Functional and metabolic consequences of aortic valve replacement

4. Conclusions Severe aortic valve stenosis leads to a decreased myocardial PCr/ATP, and to impairment of LV diastolic function. Following aortic valve replacement, myocardial PCr/ATP normalizes completely, whereas LV diastolic function improves significantly. Moreover, there is an association between altered myocardial HEP metabolism and impaired LV diastolic function.     

High-resolution MR imaging in mice

6. Conclusions Due to its high temporal and spatial resolution, the described MR technique is able to face the requirements of the small sized, fast beating mouse heart, resulting in time-resolved visualization of the cardiac morphology and function in great detail. This allows for accurate and reproducible quantification of LV performance including wall motion and contraction-relaxation dynamics. Hence, MRI offers the non-invasive investigation of physiological and pathophysiological changes of cardiac function over time, both under acute and chronic myocardial stress. Applied in models of cardiac failure, the MR method should aid understanding the mechanisms of LV remodeling after myocardial infarction and LV hypertrophy due to pressure overload in gene-targeted mouse models.     

Cardiovascular phenotype characterization in mice by high resolution magnetic resonance imaging

9. Conclusion Due to its high temporal and spatial resolution, magnetic resonance imaging meets the requirements for accurate and robust in vivo visualization of the murine cardiovascular system. As an intrinsically three-dimensional imaging technique, it allows for quantification of LV volumes without relying on geometric models. Therefore, MRI is uniquely suited for the investigation of morphologic and functional changes in models of heart failure. The potential application of MRI in the mouse comprises visualization of cardiovascular anatomy and pathology in newborn and adult mice, detection of LV geometric and functional changes both acutely and chronically, visualization of cardiac microstructures such as cardiac valves and coronary arteries, and characterization and quantification of arteriosclerotic plaques in major murine arteries. Furthermore, MR spectroscopy applied to the mouse heart can give important information on in vivo myocardial metabolism. Thus, we feel confident that high resolution MRI may substantially contribute to the understanding of the basic mechanisms of a variety of cardiovascular diseases.     

Combined 1H and 31P MR spectroscopic imaging: impaired energy metabolism in severe carotid stenosis and changes upon treatment

OBJECT: To evaluate if combined (1)H and (31)P MR spectroscopic imaging (MRSI) before and after treatment of severe internal carotid artery (ICA) stenosis detects significant changes in energy metabolism in the basal ganglia of both hemispheres. MATERIALS AND METHODS: A group of 14 patients with high-grade ICA stenosis and 11 healthy control subjects were examined with 2D (1)H MRSI and 3D (31)P MRSI at 3 T before and after treatment of severe ICA stenosis. Spectroscopic data were processed with LCModel and jMRUI software. Changes of the phosphorylated metabolites, pH, N-acetyl-acetate, creatine and choline-containing compounds prior/post intervention were analyzed and patients' data were compared with that of control subjects. RESULTS: Untreated patients had significantly higher Adenosindiphosphate (ADP) in basal ganglia ipsi- and contralateral to the side of ACI stenosis compared to controls. After treatment, ADP of both hemispheres significantly decreased by approximately 20% compared to the pre-treatment values. Further, significant decreases of phosphorylated metabolites prior/post intervention were found for patients compared to controls. CONCLUSION: This spectroscopic study reveals that unilateral high-grade ICA stenosis has an effect on cerebral high-energy metabolism of both hemispheres, which is at least partially reversible after treatment. Therefore the restoration of blood flow in high-grade ICA stenosis recovers the impaired energy balance of the brain.     

Left ventricular quantification with breath-hold MR imaging: comparison with echocardiography

To evaluate the reproducibility of measurements of left ventricular (LV) dimensions, function, and myocardial mass, segmentedk-space gradient-recalled-echo (GRE) magnetic resonance (MR) imaging was performed on two occasions on 12 healthy volunteers. To compare the MR data, all volunteers underwent a two-dimensional echocardiography with determination of LV dimensions and function. The left ventricle was imaged during breath-hold by consecutive, contiguous short-axis views at end-diastole and end-systole. An average of eight short-axis views was needed to encompass the whole left ventricle. This fast MR sequence limited the total acquisition time to 12 min. LV volumes and masses were calculated after manual delineation of epicardial and endocardial surfaces by two observers in a blinded fashion. Interstudy variability varied between 4.1% and 10.3% for LV end-diastolic volume and end-systolic volume, respectively. Differences in interobserver variability were smaller and varied between 3.6% and 7.3% for LV ejection fraction and end-diastolic volume, respectively. Intraobserver variabilities ranged between 2.0% and 7.0% for LV ejection fraction and end-systolic volume, respectively. These variability percentages agree very well with other studies in literature using other MR sequences. No significant differences in LV dimensions or function were found between MR imaging and echocardiography. In conclusion, this MR sequence allows fast and reproducible LV quantification.     

Assessment of mulibrey nanism cardiopathy with functional magnetic resonance imaging

4. Conclusions It has been proposed that thickened pericardium is the main cause of the cardiac malfunction in Mulibrey nanism cardiopathy. In contrary, we showed that the pericardial thickness was normal in all our patients. Diastolic 1/3 filling was rapid, but in normal limits when taking into account the young age of our patient population. Although, LV time volume curves did not show remarkable pathologic changes, a restrictive physiology cannot be definitively excluded. LV end diastolic volumes and cardiac output were clearly reduced in our patients. It could be possible that in the course of time the reduced cardiac output affects clinical pattern of heart failure despite of normal systolic function. The reduced LA largest volume and atrial cyclic volume change may partly contribute to the low cardiac output observed in our patients.     

新型高压真空断路器智能控制装置的设计

介绍了一种基于双稳态永磁机构的高压真空断路器的智能控制装置,它不仅具有对配电线路的接通和分断作用,而且对线路及电气设备具有各种智能保护功能.该智能控制装置以PICl6F877A单片机为核心,设置了过负荷、漏电闭锁、缺相、短路等多种保护功能,而且具有显示和通信功能,提高了真空断路器的智能化程度.     

Melatonin administration does not affect isoproterenol-induced LVH.

Left ventricular hypertrophy (LVH), a common sequella of hypertension, is associated with increased incidence of sudden cardiac death. The study reported herein measured the effect of melatonin on the heart in the setting of direct cardiac myocyte stimulation with isoproterenol, thus minimizing the role of autonomic output from the suprachiasmatic nucleus (SCN) and clarifying the effect of melatonin on LVH, an outcome of chromic hypertensions. Results show that daily injections of high dosages of melatonin do not affect heart weight:body weight or heart weight:tibia length ratios in the setting of isoproterenol-induced hypertrophy, suggesting that the cardiovascular effects of melatonin observed by others are not due primarily to a direct effect of melatonin on cardiac myocytes but to another mechanism, possibly melatonin modulation of SCN output. Melatonin has no effect on isoproterenol-induced LVH, suggesting that its cardiovascular effects are not due to a direct effect on cardiac myocytes. Melatonin has been found to have a significant effect on hypertension; however, in this study, one effect of extended hypertension, cardiac hypertrophy, which can ultimately lead to cardiac failure, was not affected, even by very large doses of melatonin in a chemically induced hypertrophy mouse model. It has been suggested that the effect of melatonin on hypertension is comparable to common antihypertensive agents.     

(31)P-MR Spectroscopy for the evaluation of energy metabolism in intact residual myocardium after acute myocardial infarction in humans

Objective experimental studies have demonstrated that acute myocardial infarction (MI) alters energy metabolism even in non-infarcted adjacent tissue. In patients with subacute MI, the influence of the regional ischemie insult on energy metabolism of intact septal myocardium was analyzed using³¹P-Magnetic resonance spectroscopy (MRS). Patients and Methods in eight patients with wall motion abnormalities in the anterior wall³¹P-spectra were obtained from non-infarcted adjacent scptal myocardium, as well as infarcted anterior myocardium (voxel size 25 ccm each) 29 ±8 days after MI using a 3D-CSI technique. Additionally, cardiac function was analyzed using breath-hold cine MRI. MR1 was repeated 6 months after revascularization to assess viability of infarcted segments. Eight age-matched healthy volunteers served as control group. Results according to follow-up MRI 4/8 patients showed regional wall motion recovery. Here, PCr/ATP-ratios were not significantly reduced in intact septal myocardium as well as infarcted anterior myocardium compared to healthy volunteers (1.28 ±0.10 and 1.14 ±0.09 vs. 1.45 ±0.29). No recovery of regional function was detected in 4/8 patients with —therefore—non-viable anterior myocardium. PCr/ATP-ratios were significantly reduced in intact and infarcted myocardium compared with healthy volunteers as well as to patients with wall motion recovery (0.77 ±0.17 and 0.49 ±0.23;P < 0.05). Discussion these preliminary results indicate that energy metabolism is reduced in patients with persisting wall motion abnormalities after myocardial infarction and revascularization in ischemically injured as well as in adjacent non-injured myocardium.     

高过载永磁同步电动机设计研究

永磁同步电动机(PMSM)的过载能力受到铁心饱和、电枢反应的制约,常规设计PMSM无法满足一些高过载应用场合的需求。分析PMSM过载能力的影响因素,研究定子裂比和气隙长度等结构参数对其影响方式,进而分析得出相关结构参数对于PMSM过载能力的影响规律。设计了1台额定功率1 kW的高过载能力PMSM,有限元仿真结果显示该电机可达到5.26倍过载能力。     

Assessment of myocardial viability with MR—the Cologne perspective

4. Conclusion Despite the evaluation of different parameters of myocardial viability by PET, TEE and MRI, their positive and negative predictive accuracies are fairly comparable. Therefore, the choice of the method to date mainly depends on expertise and available resources. An accepted reference standard to assess the diagnostic accuracy of imaging techniques is the post-revascularization recovery of regional LV function. In this respect, dobutamine-MRI proved to be a reliable and clinically feasible approach in a head to head comparison with FDG-PET and dobutamine-TEE. However, there is still limited information with respect to the potential benefit of revascularization procedures in the clinically important subset of patients with viable myocardium, markedly reduced LV function and congestive heart failure. In this patient population, the advantageous features of MRI including high spatial and temporal resolution, three-dimensional capability with unlimited field of view and the capability to measure perfusion may increase the clinical impact of MRI compared to established imaging techniques. Moreover, improvement of global LV ejection fraction, alleviation of symptoms and survival are fundamental clinical end points to additionally evaluate the predictive value of MR-studies for clinical decision making in patients with left ventricular dysfunction and persisting viable myocardial tissue.     

Cine-MRI assessment of cardiac function in mice anesthetized with ketamine/xylazine and isoflurane

Since small-animal MRI generally requires anesthesia, the effect of the anesthetic regimen on the explored organ(s) has to be taken into account for study interpretation. In this work, we assess the influence of ketamine/xylazine and isoflurane anesthesia on left-ventricular (LV) function in the mouse in vivo by cine-MRI. Three groups of animals were anesthetized with ketamine/xylazine (n = 13) and two different concentrations of isoflurane (1.25%, n = 12 and 2.00%, n = 12) delivered in O₂/N₂O mix. Long- and short-axis cine-MRI was performed to measure end-diastolic volume, stroke volume, ejection fraction and LV wall thickness. Ketamine/xylazine significantly reduced heart rate, cardiac output and wall thickness, but increased stroke volume and end-diastolic volume compared with both isoflurane groups. No differences across all groups were observed in ejection fraction or systolic wall thickening. Breath rate under isoflurane was significantly lower and concentration dependent, whereas heart function was independent of concentration in all measured parameters. These findings are in agreement with echocardiography and catheterization studies. Isoflurane is advantageous for MR studies because it better maintains cardiac function. Taking into account previously obtained myocardial perfusion measurements, isoflurane concentration should, however, be maintained at the minimum required for a stable sleep even if cardiac function is unaffected by higher isoflurane concentrations.     

Whither human cardiac spectroscopy?

Human cardiac magnetic resonance (MR) spectroscopy is presently comprised, almost exclusively, of phosphorus (³¹P) studies. These provide access to supply-side energy metabolism in the anterior myocardium of patients with hypertrophy, with cardiomyopathies including heart failure, with heart transplants, and with ischemic disease and myocardial infarction. A link between reduced phosphocreatine (PCr) to adenosine triphosphate (ATP) ratios and heart failure has been identified which might assist diagnosis in the presence of other confounding factors. PCr/ATP is often reduced in transplanted hearts for reasons not understood, but the ratio is presently an unreliable predictor of significant histological rejection for many patients. Myocardial infarction may reduce overall metabolite levels. In reversible myocardial ischemia,³¹P exercise stress-testing can produce reversible PCr/ATP reductions, at least in anterior disease: these seem to be specific for ischemic disease and may be helpful, especially if new technologies such as phased detector arrays and Overhauser enhancement can provide access to more of the heart. Human cardiac spectroscopy with nuclei other than³¹P may potentially access citric acid cycle metabolites, oxymyoglobin and deoxymyoglobin, and creatine levels, which may also be altered in heart failure.     

低厂变保护整定计算和开关配置情况分析

通过分析低厂变保护的发展现状、开关与保护的配置方案、华润电力登封有限公司的低厂变保护的整定计算和西门子F-C真空接触器开关的使用情况,阐明低厂变保护的反时限曲线、变压器过负荷曲线、高压熔断器的安—秒曲线三者之间的配合是合理的,同时也介绍了保护的整定与F-C真空接触器开关配合是否合理的一种方法。并简单介绍高压限流熔断器的选择方法和实际应用注意事项。     

永磁同步电动机过载特性及其控制策略

从永磁电机过载故障的原因入手,分析了永磁同步电动机(PMSM)在恒转矩区的最大转折速度,提出一些通过电机参数优化来改善永磁电机过载性能的方法.由于电机最大恒转矩值越大转折速度越小,因此提出了最大转矩/电流(MTPA)与弱磁控制策略相结合的方法,通过弱磁最大转矩使电机在恒转矩区的转折速度达到更大,从而提高PMSM的过载能力.     

Novel revascularization therapies — TMLR and growth factor-induced angiogenesis monitored with cardiac MRI

4. Summary Employment of cardiac MRI techniques (cine MRI, wall thickening analysis, quantitative MRFPP, MR tissue tagging) allowed non-invasive localization and assessment of early and late changes in myocardial function and perfusion produced by these new approaches of myocardial revascularization. With its precision in assessment of myocardial perfusion and collateral-dependent territories, cardiac MRI techniques may be of excellent use for the evaluation of effects on myocardial function and perfusion as well as longitudinal outcomes in clinical trials with TMLR and angiogenesis therapies in patients with CAD. As growth factor therapies approach phase III clinical trials, such vital questions as the most effective delivery system, dosages and techniques used for treatment-monitoring parameters remain unanswered. In addition, better definitions of patient selection criteria for TMLR and angiogenesis therapies for both short- and long-term maximum benefits are needed at this time. Large-scale clinical trials with cardiac MRI techniques are needed to reliably assess functional and perfusion reserves of the myocardium pre and post TMLR and angiogenesis therapies. MR-based outcome parameters may aid in answering questions pertinent to the new revascularization treatments.     

Single breath-hold slice-following CSPAMM myocardial tagging

Myocardial tagging has shown to be a useful magnetic resonance modality for the assessment and quantification of local myocardial function. Many myocardial tagging techniques suffer from a rapid fading of the tags, restricting their application mainly to systolic phases of the cardiac cycle. However, left ventricular diastolic dysfunction has been increasingly appreciated as a major cause of heart failure. Subtraction based slice-following CSPAMM myocardial tagging has shown to overcome limitations such as fading of the tags. Remaining impediments, to this technique, however, are extensive scanning times (∼10 min), the requirement of repeated breath-holds using a coached breathing pattern, and the enhanced sensitivity of artifacts related to poor patient compliance or inconsistent depths of end-expiratory breath-holds. We therefore propose a combination of slice-following CSPAMM myocardial tagging with a segmented EPI imaging sequence. Together with an optimized RF excitation scheme, this enables to acquire as many as 20 systolic and diastolic grid-tagged images per cardiac cycle with a high tagging contrast during a short period of sustained respiration.     

Left ventricular radial tagging acquisition using gradient-recalled-echo techniques: sequence optimization

Myocardial tagging with magnetic resonance (MR) imaging offers unique possibilities for noninvasive left ventricular (LV) strain analysis. True three-dimensional strain analysis can be achieved with tags implemented in cardiac short axis and long axis images. Spin-echo (SE) techniques have been used for these studies. However, this approach is time-consuming: images at different phases of the cardiac cycle have to be obtained in successive measurements and hence the total number of measurements equals the number of time frames. Moreover, the images are often degraded by flow and motion artifacts. The purpose of this study was to optimize a faster and more robust MR tagging sequence for use on a clinical whole-body 1 T MR system with optimal persistence of the tags during the entire cardiac cycle. The tagging pulses were implemented in gradient-recalled-echo (GRE) sequences and compared to SE-based acquisitions. The effects of the use of flow-compensating gradients, the excitation angles, and the angles of the saturation pulses have been studied with MR signal simulations and in comparative measurements in volunteers. GRE acquisitions with flow-compensating gradients are robust techniques for myocardial tagging acquisitions. Use of optimized flip angles and saturation pulses can significantly improve delineation of the tag and can be used up to at least 700 ms after the R-wave. Therefore, LV tagging with GRE acquisitions using optimized MR parameters is a robust and promising technique.     

Magnetic resonance imaging and67ga scan versus computed tomography in the staging and in the monitoring of mediastinal malignant lymphoma: a prospective pilot study

Purpose: To assess the potential value of magnetic resonance imaging (MRI) combined with⁶⁷Ga single-photon emission computed tomography (SPECT) versus computed tomography (CT) in the staging and in the monitoring of mediastinal malignant lymphoma. Materials and methods: Twenty-three patients, referred to our institute for the evaluation of lymphoma, underwent CT,⁶⁷Ga scan, and MRI between April 1993 and February 1996 at sequential intervals. The tests studied (MRI,^67Ga, and CT) were performed according to the following schedule: 1) before start of therapy; 2) after four courses of chemotherapy; and 3) 2, 6, 12, and 18 months after the end of treatment. Results: All patients studied at the time of diagnosis had abnormal gallium accumulation in the mediastinum as well as pathologic CT and pathologic signal intensity at MRI. Six months after the end of treatment full consistency was found between the results of MRI and SPECT, whereas during treatment and 2 months after the end of therapy MRI and⁶⁷Ga scan were not in agreement in nine patients. In the 23 patients in follow-up, in CT there were nine false-positive and three false-negative findings; in SPECT three false negatives; in MRI one false positive and one false negative. Conclusion: MRI can give morphologic information similar to CT, even superior due to multiplanarity and with major precision in the distinction between fibrosis and active disease. MRI is thus an alternative to CT. The association with SPECT allows a great diagnostic accuracy in the positive and negative predictive value.     

Highway overhead structure detection using video image sequences

A radar-based forward collision warning system has a limitation of not being able to distinguish a stopped vehicle from the false alarms caused by highway overhead structures. In this paper, we describe a system that detects the presence of overhead structures based on video images from an in-vehicle camera. The system also estimates the height and the distance of the structures to the host vehicle, which can be used to help reject false alarms in the radar detections caused by overhead structures. Our system uses a unique horizontal edge projection (HEP) as the primary feature for the detection of the overhead structures, which is computationally simple and robust to noise. Image vertical motion compensation and HEP tracking algorithms are developed to establish the HEP tracks of trajectories of the overhead structures in the image sequence. A least-squares algorithm is presented for the estimation of structure height and distance to the host vehicle using the HEP tracks. Experiments using real image sequences are presented.