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At least 163 records · Page 9Linked to original sources
PubMed1997

Leg cycling tracking by dynamic vision.

This study describes a method of tracking of human body limbs from a monocular sequence of perspective images. These objects and the associated articulations must be modelled. The principle of the method is based on the interpretation of image features as the three-dimensional perspective projections points of the object model and an iterative process method to compute the model position in accordance with the analysed image. This attitude is filtered (Kalman filter) to predict the model position relative to the next image of the sequence. The image features are extracted locally according to the computed prediction. Tracking experiments, illustrated in this study by a leg cycling sequence, have been conducted to demonstrate the viability of the approach.

Bicycling↗
PubMed1987

Nanovid tracking: a new automatic method for the study of mobility in living cells based on colloidal gold and video microscopy.

We describe a new automatic technique for the study of intracellular mobility. It is based on the visualization of colloidal gold particles by video-enhanced contrast light microscopy (nanometer video microscopy) combined with modern tracking algorithms and image processing hardware. The approach can be used for determining the complete statistics of saltatory motility of a large number of individual moving markers. Complete distributions of jump time, jump velocity, stop time, and orientation can be generated. We also show that this method allows one to study the characteristics of random motion in the cytoplasm of living cells or on cell membranes. The concept is illustrated by two studies. First we present the motility of colloidal gold in an in vitro system of microtubules and a protein extract containing a kinesin-like factor. The algorithm is thoroughly tested by manual tracking of the videotapes. The second study involves the motion of gold particles microinjected in the cytoplasm of PTK-2 cells. Here the results are compared to a study using the spreading of colloidal gold particles after microinjection.

Animals↗
PubMed1996

In vivo tracking of platelets: circulating degranulated platelets rapidly lose surface P-selectin but continue to circulate and function.

To examine the hypothesis that surface P-selectin-positive (degranulated) platelets are rapidly cleared from the circulation, we developed novel methods for tracking of platelets and measurement of platelet function in vivo. Washed platelets prepared from nonhuman primates (baboons) were labeled with PKH2 (a lipophilic fluorescent dye), thrombin-activated, washed, and reinfused into the same baboons. Three-color whole blood flow cytometry was used to simultaneously (i) identify platelets with a mAb directed against glycoprotein (GP)IIb-IIIa (integrin alpha 11b beta 3), (ii) distinguish infused platelets by their PKH2 fluorescence, and (iii) analyze platelet function with mAbs. Two hours after infusion of autologous thrombin-activated platelets (P-selectin-positive, PKH2-labeled), 95 +/- 1% (mean +/- SEM, n = 5) of the circulating PKH2-labeled platelets had become P-selectin-negative. Compared with platelets not activated with thrombin preinfusion, the recovery of these circulating PKH2-labeled, P-selectin-negative platelets was similar 24 h after infusion and only slightly less 48 h after infusion. The loss of platelet surface P-selectin was fully accounted for by a 67.1 +/- 16.7 ng/ml increase in the plasma concentration of soluble P-selectin. The circulating PKH2-labeled, P-selectin-negative platelets were still able to function in vivo, as determined by their (i) participation in platelet aggregates emerging from a bleeding time wound, (ii) binding to Dacron in an arteriovenous shunt, (iii) binding of mAb PAC1 (directed against the fibrinogen binding site on GPIIb-IIIa), and (iv) generation of procoagulant platelet-derived microparticles. In summary, (i) circulating degranulated platelets rapidly lose surface P-selectin to the plasma pool, but continue to circulate and function; and (ii) we have developed novel three-color whole blood flow cytometric methods for tracking of platelets and measurement of platelet function in vivo.

Animals↗
PubMed1996

Use of mathematically enhanced spectral analysis and spectral contrast techniques for the liquid chromatographic and capillary electrophoretic detection and identification of pharmaceutical compounds.

The use of mathematically enhanced ultraviolet/visible (UV/VIS) absorbance spectral analysis and spectral contrast software techniques in high performance liquid chromatography (HPLC) and micellar electrokinetic capillary electrophoresis (MECC) as an aid for the determination of peak homogeneity, identification, and tracking during method development was investigated. Various structurally similar pharmaceutical compounds, and compounds present as either cis/trans isomers, diastereomers, or enantiomers were used as test compounds to probe the limits of this technique. Two tricyclic antidepressants, nortriptyline and imipramine, were employed to study the effects of HPLC mobile phase composition and pH on the ability to identify and track peaks during method development. It was found that method changes altered the spectral matches used for identification, but not enough to cause incorrect peak identification. It was also shown using HPLC that the cis/trans isomers of doxepin and the diastereomers ephedrine and pseudoephedrine could be distinguished. The mathematically enhanced spectral analysis and spectral contrast software techniques were also employed with MECC. Peaks tracking during method development as pH and the concentration of surfactant changes is shown for a separation of various penicillin type antibiotics. It was shown that during chiral MECC (CMECC) analyses ephedrine/pseudoephedrine diastereomers as well as ephedrine enantiomers could be distinguished. The determination of enantiomers is possible in CMECC since enantiomers are eluted as diastereomeric complexes, as opposed to HPLC where they are eluted in their native state.

Antidepressive Agents, Tricyclic↗
PubMedDate not supplied

Dynamic scan-plane tracking using MR position monitoring.

An MR-based method for tracking subject motion is presented. The technique identifies subject motion from the three-dimensional positions of three small samples attached to the subject in a fixed, triangular configuration. The updated positions of these samples relative to their initial positions determine a rigid body transformation. Applied to the MRI scan prescription via adaptive feedback controls, this transformation yields an updated MRI scan plane that tracks the prescribed imaging section as the subject moves. The scan-plane tracking procedure is demonstrated experimentally for two-dimensional imaging of a standard imaging phantom and the head of a human subject. Sets of images were acquired sequentially, with motion (translations and/or rotations) introduced between image frames. The scan-plane tracking system provides well registered image slices of the same section, adaptively compensating for the subject motion.

Artifacts↗
PubMed1990

[Computer-assisted contour detection in a complete heart cycle by levocardiography with adaptive raster tracking--validation of the method].

A method for computer-assisted edge detection in a full heart cycle of the left ventricular cineangiogram is presented. Left ventricular cineangiograms were acquired in the 30 degrees RAO position on cinefilms with 50 frames/s. A selected heart cycle was digitized with a spatial resolution of 512 x 512 pixels and a grey-value range from 0 to 255. In the first frame of the heart cycle a raster was calculated from contour points marked by an operator. The raster was automatically adapted to the left ventricular contour in the following frames. The contour points were determined on the adaptive raster by a gradient method. The automatic calculation of all contours of the systolic contraction was possible in 28 of 30 cineangiograms, operator interaction was necessary in two cineangiograms. The calculation of the diastolic contours requested operator interaction in 4 of 30 cineangiograms. The mean deviation of the calculated from the true contours ranged from -1.2 +/- 1.9 mm to 0.9 +/- 2.9 mm. The correlation coefficients between volumes calculated from the computer-determined and manually drawn contours ranged from r = 0.98 to r = 1.0 at beginning of systole, midsystole, endsystole, middiastole, and enddiastole with a standard error of the estimate between 2.8 ml and 5.2 ml. A repeated automatic determination of the contours after an independent remarking of the starting points resulted in a linear correlation of the calculated volumes with a correlation coefficient of r = 1.0 and a standard error of the estimate between 1.3 ml and 4.7 ml. The correlation coefficient for the ejection fraction was r = 0.99 with a standard error of the estimate of 1.9%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Tracking genetically engineered microorganisms in nature.

The past year has seen the continued development of methods for tracking genetically engineered microorganisms in nature, with an emphasis on increased sensitivity, specificity and quantitative ability. In addition, novel methods have been developed for tagging bacteria targeted for environmental release. Nevertheless, the limited number of field trials published to date have primarily relied on conventional monitoring methods, despite the availability of better and theoretically safer methods.

Bacteria↗
PubMed1994

Automated electrophysiologic hearing testing using a threshold-seeking algorithm.

The efficacy of utilizing an automated algorithm to identify auditory brainstem responses (ABR) was studied. A microcomputer-based threshold-seeking algorithm utilizing click-evoked ABR was developed to determine evoked-response thresholds for automated hearing screening. The software consists of an evoked-response recognizer unit, which determines the presence or absence of a response, and a threshold-tracking unit, which controls the click intensity in order to track the threshold. The response recognizer is based upon correlation methods. Threshold tracking is accomplished using a Parameter Estimation by Sequential Testing (PEST) procedure, which is commonly used to study psychophysical properties of the auditory system. Sound level is automatically adjusted, based on the results of the recognizer and the threshold tracker. Test results were generally obtained in less than 15 minutes per ear. The results of the automated procedure correlate very highly with expert judgments of ABR threshold and show good test-retest reliability, suggesting that automated procedures are viable alternatives to traditional testing methods.

Adolescent↗
PubMed1997

Eye-tracking device comparisons of three methods of magnetic resonance image series displays.

This study evaluated the effectiveness of three kinds of display methods for magnetic resonance (MR) image interpretation using an eye-tracking device. Seven radiologists interpreted head MR studies by using a single monitor (17-inch, 1,024 X 1,280 bit) in the 4 images/screen display format. Three paging modes were compared: (A) rapid paging only, (B) multiple image series display at the same slice position with consecutive rapid paging, and (C) simultaneous display of multiple series with each image series being browsed independently. Using an eye-mark camera, the radiologist's point of fixation and the duration of fixation were recorded during actual image interpretation. In mode A, the duration of fixation was short, and the points of fixation were distributed randomly over the visual field. In mode B, the points of fixation were clustered chiefly on a specific image series. In mode C, the points of fixation were not clustered on a specified series, but the duration of viewing the T2 series was relatively long. The total tracing area in mode B and C was smaller than that in mode A. Multiple series display, in which selected key series of slices could be viewed effectively, was found to be suitable for MR image interpretation.

Data Display↗
PubMed1992

Identification of time-varying biological systems from ensemble data.

The theory underlying a new method for the identification of time-varying systems is described. The method uses singular value decomposition to obtain least-squares estimates of time-varying impulse response functions from an ensemble of input-output realizations. No a priori assumptions regarding the system structure or form of the time-variation are required and there are few restrictions on the input signal. Simulation studies, using a model of time-varying joint dynamics, show that the method can track rapid changes in system dynamics accurately and is robust in the presence of output noise. An application of the method is demonstrated by using it to track dynamic ankle stiffness during a rapid, voluntary, isometric contraction. During the transient phase of the contraction, low-frequency ankle stiffness gain decreased in a manner which could not be described with the second-order model of joint dynamics often used under stationary conditions.

Adult↗
PubMed1997

Assessment of vertebral body motion during spine surgery.

STUDY DESIGN: In vitro and in vivo assessment of the accuracy of devices proposed for tracking spine motion during surgery; in vivo assessment of vertebral motion during spine surgery. OBJECTIVES: 1) To quantify the accuracy of newly designed vertebral body trackers; 2) to demonstrate the feasibility of tracking vertebral motion in a cadaveric model; and 3) to quantify the vertebral motion that occurs during spinal surgery. SUMMARY OF BACKGROUND DATA: Computer techniques are beginning to be applied to spine surgery. Validation of accuracy of methods of spinal tracking has not been reported. No information exists on the amount of vertebral motion that occurs during surgery. Because the new techniques require accurate positional information for the vertebral body, it is important to understand and evaluate methods of tracking vertebrae. METHODS: An optical tracking system (Northern Digital, Waterloo, Ontario, Canada) was used to track custom-designed trackers. The reliability and accuracy of the trackers were evaluated in vitro. The proposed tracking methodology for human testing was performed using a cadaveric model, and after successful completion, human testing was done in the operating room to evaluate the motion of two vertebral bodies during exposure for instrumentation of the lumbar spine. This technique was used to evaluate the custom designed trackers effectiveness for tracking vertebral bodies for pedicle screw insertion. RESULTS: The trackers developed were accurate and capable of tracking the motion of the spine. Measured motion of L3 and L4 during breathing was 1.3 mm, peak to peak. Maximal intraoperative motion of the vertebral bodies was 12.3 mm during maneuvers simulating dissection of soft tissue and targeting of spinal pedicles. CONCLUSIONS: Significant motion occurs in lumbar vertebral bodies during surgery. Breathing motion alone is up to 1.3 mm, and surgeon-induced motion up to 10 times greater. Vertebral body trackers for use with an optical position sensor were capable of measuring this motion.

Adult↗
PubMed1981

Computer-monitored radionuclide tracking of three-dimensional mandibular movements. Part III: Multiple point sources--toward mapping of tooth contacts.

A method of tracking mandibular movements has been refined using a computer-assisted radionuclide kinematics technique. Several sites of interest on the same tooth of complete dentures mounted on an articulator have been simultaneously labeled with radioactive material. Accurate reproduction of the movements of the various radioactive markers was observed. The mapping of the relative displacements of the mate teeth was investigated by labeling upper and lower reciprocating teeth with a thin layer of a different radioactive material. Computer image-enhancement programs allow for following the relative trajectory in various open-close movements with increased precision and allow us to draw preliminary conclusions on the possible application of multiple sources labeling to the identification of deflective contacts.

Calibration↗
PubMed1985

Novel antigen system for tracking epithelial cell migration in serum-free culture.

We report here a unique system for tracking normal human urothelial cell migration in serum-free culture medium (HMRI-1). The key observation was that urothelial cells deposited red blood cell surface antigen on the culture dish in a remarkable pattern. Scrutiny of this pattern showed that each migrating cell left behind antigen imprints which formed parallel tracks the width of the cell. Hence the previous migratory history of the cells was instantly mapped by simply visualizing the antigen tracks deposited by the cells on the dish. Apart from providing a simple method for tracking urothelial cells, this observation has wider implications for mechanistic studies of epithelial cell movement in general. It also highlights the complicating effects associated with the addition of serum as a traditional culture supplement, since the inclusion of serum in the HMRI-1 medium abolished the above effect by inhibiting cell migration.

ABO Blood-Group System↗
PubMed1998

Kinetic analysis of the mitotic cycle of living vertebrate cells by atomic force microscopy.

The atomic force microscope (AFM) is becoming an important tool for qualitative and quantitative analyses of biological material. However, the difficulties involved in maintaining long-term, steady-state physiologic conditions and the problems associated with analyzing force curves generated from highly viscoelastic biological structures impede the use of the AFM for studies of kinetic processes in living vertebrate cells. In this report, we describe a simple method to track reproducibly kinetic changes in the localized stiffness of vertebrate cells. We tested our method on a study of vertebrate cells in mitosis and found a marked but transient decrease in stiffness occurs in the mitotic spindle region during anaphase. We propose that physical-chemical changes in the mitotic apparatus, most probably, changes in the state of polymerization of interzonal spindle fibers which also have been reported to undergo a marked reduction in birefringence during anaphase, are responsible for the observed decrease in stiffness. Our methodology affords a new approach to studying mitotic events and should be applicable to studies of a variety of viscoelastic properties of living cells.

Anaphase↗