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PubMed2006

Quantitative analysis of accuracy of an inertial/acoustic 6DOF tracking system in motion.

An increasing number of neuroscience experiments are using virtual reality to provide a more immersive and less artificial experimental environment. This is particularly useful to navigation and three-dimensional scene perception experiments. Such experiments require accurate real-time tracking of the observer's head in order to render the virtual scene. Here, we present data on the accuracy of a commonly used six degrees of freedom tracker (Intersense IS900) when it is moved in ways typical of virtual reality applications. We compared the reported location of the tracker with its location computed by an optical tracking method. When the tracker was stationary, the root mean square error in spatial accuracy was 0.64 mm. However, we found that errors increased over ten-fold (up to 17 mm) when the tracker moved at speeds common in virtual reality applications. We demonstrate that the errors we report here are predominantly due to inaccuracies of the IS900 system rather than the optical tracking against which it was compared.

Acceleration↗

PubMed2007

A new approach to assess function after sciatic nerve lesion in the mouse - adaptation of the sciatic static index.

Among the numerous ways of assessing regeneration after peripheral nerve lesions, the analysis of gait is one of the most important, because it shows the recovery of function, which is the ultimate goal of the repair machinery. The sciatic function index was introduced as a method to assess reinnervation after an experimental sciatic nerve lesion, and was adapted to the mouse model. The sciatic static index (SSI), is more simple and practical to perform, and is not so influenced by gait's velocity, but this method has not yet been adapted to the mouse model of sciatic lesion. We used 63 male Swiss mice (Mus musculus) to develop a formula to the sciatic static index in mice (SSIm). The animals were divided on three groups (control, transection and crush). They were evaluated at the preoperative and 7th, 14th, 21st, 28th, 35th and 42nd days postoperative by the ink track method (SFI), and by the acquisition of photographs of the plantar aspects of the injured and uninjured hind paws. The parameters evaluated were the 1-5 toe spread (TS), the 2-4 toe spread (ITS) and the distance between the tip of the third toe and the most posterior aspect of the paw (PL), on both methods. After verifying the temporal pattern of function, correlation and reproducibility of the measurements, we performed a multiple regression analysis using SFI values as dependent variable, and the TS, ITS and PL measured with the photo method as independent variables, and found the formula of the SSI for mice (SSIm). The three groups (control, transection and crush) had a characteristic pattern of dysfunction. The parameters measured in the ink and photo method had variable but significant correlations between them (P<0.000), but photo method of measurement showed a better reproducibility. The correlation between SFI and SSIm showed a high correlation coefficient (r=0.892, P<0.000), and demonstrates that SSIm can be used as an alternative method to assess the functional status relative of sciatic nerve activity in mice.

Animals↗

PubMed2005

White matter tractography by means of Turboprop diffusion tensor imaging.

White matter fiber-tractography by means of diffusion tensor imaging (DTI) is a noninvasive technique that provides estimates of the structural connectivity of the brain. However, conventional fiber-tracking methods using DTI are based on echo-planar image acquisitions (EPI), which suffer from image distortions and artifacts due to magnetic susceptibility variations and eddy currents. Thus, a large percentage of white matter fiber bundles that are mapped using EPI-based DTI data are distorted, and/or terminated early, while others are completely undetected. This severely limits the potential of fiber-tracking techniques. In contrast, Turboprop imaging is a multiple-shot gradient and spin-echo (GRASE) technique that provides images with significantly fewer susceptibility and eddy current-related artifacts than EPI. The purpose of this work was to evaluate the performance of fiber-tractography techniques when using data obtained with Turboprop-DTI. All fiber pathways that were mapped were found to be in agreement with the anatomy. There were no visible distortions in any of the traced fiber bundles, even when these were located in the vicinity of significant magnetic field inhomogeneities. Additionally, the Turboprop-DTI data used in this research were acquired in less than 19 min of scan time. Thus, Turboprop appears to be a promising DTI data acquisition technique for tracing white matter fibers.

Artifacts↗

PubMed2006

Effects of balloon angioplasty on perfusion- and diffusion-weighted magnetic resonance imaging results and outcome in patients with cerebral vasospasm.

OBJECT: The aim of this study was to analyze the effects and outcome of transluminal balloon angioplasty (TBA) on brain tissue perfusion by using combined perfusion- and diffusion-weighted (PW/DW) magnetic resonance (MR) imaging in patients with cerebral vasospasm after subarachnoid hemorrhage. METHODS: Ten consecutive patients with cerebral vasospasm treated using TBA were included in this prospective study. Hemodynamically relevant vasospasm was diagnosed using a standardized PW/DW MR imaging protocol. Digital subtraction angiography was used to confirm vasospasm, and TBA was performed to dilate vasospastic arteries. The PW/DW imaging protocol was repeated after TBA. The evaluation of the passage of contrast medium after standardized application using the bolus tracking method allowed for the calculation of the time to peak (TTP) before and after TBA. Tissue at risk was defined based on perfusion delays in individual vessel territories compared with those in reference territories. In cases with proximal focal vasospasm, TBA could dilate spastic arteries. Follow-up PW/DW MR imaging showed the disappearance of, or a decrease in, the mismatch. A TBA-induced reduction in the perfusion delay of 6.2 +/- 1 seconds (mean +/- standard error of the mean) to 1.5 +/- 0.45 seconds resulted in the complete prevention of infarction; a reduction in the delay of 6.2 +/- 2.7 to 4.1 +/- 1.9 seconds resulted in the preservation of those brain tissue parts having only small infarcts in the vessel territories. Without TBA, however, the perfusion delay remained or even increased (11.1 +/- 3.7 seconds), and the complete infarction of a territory occurred. CONCLUSIONS: Angioplasty of vasospastic arteries leads to hemodynamic effects that can be quantified using PW/DW MR imaging. In cases of a severe PW/DW imaging mismatch successful TBA improved tissue perfusion and prevented cerebral infarction. The clinical significance of PW/DW MR imaging and the concept of tissue at risk is shown by cerebral infarction in vessels not accessible by TBA.

Adult↗

PubMed2005

Fiber-tracking does not accurately estimate size of fiber bundle in pathological condition: initial neurosurgical experience using neuronavigation and subcortical white matter stimulation.

The fiber-tracking method enables in vivo visualization of the white matter tracts of the brain using a diffusion tensor MR imaging technique. While this method represents a promising tool in the field of neurosurgery, especially when confronted with brain tumors in eloquent areas, its reliability remains unknown. We present here our preliminary validation of tractography in human subjects harboring brain tumors by comparing the results produced by neuronavigation and electrical white matter stimulation in two patients with gliomas in the eloquent area. Although we were able to visualize the pyramidal tract with the fiber-tracking technique, the images failed to present the actual size of the fiber bundles. Here we discuss the advantages and limitations of fiber-tracking in the field of neurosurgery.

Aged↗

PubMed2002

Systolic heterogeneity of transmural myocardial function in normal subjects: physiological functional heterogeneity.

Because of the lack of a clinical method for assessing the transmural myocardial function, few studies on the heterogeneity during the myocardial contraction/relaxation sequence inside the human ventricular wall have been reported, despite the fact that the importance of the pathophysiology in the transmural heterogeneity has been stressed in previous experimental studies. We studied the transmyocardial functional heterogeneity of the basal anteroseptal segment in normal subjects (n = 8, 40.0 +/- 12.8 year, male), adopting the novel high resolution Doppler measurement "Phased Tracking Method". Each transmural layer of 0.75 mm thickness showed functional heterogeneity (physiological transmural functional heterogeneity), namely larger thickening occurred in the left ventricular endocardial side (right side 1/3: 26.1 +/- 5.2% of the total wall thickness, middle 1/3: 31.9 +/- 2.7%, left side 1/3: 42.1 +/- 6.4%) and the peak thickening shifted smoothly in time from the middle layers to the left subendocardial side during the contraction period. We concluded that transmural functional heterogeneity does exist in normal subjects as well as in the experimental animals of previous reports. Smooth and coordinate myocardial layer contraction across the ventricular wall (physiological transmural functional heterogeneity) is fundamental to maintain the normal ventricular function.

Adult↗

PubMed1995

Cutting versus conical tip designs.

The history of development in laparoscopy shows that the dilemma involving blind insertion of the trocar has not changed in over 100 years. Perforation of the abdominal wall with the cutting trocar is no longer necessary with today's anatomical and technical possibilities. The cutting trocar with its four cutting surfaces has a great disadvantage compared to the conical trocar with regard to safety. The linea alba should not be disrupted, and perforation of the abdominal wall should be performed in an area where the fascia is weaker and muscle is more abundant. The "z"-track method of trocar insertion prevents intestinal or omental herniation. For perforation and stretching of the muscle, a conical trocar with a blunt tip is recommended. After inserting the conical trocar down to the layer of subcutaneous fat or muscle, further advancement is performed under visual control using a normal straight endoscope and by rotating the bevelled end of the trocar sheath. Perforation of the abdominal wall with a conical trocar using the "z"-track incision under endoscopic control prevents incisional herniation of intestine or omentum.

Equipment Design↗

PubMed2006

Two-dimensional multi-level strain estimation for discontinuous tissue.

A large number of the strain estimation methods presented in the literature are based on the assumption of tissue continuity that establishes a continuous displacement field. However, in certain locations in the body such as the arteries in vivo scanning may produce displacement fields that are discontinuous between the two walls of the artery. Many of the displacement or strain estimators fail when the displacement fields are discontinuous. In this paper, we present a new 2D multi-level motion or displacement tracking method for accurate estimation of the strain in these situations. The final high-resolution displacement estimate is obtained using two processing steps. The first step involves an estimation of a coarse displacement estimate utilizing B-mode or envelope signals. To reduce computational time, the coarse displacement estimates are obtained starting from down-sampled B-mode pre- and post-compression image pairs using a pyramidal processing approach. The coarse displacement estimate obtained from the B-mode data is used to guide the final 2D cross-correlation computations on radio-frequency (RF) data. Results from finite element simulations and in vivo experimental data demonstrate the feasibility of this approach for imaging tissue with discontinuous displacement fields.

Algorithms↗

PubMedDate not supplied

Training in community pediatrics: a national survey of program directors.

OBJECTIVE: To describe the spectrum of residency training in community-based settings, assess the extent of resident education on community pediatrics topics, and determine whether educational activities vary by program size or availability of primary care tracks. METHODS: Survey of US pediatric residency program directors from May-September 2002. A 10-item self-administered questionnaire assessed the programs' extent of resident involvement in 15 selected community-based settings and inclusion of didactic or practical education regarding 13 community health topics. RESULTS: Of 168 programs surveyed (81% response rate), 40% were small (< or =30 residents), 35% were medium (31-50 residents), 25% were large (>50 residents), and 15% had primary care tracks. Frequently required community-based settings included schools (69%), child protection teams (62%), day care centers (57%), and home visiting (48%). Of 15 community-based settings, 28% required involvement in fewer than 4, 41% required involvement in 4-6, and 31% required involvement in 7 or more. More than two-thirds offered didactic teaching and practical experience on issues related to managed care, cultural competency, and the mental health and social service systems. There were no differences in the number of required community-based settings by program size or presence of primary care tracks. CONCLUSIONS: Most pediatric residency programs require exposure to community-based settings and provide education on various community health topics. Ongoing challenges include continued implementation amid work duty hour limitations, best practice models for practical implementation of community-based experience into residency training, and the impact of such training on future involvement in the community and physician practice.

Community Health Services↗

PubMed2003

[Spatial and temporal characteristic of eye movement in human-computer interface design].

OBJECTIVE: To examine the related spatial and temporal characteristics of eye movement in HCI design and to provide ergonomic parameters to optimize the HCI design based on eye tracking. METHOD: Task time, selected error and timeout numbers were recorded automatically, when 12 participants were performing the task of target selection, with different object size, space and dwell time. RESULT: It was significantly found that task time was influenced by object size and dwell time, the selected error was influenced by object space and dwell time significantly. CONCLUSION: The dwell time, object size and object space are all important to optimize the HCI design based on eye tracking. We recommend that the dwell time should be 500 ms, the object size and object space should be not less than 1.5 degrees and 1.0 degrees respectively for the normal interactive systems.

Adult↗

PubMedDate not supplied

Pulse wave recording--development of a method for investigating foetal circulation in utero.

The need to investigate the elastic properties of arterial vessels 'in situ' for the early recognition of degenerative disorders in arteries has long been apparent. Volume pulses in defined segments of arteries can be evaluated for this purpose, and the present paper contains a survey of earlier attempts to quantify volume pulses by means of ultrasound. A presentation is given of a recently developed digital system, comprising a phase-locked echo tracker, capable of monitoring non-invasively the diameter and its pulsatile changes of a selected artery along two chosen image lines of a linear array ultrasound scanner. The physical limitations of tracking fast-moving ultrasound echoes by means of phase-locked range gating are reported and the advantage is emphasized of using a gate length of one full period. This system has been calibrated, tested and applied in measurements of pulse wave pattern and propagation velocity in the descending aorta of human foetuses in the last trimester of gestation. The present high-resolution echo-tracking method has yielded reproducible results in the foetus and appears suitable also for screening studies on adult vessels.

Blood Circulation↗

PubMed2002

An alternative video footprint analysis to assess functional loss following injury to the rat sciatic nerve.

The rat sciatic nerve is a well-established animal model for the study of recovery from peripheral nerve injuries. Footprint analysis is the most widely used non-invasive method of measuring functional recovery after injury in this model. We describe a new, alternative video analysis of standing (or static footprint video analysis) to assess functional loss following injury to the rat sciatic nerve, while the animal is standing or at periodic rest on a flat transparent surface. We found that this alternative video analysis is technically easier to perform than the corresponding footprint video analysis while walking, but still preserves all advantages of video versus conventional ink track method: i.e. few non-measurable footprints, better repeatability, high accuracy and more precise quantification of the degree of functional loss after sciatic nerve injury in the rat.

Animals↗

PubMed1997

Heterogeneous distribution of technetium-99m-labeled microspheres in rat lungs: microautoradiographic evidence and dosimetric consequences.

UNLABELLED: The heterogeneity of 99mTc-labeled microspheres distribution within rat lung was visualized and quantified using a microautoradiographic "track" method (MAR). METHODS: MAR was used to study the uptake of radioactivity by individual microspheres, thereby enabling calculation of the range of particle activity. MAR was also used to visualize in rat lung sections the intrapulmonary distribution of the microspheres within the lungs after intravenous administration. The mean doses delivered to the cells in close contact with the labeled microspheres were calculated taking only the 99mTc electron emissions into account. RESULTS: All the microspheres were labeled. Nevertheless, the spectrum of visible tracks varied by a factor of 10, inducing a variable activity per microsphere from < 36 Bq to 325 Bq (mean activity-94 Bq/microsphere). No correlation existed between the radioactivity uptake and the size of microspheres. A very heterogeneous tridimensional distribution of the microspheres within the lungs were demonstrated with interparticle distances ranging from 57-4400 microns. On the other hand, only 1 of 2000 rat lung capillaries was obstructed. Using the mean activity, calculated delivered doses were found to reach approximately 6 Gy for the closest endothelial cells and 2 Gy for epithelial cells. However, such high doses were delivered to only a few cells. CONCLUSION: The number of obstructed capillaries in human lungs is lower than in rat lungs; the distances between microspheres should be larger. Nevertheless, the individual doses absorbed by the pulmonary cells closest to the microspheres should be very important.

Animals↗

PubMed2004

Performance measures for video object segmentation and tracking.

We propose measures to evaluate quantitatively the performance of video object segmentation and tracking methods without ground-truth (GT) segmentation maps. The proposed measures are based on spatial differences of color and motion along the boundary of the estimated video object plane and temporal differences between the color histogram of the current object plane and its predecessors. They can be used to localize (spatially and/or temporally) regions where segmentation results are good or bad; and/or they can be combined to yield a single numerical measure to indicate the goodness of the boundary segmentation and tracking results over a sequence. The validity of the proposed performance measures without GT have been demonstrated by canonical correlation analysis with another set of measures with GT on a set of sequences (where GT information is available). Experimental results are presented to evaluate the segmentation maps obtained from various sequences using different segmentation approaches.

Algorithms↗

PubMed2004

Navigation systems based on registration of endoscopic and CT-derived virtual images for bronchofiberoscopic procedures.

Bronchofiberoscopy is an essential diagnostic procedure in patients with lung cancer. Sampling methods employed during endoscopy of the respiratory tract are performed with the aim of diagnosis confirmation and staging. Transbronchial needle aspiration may be used for evaluation of lymph nodes neighbouring with trachea and bronchi. Many efforts have been undertaken to increase the sensitivity of this procedure including the application of endobronchial ultrasonography. In recent years several research groups have proposed models of navigating systems to provide computer assistance during bronchoscopic interventions. Although they have used different techniques, their objective was the same - enabling tracking location and movement of bronchofiberoscope tip with reference to previously-acquired computed tomography (CT) images. Since a fiber-optic bronchoscope is a rather long and flexible device, determination of its tip location is not an easy task. The adoption of optical tracking methods used in neurosurgery or laparoscopic surgery to endoscopy of the tracheobronchial tree is usually not possible. Another obstacle is related to the fact that bronchofiberoscopes usually have only one operational channel. This feature considerably limits the feasibility of navigation systems based on the use of small electromagnetic sensing devices or USG probes. The sources of positioning errors in such systems are respiratory movements and the lack of external referential coordinate system associated with the tracheobronchial tree.A promising option for development of a bronchoscopic guidance system is the application of image registration algorithms. Such an approach encompasses registration of endoscopic images to views derived from advanced imaging methods, e.g. CT. In the first step, reconstruction of a three-dimensional, endoluminal views is performed. Next, the position of the virtual camera in a CT-derived virtual model is determined using a complex multi-level image registering algorithm. This stage is the source of the greatest differences between proposed methods and a potential field for considerable improvements.This paper presents a review of recent as well as classical image registering methods used in navigation systems for bronchofiberoscopy. Details related to the selection of crucial elements of navigation systems based on image registering techniques, such as transformation, similarity criteria, matching and global optimization, are specified.

Algorithms↗

PubMed2002

Very high compliance in an expanded MS-MS-based newborn screening program despite written parental consent.

OBJECTIVES: In Bavaria, Germany, an expanded MS-MS-based newborn screening program was implemented in 1999. The coverage of new additional conditions and novelty of technology required introduction of written parental consent. Here we evaluated the influence of the consent procedure on compliance by systematic demographic tracking. METHODS: Comprehensive information was provided for parents, professionals, and the public. Screening notifications were matched with all birth notifications on name and date of birth. Parents of children without screening notification were contacted and counseled. RESULTS: Between August 1, 1999, and July 31, 2000, 123,284 children eligible for screening were born. Of these, 116,652 were matched successfully. Among 6,632 parents contacted, 2,516 (2%) did not respond. Three thousand thirty-four children were screened but the parents initially refused to participate in tracking. Five hundred ninety-four were screened outside the program. Four hundred eighty-eight untested newborns were identified. Three hundred twenty-five screening failures due to logistic problems were tested subsequently. Screening was definitely refused by the parents of 163 children (0.1% of target population). CONCLUSIONS: With appropriate information provided and surveillance by tracking, high compliance with newborn screening can be achieved despite a written consent requirement.

Adult↗

PubMed2004

Structure-function relationship of biological gels revealed by multiple-particle tracking and differential interference contrast microscopy: the case of human lamin networks.

Lamin B1 filaments organize into a thin dense meshwork underlying the nucleoplasmic side of the nuclear envelope. Recent experiments in vivo suggest that lamin B1 plays a key structural role in the nuclear envelope, but the intrinsic mechanical properties of lamin B1 networks remain unknown. To assess the potential mechanical contribution of lamin B1 in maintaining the integrity and providing structural support to the nucleus, we measured the micromechanical properties and examined the ultrastructural distribution of lamin B1 networks in vitro using particle tracking methods and differential interference contrast (DIC) microscopy. We exploit various surface chemistries of the probe microspheres (carboxylated, polyethylene glycol-coated, and amine-modified) to differentiate lamin-rich from lamin-poor regions and to rigorously extract local viscoelastic moduli from the mean-squared displacements of noninteracting particles. Our results show that human lamin B1 can, even in the absence of auxiliary proteins, form stiff and yet extremely porous networks that are well suited to provide structural strength to the nuclear lamina. Combining DIC microscopy and particle tracking allows us to relate directly the local organization of a material to its local mechanical properties, a general methodology that can be extended to living cells.

Diffusion↗

PubMed2006

[Effect of 1, 2-dichloroethane on blood brain barrier].

OBJECTIVE: To investigate the effect of 1, 2-dichloroethane (1, 2-DCE) on blood brain barrier. METHODS: Acute toxic encephalopathy model was copied with the consecutive static inhalation of 1, 2-DCE. The water content of brain tissue was measured, and the blood brain barrier permeability was detected with lanthanum nitrate. The brain microvascular endothelial cells and neuroglial cells were cultured in vitro, which were administrated with 1, 2-DCE. The cell morphologic structures were observed under light microscope and electron microscope. RESULTS: (1) The extracellular edema was most found in the cerebral tissue and the leakage of lanthanum particles through the barrier were found with the lanthanum tracking method. (2) The water content in cerebral cortex in the moderate and high dose groups was significantly higher than that in the control group and became severer with the increases of the intoxicated time. The water content in cerebral medulla was significantly increased only at 6 hours after the intoxication. (3) The normal morphological structure of brain microvascular endothelial cells and neuroglial cells could be injured by 1, 2-DCE, and the injury to neuroglial cells caused by 1, 2-DCE occurred earlier and severer than that to brain microvascular endothelial cells. CONCLUSION: 1, 2-DCE can damage blood brain barrier and induce cerebral edema.

Administration, Inhalation↗