SEARCH · PubMed Health

Results for “tracking methods”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 505 records · Page 28Linked to original sources

PubMed2003

Numerical simulation of opening process in a bileaflet mechanical heart valve under pulsatile flow condition.

BACKGROUND AND AIM OF THE STUDY: Most previous computational fluid dynamics (CFD) studies of blood flow in mechanical heart valves (MHVs) have not efficiently addressed the important features of moving leaflet and blood-leaflet interaction. Herein, computationally efficient approaches were developed to study these features and to obtain better insight into the pulsatile flow field in bileaflet MHVs. METHODS: A simple and effective method to track the moving boundary was proposed, and an efficient method for calculating the blood-leaflet interaction applied. In this way, a CFD code was developed to study the pulsatile flow field around bileaflet MHVs. The CFD code was parallelized on a supercomputer to reduce turn-around time in the simulation. The solver was then used to study the opening process in a St. Jude Medical (SJM) size 29 bileaflet MHV. RESULTS: CFD results showed that, in the opening process, the flow field was consistently partitioned into two side channels and a central channel due to the presence of the two leaflets. In the flow field near the surface of the two leaflets, the fluid velocity followed the local surface velocity of the leaflets, thus showing a strong blood-leaflet interaction effect. Throughout the valve-opening process, peak velocities were always observed near the tips of the valve leaflet. The CFD simulation showed that the opening process took approximately 0.044 s, which compared well with experimental findings. CONCLUSION: The new computational approaches were efficient and able to address the moving leaflet and blood-leaflet interaction. The flow field in the opening process of a SJM 29 bileaflet MHV was successfully simulated using the developed solver.

Blood Flow Velocity↗

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↗

PubMed2000

Tinea corporis gladiatorum: a cross-sectional study.

BACKGROUND: Tinea corporis gladiatorum has been an infrequently reported condition in the dermatological literature. Two previous reports have investigated wrestlers during recognized epidemics of tinea corporis gladiatorum, but no study has examined wrestlers to determine the point prevalence of tinea corporis gladiatorum in a team without a known epidemic. Furthermore, no comparative study exists. OBJECTIVE: The purpose of this article is to determine the prevalence of tinea corporis gladiatorum in high school wrestlers in comparison with high school indoor track athletes. METHODS: Members of both the high school wrestling and indoor track teams were examined for the presence of tinea corporis. Students with clinical lesions of tinea corporis were evaluated with potassium hydroxide examination. The prevalence of tinea corporis in each group was compared. RESULTS: Seven of the 29 high school wrestlers (24%) had lesions of tinea corporis. No members of the track team had evidence of tinea corporis. There was a statistical difference between the two groups (P =.005). CONCLUSION: Tinea corporis gladiatorum can be found quite frequently among high school wrestlers. Because infection with dermatophytes can disqualify a wrestler from competing in matches, vigilant surveillance and rapid initiation of therapy can reduce the suspension of a team's practice and competition.

Adolescent↗

PubMed2003

The accuracy of estimating proximal tibial translation during natural cadence walking: bone vs. skin mounted targets.

OBJECTIVE: To assess the efficacy of estimating proximal tibial translation using video-based motion capture and an array of surface-mounted targets ideal for tracking motion of the tibia. DESIGN: Superficial and bone-anchored tracking targets were used to create two independent sets of data locating the proximal tibia in a global coordinate system. BACKGROUND: Knowledge of the effect that soft tissue movement has on estimates of proximal tibial translation has not been reported to date. This basic information is necessary to establish construct validity for any study proposing to document tibial translation using standard video-based motion capture methods. METHODS: A six camera motion capture system was used to collect surface-mounted and bone-anchored data for seven healthy adult subjects walking at a self-selected speed. The subjects walked along the positive Y-axis of the global reference system, with the positive Z-axis oriented vertically. RESULTS: Average peak differences in the location of the proximal tibia calculated from the bone and surface-mounted targets were 7.1, 3.7 and 2.1 mm along the X, Y and Z axes of the global coordinate system respectively. Individual subject peak differences were as large as 14.1, 11.8 and 8.3 mm along the X, Y and Z axes. CONCLUSIONS: Estimates of tibial translation with a measurement resolution better than 3 mm are not likely using standard motion capture methods and tracking targets attached superficially to the lower leg. RELEVANCE: The results of this study clearly depict the considerable effect that soft tissue motion of the lower leg has on estimates of proximal tibial translation. Without consideration for the difficulties in measuring femoral, or patellar motion, we believe it is not feasible to routinely obtain sufficiently accurate estimates of detailed knee joint translations using superficial tracking target attachment methods.

Adult↗

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↗

PubMed2006

Noninvasive, automated and continuous cardiac output monitoring by pulmonary capnodynamics: breath-by-breath comparison with ultrasonic flow probe.

BACKGROUND: Cardiac output monitoring is most important where cardiovascular stability is potentially threatened, such as during major surgery and in critically ill patients. However, continuous monitoring of cardiac output is still not performed routinely during anesthesia and critical care, because of invasiveness, expense, and inaccuracy of available technologies. METHODS: A technique termed the capnodynamic method was tested for breath-to-breath measurement of pulmonary blood flow from lung carbon dioxide mass balance, using measured carbon dioxide elimination and end-tidal concentration. A prototype measurement system was constructed for a feasibility study in six anesthetized sheep. Large and rapid fluctuations in cardiac output were generated by repeated dobutamine and esmolol challenge. Measurements were compared with an indwelling ultrasonic flow probe placed on the ascending aorta or pulmonary artery. RESULTS: Cardiac output measured by the flow probe varied between zero and 8.67 l/min, with a mean of 3.50 l/min. Overall mean bias [SD of the difference] between the methods (capnodynamic - flow probe) was -0.25 [0.94] l/min, r = 0.79 (P < 0.001). During periods of stability in cardiac output of 5 min or more, mean bias was -0.20 [0.55] l/min. The method successfully indicated two cardiac arrest events, which were induced in one of the animals. CONCLUSIONS: The method satisfactorily tracked wide fluctuations in cardiac output in real time. The capnodynamic method may have potential for continuous noninvasive cardiac output monitoring in patients undergoing anesthesia for major surgery, and in critical care, on a routine basis.

Animals↗

PubMed2006

In vivo bioluminescence imaging of transplanted islets and early detection of graft rejection.

BACKGROUND: Bioluminescence imaging (BLI) modalities are being developed to monitor islet transplant mass and function in vivo. The aim of this study was to use the BLI system to determine how the change in functional islet mass correlated to metabolic abnormalities during the course of alloimmune rejection in a murine transplant model. METHODS: Islets obtained from a transgenic mouse strain (FVB/NJ-luc) that constitutively expressed firefly luciferase were transplanted to various implantation sites of syngeneic wild-type FVB/NJ or allogeneic Balb/C streptozotocin-induced diabetic recipients. In vivo graft luminescent signals were repeatedly measured after transplantation using the BLI system and related to blood glucose levels and graft site histologic findings. RESULTS: The BLI signals were detected in as few as 10 islets implanted in the renal subcapsular space, intrahepatic, intraabdominal, and subcutaneous locations. There was a linear relationship between the number of islets transplanted and luminescence intensity. In isografts, stable luminescence intensity signals occurred within 2 weeks of transplantation and remained consistent on a long-term basis (18 months) after transplantation. In allografts, after normoglycemia was achieved and stable luminescence intensity occurred, graft bioluminescent intensity progressively decreased several days before permanent recurrence of hyperglycemia as a result of histologically proven rejection ensued. CONCLUSIONS: Bioluminescence imaging is a sensitive method for tracking the fate of islets after transplantation and is a useful method to detect early loss of functional islet mass caused by host immune responses even before overt metabolic dysfunction is evident. Bioluminescence imaging holds promise for use in designing and testing interventions to prolong islet graft survival.

Animals↗

PubMed2000

Tracking sustained chaos: A segmentation method

We introduce a segmentation control method to sustain chaotic transients in dynamical systems. The sustained transient can be tracked as a system parameter is substantially varied, allowing sustained chaotic transients far away from crisis parameter values. The method is applied to a chaotic CO2 laser as well as to a hyperchaotic continuum mechanics model.

Journal Article↗

PubMed2003

Comparison between grating acuity measured by visual tracking and preferential looking in infants.

BACKGROUND: The aim of this study was to compare the visual acuity measured by visual tracking and by preferential looking. METHODS: We examined 51 healthy full-term infants between three and 93 days of age. Visual acuity was tested with two different methods. One method was visual tracking (smooth and saccadic pursuit), recorded with an infrared photo-oculographic technique. For stimulation of visual tracking a square of 9.4 degrees of visual angle with vertical gratings (0.1, 0.2, 0.4, 0.8 and 1.6 cycles per degree) moved at a constant velocity of 7.5 degrees/sec. for 38 sec. on a surface of equal luminance. The other method was preferential looking, determined by a second examiner, where we used plates with vertical gratings (0.1, 0.2, 0.4, 0.8, 1.6, 3.2 and 6.4 cycles per degree). RESULTS: The comparison of the two methods shows a significant correlation (p < 0.05). Visual acuity determined by visual tracking is lower than the acuity determined by preferential looking in the first 14 weeks of age. CONCLUSION: Our study shows that visual tracking is a valid method for visual acuity testing in infants. The need of sustained attention is a possible reason for the lower values in comparison with the acuity determined by preferential looking.

Female↗

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↗

PubMed2006

Single nanoparticle photothermal tracking (SNaPT) of 5-nm gold beads in live cells.

Tracking individual nano-objects in live cells during arbitrary long times is a ubiquitous need in modern biology. We present here a method for tracking individual 5-nm gold nanoparticles on live cells. It relies on the photothermal effect and the detection of the Laser Induced Scattering around a NanoAbsorber (LISNA). The key point for recording trajectories at video rate is the use of a triangulation procedure. The effectiveness of the method is tested against single fluorescent molecule tracking in live COS7 cells on subsecond timescales. We further demonstrate recordings for several minutes of AMPA receptors trajectories on the plasma membrane of live neurons. Single Nanoparticle Photothermal Tracking has the unique potential to record arbitrary long trajectory of membrane proteins using nonfluorescent nanometer-sized labels.

Animals↗

PubMed2003

Assessment of statistical methods used in library-based approaches to microbial source tracking.

Several commonly used statistical methods for fingerprint identification in microbial source tracking (MST) were examined to assess the effectiveness of pattern-matching algorithms to correctly identify sources. Although numerous statistical methods have been employed for source identification, no widespread consensus exists as to which is most appropriate. A large-scale comparison of several MST methods, using identical fecal sources, presented a unique opportunity to assess the utility of several popular statistical methods. These included discriminant analysis, nearest neighbour analysis, maximum similarity and average similarity, along with several measures of distance or similarity. Threshold criteria for excluding uncertain or poorly matched isolates from final analysis were also examined for their ability to reduce false positives and increase prediction success. Six independent libraries used in the study were constructed from indicator bacteria isolated from fecal materials of humans, seagulls, cows and dogs. Three of these libraries were constructed using the rep-PCR technique and three relied on antibiotic resistance analysis (ARA). Five of the libraries were constructed using Escherichia coli and one using Enterococcus spp. (ARA). Overall, the outcome of this study suggests a high degree of variability across statistical methods. Despite large differences in correct classification rates among the statistical methods, no single statistical approach emerged as superior. Thresholds failed to consistently increase rates of correct classification and improvement was often associated with substantial effective sample size reduction. Recommendations are provided to aid in selecting appropriate analyses for these types of data.

Animals↗

PubMed2003

[Naloxone for attenuation of interleukin 2 induced myocardial depression in rat hearts].

OBJECTIVE: To investigate the cardiac effect of interleukin-2 (IL-2) and to explore the underlying mechanism. METHODS: The video tracking system and spectrofluorometric method were used to measure the cell contraction and intracellular calcium. Fura-2/AM was used as a calcium fluorescence probe. Langendorff perfusion technique was used to determine the effect of IL-2 on the intact heart. RESULTS: Compared with the control group, IL-2 5 U/ml, 50 U/ml significantly decreased cell contraction amplitude [(74.95+/-4.79) vs (98.09+/-5.02)%, (64.30+/-5.24) vs (97.38+/-4.05)%], peak velocity of cell shortening [(70.23+/-4.85)% vs (98.09+/-5.46)%, (61.15+/-5.20)% vs (97.38+/-6.85)%], peak velocity of cell relengthening [(71.22+/-4.79)% vs (98.32+/-6.08)%, (68.16+/-5.24)% vs (97.55+/-5.00)%] and end- diastolic cell length [(88.28+/-5.84)% vs (97.95+/-5.52)%, (84.18+/-6.52)% vs (98.94+/-6.76)%]. IL-2 (5 U/ml, 50 U/ml) also markedly inhibited intracellular calcium transient [(74.94+/-4.90)% vs (98.09+/-3.74)%,(71.00+/-5.28)% vs (97.38+/-5.52)%], and elevated end-diastolic calcium level of ventricular myocytes [(113.91+/-5.93)% vs (100.10+/-3.02)%, (119.09+/-7.12)% vs (100.52+/-6.00)%], which were attenuated by the opioid receptor antagonist naloxone (Nal,10 nmol/L). In the isolated perfused rat heart,when compared with the control group, IL-2 50 U/ml markedly decreased left ventricular developed pressure [(79.91+/-2.18) vs (93.84+/-2.94)mmHg], maximal rate of rise of left ventricular pressure [(2370.7358.29) vs (2591.50+/-62.81)mmHg] maximal rate of fall of left ventricular [-(1460.95+/-38.6) vs -(1634.24+/-54.05) mmHg/s] and heart rate [(217.35+/-10.56) vs (244.52+/-11.23) beats/min], but increased left ventricular end-diastolic pressure (11.44+/-1.02 vs 9.23+/-0.46). Pretreatment with Nal (10 nmol/L) antagonized the cardiac depression and left ventricular end-diastolic pressure elevation induced by IL-2. CONCLUSION: The cardiac effect of IL-2 is mediated by opioid receptors on the membrane of cardiomyocytes.

Animals↗

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↗

PubMed2005

Automated analysis of strain rate and strain: feasibility and clinical implications.

BACKGROUND: This study evaluated 3 new automated methods, based on a combination of speckle tracking and tissue Doppler, for the analysis of strain rate (SR) and strain. Feasibility and values for peak systolic strain rate (SR s ) and end-systolic strain (S es ) were assessed. METHODS: Thirty patients with myocardial infarction and 30 normal subjects were examined. Customized software with automatic definition of segments was used for automated measurements. SR s and SR es were measured over each segment simultaneously and identified automatically. The study compared tissue Doppler-based SR and strain measurements without (method 1) and with segment tracking (method 2) to speckle tracking-based measurements (method 3). For tracking, speckle tracking and tissue Doppler were used in combination. Standard manual analysis was used as a reference. RESULTS: The automated analysis (16 segments, 3 apical views) required 2 minutes; manual analysis took 11 minutes. Accuracy was compared in 56 segments (28 mid-infarcted and 28 normal) from 28 patients and was 93.9% for method 1, 93.8% for method 2, 95.8% for method 3, and 96.2% for the manual method. In the normal group, mean SR s (0.27 s -1 ) was less with method 3 than with the other methods ( P < .001). CONCLUSIONS: Our findings indicate that automated analysis of SR and strain, with some manual adjustment, is feasible and quicker than manual analysis. Diagnostic accuracy was similar with all methods. SR s was lower in the speckle tracking-based method than in the Doppler-based methods.

Echocardiography, Doppler↗

PubMed2000

Quantification of cerebral blood flow by bolus tracking and artery spin tagging methods.

This study deals with perfusion quantification in healthy volunteers using two types of dynamic magnetic resonance imaging (MRI) methods. Absolute cerebral blood flow (CBF) measurements were performed in 11 subjects by applying both bolus tracking of exogenous contrast agent and non-invasive arterial spin labeling MRI techniques. Both methods produced CBF images with good tissue contrast and CBF values are in good agreement with literature data. The correlation between cerebral blood volume (CBV) and CBF is also discussed.

Arteries↗