Results 1 - 10 of 61110
Results 1 - 10 of 61110. Search took: 0.066 seconds
|Sort by: date | relevance|
[en] Angiotomography is a method which is particularly suitable for application in the diagnostics of the vertebrobasilar system on account of its ability to increase the selectivity of angiography, the definition of details, and spatial orientation. Available techniques include angioautotomography with and without accessory device, and simultaneous angiotomography and ists variations. Among the indications, those are predominant where disturbing vascular overtshadowing should be eliminated and certain details emphasized. Angiotomography of the vertebrobasilar system visualizes important vascular structures without overshadowing, and hence also facilitates indirectly the assessment of certain neural structures. The visualization of the contours of vascularized tumors is also improved, and visualization of cystic processe becomes possible. The contrast of discrete tumor staining is enhanced, and, last but not least, visualization of the vessels themselves, as well as of important details, is increased. (orig.) 891 MG
[de]Die Angiotomographie ist ein Verfahren, das sich aufgrund seiner Faehigkeit, stoerende Gefaess- und Knochenschatten zu beseitigen, die Selektivitaet der Gefaessdarstellung und die Detailerkennbarkeit zu erhoehen sowie die raeumliche Orientierung zu verbessern, besonders zur Anwendung in der Diagnostik des vertebrobasilaeren Systems eignet. An Techniken stehen zur Verfuegung die Angio-Autotomographie ohne und mit Zusatzgeraet und die Simultan-Angiotomographie in ihren verschiedenen Formen. Unter den Indikationen dominieren diejenigen, bei denen stoerende Gefaessueberlagerungen eliminiert und bestimmte Gefaessdetails hervorgehoben werden sollen. Die Leistung der Vertebralis-Angiotomographie besteht darin, wichtige Gefaessstrukturen ueberlagerungsfrei darzustellen und damit indirekt die Beurteilung auch der neuralen Strukturen zu erleichtern. Weiter wird die Darstellung der Grenzen vaskularisierter Tumoren verbessert und diejenige zystischer Prozesse ermoeglicht. Der Kontrast diskreter Tumoranfaerbungen wird angehoben, und nicht zuletzt wird auch die Erkennbarkeit der Gefaesse selbst samt wichtiger Details erhoeht. (orig.)
[en] Waveform acquisition and presentation forms the heart of many measurement systems. Particularly, data acquisition and presentation of repeating complex signals like sine sweep and frequency-modulated signals introduces the challenge of waveform time period estimation and live waveform presentation. This paper presents an intelligent technique, for waveform period estimation of both the complex and simple waveforms, based on the normalized auto-correlation method. The proposed technique is demonstrated using LabVIEW based intensive simulations on several simple and complex waveforms. Implementation of the technique is successfully demonstrated using LabVIEW based virtual instrumentation. Sine sweep vibration waveforms are successfully presented and measured for electrodynamic shaker system generated vibrations. The proposed method is also suitable for digital storage oscilloscope (DSO) triggering, for complex signals acquisition and presentation. This intelligence can be embodied into the DSO, making it an intelligent measurement system, catering wide varieties of the waveforms. The proposed technique, simulation results, robustness study and implementation results are presented in this paper.
[en] The development and evaluation of a prototype cardiac gating system for double-shot dual-energy (DE) imaging is described. By acquiring both low- and high-kVp images during the resting phase of the cardiac cycle (diastole), heart misalignment between images can be reduced, thereby decreasing the magnitude of cardiac motion artifacts. For this initial implementation, a fingertip pulse oximeter was employed to measure the peripheral pulse waveform ('plethysmogram'), offering potential logistic, cost and workflow advantages compared to an electrocardiogram. A gating method was developed that accommodates temporal delays due to physiological pulse propagation, oximeter waveform processing and the imaging system (software, filter-wheel, anti-scatter Bucky-grid and flat-panel detector). Modeling the diastolic period allowed the calculation of an implemented delay, timp, required to trigger correctly during diastole at any patient heart rate (HR). The model suggests a triggering scheme characterized by two HR regimes, separated by a threshold, HRthresh. For rates at or below HRthresh, sufficient time exists to expose on the same heartbeat as the plethysmogram pulse [timp(HR) = 0]. Above HRthresh, a characteristic timp(HR) delays exposure to the subsequent heartbeat, accounting for all fixed and variable system delays. Performance was evaluated in terms of accuracy and precision of diastole-trigger coincidence and quantitative evaluation of artifact severity in gated and ungated DE images. Initial implementation indicated 85% accuracy in diastole-trigger coincidence. Through the identification of an improved HR estimation method (modified temporal smoothing of the oximeter waveform), trigger accuracy of 100% could be achieved with improved precision. To quantify the effect of the gating system on DE image quality, human observer tests were conducted to measure the magnitude of cardiac artifact under conditions of successful and unsuccessful diastolic gating. Six observers independently measured the artifact in 111 patient DE images. The data indicate that successful diastolic gating results in a statistically significant reduction (p < 0.001) in the magnitude of cardiac motion artifact, with residual artifact attributed primarily to gross patient motion.
[en] We aimed to develop new equations that predict exercise-induced energy expenditure (EE) more accurately than previous ones during running by including new parameters as fitness level, body composition and/or running intensity in addition to heart rate (HR). Original equations predicting EE were created from data obtained during three running intensities (25%, 50% and 70% of HR reserve) performed by 50 subjects. Five equations were conserved according to their accuracy assessed from error rates, interchangeability and correlations analyses: one containing only basic parameters, two containing VO_2_m_a_x or speed at VO_2_m_a_x and two including running speed with or without HR. Equations accuracy was further tested in an independent sample during a 40 min validation test at 50% of HR reserve. It appeared that: (1) the new basic equation was more accurate than pre-existing equations (R"2 0.809 versus. 0,737 respectively); (2) the prediction of EE was more accurate with the addition of VO_2_m_a_x (R"2 = 0.879); and (3) the equations containing running speed were the most accurate and were considered to have good agreement with indirect calorimetry. In conclusion, EE estimation during running might be significantly improved by including running speed in the predictive models, a parameter readily available with treadmill or GPS. (paper)
[en] A new algorithm which exploits digital image processing and pattern recognition methods for automated definition of left ventricular (LV) contours is presented. Digital image processing and pattern recognition techniques are applied to digitally acquired radiographic images of the heart to extract the LV contours required for quantitative analysis of cardiac function. Knowledge of the image domain is invoked at each step of the algorithm in order to orient the data search and thereby reduce complexity of the solution. A knowledge-based image transformation, directional gradient search, expectations of object versus background location, least-cost path searches by dynamic programming, and a digital representation of possible versus impossible ventricular shape are exploited. The digital representation, composed of a set of characteristic templates, was created using contours obtained by manual tracing
[en] The dissertation deals with a methodological enhancement of a fast MR imaging technique, the snapshot-FLASH (fast low-angle shot) technique. The first and primary goal was to optimize the snapshot-FLASH technique with a view to its application for diagnostic imaging of the heart. This optimization was to achieve a further reduction of measuring time per single shot and an increase in information gained per time unit. Another very important goal was to improve the method towards more exact, faster and as efficient as possible measurement of n.m.r. parameters. With these goals in mind, new two- or three-dimensional versions and a multilayered version of the snapshot-FLASH imaging sequence were developed. The results obtained in practice are explained and discussed. (orig./DG)
[de]Die Arbeit beschaeftigt sich mit der methodischen Weiterbildung eines schnellen Bildgebungsverfahrens mittels kernmagnetischer Resonanz, der ''Snapshot-FLASH (Fast Low Angle Shot)''-Bildgebung. Im Vordergrund stand die Optimierung der ''Snapshot-FLASH''-Technik hinsichtlich einer praktikablen Anwendung zur Herzbildgebung. Damit war eine weitere Reduzierung der Messzeiten pro Einzelbild und eine Erhoehung des Informationsgewinns pro Zeiteinheit verbunden. Aber auch die Weiterbildung dieser Methode zur exakten, schnellen und moeglichst effektiven Messung von NMR-Parametern wurde beruecksichtigt. Ausgehend von diesen Anforderungen wurden neue zwei- bzw. dreidimensionale Versionen und eine Mehrschichtversion der ''Snapshot-FLASH''-Sequenz entwickelt und die damit erzielten Ergebnise in ihrer konkreten Anwendung vorgestellt und diskutiert. (orig./DG)
[en] FK506 is widely used as a potent immunosuppressive agent following organ transplantation. However, the use of FK506 is associated with a wide spectrum of neurotoxicity. FK506-induced cerebral infarctions have rarely been reported. We report here on a case of the acute cerebral infarction caused by vasospasm after FK506 administration in a kidney transplantation recipient. There were areas with increased signal intensity on the diffusion-weighted image. The areas showing increased signal intensity on the diffusion- and T2-weighted images demonstrated decreased signal intensity on the apparent diffusion coefficient mapping. MR angiography showed diffuse stenosis in both the anterior and middle cerebral arteries
[en] Highlights: • Moderate and severe caloric restriction exert different effect on cardiomyocytes. • Moderate caloric restriction alleviates the progression of pyroptosis. • Severe caloric restriction promotes the progression of pyroptosis. An unhealthy diet is a major risk factor for cardiac diseases. Most researches focus on high fat diet, little is known about the detrimental effects of starvation on heart.
[en] Rapid developments in the area of micro-sensors for various applications such as structural health monitoring, bio-chemical sensors and pressure sensors have increased the demand for portable, low cost, high efficiency energy harvesting devices. In this paper, we describe the scheme for powering a pulse rate sensor with a vibration energy harvester integrated inside a pen commonly carried by humans in the pocket close to the heart. Electromagnetic energy harvesting was selected in order to achieve high power at lower frequencies. The prototype pen harvester was found to generate 3 mW at 5 Hz and 1 mW at 3.5 Hz operating under displacement amplitude of 16 mm (corresponding to an acceleration of approximately 1.14 grms at 5 Hz and 0.56 grms at 3.5 Hz, respectively). A comprehensive mathematical modelling and simulations were performed in order to optimize the performance of the vibration energy harvester. The integrated pen harvester prototype was found to generate continuous power of 0.46-0.66 mW under normal human actions such as jogging and jumping which is enough for a small scale pulse rate sensor.
[en] The polarographic measurement of tissue oxygenation is one of the most widely used methods in clinical practice for the quantification of tumour hypoxia. However, due to the particular features of the electrode measuring process, the results of the measurements do not accurately reflect the tumour oxygenation. This study aimed to find a correlation between the electrode measurements and the tumour oxygenation in an attempt to improve the accuracy of the predictions regarding the response to treatment based on electrode measurements. A previously developed computer model that allows the simulation of tumour tissue and electrode measurements was used. The oxygenation of a large number of tumours with biologically relevant distributions of blood vessels was theoretically calculated. Simulations of electrode measurements allowed the comparison between the real tissue oxygenation and the results obtained with the electrode. A semi-empirical relationship between the hypoxic fraction measured by the electrode and the real hypoxic fraction in the tissue has been found. The impact of the correction of the electrode measurements in terms of predictions for tumour control probability was estimated for a few clinical examples. The range of possible true values corresponding to one measurement has also proven useful for explaining the apparently unexpected response to the treatment of some patients. The corrected hypoxic fraction which is believed to be closer to the real value of tissue hypoxia predicts much smaller control probabilities than the raw electrode measurements. This could provide an explanation for the apparently unexpected failure to respond to the treatment of some of the patients with apparently favourable tumour oxygenation. This also means that the electrode measurements cannot be used directly for the quantitative modelling of tumour response to the treatment. The conversion method proposed in this paper might however strengthen the statistical power of the correlations between the electrode measurements and the treatment outcome