reported for these sounds. Computerized video-tracking methods were used to evaluate kinematic differences between voiced and voiceless stops. Seven subjects produced the target utterances "my papa puppy" and "my baba puppy" in voiced and whispered speech modes. The results revealed that mean peak opening and closing velocities for /b/ were significantly greater than those for /p/ during whispered speech. No differences in peak velocity for either oral closing or opening were observed during voiced speech. The maximum distance between the lips for oral opening for /b/ was significantly greater than for /p/ during whisper, whereas no difference was observed during voiced speech. These data supported the suggestion that whispered speech and voiced speech rely on distinct motor control processes.

Adult↗
PubMed2002

An efficient speckle tracking algorithm for ultrasonic imaging.

An efficient speckle tracking algorithm is proposed for motion estimation in ultrasonic imaging. Speckle tracking involves a matching process and a searching process. The matching process of the proposed algorithm is based on a Block Sum Pyramid algorithm that significantly reduces the computational complexity while maintaining the same accuracy as the conventional sum of absolute difference approach. The searching process, on the other hand, is based on a multilevel search strategy rather than the full-search strategy used by most conventional tracking methods. Both simulated speckle images and clinical breast images were used to test the performance of the proposed algorithm. The results show that the computation efficiency is improved by up to a factor of five over the conventional approach. The improved efficiency enables real-time or near-real-time implementation of motion estimation in ultrasonic imaging, which is particularly beneficial in areas such as blood flow estimation, elasticity imaging, speckle image registration, and strain compounding.

Algorithms↗