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Results for “tracking methods”

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PubMed2004

Sample size, library composition, and genotypic diversity among natural populations of Escherichia coli from different animals influence accuracy of determining sources of fecal pollution.

A horizontal, fluorophore-enhanced, repetitive extragenic palindromic-PCR (rep-PCR) DNA fingerprinting technique (HFERP) was developed and evaluated as a means to differentiate human from animal sources of Escherichia coli. Box A1R primers and PCR were used to generate 2,466 rep-PCR and 1,531 HFERP DNA fingerprints from E. coli strains isolated from fecal material from known human and 12 animal sources: dogs, cats, horses, deer, geese, ducks, chickens, turkeys, cows, pigs, goats, and sheep. HFERP DNA fingerprinting reduced within-gel grouping of DNA fingerprints and improved alignment of DNA fingerprints between gels, relative to that achieved using rep-PCR DNA fingerprinting. Jackknife analysis of the complete rep-PCR DNA fingerprint library, done using Pearson's product-moment correlation coefficient, indicated that animal and human isolates were assigned to the correct source groups with an 82.2% average rate of correct classification. However, when only unique isolates were examined, isolates from a single animal having a unique DNA fingerprint, Jackknife analysis showed that isolates were assigned to the correct source groups with a 60.5% average rate of correct classification. The percentages of correctly classified isolates were about 15 and 17% greater for rep-PCR and HFERP, respectively, when analyses were done using the curve-based Pearson's product-moment correlation coefficient, rather than the band-based Jaccard algorithm. Rarefaction analysis indicated that, despite the relatively large size of the known-source database, genetic diversity in E. coli was very great and is most likely accounting for our inability to correctly classify many environmental E. coli isolates. Our data indicate that removal of duplicate genotypes within DNA fingerprint libraries, increased database size, proper methods of statistical analysis, and correct alignment of band data within and between gels improve the accuracy of microbial source tracking methods.

Animals↗

PubMed1992

On the feasibility of pulse-echo speed of sound estimation in small regions: simulation studies.

Computer simulations are used to study the feasibility of the estimation of sound speed in small regions with precision better than 1% using the Beam Tracking method. The speed of sound is estimated in a 10-mm by 10-mm region by considering a number of parallel tracks confined to the small region. The transducer focusing and the step sizes for the tracking and tracked transducers required to extract the maximum amount of uncorrelated data from the 10-mm by 10-mm region is evaluated. The results show that the speed of sound can be estimated with error less than 1% in a small region using a typical medical transducer. The statistical comparison of estimates in small areas with different speed of sound is also considered.

Acoustics↗

PubMed2000

Agency-based tracking of difficult-to-follow populations: runaway and homeless youth programs in St. Louis, Missouri.

OBJECTIVES: This study explored agency-based tracking methods for one of the most difficult-to-follow populations: runaway and homeless youth. METHODS: A total of 118 program discharges from three federally funded agencies serving runaway/ homeless youth in St. Louis, Missouri were tracked for a follow-up study of this population. Agency staff attempted to locate and interview program participants three months post-discharge using a protocol that systematically varied times and location of contact attempts. Separate analyses were conducted to compare the group of subjects whose locations were ascertained with those who were not, and who were successfully interviewed with those who were not. Variables related to the tracking protocol and individual descriptive and service use variables were examined in these analyses. RESULTS: Sixty-nine percent of the sample was successfully located and fifty-nine percent interviewed. Significant findings included: fewer contact attempts over fewer days were made for individuals successfully interviewed, individuals tracked through Division of Family Services were less likely to be both located and interviewed, and individuals successfully located were significantly younger. CONCLUSIONS: This report provides encouraging evidence that even relatively unsophisticated protocols for tracking agency clients developed in collaboration with community agencies can--with consistent implementation--yield follow-up samples that are acceptably representative of program participants.

Adolescent↗

PubMed2006

A prototype ultrasound-guided laparoscopic radiofrequency ablation system.

BACKGROUND: Advanced laparoscopic procedures, particularly laparoscopic liver resection and ablation, may benefit from image-guided surgery techniques that involve interactive three-dimensional imaging and instrument tracking. METHODS: A prototype system for laparoscopic ultrasound-guided radiofrequency ablation was designed and implemented. This system uses an infrared camera to track instruments and runs on a personal computer. Features of the system include spatially registered ultrasound visualization, volume reconstruction, and interactive targeting. Targeting of accuracy studies was performed by directing a tracked needle to a phantom target. RESULTS: Ultrasound data collection and volume reconstruction can be achieved within minutes and interactively reviewed by the surgeon. Early results with phantom experiments demonstrate a targeting accuracy of 5 to 10 mm. CONCLUSIONS: These results support the further development of this and similar image-guided surgery systems for specific laparoscopic procedures. Eventually, rigorous clinical evaluation will be necessary to prove their value.

Algorithms↗

PubMed2005

An automated method for analysis of flow characteristics of circulating particles from in vivo video microscopy.

The behavior of white and red blood cells, platelets, and circulating injected particles is one of the most studied areas of physiology. Most methods used to analyze the circulatory patterns of cells are time consuming. We describe a system named CellTrack, designed for fully automated tracking of circulating cells and micro-particles and retrieval of their behavioral characteristics. The task of automated blood cell tracking in vessels from in vivo video is particularly challenging because of the blood cells' nonrigid shapes, the instability inherent in in vivo videos, the abundance of moving objects and their frequent superposition. To tackle this, the CellTrack system operates on two levels: first, a global processing module extracts vessel borders and center lines based on color and temporal patterns. This enables the computation of the approximate direction of the blood flow in each vessel. Second, a local processing module extracts the locations and velocities of circulating cells. This is performed by artificial neural network classifiers that are designed to detect specific types of blood cells and micro-particles. The motion correspondence problem is then resolved by a novel algorithm that incorporates both the local and the global information. The system has been tested on a series of in vivo color video recordings of rat mesentery. Our results show that the synergy between the global and local information enables CellTrack to overcome many of the difficulties inherent in tracking methods that rely solely on local information. A comparison was made between manual measurements and the automatically extracted measurements of leukocytes and fluorescent microspheres circulatory velocities. This comparison revealed an accuracy of 97%. CellTrack also enabled a much larger volume of sampling in a fraction of time compared to the manual measurements. All these results suggest that our method can in fact constitute a reliable replacement for manual extraction of blood flow characteristics from in vivo videos.

Algorithms↗

PubMed2004

Respiration tracking in radiosurgery.

Respiratory motion is difficult to compensate for with conventional radiotherapy systems. An accurate tracking method for following the motion of the tumor is of considerable clinical relevance. We investigate methods to compensate for respiratory motion using robotic radiosurgery. In this system the therapeutic beam is moved by a robotic arm, and follows the moving target through a combination of infrared tracking and synchronized x-ray imaging. Infrared emitters are used to record the motion of the patient's skin surface. The position of internal gold fiducials is computed repeatedly during treatment, via x-ray image processing. We correlate the motion between external and internal markers. From this correlation model we infer the placement of the internal target during time intervals where no x-ray images are taken. Fifteen patients with lung tumors have recently been treated with a fully integrated system implementing this new method. The clinical trials confirm our hypothesis that internal motion and external motion are indeed correlated. In a preliminar study we have extended our work to tracking without implanted fiducials, based on algorithms for computing deformation motions and digitally reconstructed radiographs.

Clinical Trials as Topic↗

PubMed2005

Probabilistic anatomical connectivity derived from the microscopic persistent angular structure of cerebral tissue.

Recently developed methods to extract the persistent angular structure (PAS) of axonal fibre bundles from diffusion-weighted magnetic resonance imaging (MRI) data are applied to drive probabilistic fibre tracking, designed to provide estimates of anatomical cerebral connectivity. The behaviour of the PAS function in the presence of realistic data noise is modelled for a range of single and multiple fibre configurations. This allows probability density functions (PDFs) to be generated that are parametrized according to the anisotropy of individual fibre populations. The PDFs are incorporated in a probabilistic fibre-tracking method to allow the estimation of whole-brain maps of anatomical connection probability. These methods are applied in two exemplar experiments in the corticospinal tract to show that it is possible to connect the entire primary motor cortex (M1) when tracing from the cerebral peduncles, and that the reverse experiment of tracking from M1 successfully identifies high probability connection via the pyramidal tracts. Using the extracted PAS in probabilistic fibre tracking allows higher specificity and sensitivity than previously reported fibre tracking using diffusion-weighted MRI in the corticospinal tract.

Anisotropy↗

PubMed2006

Cortical projections to the human red nucleus: a diffusion tensor tractography study with a 1.5-T MRI machine.

INTRODUCTION: Previous studies in apes and monkeys have shown that the red nucleus receives projections from the sensorimotor and premotor cortices, whereas other experiments carried out with injured human brains have found corticorubral projections issuing from associative areas. Therefore, we reassessed in vivo the human anatomical projections from the cerebral cortex to the red nucleus using diffusion tensor imaging (DTI) axonal tracking. METHODS: The connectivity between the cerebral cortex and the red nuclei of seven volunteers was studied at 1.5 T using streamlined DTI axonal tracking. RESULTS: Trajectories were constantly tracked between the red nuclei and the ipsilateral pericentral and prefrontal cortices, as well as the temporal cortex and the striatum in two subjects. Within the cerebral trunk, trajectories also include the superior cerebellar peduncle and the central tegmental tract. CONCLUSION: The human red nucleus receives its main afferences from the sensorimotor and prefrontal cortices.

Adult↗

PubMed2003

Elasticity imaging of atheroma with transcutaneous ultrasound: preliminary study.

BACKGROUND: Knowledge of the physical properties of atherosclerotic plaque is essential when evaluating its vulnerability in a clinical setting. Such knowledge, however, is still difficult to obtain with the various approaches developed to date. METHODS AND RESULTS: This article describes a noninvasive method for evaluating the regional elasticity (the elastic modulus in the circumferential direction) of tissue surrounding atherosclerotic plaque in which a novel phased tracking method is applied to measure minute changes in thickness of each of the multiple layers of the arterial wall during one heartbeat. By comparing the pathological findings with the distribution of elasticity, average elasticity of lipid and that of a mixture of smooth muscle and collagen fiber can be determined. On the basis of these reference parameters, each point is statistically categorized as lipid, mixture, or other. Thus, the plaque is electronically stained using transcutaneous ultrasound. By applying the method to the common carotid arteries, the presence of thin collagen fiber was clarified along the arterial axis for normal subjects, whereas soft inclusion of lipid was found for every plaque in subjects with hyperlipidemia. CONCLUSIONS: This novel method offers potential as a diagnostic technique for detection of plaque vulnerability with high spatial resolution.

Adult↗

PubMed2004

Realignment of myocardial first-pass MR perfusion images using an automatic detection of the heart-lung interface.

Magnetic resonance first-pass imaging of a bolus of contrast agent is well adapted to distinguish normal and hypoperfused areas of the myocardium. In most cases, the signal intensity-time curves in user defined regions of interest (ROI) are studied. As image acquisition is ECG-gated, the images are acquired at the same moment in the cardiac cycle, and the basic shape of the heart is similar from one view to the next. However, superficial respiratory motion can displace the heart in the short-axis plane. The aim of this study is to correct for the respiratory motion of the heart by performing an automatic realignment of the myocardial ROI based on a method tracking the movement of the lung-myocardium interface. Visual and quantitative analyses performed on 120 curves show a very good concordance between two automatic methods and the manual one.

Adult↗

PubMed2003

In vivo MR tractography using diffusion imaging.

Diffusion in structured tissue, such as white matter or muscle, is anisotropic. MR diffusion tensor imaging (DTI) measures anisotropy per pixel and provides the directional information relevant for MR tractography or fiber tracking in vivo. MR tractography is non-invasive, relatively fast, and can be repeated multiple times without destructing important tissue. Moreover, the combination with other MR images is relatively simple. In this paper, the basic principles of tractography are presented. Different tracking methods with varying degrees of complexity are introduced and their potential strengths and weaknesses are discussed. Clinical applications and different strategies for evaluating the fidelity of tracking results are reviewed.

Anisotropy↗

PubMed2006

Fourier transform ultraviolet-visible spectrometer based on a beam-folding technique.

A beam-folding technique in optical interferometry, where the number of beam folds used can be very large, is reported. This technique can be used as a low-cost position-tracking method in a Fourier transform spectrometer (FTS) to cover the broad spectral range from UV to IR. The main advantage gained is the simple position-tracking algorithm used in sampling the interferogram. We have developed a UV-visible FTS, whose wavelength coverage is limited only by the optical elements (350 nm(-1) microm with off-the-shelf components). Preliminary results show that it can achieve a resolution of approximately 4 cm(-1) even with a ball-bearing translation stage.

Algorithms↗

PubMed2005

Eye-tracking architecture for biometrics and remote monitoring.

Eye tracking is one of the latest technologies that has shown potential in several areas, including biometrics; human-computer interactions for people with and without disabilities; and noninvasive monitoring, detection, and even diagnosis of physiological and neurological problems in individuals. Current noninvasive eye-tracking methods achieve a 30-Hz rate with a low accuracy in gaze estimation, which is insufficient for many applications. We propose a new noninvasive optical eye-tracking system that is capable of operating at speeds as high as 6-12 kHz. A new CCD video camera and hardware architecture are used, and a novel fast algorithm leverages specific features of the input CCD camera to yield a real-time eye-tracking system. A field-programmable gate array is used to control the CCD camera and to execute the operations. Initial results show the excellent performance of our system under severe head-motion and low-contrast conditions.

Algorithms↗

PubMed2006

Improved delineation of glioma margins and regions of infiltration with the use of diffusion tensor imaging: an image-guided biopsy study.

BACKGROUND AND PURPOSE: The efficacy of radiation therapy, the mainstay of treatment for malignant gliomas, is limited by our inability to accurately determine tumor margins. As a result, despite recent advances, the prognosis remains appalling. Because gliomas preferentially infiltrate along white matter tracks, methods that show white matter disruption should improve this delineation. In this study, results of histologic examination from samples obtained from image-guided brain biopsies were correlated with diffusion tensor images. METHODS: Twenty patients requiring image-guided biopsies for presumed gliomas were imaged preoperatively. Patients underwent image-guided biopsies with multiple biopsies taken along a single track that went into normal-appearing brain. Regions of interest were determined from the sites of the biopsies, and diffusion tensor imaging findings were compared with glioma histology. RESULTS: Using diffusion tissue signatures, it was possible to differentiate gross tumor (reduction of the anisotropic component, q > 12% from contralateral region), from tumor infiltration (increase in the isotropic component, p > 10% from contralateral region). This technique has a sensitivity of 98% and specificity of 81%. T2-weighted abnormalities failed to identify the margin in half of all specimens. CONCLUSION: Diffusion tensor imaging can better delineate the tumor margin in gliomas. Such techniques can improve the delineation of the radiation therapy target volume for gliomas and potentially can direct local therapies for tumor infiltration.

Adolescent↗

PubMed1989

[Interactive Microcomputer Method of Lipreading (MIMILLE): an interactive microcomputerized method of lipreading].

A computer-aided speechreading assessment and training system is presented. It is intended to be one component of a comprehensive aural rehabilitation program for preretirement adults with acquired mild-to-moderate hearing loss. Each lesson focuses on a different viseme which is practiced using the 'discourse tracking' method. The system allows the evaluation of the basic skills necessary for lipreading, i.e. good visual speech decoding and effective use of lingustic redundancy and transmitter feedback, by evaluating separately tracking rate, strategy, and types of errors.

Algorithms↗

PubMed2000

Robotic motion compensation for respiratory movement during radiosurgery.

Tumors in the chest and abdomen move during respiration. The ability of conventional radiation therapy systems to compensate for respiratory motion by moving the radiation source is inherently limited. Since safety margins currently used in radiation therapy increase the radiation dose by a very large amount, an accurate tracking method for following the motion of the tumor is of the utmost clinical relevance. We investigate methods to compensate for respiratory motion using robotic radiosurgery. Thus, the therapeutic beam is moved by a robotic arm, and follows the moving target tumor. To determine the precise position of the moving target, we combine infrared tracking with synchronized X-ray imaging. Infrared emitters are used to record the motion of the patient's skin surface. A stereo X-ray imaging system provides information about the location of internal markers. During an initialization phase (prior to treatment), the correlation between the motions observed by the two sensors (X-ray imaging and infrared tracking) is computed. This model is also continuously updated during treatment to compensate for other, non-respiratory motion. Experiments and clinical trials suggest that robot-based methods can substantially reduce the safety margins currently needed in radiation therapy.

Humans↗

PubMed1996

Resistive-load detection in healthy school-aged children.

The ability to detect changes in respiratory resistance, which may be important in acute and chronic adaptations to airways obstruction, has not been measured previously in children. Two methods were used to measure the resistive-load detection thresholds (the added resistance that produced a "just noticeable difference" in perception) in a group of 38 healthy children and adolescents aged 7-16 years. Total respiratory system resistance (Rrs), as measured by forced oscillation, was used as an index of each child's intrinsic baseline (pre-test) resistance. To determine thresholds a computer program added various percentages of baseline resistance according to response (first method) and then in random order (second method). Thresholds by at least one of the two methods were detectable in 32 of the children (84%), and failure to detect a threshold was less common in older than in young children. Thresholds obtained by each method were significantly related to one another (r = 0.54, P < 0.05). Baseline resistance accounted for a marginally significant proportion of the variation in thresholds as assessed by the tracking method (R2 = 0.12, P < 0.10) and a large proportion of the variation in thresholds as assessed by the random method (R2 = 0.66, P < 0.0001). Thresholds expressed in terms of percent of baseline resistance were found to have mean values of 100.4-105.0%, regardless of gender or age. Results from a comparison group of adults (n = 10) indicated lower threshold by both procedures (mean values, 71.90-76.50%). We conclude that perceptual thresholds for added resistive loads are determined, in part, by growth-related changes in intrinsic resistance.

Adolescent↗

PubMed2006

An improved adaptive power line interference canceller for electrocardiography.

Power line interference may severely corrupt a biomedical recording. Notch filters and adaptive cancellers have been suggested to suppress this interference. We propose an improved adaptive canceller for the reduction of the fundamental power line interference component and harmonics in electrocardiogram (ECG) recordings. The method tracks. the amplitude, phase, and frequency of all the interference components for power line frequency deviations up to about 4 Hz. A comparison is made between the performance of our method, former adaptive cancellers, and a narrow and a wide notch filter in suppressing the fundamental power line interference component. For this purpose a real ECG signal is corrupted by an artificial power line interference signal. The cleaned signal after applying all methods is compared with the original ECG signal. Our improved adaptive canceller shows a signal-to-power-line-interference ratio for the fundamental component up to 30 dB higher than that produced by the other methods. Moreover, our method is also effective for the suppression of the harmonics of the power line interference.

Algorithms↗