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At least 433 records · Page 24Linked to original sources
PubMed2006

A quadrature demodulation method based on tracking the ultrasound echo frequency.

The ultrasound echo attenuation depends on frequency, propagating depth and tissue characteristics. Thus, the attenuation dependent on frequency results in a larger attenuation of high frequencies than lower when the wave propagates through the tissue. As a result, the central frequency of the echo generates the increasing downshift with the increasing of depth. In the traditional I/Q demodulation method, it is assumed that the central frequency of the echo is the same as the transmitting frequency and unchanged all time. The assumption directly causes that the acquired I/Q signals are not perfect baseband ones but biased due to the echo attenuation. In addition, the unreasonable assumption will keep the echo from getting better signal-to-noise ratio. A quadrature demodulation method based on tracking the ultrasound echo frequency is proposed in this paper. The method consists of the traditional I/Q demodulator, the frequency tracking module, the phase compensation module and the dynamic filtering module. The outputs of I/Q demodulator are biased. Autocorrelation technique is utilized in the frequency tracking unit to estimate the frequency bias according to the outputs of I/Q demodulator. The estimated bias feeds to the phase compensation unit which can eliminate the frequency bias by simple trigonometric function transform. The compensated signals feed to the dynamic filter and are further processed. The bandwidth of the dynamic filter decreases with the increasing of the depth, which makes the echo acquire better SNR in different depth. The efficiency of the proposed method is testified by both simulations and experiments.

Algorithms↗
PubMed2003

Three-dimensional motion tracking of coronary arteries in biplane cineangiograms.

A three-dimensional (3-D) method for tracking the coronary arteries through a temporal sequence of biplane X-ray angiography images is presented. A 3-D centerline model of the coronary vasculature is reconstructed from a biplane image pair at one time frame, and its motion is tracked using a coarse-to-fine hierarchy of motion models. Three-dimensional constraints on the length of the arteries and on the spatial regularity of the motion field are used to overcome limitations of classical two-dimensional vessel tracking methods, such as tracking vessels through projective occlusions. This algorithm was clinically validated in five patients by tracking the motion of the left coronary tree over one cardiac cycle. The root mean square reprojection errors were found to be submillimeter in 93% (54/58) of the image pairs. The performance of the tracking algorithm was quantified in three dimensions using a deforming vascular phantom. RMS 3-D distance errors were computed between centerline models tracked in the X-ray images and gold-standard centerline models of the phantom generated from a gated 3-D magnetic resonance image acquisition. The mean error was 0.69 (+/- 0.06) mm over eight temporal phases and four different biplane orientations.

Arteries↗
PubMed1993

Mechanisms of adoptive immunotherapy: improved methods for in vivo tracking of tumor-infiltrating lymphocytes and lymphokine-activated killer cells.

Adoptive immunotherapy with tumor-infiltrating lymphocytes (TIL) and lymphokine-activated killer cells has been demonstrated to mediate regression of tumors in murine models and in selected patients with advanced cancer. Improved methods for monitoring immune cell traffic, particularly to sites of tumor, are needed to elucidate mechanisms of antitumor activity and optimize treatment protocols. Traditional cell tracking methods such as fluorescent protein labeling and radiolabeling using 111In, 125I, or 51Cr are limited by isotope half-life, leakage or transfer of label from immune cells, and toxicity or altered cell function caused by the labeling process. Labeling with genetic markers allows long-term cell tracking but is laborious to perform and difficult to quantitate. We have used two recently described lipophilic cell tracking compounds (PKH26 and 125I-PKH95) which stably partition into lipid regions of the cell membrane to track immune cells in vivo. Concentrations of each tracking compound which had no adverse effects were determined for a variety of murine TIL and lymphokine-activated killer cell functions. Viability was unimpaired at labeling concentrations of up to 5 microM for PKH95 and 20 microM for PKH26. TIL proliferation was unaltered by labeling with up to 5 microM PKH95, 20 microM PKH26, or a combination of 15 microM PKH26 and 5 microM PKH95. In vivo cytotoxic effector function and in vivo therapeutic efficacy of lymphokine-activated killer cells and TIL were also unimpaired by labeling with 20 microM PKH26 or 1 microM 125I-PKH95. Subsequent studies in an adoptive transfer immunotherapy model used 125I-PKH95 to track the biodistribution of TIL in tumor and in non-tumor-bearing animals and PKH26 fluorescence to monitor microdistribution within tissues and distinguish TIL from host T-cells. The results suggest that differential accumulation, selective retention, or proliferation at the tumor site cannot account for the observed pattern of therapeutic efficacy. We hypothesize that a minimum number of TIL must reach the tumor site in order to achieve a demonstrable therapeutic effect.

Animals↗
PubMed2001

Myocardial tracking, a new method to calculate ejection fraction with gated SPECT: validation with (201)Tl versus planar angiography.

UNLABELLED: Left ventricular ejection fraction (LVEF) and viability are essential variables for the prognosis of myocardial infarction and can be measured simultaneously by (201)Tl gated SPECT; however, most algorithms tend to underestimate LVEF. This study aimed to evaluate a new myocardial tracking algorithm, MyoTrack (MTK), for automatic LVEF calculation. METHODS: A rest/redistribution (20 min/4 h) (201)Tl gated SPECT protocol followed immediately by a (99m)Tc equilibrium radionuclide angiography (ERNA) was performed in 75 patients with history of myocardial infarction. Quality of myocardial uptake was evaluated from count statistics and automatic quantification of defect sizes and severities (CardioMatch). LVEFs were calculated both with Germano's quantitative gated SPECT (QGS) algorithm and with MTK. Briefly, the originality of this algorithm resides in the unique end-diastole segmentation, matching to a template and motion field tracking throughout the cardiac cycle. RESULTS: ERNA LVEF averaged 33% +/- 14%. QGS significantly underestimated this value at 20 min (30% +/- 13%, P < 0.001) and at 4 h (30% +/- 13%, P < 0.0001). By contrast, MTK did not miscalculate LVEF at 20 min (34% +/- 14%, probability value was not significant) though a similar underestimation occurred at 4 h (31% +/- 13%, P < 0.02). Individual differences between early and late gated SPECT values and differences between gated SPECT and ERNA values did not correlate with the extension of perfusion defects, count statistics, or heart rate. CONCLUSION: MTK algorithm accurately calculates LVEF on early/high-count images compared with ERNA [corrected], even in patients with severe perfusion defects, but tends to underestimate LVEF on delayed/low-contrast images, as other algorithms do.

Adult↗
PubMed2006

Magnetic tracking: a novel method of assessing anterior cruciate ligament deficiency.

INTRODUCTION: The Lachman test is commonly performed as part of the routine assessment of patients with suspected anterior cruciate ligament (ACL) deficiency. A major drawback is its reliance on the clinician's subjective judgement of movement. The aim of this study was to quantify Lachman movement using a magnetic tracking device thereby providing a more accurate objective measure of movement. PATIENTS AND METHODS: Ten patients aged 21-51 years were assessed as having unilateral ACL deficiency with conventional clinical tests. These patients were then re-assessed using a Polhemus Fastrak magnetic tracking device. RESULTS: The mean anterior tibial displacement was 5.6 mm (SD = 2.5) for the normal knees and 10.2 mm (SD = 4.2) for the ACL-deficient knees. This gave an 82% increase in anterior tibial displacement for the ACL deficient knees. This was shown to be highly significant with P = 0.005. CONCLUSIONS: The magnetic tracking system offers an objective quantification of displacements during the Lachman test. It is convenient, non-invasive and comfortable for the patient and is, therefore, ideally suited for use as an investigative tool.

Adult↗
PubMed1996

[New method for automatic tracking of the endocardial boundary in clinical use].

This study attempted to detect the left ventricular endocardial boundary in six healthy men (volunteers) using a newly developed computerized two-dimensional echocardiography method. Automatic detection of the left ventricular endocardium was achieved by; sampling of pictures, noise reduction of the pictures, filtering, decision of the early loop, detection of the left ventricular endocardial boundary, smoothing the boundary, and correction of the boundary. This process requires only 2-3 sec. Areas of the short-axis cross-sections in systolic and diastolic phases of one cardiac cycle were obtained and the percent change rate of these areas on a cardiac cycle were calculated. These were compared with the results obtained by the manual method. The boundary of the left ventricular endocardium detected by the computerized method almost coincided with that found by the manual method. Areas and the change rates obtained were correlated with those by the manual method (areas: r = 0.86, % change rate of area: r = 0.94). This new method is suitable for clinical use.

Adult↗
PubMed2003

Synthetic single-nanopore and nanotube membranes.

There is increasing interest in investigating transport and electrochemical phenomena in synthetic membrane samples that contain a single pore of nanoscopic diameter. Approaches used to date for preparing such single-nanopore membranes include microfabrication-based methods, the track-etch method, and a method based on the incorporation of a single fullerene nanotube within a synthetic membrane. We describe here an alternative approach that we believe is easier and more accessible than the previously described methods. This method is based on a very low pore density track-etch membrane obtained from commercial sources. Fluorescence microscopy is used to identify and isolate a single nanopore in this membrane. Membrane samples containing single nanopores with diameters as small as 30 nm have been prepared. Furthermore, we show here that an electroless plating method can be used to deposit a gold nanotube within the single nanopore, and this provides a route for further decreasing the inside diameter of the pore. A single-nanotube membrane with an electrochemically determined inside diameter of approximately 2 nm was prepared and evaluated.

Journal Article↗
PubMed1980

The hemodynamic tracking system: a method of data management and guide for cardiovascular therapy.

In the operating room or intensive care unit, multiple measurements of circulatory function are almost mandatory in patients with significant cardiovascular disease. Use in these areas requires that the information must be easily organized, rapidly obtained, and inexpensive. A hemodynamic tracking system that meets these criteria is described. This system incorporates a hand-held programmable calculator (cost = $210 to $300) to derive variables computed from standard cardiovascular measurements. The time required to obtain a set of measurements (including thermodilution cardiac output determinations in duplicate), key the numbers into the calculator, and obtain the derived indices is 4 minutes. Two patients, who had acute mitral insufficiency and whose clinical management differed substantially are presented to illustrate the use of data obtained from the hemodynamic tracking system.

Aged↗
PubMed2003

Scanning FCS, a novel method for three-dimensional particle tracking.

We describe a novel method to track fluorescent particles in three dimensions with nanometre precision and millisecond time resolution. In this method, we use our two-photon excitation microscope. The galvomotor-driven x-y scanning mirrors allow the laser beam to move repetitively in a circular path with a radius of half the width of the point spread function of the laser. When the fluorescent particle is located within the scanning radius of the laser, the precise position of the particle in the x-x plane can be determined by its fluorescence intensity distribution along the circular scanning path. A z-nanopositioner on the objective was used to change the laser focus at two planes (half width of the point spread function apart). The difference of the fluorescence intensity in the two planes is used to calculate the z-position of the fluorescent particle. The laser beam is allowed to scan multiple circular orbits before it is moved to the other plane, thus improving the signal to noise ratio. With a fast feedback mechanism, the position of the laser beam is directed to the centre of the fluorescent particle, thus allowing us to track a particle in three dimensions. In this contribution we describe some calibration experiments performed to test the three-dimensional tracking capability of our system over a large range.

Diffusion↗
PubMed2006

Classification tree method for bacterial source tracking with antibiotic resistance analysis data.

Various statistical classification methods, including discriminant analysis, logistic regression, and cluster analysis, have been used with antibiotic resistance analysis (ARA) data to construct models for bacterial source tracking (BST). We applied the statistical method known as classification trees to build a model for BST for the Anacostia Watershed in Maryland. Classification trees have more flexibility than other statistical classification approaches based on standard statistical methods to accommodate complex interactions among ARA variables. This article describes the use of classification trees for BST and includes discussion of its principal parameters and features. Anacostia Watershed ARA data are used to illustrate the application of classification trees, and we report the BST results for the watershed.

Animals↗
PubMed1997

The effects of salmeterol on power output in nonasthmatic athletes.

BACKGROUND: Salmeterol xinafoate is a new aerosol inhalant that is used in the treatment of asthma. It is currently banned by the International Olympic Committee because of the concern that it may lend an unfair competitive advantage to the user. OBJECTIVE: The purpose of this study was to determine whether salmeterol improves short-term anaerobic performance in elite nonasthmatic track cyclists. METHODS: Eleven elite track cyclists volunteered to perform a 30-second all-out cycle ergometer test 3 hours after receiving either 42 micrograms of salmeterol xinafoate or placebo applied in a double-blind crossover procedure. During the ergometer test, peak power output, total work, time to peak power, and percent fatigue (decline in power output) were measured. Pulmonary measurements were also taken before and at various time points after inhalation and the ergometer test. A methacholine challenge was administered to each subject before participation in the study to ensure that none of the subjects had any reactive airway diseases. RESULTS: There were no significant differences (p > 0.05) between the placebo and salmeterol trials for peak power output, total work performed during the 30-second test, percent fatigue, and time to peak power. No differences between trials were observed for the pulmonary function test variables at any of the time points. Blood lactate concentrations before and after administration of drug or placebo were also not significantly different between trials. Additionally, salmeterol did not affect the maximal heart rate achieved during the test as compared with the placebo. CONCLUSIONS: Short-term salmeterol use within the prescribed dosage was not shown to increase short-term power output in nonasthmatic cyclists.

Adult↗
PubMed1996

A simple method for automatic tracking of actin filaments in the motility assay.

A great deal of quantitative information about the actomyosin interaction can be obtained from the basic Kron and Spudich in vitro motility assay provided that care is taken to obtain consistency between experiments and that the data is examined comprehensively and not selectively. From observations of filament movement under a wide variety of conditions we have formulated the hypothesis that a large number of filaments moving over a short time period is indistinguishable from fewer filaments moving over a longer sequence of frames. This has been used to devise a simple automation of filament detection procedures. A sequence of images is digitized through a frame-grabber. If successive pairs of frames are compared the program will search for and detect the new position of every filament and show its vector on screen. Velocity is calculated and shown as a frequency histogram. The program regularly detects over 100 filaments moving in each pair of frames; usually a sequence of up to 15 pairs of frames are studied yielding 500-1000 vectors in total. The algorithm cannot deal with filaments that meet, cross or divide, however, when filaments are moving less than 2 microns between frames this is only a small proportion of the whole. The program outputs fraction of filaments motile, mean velocity with standard deviation and density of filaments (filaments microns-2). A cumulative frequency histogram gives an immediate visual indication of the performance of the population of filaments. Direct comparisons show that the data produced by automatic tracking is indistinguishable from manual tracking apart from the small apparent velocity of non-mobile filaments. The detection process takes about 5 min and requires little skill or judgement. This can lead to great increases in the rate of data analysis in motility work.

Actin Cytoskeleton↗
PubMed1990

Is resistance to ischaemia of motor axons in diabetic subjects due to membrane depolarization?

The reasons for the resistance to ischaemia of peripheral nerves in diabetics are not well understood. We have now explored whether axonal depolarization underlies this phenomenon, as has previously been proposed. Resistance to ischaemia was determined by the new method of "threshold tracking". This method revealed an increase in excitability of the peroneal nerve at the popliteal fossa during ischaemia, and a decrease in excitability in the post-ischaemic period. The extent of these alterations in 28 type 1 diabetics without peripheral neuropathy showed a strong correlation with the mean blood glucose concentrations during the last 24 h before examination. To test whether the ischaemic resistance was related to membrane potential, we also measured axonal superexcitability in 11 selected diabetics, since it has been shown that post-spike changes in excitability depend on membrane potential. Changes in excitability of the peroneal nerve were measured in the period between 10 and 30 msec following a conditioning supramaximal compound action potential. Under resting conditions, no differences in the post-spike superexcitability were found between controls and diabetics, despite striking differences in their responses to a 10-min pressure cuff. These observations indicate that membrane depolarization is not involved in the resistance to ischaemia of motor axons in diabetic subjects.

Action Potentials↗
PubMed1986

Phase plane tracking: a new method for shaping movements.

Study of the relation between muscular activation patterns and movements has largely been based on the control of discrete movement parameters as amplitude, duration and maximum velocity. A new method is described for shaping voluntary limb movements in order to reliably obtain movements of different dynamic characteristics. A template of the desired movement is calculated with a micro-computer. This template is displayed on a storage oscilloscope as a phase plane (velocity vs. position during movement). By moving an instrumented handle the subject reproduces the template movement. Subjects readily adapt to this display and reliably make movements of different dynamic characteristics.

Humans↗