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PubMed2005

Response characterstics of spinothalamic tract neurons that project to the posterior thalamus in rats.

A sizeable number of spinothalamic tract axons terminate in the posterior thalamus. The functional roles and precise areas of termination of these axons have been a subject of recent controversy. The goals of this study were to identify spinothalamic tract neurons (STT) within the cervical enlargement that project to this area, characterize their responses to mechanical and thermal stimulation of their receptive fields, and use microantidromic tracking methods to determine the nuclei in which their axons terminate. Forty-seven neurons were antidromically activated using low-amplitude (< or =30 microA) current pulses in the contralateral posterior thalamus. The 51 points at which antidromic activation thresholds were lowest were surrounded by ineffective tracks indicating that the surrounded axons terminated within the posterior thalamus. The areas of termination were located primarily in the posterior triangular, medial geniculate, posterior and posterior intralaminar, and suprageniculate nuclei. Recording points were located in the superficial and deep dorsal horn. The mean antidromic conduction velocity was 6.4 m/s, a conduction velocity slower than that of other projections to the thalamus or hypothalamus in rats. Cutaneous receptive fields appeared to be smaller than those of neurons projecting to other areas of the thalamus or to the hypothalamus. Each of the examined neurons responded exclusively or preferentially to noxious stimuli. These findings indicate that the STT carries nociceptive information to several target nuclei within the posterior thalamus. We discuss the evidence that this projection provides nociceptive information that plays an important role in fear conditioning.

Action Potentials↗

PubMed2006

Repetitive rectal painful distention induces rectal hypersensitivity in patients with irritable bowel syndrome.

BACKGROUND: A reduced rectal perceptual threshold has been reported in patients with irritable bowel syndrome (IBS), but this phenomenon may be induced by a comorbid psychological state. We evaluated the rectal pain threshold at baseline and after conditioning (repetitive rectal painful distention: RRD) in patients with IBS or functional abdominal pain syndrome (FAPS), which is an abdominal pain disorder, and in healthy controls, and determined whether rectal hypersensitivity is a reliable marker for IBS. METHODS: The rectal sensory threshold was assessed by a barostat. First, a ramp distention of 40 ml/min was induced, and the threshold of pain and the maximum tolerable pressure (mmHg) were measured. Next, RRD (phasic distentions of 60-s duration separated by 30-s intervals) was given with a tracking method until the subjects had complained of pain six times. Finally, ramp distention was induced again, and the same parameters were measured. The normal value was defined by calculating the 95% confidence intervals of controls. RESULTS: Five or six of the seven IBS patients showed a reduced rectal pain threshold or maximum tolerable pressure, respectively, at baseline. In all patients with IBS, both thresholds were reduced after RRD load, but they were reduced in none of the patients with FAPS. RRD significantly reduced both thresholds in the IBS group (P < 0.05), but it had no effect in the control or FAPS groups. CONCLUSIONS: Rectal hypersensitivity induced by RRD may be a reliable marker for IBS. Conditioning-induced visceral hypersensitivity may play a pathophysiologic role in IBS.

Abdominal Pain↗

PubMed1988

Spatial contrast sensitivity: effects of age, test-retest, and psychophysical method.

Spatial contrast sensitivity was tested twice in normal subjects from five age groups by using each of two different psychophysical methods. Results obtained by the method of adjustment showed a decline in sensitivity with increasing age at all spatial frequencies. In contrast, the forced-choice procedure yielded results indicating an age-related decline predominantly at high spatial frequencies, with the magnitude of the decline being generally similar to that obtained earlier by a tracking method [Vision Res. 23, 689 (1983)]. The decline that we observed cannot be due to pupillary changes with age, since this factor was controlled. Moreover, we suggest that the high-spatial-frequency decline in contrast sensitivity, although it is comparatively small, is too large to be due to changes in lens density. We therefore suggest that a neural component is responsible. In addition, interactions among the age of the subject, the spatial frequency used, and the psychophysical method used suggest that the method of adjustment should be avoided for age-related studies of vision.

Adult↗

PubMed1989

Conformation therapy to improve the irradiation of the spinal axis.

Techniques for the irradiation of the spine have remained largely unchanged since the introduction of megavoltage therapy. The main disadvantages of these techniques are the inhomogeneous dose distribution and the problems associated with field joins. The tracking method of conformation therapy employs a short field length and translates the patient through the beam on the couch of a computer controlled treatment unit. Dose uniformity along the spinal axis is achieved by controlling the speed at which the target travels through the radiation field. Treatment is given at standard source-axis distance (SAD) and the need for external shielding is eliminated by shaping the width of the field. The join with the cranial fields is independent of any skin marks, removing the risk of over- or under-dosage. Treatments are planned automatically from computed tomography (CT) information by an in-house planning system. The calculated doses have consistently shown good agreement with phantom measurements. Three cobalt dose distributions are presented and compared: a tracking treatment; a single posterior field, and two matched fields. The superiority of conformation therapy over the other commonly used treatment methods is clearly demonstrated.

Humans↗

PubMedDate not supplied

A transcutaneous energy and information transfer system for implanted medical devices.

During the last four decades there has been a rapid increase in the development and usage of medical devices. Currently, there are more than 500,000 devices on the market and 25,000 new devices enter the market each year. Many medical devices are now designed to be implantable (pacemakers, defibrillators, circulatory assist devices, artificial hearts, cochlear implants, neuromuscular stimulators, biosensors, etc.). Almost all of the active devices (those that perform work) and many of the passive devices (those that do not perform work) require a source of power. In addition, these devices need to be monitored and controlled, which can be accomplished by utilizing remote communication methods. A transcutaneous energy transfer system combined with a remote communications system has been developed and evaluated in vitro and in vivo (bovine, porcine, and human cadaver experiments). The energy transfer system can deliver up to 60 W with power transfer efficiencies between 60 and 83%. An automatically tuned, resonant frequency tracking method is used to obtain optimum power transfer over a range of operating conditions. The remote communications system can transfer digital data bidirectionally through intact skin at rates up to 9600 baud. The system transmits information by frequency modulating an 890 nm infrared carrier signal. The system has demonstrated satisfactory performance during multicenter evaluation with ventricular assist and total artificial heart devices. Design improvements have been identified, which will be implemented to produce an optimized system for energy transfer to and remote communications with various implantable medical devices.

Animals↗

PubMed2005

Design considerations of volute geometry of a centrifugal blood pump.

This article compares two different design techniques that are conventionally used in the design of volutes for centrifugal pumps. The imbalanced forces due to the geometry of the volute need to be taken into consideration especially in centrifugal blood pumps with magnetically suspended impeller. A reduction of these forces can reduce the instability of the impeller motion as well as the power needed to counteract its influence. Volutes using the constant angular momentum (CAM) and the constant mean velocity (CMV) methods were developed and modeled numerically. The computational results on the effect of volute geometry on the performance of a centrifugal blood pump impeller for six different volutes are presented here. For volutes designed using the CAM method, model B (volute expansion angle of 3 degrees ) had the lowest radial force of 0.26 N while the pressure head generated was 12,900 Pa. For volutes designed using the CMV method, model F (1.6 m/s) had the lowest imbalanced force of 0.45 N. However, the pressure developed by this pump was also one of the lowest at 10,652 Pa. Furthermore, when the peak scalar stresses and the mean exposure time of particles for all designs were determined using Lagrangian particle tracking method, it was observed that in general, the peak scalar stresses in CAM designed volutes are lower than those designed using CMV method. The mean exposure time of particles in the pump ranged from 400 to 500 ms. The simulation results showed that the volute designed using CAM method was superior to that of a CMV volute in terms of the magnitude of the radial force and the peak scalar stresses for the same pressure head generated. Results show that the design of volutes for blood pumps should go beyond conventional empirical methods to obtain optimal results.

Centrifugation↗

PubMed2003

Effects of performance-based compensation and faculty track on the clinical activity, research portfolio, and teaching mission of a large academic department of medicine.

PURPOSE: Academic departments of medicine must compete effectively for extramural research support and access to patients while preserving their teaching mission. There is not much literature describing plausible mechanisms for ensuring success. The authors describe the design, implementation, and testing of a performance-based compensation plan in a department of medicine that is closely linked to the faculty appointment track. METHOD: Over a three-year period, the changes this plan effected in research portfolio, clinical enterprise, and faculty satisfaction as well as the teaching perceptions of students and housestaff were measured. RESULTS: The compound annual growth rate (CAGR) for clinical work grew 40% faster after plan implementation. Federal funding increased at a CAGR that was 170% greater than before. The department halved its award rankings at the National Institutes of Health and faculty satisfaction improved compared with the former method of compensation. Faculty who better understood the plan were more satisfied with the conversion. High measures of teaching quality were maintained by faculty with no apparent change in satisfaction among students or housestaff. CONCLUSIONS: This performance-based compensation plan with its emphasis on the objectives of career orientation and faculty track assignment strengthened the opportunity to grow both clinical productivity and the funded research portfolio.

Academic Medical Centers↗

PubMed2006

Automated detection of videotaped neonatal seizures based on motion segmentation methods.

OBJECTIVE: This study was aimed at the development of a seizure detection system by training neural networks using quantitative motion information extracted by motion segmentation methods from short video recordings of infants monitored for seizures. METHODS: The motion of the infants' body parts was quantified by temporal motion strength signals extracted from video recordings by motion segmentation methods based on optical flow computation. The area of each frame occupied by the infants' moving body parts was segmented by direct thresholding, by clustering of the pixel velocities, and by clustering the motion parameters obtained by fitting an affine model to the pixel velocities. The computational tools and procedures developed for automated seizure detection were tested and evaluated on 240 short video segments selected and labeled by physicians from a set of video recordings of 54 patients exhibiting myoclonic seizures (80 segments), focal clonic seizures (80 segments), and random infant movements (80 segments). RESULTS: The experimental study described in this paper provided the basis for selecting the most effective strategy for training neural networks to detect neonatal seizures as well as the decision scheme used for interpreting the responses of the trained neural networks. Depending on the decision scheme used for interpreting the responses of the trained neural networks, the best neural networks exhibited sensitivity above 90% or specificity above 90%. CONCLUSIONS: The best among the motion segmentation methods developed in this study produced quantitative features that constitute a reliable basis for detecting myoclonic and focal clonic neonatal seizures. The performance targets of this phase of the project may be achieved by combining the quantitative features described in this paper with those obtained by analyzing motion trajectory signals produced by motion tracking methods. SIGNIFICANCE: A video system based upon automated analysis potentially offers a number of advantages. Infants who are at risk for seizures could be monitored continuously using relatively inexpensive and non-invasive video techniques that supplement direct observation by nursery personnel. This would represent a major advance in seizure surveillance and offers the possibility for earlier identification of potential neurological problems and subsequent intervention.

Cluster Analysis↗

PubMed2006

Flexible ex vivo phantoms for validation of diffusion tensor tractography on a clinical scanner.

PURPOSE: The aim of this study was to develop ex vivo diffusion tensor (DT) flexible phantoms. MATERIALS AND METHODS: Materials were bundles of textile threads of cotton, monofilament nylon, rayon, and polyester bunched with spiral wrapping bands and immersed in water. DT images were acquired on a 1.5-Tesla clinical magnetic resonance scanner using echo planar imaging sequences with 15 motion probing gradient directions. DT tractography with seeding and a line-tracking method was carried out by software originally developed on a PC-based workstation. RESULTS: We observed relatively high fractional anisotropy on the polyester phantom and were able to reconstruct tractography. Straight tracts along the bundle were displayed when it was arranged linearly. It was easy to bend arcuately or bifurcate at one end; and tracts followed the course of the bundle, whether it was curved or branched and had good agreement with direct visual observation. Tractography with the other fibers was unsuccessful. CONCLUSION: The polyester phantom revealed a diffusion anisotropic structure according to its shape and would be utilizable repeatedly under the same conditions, differently from living central neuronal system. It would be useful to validate DT sequences and to optimize an algorithm or parameters of DT tractography software. Additionally, the flexibility of the phantom would enable us to model human axonal projections.

Anisotropy↗

PubMed2004

Retrospective respiratory motion correction for navigated cine velocity mapping.

In general, high spatial and temporal resolutions in cine cardiac imaging require long scan times, making breath-hold acquisition impossible in many cases. To enable free-breathing cardiac imaging, methods such as navigator gating were developed to reduce image artifacts due to respiratory motion. Nevertheless, residual image blurring is seen in images acquired late in the cardiac cycle. Image blurring itself hampers accurate blood flow quantification, especially in vessels exhibiting high flows during diastole. In the present work, the navigator gating and slice tracking method was extended by using navigator information to correct for in-slice motion components throughout the cardiac cycle. For this purpose, a standard two-dimensional (2D) cine phase contrast sequence with navigator gating and slice position correction was used, and navigator information was recorded along with the raw k-space data. In postprocessing, in-plane motion components arising from respiration during the actual data acquisition were estimated and corrected according to the Fourier shift theorem. In phantom experiments, the performance of the correction algorithm for different slice angulations with respect to the navigator orientation was validated. In vivo, coronary flow measurements were performed in 9 healthy volunteers. The correction algorithm led to considerably improved vessel sharpness throughout the cardiac cycle in all measured subjects [increase in vessel sharpness: 16+/-11% (mean+/-SD)]. Furthermore, these improvements resulted in increased volume flow rates [16+/-13% (mean+/-SD)] after retrospective correction indicating the impact of the method. It is concluded that retrospective respiratory motion corrections for navigated cine two-dimensional (2D) velocity mapping can correct for in-plane motion components, providing better image quality for phases acquired late in the cardiac cycle. Therefore, this method holds promise in particular for free-breathing coronary flow quantification.

Blood Flow Velocity↗

PubMed2005

Physiological adaptations to soccer specific endurance training in professional youth soccer players.

BACKGROUND: Improved oxygen uptake improves soccer performance as regards distance covered, involvements with the ball, and number of sprints. Large improvements in oxygen uptake have been shown using interval running. A similar physiological load arising from interval running could be obtained using the soccer ball in training. OBJECTIVES: The main aim was to study physiological adaptations to a 10 week high intensity aerobic interval training program performed by professional youth soccer players, using a soccer specific ball dribbling track. METHODS: Eleven youth soccer players with a mean (SD) age of 16.9 (0.4) years performed high intensity aerobic interval training sessions twice per week for 10 weeks in addition to normal soccer training. The specific aerobic training consisted of four sets of 4 min work periods dribbling a soccer ball around a specially designed track at 90-95% of maximal heart frequency, with a 3 min recovery jog at 70% of maximal heart frequency between intervals. RESULTS: Mean VO2max improved significantly from 63.4 (5.6) to 69.8 (6.6) ml kg(-1) min(-1), or 183.3 (13.2) to 201.5 (16.2) ml kg(-0.75) min(-1) (p<0.001). Squat jump and counter movement jump height increased significantly from 37.7 (6.2) to 40.3 (6.1) cm and 52.0 (4.0) to 53.4 (4.2) cm, respectively (p<0.05). No significant changes in body mass, running economy, rate of force development, or 10 m sprint times occurred. CONCLUSION: Performing high intensity 4 min intervals dribbling a soccer ball around a specially designed track together with regular soccer training is effective for improving the VO2max of soccer players, with no negative interference effects on strength, jumping ability, and sprinting performance.

Adaptation, Physiological↗

PubMed2000

Measurement of aortic arch distension wave with the echo-track technique.

The aim of this study was to use the echo-track method for measuring aortic arch diameter, distension waveform and elastic parameters. Data were obtained from 50 healthy volunteers of 32 +/- 15 y (mean +/- 1 SD). The aortic arch was interrogated from the suprasternal position with M-mode ultrasonography using a 3.5-MHz transducer; diameter and distension waves were determined by means of an echo-track algorithm (WTS, Pie Medical); arterial blood pressure was measured in the arm with sphygmomanometry. Aortic arch diameter, distension, distensibility and compliance were 24.55 +/- 2.99 mm, 2199 +/- 726 micrometer, 3.9 +/- 1.4. 10(-3) mmHg(-1) and 1.86 +/- 0.61 mm(2). mmHg(-1), respectively. Intrasession, interobserver and intersession variability was less than 10%, 10% and 18%, respectively. It is concluded that aortic arch distension wave can be recorded noninvasively with acceptable reproducibility, allowing assessment of aortic elastic parameters, and yielding insight into pressure wave reflection within the arterial system.

Adult↗

PubMed2004

Sequential characterization of atrial tachyarrhythmias based on ECG time-frequency analysis.

A new method for characterization of atrial arrhythmias is presented which is based on the time-frequency distribution of an atrial electrocardiographic signal. A set of parameters are derived which describe fundamental frequency, amplitude, shape, and signal-to-noise ratio. The method uses frequency-shifting of an adaptively updated spectral profile, representing the shape of the atrial waveforms, in order to match each new spectrum of the distribution. The method tracks how well the spectral profile fits each spectrum as well as if a valid atrial signal is present. The results are based on the analysis of a learning database with signals from 40 subjects, of which 24 have atrial arrhythmias, and an evaluation database with 211 patients diagnosed with atrial fibrillation. It is shown that the method robustly estimates fibrillation frequency and amplitude and produces spectral profiles with narrower peaks and more discernible harmonics when compared to the conventional power spectrum. The results suggest that a rather strong correlation exist between atrial fibrillation frequency and f wave shape. The developed set of parameters may be used as a basis for automated classification of different atrial rhythms.

Algorithms↗

PubMedDate not supplied

Performance of elbow tracking under constant torque disturbance in normotonic stroke patients and normal subjects.

OBJECTIVE: In this study, the influences of externally imposed constant torque on the voluntary elbow movements of stroke and normal subjects were investigated quantitatively. BACKGROUND: Muscle weakness, spasticity and incoordination are the major factors that interfere with stroke patient's limb functions. Imposing external torque disturbance may worsen the motor performance. This experiment was designed to investigate the effects of small constant external torque on the performance of voluntary elbow movements. METHODS: Tracking of a ramp-and-hold angle trajectory in the direction of extension was used as the main task for performance assessment. Each subject repeated the same tracking movement six times in each of three loading conditions: no, assistive or resistive loading. Five normal and six stroke subjects were recruited for this study. We used parameters extracted from movement trajectory and processed electromyograms as the performance indicators. RESULTS: For normal subjects, there was no difference in the tracking performance in the three loading conditions. For stroke patients, the affected side had inferior performance to the healthy side in the free loading condition and the difference diminished in assistive and resistive loading conditions as the performance of the affected side improved. Integrated electromyograms of biceps or triceps did not show significant changes in different loading conditions. CONCLUSIONS: Small externally imposed constant torque, either resistive or assistive, may improve motor performance of affected elbows in stroke patients. RELEVANCE: Most of the currently available prostheses are passive devices, aiming at providing better support and improving stability. The results of the current study imply that an active prosthetic device that applies a small constant torque to the hemiparetic elbow can improve its motor performance in stroke patients. The direction of external torque is to assist the weaker side of the antagonistic muscle pair.

Elbow↗

PubMed2004

Frameless stereotaxy in the nonhuman primate.

With the advent of magnetic resonance imaging (MRI), it is possible to obtain high-resolution anatomical images of the monkey brain. Accuracy, however, is lost in the laboratory or surgical setting when the localization of brain structures depends on nonstereotaxic tracking methods. Here we present an image-guided stereotaxic system that is able to localize and access anatomical brain structures using the monkey's MRI. This system, which is also known as frameless stereotaxy, is capable of computing the relation of the physical "real space" of the monkey's head to the corresponding image space, while a position sensor enables the tracking of the animal's head and the localization of brain areas and favorable paths to targets within the brain using real time display software. Surgical procedures make use of an adjustable upright chair and a surgical headclamp instead of the traditional restrictive head holder with ear bars. This novel system allows for the flexible positioning of the animal and the ability to reach areas of the brain that were difficult to access in the past. The headclamp also serves as a tool holder, which in the present application guided a cannula of retrograde tracer to the desired location in the frontal lobe. Histological examination of the brain showed that the injection reached the target site, and tests using an MRI compatible phantom demonstrated that the precision of the system in bringing an injection to target is less than 1.2 mm. This system can be used to inject accurately tracers for anatomical tract-tracing, to make precise lesions, and to position electrodes for electrophysiological studies.

Animals↗

PubMed1998

Methods of ensuring high follow-up rates: lessons from a longitudinal study of dual diagnosed participants.

Despite growing research interest in co-occurring psychiatric and substance misuse disorders, relatively few longitudinal studies have been conducted with dual diagnosis populations. Many of the longitudinal studies that have been done have experienced excessive attrition. Thus, investigators have noted that one of the primary difficulties of conducting longitudinal studies with this population is successfully minimizing attrition during follow-up. This study, conducted in 1991 1993, describes retention and tracking methods employed in a longitudinal study of 485 dual diagnosis participants. Follow-up interview completion rates at the 2-, 6-, 10-, 14-, and 18-month interviews were 86.7, 85.6, 85.1, 84.5, and 88.4%, respectively. Several case studies are provided that document some of the challenges facing project staff and successful strategies for handling them. A notable finding from this study was that participants reported that the relationship established with the interviewer was more important than material incentives in preventing study attrition.

Diagnosis, Dual (Psychiatry)↗

PubMed2002

Measurements of effective doses of natural background level of neutrons with etched-track detectors.

An etched-track method was applied for a measurement of the effective dose of natural background neutrons. Ten assemblies of polycarbonate film and 10B were placed at the center of a rem-counter type moderator. The assemblies were put in an air-tight container in order to avoid a continuous contribution from radon. Electrochemical etching was adopted. The sensitivity of the detector was 0.21 +/- 0.02 microSv pit(-1) cm2. After a period of storage of 4.3 y, the number of recorded artifact pits in the films corresponded to an effective dose rate of 0.8 +/- 0.2 microSv y(-1). The effective dose rate of natural background neutrons was 18.1 +/- 3.6 microSv year(-1) for the same period, with an artifact dose being subtracted. The total net number of etched-track pits of the present detector was 75 +/- 15 when used for measuring an effective dose of natural background level neutrons for 1 mo, which gives enough counting statistics. The method can thus be applied for monitoring the effective dose of neutrons around nuclear sites and high-energy accelerator facilities.

Calibration↗

PubMed1981

Contribution of kinesthesia on human visuomotor elbow tracking movements.

The role of peripheral information in smooth motor performance was analyzed in normal subjects and patients with deep sensory disturbance by the modified visually guided tracking method. The subject's task was to make the control cursor match the slowly moving target by elbow flexion movement. Performance of normal subjects was scarcely affected, but that of the patients was deteriorated by the withdrawal of the visual cue for handle movement. It is suggested that afferent information from the moving limb plays an important role in smooth and accurate tracking movements.

Adult↗